Note: Descriptions are shown in the official language in which they were submitted.
CA 02617233 2008-01-29
ELECTRICAL POWER DISTRIBUTION AND COMMUNICATION
SYSTEM FOR AN UNDERWATER CABLE
Field of the Invention
The invention relates to underwater cable assemblies and, more particularly,
to
apparatuses for powering and communicating with and powering electrical
devices, such
as sensors and cable-control devices, deployed at spaced locations along an
instrumented
underwater cable, such as a towed seismic streamer cable used in offshore
seismic
prospecting or other applications.
Background of the Invention
Towed seismic streamer cable assemblies typically include a plurality of
spaced
electrical devices selectively disposed therealong. Where the electrical
devices are
connected around an exterior of the towed seismic streamer cable, they are
commonly
referred to as wet units. In many applications, the wet units are inductively
coupled to
data communication lines within the seismic streamer.
_ One or more of the seismic streamer cable assemblies may be towed by a
survey
vessel. The wet units communicate with dry-end electronics disposed, for
example, on the
survey vessel via one or more communication channels. Communication channels
between the wet units and dry-end electronics conventionally include either a
single-ended
or twisted-pair data communication line inductively coupled to the wet units.
Electromagnetic coupling may be utilized to allow communication with the wet
units
without breaching the exterior sheath of the towed seismic streamer cable.
Conventionally, each of the wet units receives operational power from a
battery
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disposed within the wet unit. The use of batteries as a primary power source
in the
plurality of spaced electrical devices may be required in practical
applications because of
low coupling coefficients between the underwater cable and the wet units.
However, the
use of batteries as the primary power source is frequently undesirable since
the batteries
may require replacement every few weeks or months. Replacing the batteries
typically
involves removing the wet units as the seismic cable is retrieved onto rolls
on the survey
vessel. The wet units are then individually serviced by opening the wet unit
and replacing
and/or recharging the existing batteries. This battery maintenance process may
be highly
inefficient and results in unwanted down time. Further, when lithium batteries
are used,
the cost of disposal and replacement of the batteries for a single vessel may
exceed several
hundred thousand dollars per year. Accordingly, conventional wet unit designs
suffer
from a number of problems.
A major problem associated with eliminating batteries from the wet unit
devices is
the low coupling coefficient between the wet units and the underwater cable.
Although
numerous attempts have been made to improve this coupling coefficient, these
attempts
have been less than satisfactory.
U.S. Patent No. 4,912,684 to John T. Fowler describes a communication system
which transmits both power and data signals along a one- or two-wire
transmission line
running the length of the underwater cable. The power signals may be used to
charge
batteries in wet units such as cable-leveling birds attached along the cable.
The power and
data signals are inductively coupled between the transmission line and the wet
units by
means of coils connected to the transmission line at specific locations along
the streamer
and associated coils disposed within each bird. However, due to a number of
technical
difficulties, a seismic streamer cable assembly which transfers operational
power from the
underwater cable directly to the wet units or to the wet units and in-streamer
devices has
not yet proven commercially practical.
For example, conventional transmission lines are typically configured as
continuous,
unbroken transmission lines running the length of the streamer cable which has
traditionally been about 6 km or less. Transmission line losses in
transmission lines of
underwater streamer cables having a length longer than 6 km exacerbate the
problems
associated with powering the spaced electrical devices directly from the
underwater
streamer cable. Furthermore, data and/or power transmitted to electrical
devices at the aft
end of an underwater streamer cable are often severely attenuated. This
problem may be
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particularly acute where dat,_ .nes are also utilized to transmit power. It
has been found
that transmission line losses and noise levels in such a system often make the
system
commercially impractical. Thus, communication with and power delivery to aft
electrical
devices may be difficult, particularly for ever increasing cable lengths. Much
research
has been directed at solving this problem, but to date there has been little
success.
One approach is to resort to heavy gauge wire and increase the power level
transmitted to the cable. However, this is typically unacceptable because
additional
weight may be added to the underwater cable and because higher power levels
may
interfere with the operations of the seismic equipment, such as the underwater
hydrophones.
Another shortcoming of conventional power distribution and/or data
communication
systems is that the inductive circuits utilized to couple between the
underwater cable and
the wet units are required to be precisely tuned within narrow margins to
ensure adequate
coupling of power and data to or from the electrical devices. If an electrical
device fails,
falls off, or is otherwise damaged or removed from the underwater cable, the
associated
coil on the transmission line may have an open secondary, detuning the tuned
circuit.
Often, the transmission line may be detuned to the point where reliable data
and power
transfer is compromised.
In typical underwater sonar cables, it is difficult to transfer power along
the cable at
a high frequency due to the length of the cable, amount of power required to
be
distributed, and the noise generated by such a transfer. Accordingly, power is
typically
transferred along the entire length of the cable at a low frequency. However,
low
frequency signals are extremely inefficient when coupled across a transformer
having a
low coupling coefficient. Thus, configurations which couple power from the
main power
line may be commercially impractical in many applications.
Another shortcoming of conventional streamer power distribution and/or data
communication systems may be reliability problems due to the leakage of
seawater into
one or more of the sections of the streamer cable. As seawater leaks into a
section of the
underwater streamer cable, a low-impedance path or short circuit may be formed
across
the transmission line. In a continuous-wire transmission line running the
length of the
underwater cable, the short circuit may disable the entire transmission line.
When the
transmission line is disabled, sensor data cannot be collected, the electrical
devices cannot
be powered from the underwater cable, and depth control from the survey vessel
may be
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precluded.
Thus, there is a need for an underwater cable power distribution and/or data
communication system that overcomes these and other problems and enables
highly
efficient and reliable transmission of power and data between the underwater
cable and the
electrical devices even under demanding operational conditions.
Summary of the Invention
A principal object of the present invention is to provide a power distribution
and/or
data communication system which provides an elegant and reliable power
distribution and
data communication system for supplying power and data to a plurality of
electrical
devices disposed along an underwater cable. The power distribution and/or data
communication system may also provide an improved structure and/or operation
which
enhances the reliability of the seismic streamer cable assembly even when the
cable is
damaged and/or electrical devices are removed.
Additional objects of various aspects of the present invention include
providing an
underwater cable structure which enables the transferring of operational power
to the
electrical devices without breaching the outer sheath of the underwater cable;
eliminating
batteries as the primary source of operational power for the electrical
devices coupled to
the underwater cable; eliminating and/or reducing the need to change
batteries; providing
better economy by enabling an underwater cable assembly to survey for more
hours
without interruptions; extending the operational length of underwater cables
by 5, 10, 15,
20 km or more without altering the basic structure and/or operation of the
underwater
cable power distribution and/or data communication system; increasing the
bandwidth of
data transmitted to and received from the electrical devices; minimizing the
weight of
wires (e.g., copper wires) in the underwater cable; reducing the weight, size,
and number
of inductive cores used along the underwater cable; allowing brittle cores to
be used in
inductors along the underwater cable; increasing the power transfer efficiency
from a
main power supply to the electrical devices disposed along the underwater
cable; reducing
noise generated by the power transfer which may interfere with the seismic
equipment;
reducing capacitive coupling and mutual inductance between the electrical
devices and
other parts of the underwater cable; improving the coupling coefficient of a
transformer
disposed about the outer sheath of the underwater cable; providing a fault
tolerant power
distribution and data communication system in an underwater cable assembly;
reducing the
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number of data and power transmission lines coupled to each of the electrical
devices and
disposed in the underwater cable; reducing the latency time associated with
communications through the underwater cable with the electrical devices;
allowing the
electrical devices to respond directly to detected fault conditions without
intervention of
dry-end electronics; and providing for degraded mode operations which allow
the most
critical electrical device operations to be maintained even during fault
conditions.
Accordingly, the present invention provides an underwater power distribution
system
including an underwater cable for powering a plurality of electrical devices
disposed along
the cable. A main power line extends through the underwater cable. Two or more
power
distribution lines and two or more power distributors are also disposed in the
underwater
cable. Each power distributor is electrically coupled between the main power
line and one
of the power distribution lines to transfer power from the main power line to
the
associated power distribution line. One or more power couplers are disposed at
selected
locations along the underwater cable. Each power distribution line is coupled
to one or
more power couplers proximate to one of the electrical devices for coupling
power to the
proximate device.
In underwater systems embodying this aspect of the invention, power may be
transmitted along the main line and then distributed to the electrical devices
by the power
distribution lines. Each power distribution line distributes power directly to
a small
subgroup of the electrical devices. This arrangement is particularly
advantageous. It
allows both power transmission along the main line and power distribution
along the
distribution lines to be independently optimized regardless of the length of
the underwater
cable assembly, resulting in a highly reliable and efficient underwater power
distribution
system. Systems embodying this aspect of the invention are so reliable and so
efficient
that batteries may either be eliminated entirely from the electrical devices
or used only
rarely in a fail safe capacity. Thus, this aspect of the invention virtually
eliminates the
economic loss associated with retrieving an underwater cable and replacing or
recharging
the batteries in the electrical devices and greatly extends the operational
life of an
underwater cable assembly.
In addition, this arrangement of a main power line and several power
distribution
lines allows segmentation of the underwater cable assembly. For example, each
power
distribution line and the subgroup of electrical devices coupled to that power
distribution
line may define a different segment of the underwater cable assembly. This
arrangement
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further enhances the reliability of an underwater cable assembly because it
provides a
highly fault-tolerant system. Each segment may be provided with fault
protective features
that isolate a fault, such as seawater intrusion or loss of an electrical
device, in that
segment but preserve power transfer and data communications to the remaining
segments
of the underwater cable assembly. Further, segmentation of the underwater
cable
assembly allows the cable assembly to be easily lengthened simply by adding
additional
segments, i.e., by extending the main power line and adding additional power
distribution
lines.
The invention also provides an underwater power distribution system for
powering
electrical devices. The underwater power distribution system includes an
underwater
cable including two or more streamer electronics modules and two or more cable
segments. At least one of the electrical devices is disposed along each cable
segment, and
the streamer electronics modules are alternately arranged with the cable
segments and
spaced from the electrical devices. A main power line extends through the
underwater
cable. Two or more power distribution lines are disposed in the underwater
cable with at
least one power distribution line extending through each cable segment. Each
streamer
electronics module includes a circuit for coupling electric power from the
main power line
to an adjacent power distribution line. Two or more power couplers are
disposed at
selected locations along the underwater cable. Each power distribution line is
coupled to
one or more power couplers and each power coupler is positioned proximate to
at least
one of the electrical devices to couple power, to the proximate device.
Systems embodying this aspect of the invention may be similar to, and have
many of
the same advantages as, the previously described underwater power distribution
system.
However, in systems embodying this aspect of the invention, the underwater
cable
comprises alternately arranged streamer electronics modules and cable
segments, and at
least -one power distribution line branches from the main power line at a
streamer
electronics module. This arrangement allows much of the circuitry, including
power
supplies, data circuits, and circuit cards to be consolidated with existing
circuitry in the
streamer electronics modules and, therefore, significantly reduces the weight
and
complexity added to the underwater cable assembly to effect power transfer to
the power
distribution lines.
The invention provides a method for distributing power underwater to one or
more
electrical devices disposed along an underwater cable. The method comprises
transmitting
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power at a first frequency on a main power line of the underwater cable,
converting the
power on the main power line to a second frequency, higher than the first
frequency, and
distributing the power at the second frequency on two or more power
distribution lines to
the electrical devices. The first frequency may be either a DC frequency of
zero or an
AC frequency having a value greater than zero.
The invention also provides an underwater power distribution system for
powering
two or more electrical devices. The underwater power distribution system
includes an
underwater cable and the devices are disposed along the underwater cable. A
main power
line extends through the underwater cable and is arranged to transmit a main
power signal
at a first frequency. A plurality of conversion circuits are disposed at
spaced locations
along the underwater cable and are respectively coupled between the main power
line and
the electrical devices. Each conversion circuit is arranged to convert the
main power
signal into a power distribution signal at a second frequency higher than the
first
frequency.
In methods and systems embodying these aspects of the invention, power is
transmitted along the main power line at one frequency and is distributed to
the electrical
devices along the underwater cable at a higher frequency. This arrangement
greatly
increases the power transfer efficiency along the main line and to the
electrical devices.
Transmitting power at a relatively low frequency along the main power line
allows the
power to be most efficiently transmitted to the aft end of the underwater
cable.
Converting the lower frequency main power signal to a higher frequency power
distribution signal allows the power to be most efficiently distributed from
the main power
line to the electrical devices. This is especially advantageous where the
electrical devices
are mounted external to the underwater cable and power is inductively or
capacitively
coupled through the sheath of the underwater cable without any connectors
physically
penetrating the sheath. The high frequency signal inductively couples power
through the
sheath far better than a low frequency signal.
In some embodiments employing these aspects of the invention, it may be
desirable
to first convert the main power signal into a DC signal and then to convert
the DC signal
into a higher frequency power distribution signal. Conversion first to a DC
signal may
further improve the efficiency of the power conversion process.
The invention provides an underwater power distribution system for supplying
power. The underwater power distribution system includes an underwater cable
and two
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or more 'electrical devices selectively disposed along the underwater cable.
The
underwater cable has an outer sheath and is filled with a lossy dielectric
material having a
dissipation factor of about 0.01 or greater. A main power line extends through
the
underwater cable. A plurality of insulated twisted pair transmission wires
extend through
the underwater cable and are coupled between the main power line and the
electrical
devices. Each twisted pair transmission wire has an outer sheath and a
dissipation factor
of less than about 0.01 when surrounded by the lossy dielectric material.
Systems embodying this aspect of the invention very effectively transfer power
along
an underwater cable to electrical devices even when the underwater cable is
filled with a
lossy dielectric material, such as a non-aqueous liquid that maintains the
underwater cable
in a neutrally buoyant state. By providing an outer sheath on the transmission
wires that
has a dissipation factor of less than about 0.01 in the lossy material, power
can
nonetheless be very effectively transferred along the underwater cable,
through the power
distribution lines, to the electrical devices.
The invention also provides an underwater system for distributing power to and
communicating with two or more electrical devices. The underwater system
includes an
underwater cable and the electrical devices are selectively disposed along the
cable. Each
device includes one or more loads. A first line extends through the underwater
cable and
is coupled to the electrical devices. Fault detection circuitry is coupled to
the first line to
detect when a fault is present. Disabling circuitry is coupled to the fault
detection
circuitry to disable one or more of the loads in a hierarchical order in
response to a fault.
The invention also provides a method for distributing power along an
underwater
transmission system. The under water transmission system includes an
underwater cable
having two or more electrical devices spaced along the underwater cable, and
each device
includes one or more loads. The method includes transferring electrical
signals along the
underwater cable, detecting a fault in the underwater transmission system,
removing loads
along the underwater cable in a hierarchical order in response to the fault,
and powering
the remaining loads.
The invention further provides a method for distributing both power and data
along
an underwater cable. Two or more spaced electrical devices are coupled to the
underwater cable and each device includes one or more electrical loads. The
method
includes transferring power and data along a line in the underwater cable,
detecting a
fault, and selectively removing one or more of the electrical loads from the
underwater
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cable according to a predetermined hierarchy in response to the fault.
Systems and methods embodying these aspects of the invention respond to a
failure
in a power line or a data distribution line by selectively removing, e.g.,
shutting down,
various loads and associated functions in a controlled, hierarchical manner.
The least
important functions or electrical devices are shut down first and the most
important
functions or electrical devices are shut down last. Alternatively, all
electrical devices or
functions may be shut down responsive to the fault, and then the most
important electrical
devices added in a controlled, hierarchical manner provided sufficient power
is present.
This management enhances the survivability of the more critical functions or
devices
in the damaged section of the cable as well as the survivability of other
functions or
devices disposed at undamaged sections of the cable. Shedding the electrical
load
associated with various functions or devices, and particularly hierarchical
load shedding,
has even greater importance where both power and data are disposed on a single
distribution line. Load shedding allows power transfer and communications to
or from aft
electrical devices to remain intact even when an intermediate cable segment
has been
damaged.
The invention provides an underwater power distribution system for powering
two
or more electrical devices. The underwater power distribution system includes
an
underwater cable with the electrical devices selectively spaced along the
cable. A power
line extends through the underwater cable and is coupled to the electrical
devices. A
current limited driver circuit is coupled to the power line to drive a power
distribution
signal on the power line at or below a predetermined current level. A fault
detection
circuit is also coupled to the power line. The fault detection circuit
includes a voltage
detection circuit for detecting a change in the voltage on the power line.
Systems embodying this aspect of the invention allow a fault to be quickly
detected
autonomously by each of the electrical devices or by each segment of the
underwater cable
without intervention of the survey vessel. For example, where the current on
each power
line is limited, a short circuit or other current leakage fault, such as sea
water intrusion,
causes a drop in voltage to occur on the power distribution lines. A fault
(e.g., sea water
intrusion) may be detected simply by a monitoring a voltage received from the
power line,
e.g., by detecting a reduction in the voltage on the power line. Further, the
current
limited driver not only provides for autonomous fault detection, but also
prevents a section
of the underwater cable from exceeding a predetermined power budget due to the
fault.
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Excess power drawn from one or more cable sections may adversely affect the
entire
operation of the underwater cable.
The invention further provides an underwater power/data transfer system
comprising
an underwater cable and a mechanism associated with the cable for transfering
power
and/or data along, into, or out of the cable.
The invention further provides a device associated with an underwater cable
comprising a mechanism for sending, receiving, or generating power and/or
data.
The invention further provides an underwater data communications system for
communicating with a plurality of electrical devices, and includes a primary
data
communications circuit, a backup data communications circuit, and circuitry
coupled to
the primary data communications circuit and the backup data communications
circuit to
switch between the primary data communications circuit and the backup data
communications circuit in response to a loss of power to the electrical
devices.
The invention provides an underwater communication system for communicating
with two or more electrical devices. The underwater communication system
includes an
underwater cable with the electrical devices selectively disposed along the
underwater
cable. An inbound data distribution line and an outbound data distribution
line extend
through the underwater cable and are coupled to one or more of the electrical
devices. At
least one repeater circuit is disposed in the underwater cable. The repeater
circuit
includes synchronization circuitry coupled to the inbound and outbound data
distribution
lines to derive clock data from the outbound data and to transmit the inbound
data in
accordance with the derived clock data so that a timing relationship exists
between
inbound and outbound data.
The invention also provides a method of communicating data underwater. The
method comprises transmitting outbound data and inbound data through a
repeater circuit
cover clock
in an-underwater cable, decoding the outbound data in the repeater circuit to
re
data, and transmitting inbound data from the repeater circuit in synchronism
with the
clock data.
The invention further provides another method for communicating data
underwater.
The method comprises receiving outbound data along an underwater cable,
decoding the
outbound data to recover a clock signal, and transmitting inbound data along
the
underwater cable in synchronism with the data clock.
In systems and methods embodying these aspects of the invention, transmission
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CA 02617233 2008-01-29
inbound data along an underwater cable is synchronized according to a clock
derived from
the outbound data. Synchronization of the inbound data with the outbound data
by the
repeaters, electrical devices, and dry-end electronics greatly reduces the
latency, i.e., the
time delay, associated with sending an inbound electrical signal from an
electrical device,
resulting in more efficient utilization of the available bandwidth. Further,
since the
electrical devices are already synchronized with each of the repeaters and the
dry-end
electronics, there is no need to send out a long preamble to achieve
synchronization with
each repeater and the dry-end electronics. Thus, in accordance with these
aspects of the
invention, data may be sent inbound from the electrical devices to the survey
vessel very
quickly and efficiently.
The invention provides an underwater system for transferring power. The
underwater power transferring system includes an underwater cable and two or
more wet
units selectively disposed along an underwater cable. Each wet unit has a
first inductor
for receiving power. The underwater cable includes two or more second
inductors
respectively disposed adjacent to the first inductors in the wet units.
Hydrophones are
also selectively disposed along the cable and operate in one or more first
operating
frequency bands. Power conversion circuits are respectively coupled to one or
more of
the second inductors to output a signal having a second operating frequency
band to the
wet units. The first operating frequency bands and the second operating
frequency band
do not overlap.
The invention also provides a method of transferring power underwater. The
method comprises having hydrophones in an underwater cable which operate at
one or
more first frequency bands and transferring power inductively from an
underwater cable to
two or more wet units using a second frequency band which does not overlap the
first
frequency bands.
.Frequency band separation was found to prevent coupling noise from the power
transfer into the hydrophone circuits even when a high power, high voltage
signal was
continually active.
Further, frequency band separation was found to be particularly effective when
coupled with an efficient filter. Efficient filtering coupled with frequency
constraints on
the power distribution signal increases the hydrophone sensitivity and noise
immunity as
the power transfer frequency to the wet units increases. In some embodiments,
an
efficient filter for separating the hydrophone signal frequency bands and the
power
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transfer frequency band may be implemented by configuring the lumped and
distributed
parameters of each power distribution line to form a distributed bandpass
filter centered
about the power transfer frequency band.
The invention provides an underwater power distribution system for supplying
electric power to two or more electrical devices. The underwater power
distribution
system includes an underwater cable with the electrical devices disposed along
the
underwater cable. Two or more data distribution lines extend through portions
of the
underwater cable. Two or more repeater circuits are respectively coupled
between
adjacent data distribution lines to form a data communication channel. Each
data
distribution line is coupled to one or more electrical devices and is tuned to
resonate at a
first frequency having a predetermined bandwidth. Further, each data
distribution line
includes at least one load adjusting circuit to maintain each data
distribution line tuned to
about the first frequency with the predetermined bandwidth, in response to a
failure mode,
for example, a missing device, a device failure, or a seawater intrusion.
Underwater cable power distribution systems embodying this aspect of the
invention
allow power transfer along a particular cable segment to continue even though
the cable
segment and/or electrical devices along the cable segment have been damaged
and/or
removed. Where groups of electrical devices are buffered by repeater units,
the electrical
effects of losing a device or a seawater intrusion in one cable segment are
electrically
isolated from the remaining cable segments. Thus, in these configurations, the
load
adjusting circuit is even more effective in preventing detuning of a
particular cable
segment so the communications and power transfer can continue across the
entire
communication channel. Further, the retransmission of message signals at a
predetermined level by the repeater at an end of the detuned segment with a
load adjusting
circuit overcomes the detuning effects of a missing device or a seawater
intrusion and
allows transmission of data to aft devices.
In addition to an underwater cable system, the invention also provides
electrical
devices for use in an underwater cable system. For example, the invention
provides an
underwater electrical device for an underwater cable including a housing, a
load circuit
disposed in the housing, and an inductor circuit coupled to the load circuit.
The inductor
circuit transfers a power distribution signal from the underwater cable to the
load circuit
such that the load circuit loads the power distribution signal. A control
circuit is coupled
to the inductor circuit and/or the load circuit to reduce the loading* in
response to the
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power distribution signal falling below a predetermined level.
The invention also provides an underwater electrical device for an underwater
cable
which includes a line having a voltage. The underwater electrical device
includes a
housing, at least one electrical load in the housing, and a control circuit in
the housing.
The control circuit includes circuitry for monitoring a voltage on a line in
an underwater
cable to reduce the electrical load in response to the voltage falling below a
predetermined
level.
The invention further provides an underwater electrical device for an
underwater
cable. The underwater electrical device includes a controller circuit which is
arranged to
be coupled to send and receive power from the underwater cable. The controller
circuit
includes fault detection circuitry to detect a fault and load shedding
circuitry to reduce the
amount of power received from the underwater cable in a hierarchical order
responsive to
the fault.
Underwater electrical devices embodying these aspects of the invention can
autonomously detect when a fault occurs in the device or a proximate cable
segment and
automatically reduce the load on the cable segment independent of any commands
received
from the cable assembly or survey vessel. In other words, the electrical
devices
themselves may perform fault recovery autonomously without any explicit
control received
from the underwater cable or survey vessel. Thus, reliability is increased and
the
underwater cable assembly may recover communications and/or power transfer
over the
underwater cable even where communications and/or power transfer across a
portion of
the cable has been interrupted. Further, by hierarchical load shedding, more
important
functions of the electrical devices may remain operative while less important
functions are
removed first. This allows for an intelligent, hierarchical degraded mode
operation even
along damaged portions of the underwater cable.
The invention provides an underwater electrical device for an underwater
cable.
The underwater electrical device includes a housing, an input circuit, and an
output
circuit. The housing is arranged to be connected to the underwater cable. The
input
circuit is disposed in the housing for inputting data from an underwater
cable. The input
circuit includes synchronization circuitry to derive a timing signal from the
data. The
output circuit is coupled to the input circuit and is arranged to output data
to the
underwater cable in synchronism with the timing signal.
The invention provides an underwater coupling system including an underwater
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cable, at least one coupler, and two or more inductive coils. The coupler is
disposed in
the underwater cable and the inductive coils are selectively disposed outside
the
underwater cable at circumferentially spaced locations about the coupler.
Underwater coupling systems embodying this aspect of the invention have two or
more coils, such as circumferentially spaced coils mounted about the coupler.
This
arrangement is particularly advantageous for embodiments where the inductive
coils are in
the wet units. It allows for rotation of the wet units while still maintaining
a high
coupling coefficient for various orientations. Additionally, each of the
plurality of coils
may include a core and be electrically connected together to further improve
the coupling
coefficient.
The invention further provides an underwater coupling system which includes an
underwater cable, at least one coupler disposed in the underwater cable, and a
plurality of
inductive coils circumferentially spaced inside the coupler. Systems involving
this aspect
of the invention allow an electrical device to rotate with respect to the
cable without losing
power and/or data communications with the survey vessel.
The invention also provides an underwater coupling system including an
underwater
cable and two or more inductive couplers. The inductive couplers are disposed
at selected
locations along the underwater cable. Each coupler includes at least one coil
having a
core with a substantially triangular-shaped cross section and a winding wound
around the
substantially triangular-shaped core.
Underwater coupling systems embodying this aspect of the invention provide
excellent coupling efficiency. The triangular-shaped core provides an
extremely efficient
utilization of space within the underwater cable so as to provide a relatively
large core
with a high coupling coefficient within the mechanical constraints of a
coupler and/or
underwater cable.
The invention further provides an underwater coupling system including an
underwater cable, first and second lines, and two or more couplers. The first
and second
lines extend through an underwater cable and the couplers are disposed at
selected
locations along the underwater cable. Each coupler includes an integral core
having first
and second portions and first and second coils respectively wound around the
first and
second portions of the integral core. The first and second lines are
respectively connected
to the first and second coils.
In underwater coupling systems embodying this aspect of the invention, each
coupler
14
CA 02617233 2008-01-29
includes an integral core. This arrangement substantially improves the
coupling
coefficient between the underwater cable and any electrical devices coupled to
the cable at
the coupler.
The invention additionally provides an underwater coupling system including an
underwater cable, first and second lines extending through the underwater
cable and two
or more couplers. The couplers are disposed at selected locations along the
underwater
cable. Each coupler includes a first coil connected to the first line and
second and third
coils connected to the second line. The first and second coils are spaced from
each other
and the first and third coils are in close proximity for canceling cross-talk
between the
first and second coils.
In underwater coupling systems embodying this aspect of the invention, the
first and
third coils are arranged in close proximity to prevent cross-talk between the
first and
second coils. This arrangement significantly reduces noise and, therefore,
enhances the
reliability of communication with the electrical devices along the underwater
cable.
The present invention also provides a power distribution, communication,
electrical
device, and/or coupler system having one or more of the elements described
herein and/or
shown in Figs. 1-49, in any combination or subcombination. The invention is
contemplated to include any number of combinations and subcombinations of
elements
described and shown herein.
Brief Description of the Drawings
The above described advantages, features, and objects of the invention will be
better
understood by reference to the appended claims, description of preferred
embodiments,
and the accompanying drawings in which:
Fig. 1 is a view of a seismic surveying vessel towing an underwater streamer
cable;
Fig. 2 is a partial sectional view of an underwater streamer cable which
includes a
plurality of electrical devices;
Fig. 3 is a block diagram of an embodiment of an underwater power distribution
and/or data communication system for use in an underwater cable;
Fig. 4 is a block diagram of another embodiment of an underwater power
distribution and/or data communication system for use in an underwater cable;
Fig. 5 is a block diagram of another embodiment of an underwater power
distribution and/or data communication system for use in an underwater cable;
CA 02617233 2008-01-29
Fig. 6 is a block diagram of another embodiment of an underwater power
distribution and/or data communication system for use in an underwater cable;
Fig. 7 is a block diagram of the underwater cable power conversion circuits;
Fig. 8 is a block diagram of another embodiment of the underwater cable power
conversion circuits;
Fig. 9 is a partial block/partial circuit diagram of another embodiment of the
underwater cable power conversion circuits;
Fig. 10 is a timing diagram showing exemplary timing of an outbound data and
power distribution line employing the power conversion circuits of Fig. 9;
Fig. 11 is one embodiment of an electrical device power circuit and an
electrical
device decoder;
Fig. 12 is an equivalent circuit of one embodiment of the power distribution
lines;
Fig. 13 is a frequency spectrum of the equivalent circuit shown in Fig. 12;
Fig. 14 is a traverse cross sectional view of the underwater cable;
Fig. 15 is a longitudinal cross sectional view of a power distribution line
for use in
the underwater cable;
Fig. 16 is a top view of a coil for use in an underwater cable coupler;
Fig. 17 is a side view of the coil of Fig. 16;
Fig. 18 is a cross sectional view of the coil of Fig. 16;
Fig. 19 is a circuit/block diagram of coils for use in a coupler in the
underwater
cable;
Fig. 20 is a partial cross sectional view of a first side of a coil housing
for use in a
coupler in the underwater cable;
Fig. 21 is a partial cross sectional view of a second side of a coil housing
for use in
a coupler in the underwater cable;
Fig. 22 is a traverse cross sectional view of the underwater cable including a
coupler
and a coil housing disposed within the coupler;
Fig. 23 is a partial longitudinal cross sectional view of an embodiment of the
underwater cable including a coupler and a coil housing disposed within the
coupler;
Fig. 24 is a partial longitudinal cross sectional view of another embodiment
of the
underwater cable including a coupler and a plurality of coil housings disposed
within the
coupler;
Fig. 25 is a traverse cross sectional view of another embodiment of the
underwater
16
CA 02617233 2008-01-29
cable including a coupler and a coil housing disposed within the coupler;
Fig. 26 is a circuit diagram of a circuit for use with embodiments of
electrical
devices having a coupler employing multiple coils;
Fig. 27 is a traverse cross sectional view of another embodiment the
underwater
cable including a coupler and a first coil having an integral core disposed
within the
underwater cable sheath and a second coil having an integral core disposed
about the
underwater cable sheath;
Fig. 28 is a circuit diagram of circuits which may be utilized with couplers
having
an integral core;
Figs. 29A-29C are diagrams showing magnetic flux lines of an inner integral
core
configured as shown in Fig. 28;
Fig. 30 is a transverse cross sectional view of the underwater cable including
another version of a coupler and a partially shown wet unit;
Fig. 31 is a longitudinal cross sectional view of the coupler of Fig. 30
including a
core assembly disposed within the coupler;
Fig. 32 is a partial longitudinal view of the core assembly of Fig. 31;
Fig. 33 is a circuit diagram of core assembly circuits that may be used with
couplers
of Fig. 30;
Figs. 33A and 33B illustrate the magnetic flux lines of the circuit of Fig.
33;
Fig. 34 is a transverse cross sectional view of the underwater cable of Fig.
30 with
a wet unit having an arrangement of two core assemblies;
Figs. 35 and 36 are a partial block/partial circuit diagrams of embodiments of
a
repeater;
Fig. 37 is a block diagram of a bit/clock recovery circuit;
Fig. 38 is a partial block/partial circuit diagram of an embodiment of a
repeater;
Fig. 39 is a block diagram of a simplified version of the underwater cable
power
distribution and/or data communication system;
Fig. 40 is a partial block/partial circuit diagram of an embodiment of a
repeater;
Fig. 41 is a detailed block diagram of the repeater encodeldecode circuits;
Figs. 42A, 42B are a partial block/partial circuit diagram of an embodiment of
a
electrical device;
Fig. 43 is a circuit diagram of an inbound data driver circuit;
Fig. 44 is a timing diagram of signals related to the transmission of inbound
data;
17
CA 02617233 2008-01-29
Fig. 45 is a detailed block diagram of the electrical device encode/decode
circuits;
Fig. 46 is a block diagram of a load adjusting circuit for use in the
underwater
cable;
Fig. 47 is a flow diagram of one embodiment of an apparatus having
hierarchical
load shedding;
Fig. 48 illustrates the hierarchical load shedding function which may be
associated
with an electrical device; and
Fig. 49 illustrates the switching between primary and backup communications.
Description of The Preferred Embodiments:
Referring to Figs. 1 and 2, a typical marine seismic data acquisition system 1
may
include a survey vessel 8 which tows one or more underwater streamer cables
such as
underwater cable 2. The underwater cable 2 may include one or more sections
such as
lead-in section and underwater section 4. The lead-in section 3 is typically
connected
between the underwater section 4 and dry-end electronics 5. The dry-end
electronics 5
are typically disposed on the survey vessel 8 and may include a plurality of
data
acquisition, processing, storage, and control devices. In some embodiments, it
may be
desirable to couple first and second ends of the underwater section 4 to first
and second
buoys 6, respectively.
The underwater cable 2 may be a continuous streamer cable or be discontinuous
and divided into a plurality of cable segments. For example, Fig. 2 shows a
portion of an
underwater cable 2 which may be divided into a plurality of cable segments 13
by a
plurality of streamer electronics modules (SEM's) 14. In the illustrated
embodiment, the
cable segments 13 are alternately arranged with the SEM's 14 to form the
underwater
section 4. The SEM's 14 may be larger, smaller, or have the same cross
sectional size as
the cable segments 13. In a preferred embodiment, the SEM's 14 have a larger
cross
sectional size than the cable segments 13 so that the SEM's may accommodate
electronics
such as one or more circuit cards. Further, each cable segment may include an
outer
sheath 15 secured to waterproof connectors that attach to the SEM's 14. This
configuration allows access for servicing the electronics in the individual
SEM's.
However, the underwater cable 2 need not be limited to this arrangement. For
example,
the outer sheath 15 may extend throughout the entire length of the underwater
cable 2 and
enclose the SEM's 14.
18
CA 02617233 2008-01-29
As illustrated in Fig. 2, he underwater cable 2 typically includes a plurality
of units
selectively disposed therealong. For example, a plurality of hydrophones 7 may
be
selectively disposed along the underwater section 4 for measuring reflected
seismic
signals. Further, one or more electrical devices 18 may be selectively
disposed along the
underwater section 4 either inside and/or outside of the outer sheath 15. When
the
electrical devices 18 are disposed within the outer sheath 15, they may be
referred to as
in-streamer units 31. Alternatively, when the electrical devices 18 are
disposed on the
exterior of the outer sheath 15, the electrical devices 18 may be referred to
as wet units
30. The wet units 30 are preferably secured to the underwater cable using one
or more
wet unit couplers 16.
In exemplary embodiments, the electrical devices 18 may be variously
configured.
For example, a single electrical 18 device may include a leveling function,
depth sensing
function, acoustic ranging/bearing function and/or a compass/heading function,
as well as
other functions, e.g., inclinometer, gyro, accelerometer, magnetometer,
optical
range/bearing, retrieval aids. Further, in some embodiments, it may be
desirable to
divide one or more functions into two or more electrical devices 18. For
example,
leveling devices or birds 10A, compass/heading devices 11A, and acoustic
ranging devices
12A may be configured as separate in-streamer units within the underwater
cable 2. In
many embodiments, the electrical devices 18 are configured as separate
leveling/depth
sensing devices or birds 10, compass/heading devices 11, and acoustic ranging
devices 12
and are disposed on the exterior of the sheath 15 as wet units 30.
Using known techniques, the electrical devices 18 may be utilized to measure
and
control the shape, heading, and configuration of the underwater cable 2. In
many
embodiments, the leveling devices, or birds 10, 10A include one or more vanes
17 to
control the depth and/or orientation of the underwater cable 2. The electrical
devices 18-
typically communicate with and are controlled by the dry-end electronics 5 on
board the
survey vessel 8 over one or more communication channels.
Part I: Power Distribution/Communication Structure
Referring to Fig. 3, a power distribution and/or data communication system 20
is
shown in block diagram form with the physical relationship to the marine
seismic data
acquisition system of Figs. 1 and 2 illustrated as dashed lines. In the
illustrated
embodiment, the dry-end electronics 5 include a control processor 21 and a
main power
19
CA 02617233 2008-01-29
supply 22.
The main power supply 22 is preferably coupled to a main power line 23 which
runs
through the lead-in section and then through substantially the entire length
of the
underwater section 4. A plurality of repeaters 25A-25C may be selectively
disposed along
the length of the underwater cable 2 and may be coupled in series or in
parallel with the
main power line 23. As discussed throughout the specification, the repeaters
25A-25C
may be variously configured to include a plurality of functions, such as, data
waveform
reformatting, power conversion, management and control, fault processing and
control,
power transmission, line driving-receiving, line termination, null character
transmission,
data/clock synchronization, data link control, data encoding, data decoding,
clock
recovery, error detection-correction, signal filtering, and/or hierarchical
load shedding
control.
The main power supply 22 may supply either AC or DC current to the main power
line 23. Where the underwater cables 2 extend over long distances, it may be
desirable
for the main power supply 22 to output either low frequency AC or DC power and
for the
main power line 23 to use a relatively heavy gauge wire. Many underwater
cables 2
utilize a main power supply 22 configured to output a main AC power signal
having a
frequency of between 1 and 4 kHz onto the main power line 23. In many
applications,
the main power line 23 includes one or more transmission wires which are at
least as
heavy as 8 gauge wire and which are several thousand meters in length.
The control processor 21 may be coupled to the electrical devices 18 in the
underwater cable 2 by a lead-in line or lines 26 which may be buffered on each
end by
interface circuits 27. In typical embodiments, the lead-in line may be up to
600 meters in
length and normally does not interface to any parallel connected electrical
devices 18. In
many of the preferred embodiments, data may be transmitted across the lead-in
section at
a rate-of up to 64 kbps or higher. Accordingly, conventional line drivers and
receivers
may be utilized as the interface circuits 27 to interface the control
processor 21 to the first
repeater 25A. For example, the interface circuits 27 may include
drivers/receivers
compatible with the EIA RS-422-A (CCITT V.10) and/or the ETA RS-423-A (CCITT
V.11) standards.
The repeaters 25A-25C are alternately arranged with a plurality of data and/or
power distribution line(s) 28A-28C to form a data communication channel
running
substantially throughout the underwater cable 2. The data communication
channel
CA 02617233 2008-01-29
transfers data between the control processor 21 and a plurality oL electrical
devices 18
selectively disposed along the underwater cable. In Fig. 3, the electrical
devices 18 are
shown as being either wet units 30 or in-streamer units 31. As previously
discussed with
regard to Fig. 2, the wet and in-streamer units 30, 31 may be variously
configured to
include, for example, a compass/heading function, depth control function,
acoustic ranging
functions, and/or other functions.
Each wet unit 30 is preferably coupled to one of the data/power distribution
line(s)
28A-28C using a wet unit coupler 16. Similarly, each in-streamer unit 31 is
preferably
coupled to one of the data/power distribution line(s) 28A-28C using an in-
streamer coupler
32. Again referring to Fig. 3, a plurality of couplers 16, 32 are disposed
along a
data/power distribution line to couple electric power from the data/power
distribution line
to the electrical devices 18 (e.g., wet and in-streamer units 30, 31). As
shown by the
dotted lines in Fig. 3, the data and/or power distribution lines 28A-28C
preferably extend
through and are substantially coextensive with each cable segment.
Additionally, in many
of the preferred embodiments, the data and/or power distribution lines 28A -
28C are
coupled to the main power line 23 via the respective repeaters 25A - 25C
located in each
of the streamer electronic modules 14. In the many of the preferred
embodiments, the
couplers 16, 32 are inductive couplers. However, any suitable coupling
mechanism may
be employed, including capacitive coupling, ohmic connections, and/or optical
links.
In some embodiments, it may be desirable to include a terminating circuit 34
at the
end of the last data/power distribution line(s) 28C in the underwater cable 2.
The
terminating circuit 34 is preferably configured to provide proper termination
for the
data/power distribution line(s) 28A-28C. In alternative embodiments, the
terminating
circuit 34 may also be configured to transmit synchronization information
and/or idle
signals along the data/power distribution line(s) 28A-28C. In many of the
preferred
embodiments, two oppositely connected Zener diodes (i.e., a voltage adjusting
circuit as
discussed below) may be utilized to terminate the outbound data/power
distribution lines
while the inbound datalpower distribution lines may have a resistive
termination.
In Fig. 3, the data and/or power distribution line(s) 28A-28C are shown
generally
and may comprise any number of physical connections. The distribution lines
may be
variously configured to include an optical, single ended, and/or balanced
electrical
connection. Further, the configuration shown in Fig. 3 may represent a half-
duplex or
full-duplex system. Conventionally, data transmitted from the electrical
devices 18 to the
21
CA 02617233 2008-01-29
dry-end electronics 5 may be referred to as "inbound data" and data
transmitted from the
dry-end electronics 5 to the electrical devices 18 may be referred to as
"outbound data."
In some embodiments, each datalpower distribution line 28A-28C may be a single
line. For a single line system, it may be preferable to time and/or frequency
multiplex the
inbound and outbound data. In other embodiments, each data/power distribution
line(s)
28A-28C may comprise multiple lines. For a multiple line system, it may be
preferable to
utilize a full-duplex communication system where outbound data is distributed
on a
separate distribution line from the inbound data. For example, each of the
data/power
distribution line(s) 28A - 28C may be a dual line system having an inbound
data
distribution line and an outbound data distribution line. In such embodiments,
it may be
desirable to multiplex a power signal onto either the inbound and/or outbound
data
distribution line. Alternatively, each data/power distribution line(s) 28A -
28C may
include three lines where inbound data, outbound data, and the power signal
are
transmitted on a separate distribution line.
Fig. 4 shows an embodiment where the outbound data and power signal may be
multiplexed together on a single outbound data and power distribution line 38A-
38C while
inbound data may be distributed on a single inbound data line 39A-39C. In many
of the
preferred embodiments, the power distribution and/or data communication system
20 is
configured as shown in Fig. 4 using a first twisted pair wire for each cable
segment of the
outbound data/power distribution lines 38A-38C and a second twisted pair wire
for each
cable segment of the inbound data distribution lines 39A-39C. The embodiment
shown in
Fig. 4 may be preferable for many applications since this embodiment reduces
the weight
and cost of the copper transmission lines while still maintaining a data
channel having a
relatively high bandwidth.
Fig. 5 shows an embodiment of the power distribution and/or data communication
system 20 having separate inbound data, outbound data, and power distribution
lines.
This configuration may be useful in systems which require large amounts of
data to be
transmitted in both the outbound and inbound direction, where the electrical
devices 18
have large power requirements, and/or where the additional weight of a
separate power
line may be acceptable.
Separate power distribution lines may extend either partially or completely
through
an individual cable segment. For example, each cable segment may include two
or more
power distribution lines. As illustrated in Fig. 5, cable segment A includes
first and
22
CA 02617233 2008-01-29
second power distribution lines 41, 42. The first and second power
distribution lines 41,
42 may be substantially disposed through first and second halves of each cable
segment,
respectively. In this configuration, the length of each power distribution
line may be
reduced by about one-half the length of the cable segment, with repeaters
disposed on
each end of the cable segment supplying the power for about one-half of the
electrical
devices 18 disposed along the cable segment. Reducing the length and current
requirements of the power distribution lines by half provides for more
efficient power
transfers and a reduction in the size/weight of the wire utilized for the
power distribution
lines 41, 42. Where two or more power distribution lines are utilized on a
single cable
segment, a termination circuit 44 may be included to provide proper
termination of each
power distribution line.
Fig. 6 shows an embodiment of the power and/or data communication system 20
where each repeater 25A'-25C' is preferably adapted for repeating data along a
primary
data channel 48, such as a main data channel utilized to transmit acoustic
hydrophone data
to the control processor 21. The primary data channel 48 may include fiber
optic data
transmission lines. Each repeater 25A'-25C' may be connected to one or more
secondary
data/power distribution line(s) 46, 47 which communicate with some or all of
the wet and
in-streamer units 30, 31 disposed along a cable segment 13. In the illustrated
embodiment, the cable segment 13 may be divided such that the repeaters at
either end of
the cable segment communicate with about half of the wet and in-steamer units
30, 31
disposed along the cable segment 13 using separate data/power distribution
lines.
In the embodiment illustrated in Fig. 6, the secondary datalpower distribution
line(s)
may distribute data at a relatively slow speed as compared with the primary
data channel.
For example, the secondary data/power distribution lines may utilize one or
more twisted
pair copper wires to transmit data and power as ' discussed above with regard
to the
data/power distribution lines shown in Figs. 3-6. The repeaters 25A'-25C' may
be
arranged to provide data link control and other data management functions for
formatting
data transferred between the primary data channel 48 and the secondary
data/power
distribution lines 46, 47 depending on the protocols utilized on the
respective channels.
The configuration illustrated in Fig. 6 may be useful in systems where the
primary
data channel 48 (e.g., a fiber optic backbone communication channel) has
sufficient excess
capacity to accommodate the additional data to be transferred between the dry-
end
electronics 5 and the electrical devices 18. An advantage of the system
illustrated in Fig.
23
CA 02617233 2008-01-29
6 is that the secondary data/power distribution lines may span only a limited
distance over
all or a portion of a cable segment 13. Accordingly, where the length of the
secondary
data/power distribution lines 46, 47 is less than the cable segment, data
rates may be
increased and wire size reduced without adversely impacting power and data
transfer with
the electrical devices 18.
In each of the above embodiments of the power and/or data communication system
20, power is preferably distributed using a hierarchical tree structure with
the main power
supply 22 forming the roots or base, the main power line 23 forming the trunk,
datalpower distribution line(s) 28A-28C, 38A-38C, 41, 42, 46, 47 forming
branches, and
each coupler 16, 32 forming a leaf. Each branch may be disposed in parallel
with the
trunk and may extend along the cable either toward the survey vessel 8 or
toward the aft
end of the underwater cable 2 depending on the particular embodiment employed.
When
the tree power structure shown in Figs. 3-6 is utilized, a) the power and/or
data
distribution lines may be isolated from each other and provided with fault
tolerant features
that preserve communications and/or power distribution even though a fault
occurs along
a particular cable segment, b) the power to the electrical devices may be
transferred along
a relatively short power distribution line at a high frequency, thus improving
the coupling
coefficient for a given coil core weight, c) the circuits for converting the
main power
signal into a high frequency AC power signal can be the same circuits utilized
for
transmitting data, and d) the power supply, circuit cards, and housing of the
existing
SEM's can be shared with the repeater circuits to minimize the weight and
complexity
added to the underwater cable system while transferring operational power to
the electrical
devices.
Part II: Facilitating Power Distribution to Wet Units
The above described power distribution and/or data communication systems 20
may
be facilitated by the addition of a number of elements designed to enhance the
power
transfer efficiency to each of the electrical devices 18 and particularly to
the wet units 30
which may have a low coupling coefficient. For example, referring to Fig. 7,
power
conversion circuits for use in the above described embodiments are shown in
detail. As
discussed above, a main power signal is supplied from main power supply 22.
Preferably
the main power signal is a low frequency AC signal or a DC signal output on
main power
line 23. The main power signal may be coupled to a plurality of underwater
cable power
24
CA 02617233 2008-01-29
conversion circuits 50 disposed along the main power line 23.
The power distribution and communication system 20 may be variously configured
to include any number of power conversion circuits located at any number of
locations
along the underwater cable 2. Where the underwater cable 2 includes streamer
electronics
modules (SEM's) 14, the underwater cable power conversion circuits may be
disposed
inside and/or outside of the SEM's, but are preferably respectively disposed
within the
SEM's. Further, the underwater cable power conversion circuits 50 may share
some or
all of their circuitry with the repeaters 25. Incorporating the power
conversion circuits in'
the repeater circuits and locating the power conversion circuits in the SEM's
enables the
power conversion circuits to share common circuits/circuit cards with the
repeater circuits.
Thus, the overall weight and cost of the power distribution and communication
system 20
may be reduced. Alternatively or additionally, some or all of the power
conversion
circuits 50 may be separate from the repeater circuits and disposed along the
underwater
cable at locations spaced from the SEM's.
Each underwater cable power conversion circuit 50 preferably converts the main
power signal on the main power line 23 into a power distribution signal (e.g.,
a high
frequency AC power signal). The power distribution signal may then be
transferred to
each of the electrical devices 18 via a coupler 16, 32, preferably via an
inductive coil
having a core. In some of the preferred embodiments, the power distribution
signal is
supplied to two or more couplers via a dataipower distribution line. The power
distribution signal may have a frequency of between about 25 kHz and 400 kHz,
and
preferably between about 30 kHz and 300 kHz and even more preferably between
about
40 kHz and 200 kHz and even more preferably between about 50 kHz and 100 kHz
and
most preferably about 64 kHz. The weight of a core necessary to achieve a
particular
level of power transfer efficiency is inversely proportional to the frequency
of the power
distribution signal. For example, a lower frequency power distribution signal
requires a
heavier core to provide the same power transfer efficiency as a lighter core
used with a
higher frequency power distribution signal. Accordingly, if the frequency of
the power
distribution signal was the same as the frequency of the main power signal,
e.g., 2 kHz,
then the core weight in the coupler would be about 32 times more massive than
that
required for a power distribution signal having a frequency of 64 kHz.
However, a
substantially higher frequency power signal may be difficult to maintain for
long cable
lengths because of losses, e.g., due to loading and cable capacitance and skin
effect of the
CA 02617233 2008-01-29
underwater cable. Further, a substantially higher frequency power signal
generates noise
that may be difficult to control and exclude from guarded frequency bands used
by the
hydrophones.
The frequency of the power distribution signal is preferably chosen within the
ranges
specified above and matched to the physical wire gauge, length, the insulation
characteristics (which determine capacitance), loading of the dataipower
distribution lines,
and core weight of the coil. Accordingly, in some of the preferred embodiments
a power
distribution signal having a frequency of about 64 kHz has been found to
provide excellent
operational characteristics when utilized to transfer power to a plurality of
wet units 30 in
the underwater cable 2.
Although the frequency of the main power signal may be variously configured as
discussed above, an underwater seismic cable may utilize a frequency of about
2 kHz. If
a power signal having a 2 kHz frequency were coupled directly to the wet units
via an
inductor, for many embodiments the coupling coefficient may be so low that it
would be
impractical to power the wet units 30 from the underwater cable 2 without a
massive core.
However, by converting the main power signal into a higher frequency, power
distribution
signal at spaced locations within the underwater cable, it is possible to
efficiently couple
power to the wet units 30 even where a low coupling coefficient is present.
As discussed above, transmitting power at a relatively low frequency along the
main
power line allows the power to be efficiently transmitted to the aft end of
the underwater
cable. Converting the lower frequency main power signal to a higher frequency
power
distribution signal allows the power to be efficiently distributed from the
main power line
to the electrical devices. This is especially advantageous where the
electrical devices are
mounted external to the underwater cable and power is inductively or
capacitively coupled
through the sheath of the underwater cable without any connectors physically
penetrating
the sheath. The high frequency signal inductively couples power through the
sheath far
better than a low frequency signal.
The underwater cable power conversion circuit may be variously configured
depending on the operational environment. For example, if the main power
signal on the
main power line is a low frequency AC power signal, the underwater cable power
conversion circuit may comprise a cyclo-converter or other device which
converts one AC
signal directly into another AC signal. However, in preferred embodiments, it
is often
desirable and more efficient to first convert the low frequency AC power
signal on the
26
CA 02617233 2008-01-29
main power line into a DC signal and then to convert the DC signal into a high
frequency
AC power distribution signal.
In the configuration shown in Fig. 7, each of the underwater cable power
conversion
circuits 50 may include a first power circuit 51 for converting the main power
signal
(e.g., either an AC or DC signal) into a regulated DC signal and a second
power circuit
52 for converting the regulated DC signal (V2) into a high frequency AC signal
(V5).
Where the main power line 23 includes a DC power signal, it may be desirable
to omit
the first power circuit 51 entirely. In this embodiment, the main power line
23 would be
electrically connected directly to the second power circuit 52, and V2 would
equal the DC
power signal.
In some embodiments, it may be desirable to limit the current supplied by the
underwater cable power conversion circuits. In these embodiments, the current
limiting
function may be variously configured to be positioned at any location within
the
underwater cable power conversion circuits 50 and/or at other locations. In
some of the
preferred embodiments, the first power circuit 51 includes a DC current
limiter which
serves to limit the current supplied to the outbound data and/or power
distribution lines.
The second power conversion circuit 52 may receive a carrier clock signal
directly or
receive a carrier signal after modulation by an optional encoding circuit 56.
If the
encoding circuit 56 is utilized, the encoding circuit 56 preferably
multiplexes data onto the
power carrier signal input 54. Further, the encoder 56 may utilize one or more
clock
inputs to synchronize the data/power signals with one or more system clocks.
One
example of an encoding circuit is shown in Fig. 9 where the modulation scheme
utilized is
binary phase shift keying (BPSK). Accordingly, the encoder 56 may be
implemented by
an exclusive-OR (XOR) gate 70.
In embodiments, such as those shown in Figs. 5-6, where power may be
distributed
to two power distribution lines respectively located in two adjacent cable
segments, it may
be preferable to include an additional second power circuit 52A in each of the
underwater
cable power conversion circuits 50. The second power circuit 52A may receive a
carrier
clock signal directly or after modulation by an optional encoding circuit 56A
via carrier
input 54A. The additional second power circuit 52A may output a power and/or
data
signal to one or more couplers and associated electrical devices 18 via a
second set of
power distribution lines.
The repeater circuits may receive operating voltages from V2 of the first
power
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CA 02617233 2008-01-29
circuit, from one or more voltage regulators and/or from one or more DC-DC
converters.
Where the repeaters require multiple DC voltages, one or more DC-DC converters
53
may be optionally provided to supply one or more DC voltages V3, V4, or the
first power
circuit 51 may provide one or more DC voltages V3A, V4A.
The underwater cable power conversion circuit 50 may optionally include one or
more transformers 55 to isolate the power conversion circuit 50 from the
data/power
distribution lines. In some of the preferred embodiments, the transformer 55
may also be
utilized to increase the voltage on the data/power distribution line to
facilitate power
transfer along the cable segments 13. For example, it may be desirable to
increase the
voltage to between 10 and 400 volts, and preferably to between 15 and 200
volts, and
even more preferably to between 30 and 100 volts, and most preferably to about
42 volts.
As the wire size of the data/power distribution lines becomes smaller (e.g. as
the
wire gauge increases), the voltage on the data/power distribution lines
preferably increases
in order to achieve the same efficiency. However, there may be a lower limit
to how
small a wire may be utilized before the voltage increases so much that the
power
distribution signal begins to couple to the remainder of the underwater cable
electronics
(particularly into the hydrophone circuits). In some of the preferred
embodiments, a
voltage of about 42 volts on the data/power distribution lines having a wire
gauge of 26
AWG provides sufficient power transfer for up to about 3 watts, preferably
about 1.4
watts to each of two devices, without adversely impacting other electronics in
the
underwater cable 2 and while maintaining a high power transfer efficiency.
The wire gauge for the main power line 23 and for the dataipower distribution
lines
may be variously configured. For example, in exemplary embodiments the wire
gauge on
the main power line may be between 2 and 14 AWG, and preferably between 4 and
12
AWG, and even more preferably between 6 and 10 AWG and most preferably about 8
AWG. By contrast, the wire gauge for the data/power distribution lines may be
between
20 and 36 AWG, and preferably between 22 and 32 AWG, and even more preferably
between 24 and 30 AWG and most preferably about 26 AWG.
The underwater cable power conversion circuits 50 may be located in any
suitable
location in the power distribution and/or data communication system 20. In
some
embodiments it may be desirable to distribute the underwater cable power
conversion
circuits 50 along a cable segment in the underwater cable 2. For example, a
power
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CA 02617233 2008-01-29
conversion circuit may be located in each repeater and/or each coupler.
In some embodiments, incorporating an underwater cable power conversion
circuit
50 in each coupler 16, 32 may minimize noise in the underwater cable. Fig. 8
shows an
embodiment where each coupler includes an underwater cable power conversion
circuit
50. In the embodiment shown in Fig. 8, the couplers (e.g., first coupler 16',
32') may be
configured as a three-inductor coupler where power, inbound data, and outbound
data are
coupled to an electrical device 18 using three different coils. The underwater
cable power
conversion circuits 50 in coupler 16', 32' may receive a clock from clock
generator circuit
59 at the carrier input 54A. Thus, in this embodiment, the carrier frequency
of the power
transfer is preferably generated by the clock generator circuit and may be
independent of
the data transfer rate of inbound and outbound data. The clock generator
circuit 59 may
be any suitable circuit such as a crystal oscillator.
In the embodiment shown in Fig. 8, the couplers (e.g., second coupler 16",
32")
may be configured as a two-inductor coupler where, for example, power and
outbound
data may be coupled to an electrical device 18 using a first coil and inbound
data may be
coupled to an electrical device 18 using a second coil. The carrier input 54
(not shown in
Fig. 8) of the underwater cable power conversion circuits 50 in coupler 16",
32" may
receive a signal directly from the outbound data line or indirectly through an
encoder 56
(not shown). If data from the outbound data line is to be encoded via encoder
56, a
carrier clock may be input into the encoder 56 from any suitable source such
as a second
clock generator circuit 59A (not shown).
Distributing the underwater cable power conversion circuits 50 to respective
locations proximate to each of the electrical devices 18 has an advantage in
that the
amount of noise generated by the power transfer to the electrical devices 18
may be
minimized. However, the configurations shown in Fig. 8 are less preferred in
many
environments due to space constraints within some coupler configurations which
can make
it difficult to include the power conversion circuits within the couplers
without the use of
custom integrated circuits.
Fig. 9 shows one embodiment of the underwater cable power conversion circuits
50.
In this embodiment, the data input is shown being gated by XOR gate 70 with
the power
carrier clock. The output of the XOR gate may be input into the power
conversion
circuits 50. In embodiments where data is not modulated on the power signal,
the
unmodulated carrier signal may be input directly into the power conversion
circuits.
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CA 02617233 2008-01-29
The modulated or unmodulated carrier output from the XOR gate 70 is preferably
input into inverting buffer 72 and non-inverting buffer 71 disposed within the
power
conversion circuits 50. In embodiments where data is not multiplexed onto the
data/power
distribution lines, the optional data input and XOR gate 70 may be omitted
with the power
carrier clock being input directly into inverting buffer 72 and non-inverting
buffer 71.
The output of the buffers 71, 72 control the switching of transistors 73, 74,
which in turn,
control the outbound data and/or power distribution signal on the data/power
distribution
lines.
Fig. 10 shows a timing diagram for the operation of one embodiment of the
circuit
shown in Fig. 9. In the illustrated embodiment, the power carrier clock has a
frequency
of 64 kHz (Fig. 10a). In preferred embodiments, the outbound data (e.g., data
modulated
by XOR gate 70) may be distributed at a lower frequency than the power carrier
due to
capacitive loading and other noise considerations. It was found that
modulating the data
onto the carrier using a data rate different from the carrier frequency band
substantially
improved the reliability of the system, particularly where data and power are
transmitted
along a data/power distribution line. Accordingly, data may be transferred at
a rate of
about one-half of the carrier frequency, and preferably about one-quarter of
the carrier
frequency and even more preferably about one-eighth of the carrier frequency
and most
preferably about one-sixteenth of the carrier frequency or less. When data and
power are
transferred on the same line, transferring a data signal at a substantially
lower bit rate than
the center carrier frequency of a power signal provides for high power
transfer efficiencies
while maintaining reliable communications. In the illustrated embodiment, data
is
transferred at a rate of 4 kbps (Fig. 10b) which is one sixteenth of the
carrier frequency of
64 kHz.
Power transfer efficiencies are influenced by a load resistance at the point
along the
data/power distribution lines where the power is extracted and by the
capacitance of the
line and the bandwidth of the signal. Due to capacitive coupling and a
relatively high load
resistance on the data/power distribution lines, the RC time constant of the
outbound link
may be relatively large. Accordingly, high power transfer efficiencies and
reliable data
transfer may be achieved where the ratio of data transfer rate to power
transfer frequency
is maintained at about 1:2 or less, and preferably about 1:4 or less and even
more
preferably about 1:8 or less, and most preferably about 1:16 or less.
One technique for transferring a data signal and a power signal on the same
line is
CA 02617233 2008-01-29
binary phase shift keying (BPSK). As shown in Fig. 9, the BPSK encoder may
simply be
an XOR gate such as XDR gate 70. An exemplary timing diagram of the output
from the
XOR gate 70 is shown in Fig. 10c. As shown in Fig. 10c, a change in the
outbound data
signal corresponds to a phase change of the BPSK signal. Fig. 10d shows one
example of
the outbound data/power signal output to the power distribution line(s) in
each cable
segment after encoding by the BPSK encoder 70. In some of the preferred
embodiments,
transformer 55 boosts the output voltage on the data/power distribution lines
to about 42V.
Referring to Fig. 11, when each of the electrical devices 18 are inductively
coupled
to the data/power distribution lines, the electrical devices preferably
include an electrical
device power circuit 60 for converting the AC signal received from couplers
16, 32 into a
DC signal. Although the device power circuit may be variously configured, in
the
embodiment illustrated in Fig. 11, the device power circuit 60 includes a
resonating
capacitor 65, a full-wave bridge rectifier 61 for outputting a rectified
signal, a low-pass
filter (e.g., a smoothing capacitor 64) for filtering the rectified signal
into a DC signal,
and a voltage regulator (not shown) to regulate the DC signal at a desired
voltage. One or
more DC/DC converters (not shown) may optionally be included to provide DC
outputs
having differing voltages.
As shown in Fig. 11, where data is modulated onto the data/power distribution
lines,
it may be desirable to separate the outbound data signal from the power signal
in the
electrical device, for example, by using voltage divider 62 and comparator 63.
The
resonating capacitor 65 produces voltage square waves at the inputs of the
full-wave
bridge rectifier. These followed by the comparator produce a very reliable
recovery of
the data waveform. The outbound data signal may then be output to data
communication
circuits such as data encoders and decoders.
As discussed above, it may be preferable to transmit a power distribution
signal on
the data/power distribution lines utilizing an elevated voltage in order to
enhance power
transfer efficiency to the electrical devices 18 and particularly for
inductively powering the
wet units 30. However, this power transfer may produce noise which can have an
adverse
impact on other systems in the underwater cable such as the hydrophones 7.
It has been found that by limiting the bandwidth of the frequency spectrum of
the
power distribution signal on the dataipower distribution lines to occupy a
band which is
different from, and preferably spaced from, the frequency band used by the
hydrophones,
significant improvements in the hydrophone signal-to-noise ratio can be
achieved.
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CA 02617233 2008-01-29
Heretofore, this has been difficult to achieve while maintaining an adequate
data
communication bandwidth and a high efficiency power transfer. However, it has
been
found that these problems may be overcome by limiting the length of the
data/power
distribution lines and by employing a distributed filter along these lines.
When each cable segment is limited to about 500 meters or less, and preferably
about 400 meters or less, and even more preferably about 300 meters or less,
and most
preferably about 200 meters or less, it is possible to treat each of the
datalpower
distribution lines as a lumped parameter element and design an electric wave
filter using
elements distributed along the cable segment. Best results occur when the
wavelength of
the power distribution line is preferably no more than one tenth the
wavelength of the
power carrier signal. For example, where the dataipower distribution lines are
200 meters
in length, it is preferable for the power carrier signal to have a frequency
of no greater
than about 100 kHz. Under these conditions, a distributed filter can be
constructed which
limits the frequency spectrum of the power signal to be outside the hydrophone
guard
bands.
The longer the wire length, the lower the allowable frequency using a
distributed
filter technique. Lower frequencies have the undesirable effect of requiring
bigger and
heavier coil cores to achieve adequate power transfer.
The power/data distribution lines, driver circuits, coupler transformers, and
electrical device electronics are preferably operated as a tuned power
transfer circuit. Fig.
12 shows a Thevenin equivalent circuit for one embodiment of a power transfer
circuit 79
which includes the distributed filter technique discussed above. The
equivalent circuit for
one embodiment of an output or driver section of the underwater cable power
conversion
circuit 50 is designated as block 80. In the illustrated embodiment, the
Thevenin
equivalent circuit for the underwater cable power conversion driver circuits
80 includes
voltage source V;,, an inductor Ll, a resistor R1, and a capacitor C1. The
inductor Li
and capacitor C1 are discrete components which may be utilized to adjust and
improve the
filter characteristics of the distributed filter. Resistor Rl represents the
internal resistance
of the inductor Ll and the other losses in the power conversion circuit 50.
The equivalent
circuit for one embodiment of the power distribution line is designated as
block 81 and
includes series connection of R2 and L2 followed by a parallel connection of
C2, R3.
The equivalent circuit for the parallel connected couplers (assuming all
couplers are
inductive) is designated by block 82 showing resistor R4 connected in parallel
with a
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CA 02617233 2008-01-29
series circuit comprising resistor R5 and inductor L2, mutual inductance M23,
inductor L3
and series resistor R6. The load includes resonating capacitor C3 and resistor
R7. (See
Fig. 12.)
An important aspect of the power transfer circuit approximated by the Thevenin
equivalent circuit shown in Fig. 12 is configuring the power transfer circuit
to resonate at
the carrier frequency of the power distribution signal and configuring the
circuit to form a
filter, preferably a bandpass filter, centered at the carrier frequency. One
example of a
frequency response of the power transfer circuit approximated by Fig. 12 is
shown in Fig.
13. As shown in Fig. 13, by adjusting the lumped and distributed parameters of
each
power/data distribution line as well as the values of the discrete components
L1, C1, L2,
M23, L3, C3, a distributed bandpass filter may be constructed with a frequency
band
centered about the power distribution signal carrier frequency (e.g., 64 kHz)
while
maintaining a sufficiently sharp cut-off to avoid coupling any significant
energy from the
power distribution signal into the hydrophone operating frequency bands.
The outer sheath 15 of the underwater cable 2 may have a plastic jacket having
a
thickness of approximately one-eighth of an inch. Accordingly, a large core
gap may
exist in the transformers composed of couplers 16 and wet units 30. A
conventional
transformer has a coupling coefficient of about 0.98 or better. However,
transformers
utilized to couple the power/data distribution lines and the wet units 30 may
have a
coupling coefficient of as low as 0.1 or lower. It was found that if the
data/power
distribution lines are designed as an electric wave filter, e.g., a three-
resonator bandpass
filter, it is possible to incorporate the transformer into the filter and thus
to increase the
power transfer efficiencies between the power/data distribution lines and the
wet units 30.
Again referring to Fig. 13, the three-section bandpass filter may, for
example, have a
center frequency of 64 kHz and a two sided bandwidth of 8 kHz. In this
configuration,
the data/power distribution lines will transmit 4 kbps BPSK data on a 64 kHz
carrier
without distortion.
The right hand portion of Fig. 13 shows an exemplary frequency band in which
the
plurality of hydrophones operate (often referred to as the forbidden bands).
The forbidden
bands may be variously configured to include one or more frequency bands,
preferably
distinct and/or spaced from the frequency band of the distribution lines. In
one exemplary
embodiment, the forbidden bands reserved for hydrophone operations are the
integer
multiples of 128 kHz with 500 Hz guard bands. Accordingly, in such a system it
is
33
CA 02617233 2008-01-29
desirable to configure the frequency band of the power distribution signal and
the data
signal to avoid the frequency bands used for hydrophone operations. The three-
section
bandpass filter may be designed to reduce the signal energy in these bands to
a
predetermined low level.
Wire utilized for the data/power distribution lines in each cable segment is
preferably a low loss cable having a dissipation factor maintained within low
tolerances.
The low loss cable preferably is configured to have a capacitance specified to
tune the
power transfer circuit, to control the frequency band of the filter, and to
minimize power
loss in the data/power distribution lines due to capacitive coupling to other
portions of the
underwater cable 2.
Typically, the underwater cable 2 may be filled with a lossy dielectric
material. By
a lossy dielectric material it is meant that the material has a dissipation
factor of about
0.01 or greater including, for example, about 0.1 or greater. The lossy
dielectric material
may be a petroleum based material such as an isoparaffm solvent (e.g.,
kerosene), a wax,
a liquid, and/or a solid plastic material. If the lossy dielectric material is
a liquid, it is
preferred to have an outer sheath 15 disposed about the underwater cable 2 to
contain the
liquid. If the lossy dielectric material is a solid, the outer sheath may be
formed of the
solid material and the solid material may extend throughout the underwater
cable 2.
The lossy dielectric material is typically utilized in an underwater cable to
provide
buoyancy. Any liquid, solid, or semi-solid lossy dielectric material that is
less dense than
seawater will suffice to adjust the buoyancy of the underwater cable 2. One
problem with
distributing power through a lossy dielectric material is that the lossy
dielectric has a large
relative permittivity. For example, an isoparaffin solvent may have a relative
permittivity
of about 3. Thus, by filling the underwater cable with a lossy dielectric
having, a relative
permittivity of, for example, 0.1, 1.0, 2.0, 3.0, 10.0 or more, the
capacitance of the
data/power distribution lines may be changed. Research has shown that even
with
excellent insulation disposed on the power distribution line, the loss due to
the lossy
dielectric may be prohibitively large, particularly when using twisted pair
wires, high
voltages, and high frequencies. In many embodiments, it was found that the
presence of
the lossy dielectric caused the efficiency of the data/power distribution
lines to be
degraded to an inoperable level.
Research demonstrated that this problem may be overcome by placing an outer
plastic jacket or sheath around the insulated power distribution line. For
example, where
34
CA 02617233 2008-01-29
the data/power distribution pines are insulated twisted pairs wires, an outer
sheath may be
disposed around the insulated twisted pairs. Referring to Figs. 14 and 15, the
underwater
cable 2 is shown disposed underwater 86 and filled with a lossy dielectric
material 87. In
some embodiments, the underwater cable 2 may include a number of support or
stiffening
cables 84, fiber optic cables 85 and/or electric cables 89 (e.g., main power
line 23) in
addition to an inbound data distribution line 43 and an outbound power/data
distribution
line 38, 41, 42, 46. In some embodiments, the stiffening cables 84 may be
configured to
transmit main power to replace and/or supplement main power line 23. In
preferred
embodiments, an outer jacket or outer sheath 83 (preferably plastic) is
disposed about the
power/data distribution lines which are formed from a twisted pair wire where
each wire
is itself insulated using a sheath 88.
In some of the preferred embodiments, the outer sheath 83 may not be placed
around data lines such as inbound data distribution line 43. In many
applications, there
may be no need for a low loss cable or a jacketed cable on the inbound data
distribution
lines because these lines are typically terminated with a low resistance and
because
capacitance typically does not have to be controlled to the same level as when
power is
being distributed. Thus, a significant reduction in cost can be achieved while
still
maintaining highly reliable data transfers on the inbound data distribution
lines.
Fig. 15 shows a longitudinal cross section of the data/power distribution
lines 38,
41, 42, 46 including the outer jacket 83. In preferred embodiments, the
power/data
distribution lines with the outer jacket 83 have a dissipation factor D less
than about 0.01
and preferably less than about 0.008, and more preferably less than about
0.006, and even
more preferably less than about 0.004, and most preferably about 0.002 or less
when
surrounded by the lossy dielectric material. The outer jacket 83 is preferably
configured
to space the lossy dielectric a sufficient distance from the power/data
distribution lines
such that most of the electric flux lines stay inside the outer jacket 83 and
do not stray
into the lossy dielectric where losses may be generated. This further prevents
an increase
of line capacitance due to the high relative permittivity of the lossy
dielectric material.
The coupling loss coefficient for the data/power distribution lines may also
be
determined such that the above described distributed filter produces the
desired filtering
characteristics since specifying the thickness of the insulation also
determines the
capacitance. The power distribution lines are typically specified in henrys
per meter and
farads per meter. To achieve a highly reliable filter, in some of the
preferred
CA 02617233 2008-01-29
embodiments, the cable capacitance may be controlled to within about 5 %
tolerance so
that the power transfer circuit remains tuned and the filter remains centered
at the carrier
frequency of the power distribution signal.
Experiments have demonstrated that distributing power to the electrical
devices 18
over twisted pair wires disposed in an outer jacket is highly efficient, and
especially where
the power distribution signal includes relatively high voltages and relatively
high
frequencies. It has been found that the outer jacket 83 disposed over the
twisted pair
power distribution line, remarkably increases the power transfer efficiency
particularly
when the data/power distribution lines form a tuned power transfer circuit.
The
data/power distribution lines are preferably configured to include both an
outer jacket 83
and insulation 88 on the twisted pair wires themselves. Further, the outer
jacket 83 is
preferably a low loss cable jacket such that each power/data distribution line
has a low
dissipation factor D as discussed above. Conventionally, jacketed/ insulated
low-loss
twisted cables have not been utilized to distribute power to electrical
devices in underwater
cables.
Extensive problems exist for inductive couplers disposed in underwater cables.
For
example, the underwater cable 2 has limited area to accommodate the inductive
coils due
to numerous support, electrical, and optical cables as well as electrical
devices 18
disposed within the underwater cable 2. Although certain coil core materials
are
preferable from an electromagnetic perspective, these core materials have been
found to be
prohibitively brittle. A brittle core may cause reliability problems when the
underwater
cable 2 is retrieved and rolled up over one or more steel rollers 9 on the
survey vessel 8.
Further, alignment problems often occur as the couplers are assembled and
disassembled
in the field. For example, the core in the underwater cable may be misaligned
with the
core in the wet unit. An alignment problem can often severely reduce the
coupling
coefficient of the coupler. Additionally, where more than one coil is
associated with a
particular coupler, cross-talk among the coils was found to be a problem.
Further still,
even a single coil may couple into the hydrophone lines and adversely affect
other
underwater cable systems. Accordingly, substantial research was directed
toward defining
high efficiency inductive couplers suitable for use in providing operational
power to
electrical devices 18 disposed in underwater seismic cables.
Referring to Figs. 16-18, a first preferred embodiment of an inductive
coupling coil
90 for use in the couplers is shown. As shown in Fig. 18, the inductive
coupling coil 90
36
CA 02617233 2008-01-29
has a substantially triangular shaped cross section and a winding 91 wound
around at least
a portion of the substantially triangular-shaped core 92. In some embodiments,
it may be
desirable to include a truncated portion 96 on one or more points of the
substantially
triangular-shaped core 92.
The substantially triangular-shaped core 92 preferably has first, second, and
third
substantially planar surfaces 93, 94, and 95. The first planar surface may be
substantially
larger than the second or third planar surfaces. The first planar surface 93
preferably is
disposed facing the exterior of the underwater cable 2 abutting the outer
sheath 15. The
coupling coil 90 is preferably disposed with a longitudinal axis 97 disposed
in parallel
with the longitudinal axis of the underwater cable 2 such that the first
substantially planar
surface is disposed longitudinally along the underwater cable 2. In exemplary
embodiments, it may be desirable for the first planar surface 93 to have a
rounded shape
such that the first planar surface is contoured to about the same curvature as
the inner
surface of the underwater cable 2. Further, the second and third surfaces 94,
95 may be
substantially flat.
The winding direction 98 and configuration of the coils is preferably
precisely
specified. Precise windings of the coils may minimize cross-talk when two or
more coils
are placed in close proximity, increase power transfer efficiencies, and
minimize inductive
coupling to the hydrophone electromagnetic system. These precise windings may
be
particularly important in underwater seismic cables where operational power is
inductively
coupled to the wet units 30.
Substantial research has been directed at determining an optimal inductor/coil
core
configuration. Referring to Fig. 17, paint dot 99 indicates the coil
orientation with regard
to cross section A-A shown in Fig. 18. Fig. 18 illustrates a winding direction
98 of the
coils. In exemplary embodiments, the winding direction of each coil is
preferably the
same (either clockwise or counter clockwise) with respect to paint dot 99 in
order to
facilitate correct installation.
As shown in Fig. 19, it may be desirable to include two or more coils in close
proximity to each other. In this embodiment, coil A 90A may be utilized, for
example,
for transferring outbound dataipower to a wet unit 30 and coil B 90B may be
used, for
example, for transferring inbound data from a wet unit 30. Paint dot 99 may be
utilized
as a reference point to illustrate that it is desirable for the windings of
coils A and B to be
in opposite directions for controlling cross-talk. For example, the windings
of coil A 90A
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CA 02617233 2008-01-29
are in the clockwise direction while the windings of coil B 90B are in the
counter
clockwise direction.
In preferred embodiments, each coupler 16, 32 includes an outbound data/power
tap
wire 110 for connecting the coupler to the outbound data/power distribution
line 38 and an
inbound data tap wire 111 for connecting the coupler 16, 32 to the inbound
data
distribution line 39. Each tap wire may have larger, smaller, or the same wire
size as an
associated distribution line. In exemplary embodiments, the tap wires 110, 111
have a
wire size that is smaller than the distribution lines 38, 39. In preferred
embodiments the
wire gauge may differ by one, two, or more AWG. In some of the more preferred
embodiments, each tap wire is smaller than an associated distribution line.
The inbound data tap wire 111 is preferably coupled to wire wound around the
core
of coil B 90B and designated blue wire BLU. Although the windings of coil B
90B may
be variously configured, the winding wire is preferably wire having a wire
gauge of 26
AWG or greater, and preferably 28 AWG or greater, and more preferably 30 AWG
or
greater, and most preferably about 32 AWG. The number of turns of blue wire
BLU may
be variously configured to match the frequency of the data transferred across
this coil. In
some of the preferred embodiments where the inbound data is transferred at 64
kHz, the
blue wire BLU preferably has about 353 turns.
The outbound data/power tap wire 110 is preferably coupled to wire wound
around
the core of coil A 90A and designated red wire RED. Although the windings of
coil A
90A may be variously configured, the winding wire is preferably wire having a
wire
gauge of 26 AWG or greater, and preferably 28 AWG or greater, and more
preferably
about 30 AWG. The number of turns of red wire RED may be variously configured
to
match the frequency of the data/power transferred through this coil. In some
of the
preferred embodiments the red wire RED has about 158 turns.
Under certain circumstances, the power transferred to the wet units 30 may
still
couple into the data distribution lines. However, it was found that this
problem may be
alleviated by including a bucking coil 112 (green wire GRN) electrically
connected
between the blue coil and the inbound data tap wire 111 and physically wound
around the
core of coil A 90A. Although the bucking coil may be variously configured, the
winding
wire is preferably wire having a wire gauge of 26 AWG or greater, and
preferably 28
AWG or greater, and more preferably about 30 AWG. The number of turns of green
wire GRN may be matched to the anticipated electromagnetic coupling between
the two
38
CA 02617233 2008-01-29
signals on Coil A 90A anu Coil B 90B, but is preferably about 21 (urns. In
general, a
bucking coil results where each coupler includes a first coil connected to a
first line (e.g.,
an outbound data and/or power distribution line) and second and third coils
connected to a
second line (e.g., an inbound data distribution line), where the first and
second coils are
spaced from each other (typically wound around separate coil cores) and where
the first
and third coil are in close proximity (typically wound around the same core)
for
controlling cross-talk between the first and second coils as well as the first
and second
lines.
In many embodiments, the cores of the coil may be brittle. Accordingly, it was
found that the reliability of the underwater cable can be remarkably improved
by disposing
the coils (e.g., coils 90A, 90B) in a housing. Referring to Fig. 20, a cut-
away side view
of a portion of the underwater cable 2 shows coil A 90A disposed in a first
pocket 121 of
a housing 120. Similarly, Fig. 21 shows a rotated cut-away side view of the
same portion
of the underwater cable 2 with the coil B 90B disposed in a second pocket 122
of the
housing 120. The housing 120 is preferably formed of a substantially rigid
material such
as a plastic or metal alloy which has sufficient structural integrity to
protect the coils 90A,
90B.
The pockets 121, 122 may be variously configured. In some embodiments, the
pockets 121, 122 may fit tightly against the coils 90A, 90B. However, in some
of the
preferred embodiments, the pockets are slightly larger than the coils 90A, 90B
to permit
some flexing of the housing 120 without adversely affecting the reliability of
the coils
90A, 90B. The pockets may be sealed from the remainder of the underwater
cable.
Further, the pockets may be filled with any suitable cushioning material such
as a foam,
high viscosity oil, grease, gel and/or other spongy substance. It may be
desirable to
configure the cushioning material to urge and/or position the coils toward the
outer sheath
15 of the underwater cable to minimize the gap between coils 90A, 90B and
coils 129,
130, respectively. In embodiments where the underwater cable 2 is filled with
a liquid
lossy dielectric material 87 (e.g. kerosene), the pockets 121, 122 may be in
fluid
communication with the liquid lossy dielectric material 87 or, more
preferably, sealed
from the lossy dielectric material.
As the underwater cable 2 is rolled up onto the survey vessel 8 and over one
or
more steel rollers 9, tremendous forces are exerted on the underwater cable 2.
The
housing 120 disposed about the coils 90A, 90B may protect the brittle core 92
from
39
CA 02617233 2010-10-14
breaking. In some embodiments, the coils 90A, 90B may be designed to float
within the
first and second pockets 121, 122, respectively. By floating, it is meant that
the coils are
not rigidly connected to the housing 120. In these embodiments, even where the
forces
are sufficient to cause the housing 120 to flex, the core 92 may remain intact
because the
core floats (i.e., is not fixedly attached) within the pockets 121, 122 in
housing 120.
Fig. 22 shows a traverse cross-sectional view of the underwater cable 2
including
the sheath 15, the coil housing 120, and a wet unit housing 128. First and
second coils
129, 130 are respectively disposed in the wet unit housing 128 opposed to the
coils 90A,
90B disposed in the coil housing 120. The first coil 129 preferably includes a
winding
127 disposed about a core 126. Similarly, the second coil 130 preferably
includes a
winding 125 disposed about a core 124. In some of the preferred embodiments,
the cores
124, 126 are elongated and disposed longitudinally in the underwater cable in
a similar
fashion as coils 90A, 90B.
Details of the wet unit housing 128, the coil housing 120, and the coupler 116
are
provided in one or more of U.S. Provisional Applications No. 60/004,203, filed
September 22, 1995; 60/004,209, filed September 22, 1995;
60/004,493, filed September 22, 1995; 60/004,494, filed September 22, 1995
and in co-pending International Application entitled Underwater Cable
Arrangement by
Andre W. Olivier, Brien G. Rau, and Robert E. Rouquette, filed on the same day
as the
present International Application.
The coils 90A, 90B may be separated by any radial angle 0 123. Electrically,
an
angle of 180 degrees provides the optimum noise immunity between the coils.
However,
in some embodiments which include an odd number of stiffening and/or power
cables such
as the five cables 84 shown in Fig. 22, another angle may be preferred. In the
illustrated
embodiment, an angle of about 144 degrees is utilized and found to provide the
greatest
noise immunity while providing the highest coupling coefficients and/or
minimal core
sizes for use with five stiffening and/or power cables 84. Further, where the
wet unit
housing includes two halves, an angle of about 144 degrees between the coils
may allow
both coils to be disposed in the same half of the wet unit housing.
One problem with conventional core configurations is that the coils can not
tolerate
any substantial misalignment between the coils in the underwater cable 2 and
the coils in
the wet unit housing 128. Experimentally, it has been found that a coil will
typically
tolerate a misalignment that is equal to about the width of the pole face and
a longitudinal
CA 02617233 2008-01-29
misalignment that is equal o about the length of the pole face. Accordingly,
the geometry
of the coils shown in Figs. 16-18 has been configured to have a relatively
large outer face
93 to allow substantial misalignment, e.g., up to half an inch (1.25 cm) or
more, without
detuning the circuit powering the coils. The wet units may then be fitted with
couplers
which can maintain a precision of plus or minus half an inch. In this
configuration, the
inductances may not change by more than about 6%, and hence the distributed
filters and
tuned circuit are maintained within operating tolerances. The power transfer
circuit may
be configured so that when the inductances change by about 6 %, the overall
filter tune
changes by only about 3% (i.e., one over the square root of LC). Further,
because the
power transfer circuit is a resonant circuit, the waveforms change but the
power
transferred to the loads normally does not decrease. Hence, the relatively
wide,
substantially flat faced coil configurations and particularly the triangular
shaped coils have
demonstrated excellent reliability and power transfer efficiencies.
A longitudinally sectioned view of the underwater cable 2 having a single coil
housing 122 disposed in coupler 16 is shown in Fig. 23. However, the couplers
16 are
not limited to this configuration and may be variously configured to include
any number
of coil housings. For example, Fig. 24 shows a longitudinal cross-sectional
view of a
coupler 16 having a plurality of coil housings 122A, 122B associated with a
wet unit
housing 128. Figs. 23 and 24 show one or more chambers 131 within the wet unit
housing 128 which may include the electronics for operation of the electrical
devices 18.
Fig. 25 shows another embodiment of the coupler 16 in which the wet unit
housing
128 includes a plurality of coils 129A-129G. As with previous embodiments,
coils 129A-
129G may include cores 126A-126G and windings 127A-127G, respectively. Any
number
of coils may be utilized as, for example, three, four, five, six, seven,
eight, nine, ten,
eleven, twelve, thirteen, fourteen, fifteen, or more. In the illustrated
embodiment, seven
coils are utilized in the wet unit housing 128.
The embodiment shown in Fig. 25 may be advantageous in that the housing 128
may be coupled to the underwater cable 2 in any circumferential orientation
without
significantly impacting the power transfer efficiency between the underwater
cable and the
wet unit 30. This arrangement may be particularly useful where the coils 126A-
126G
within the wet unit 30 rotate with respect to the underwater cable 2. To
achieve complete
rotational tolerance, the coils in the housing 128 are preferably spaced such
that the
distance between adjacent coils (e.g., between coil 129A and 129B) is less
than the
41
CA 02617233 2008-01-29
circumferential width of the pole face of coils 90A, 90B.
Where a plurality of coils are utilized, it may be desirable to include a semi-
solid or
completely solid wet unit housing 128 in the area near the coils 129A-129G to
provide
added support.
The electrical connection between the coils 129A-129G shown in Fig. 25 may be
variously configured. For example, Fig. 26 illustrates one embodiment where
the
electrical coils are all coupled to a multi-input full-wave bridge rectifier
135 which
includes diodes D1A-D1G, D2A-D2G, D3, and D4. A filter capacitor 131 is
coupled to
the output of the multi-input full-wave bridge rectifier 135. A DC voltage 138
output
from filter capacitor 131 is preferably supplied to, for example, voltage
regulators (not
shown) for supplying DC power to associated wet unit electronics. Outbound
data may be
extracted using voltage divider 133 and comparator 134. Inbound data may be
coupled to
the plurality of coils 129A-129G by incorporating a plurality of second
windings 139A-
139G.
Referring to Fig. 27, another alternate embodiment of the coupler 16 is shown
where the underwater cable 2 includes, for example, an inner integral core 140
disposed
in the outer sheath 15 and the electric device 18 includes, for example, an
outer integral
core 147 disposed about the outer sheath 15. The outer integral core 147 may
be disposed
in a wet unit housing 128 to cushion and protect the outer integral core 147
within the
coupler 16. The inner integral core 140 preferably includes a hollow passage
141 having,
for example, a plurality of fiber optic and electrical lines 141A passing
therethrough.
The inner and outer integral cores 140, 147 may each include a plurality of
extending sections around which a plurality of coils may be disposed. In the
embodiment
illustrated in Fig. 27, the inner integral core 140 includes four windings
146A-146D
disposed about four extending sections 142A-142D which extend outward from and
are
integral with the inner integral core 140. Similarly, the outer integral core
147 shown in
Fig. 27 includes four windings 145A-145D disposed about four extending
sections 148A-
148D which may extend inwardly from and are integral with the outer integral
core 147.
The inner and outer extending sections 142A/ 148A, 142B/ 148B, 142C/ 148C,
142D/ 148D
oppose each other and respectively form pole faces 1-4.
In exemplary embodiments as shown in Fig. 27, the inner integral core
extending
sections 142A-142D and/or the outer integral core extending sections 148A-148D
may be
contoured to match the curvature of the underwater cable 2 to increase the
coupling
42
CA 02617233 2008-01-29
coefficient. The extending portions may also be in the form of a truncated
triangle with a
curved outer surface abutting the outer sheath 15 of the underwater cable 2.
In many applications, the coils shown in Fig. 27 may be advantageous over
conventional coils because the geometry of the coupler allows a relatively
large pole face
area. Thus, this flux line configuration allows for excellent coupling between
coils in the
underwater cable 2 and coils in the wet units 18.
The integral core 140 may include any number of extending sections (e.g., from
2
to 20) depending on the number of wires to be wound around each extending
section.
Where the integral core has only a single wire wound around each extending
section, then
the integral cores may utilize any even number of extending sections. Where
each
winding 145A-145D, 146A-146D includes two or more wires, it is preferable to
dispose
four, eight, sixteen, or more extending sections about the integral core.
For example, an integral core having four extending sections allows up to
three
wires to be wound around each of the extending sections in a manner which
cancels the
mutual coupling among the windings such that multiple signals may be passed
using a
single integral core.
For example, Fig. 28 shows a circuit diagram of a three-wire, four-pole face
configuration which is configured for canceling and/or controlling the mutual
inductance
between the wires. In the illustrated embodiment, for each pole face, the
windings in the
underwater cable 2 portion and in the wet unit 30 portion of the couplers 16
are the same.
For example, wire A may have windings on the first and fourth pole faces wound
in a
first direction (either clockwise or counter clockwise) and windings on the
second and
third pole faces wound in an opposite direction in both the underwater cable
portion and
the wet unit portion of the couplers 16. Wire B may have windings on pole
faces one and
two wound in a first direction and the windings on pole face three and four
wound in the
opposite direction. In this manner, the configuration of the windings of wire
B cancel any
mutual coupling of signal B to wire A. Similarly, wire C may have windings on
pole
faces one and three wound in a first direction and the windings on pole faces
two and four
wound in the opposite direction. In this manner, the configuration of the
windings of wire C cancel any mutual coupling of signal C which may be coupled
to
wires A and B. The winding directions allow for mutually orthogonal signals
where half
of the windings add signals and half of the windings subtract signals with
respect to every
other winding except the intended signal transfer winding. Thus, none of the
voltage from
43
CA 02617233 2008-01-29
signal A appears on wire B and C; none of the voltage from signal B appears on
wire A
and C; and none of the voltage from signal C appears on wire A and B. Hence,
signals
A, B, and C may use the same and/or different voltage levels and the same
and/or a
different number of windings without interfering with each other. A signal
applied to
wire A in the under water cable would appear on wire A in the coupler with no
voltage
appearing on wires B and C. The magnetic flux lines associated with windings
A, B, and
C, are respectively shown in Figs. 29A-29C.
Exemplary winding configurations which may be suitable for use with the
embodiment of Fig. 28 may be summarized in Table 1 where letters A, B, and C
represent windings of the respective wires A, B, and C in a first direction,
and and
C represent windings of the respective wires A, B, and C in an opposite second
direction.
Pole Face Pole Face Pole Face Pole Face
1 2 3 4
Wire Winding
Direction ABC ABC ABC ABC
Table 1
The above winding configurations shown in Figs. 29A-29C and in Table I are
exemplary. A winding inverse to that shown for each pole face may be utilized
for any given
wire. In this manner, there may be eight different operative winding
permutations. For
example, in Table 1, the wire winding direction for wire A may be inverted as
k A A A.
The inverted wire winding direction for wire A may be utilized in conjunction
with the wire
winding directions for wires B and C shown in Table 1 or their inverse.
Similarly, the wire
winding direction for wire B may be inverted as B B B B and utilized with the
wire winding
direction of wires A and C or their inverse. In general, each of the wire
winding directions
for wires A, B, and C may be inverted individually or in combination such that
there may be
eight operative combinations.
The integral core embodiments of the coupler are very advantageous and
represent a
significant advance in the efficiency in coupling between a wet unit 30 and an
underwater
cable 2. In the illustrated embodiment, the wires for different signals may be
placed in close
44
CA 02617233 2008-01-29
proximity and share a siugie core while avoiding significant mutuai inductance
between the
different signals. Hence, the signal-to-noise ratio of the underwater cable
power distribution
and/or data communication system 20 is improved and power transfer efficiency
is increased.
Further, because the geometry of the coupler allows a relatively large pole
face area, the
coupling between the inner and outer cores is substantially improved.
The integral core coupler may be adapted to facilitate coupling with any of
the
embodiments of the underwater cable power distribution and/or data
communication system
20. For example, signal A may be the main power signal from the main power
line or the
power distribution signal from one of the data/power distribution lines,
signal B may be the
outbound data signal from one of the outbound data distribution lines, and
signal C may be the
inbound data signal from the wet units 30 to the underwater cable inbound data
distribution
lines.
Still other embodiments are also possible. For example, in the four pole
embodiment it
may be desirable to utilize only wire A to transfer, for example, power and
outbound data and
wire B to transfer inbound data with wire C omitted entirely.
Embodiments having an integral core allow the length of the coils in the axial
direction
to be reduced over the coils shown in Figs. 16-18. For example, the length of
the coil shown
in Fig. 27 in the axial direction may be less than 7 cm, and preferably less
than 5 cm, and
even more preferably less than 4 cm and most preferably less than about 3 cm.
A substantial
reduction in the length in the axial direction helps to improve the
reliability of the coils and
reduce the instances where the coils crack due to bending of the underwater
cable 2 when
moved over the rollers 9.
The integral core couplers may be particularly advantageous where the
underwater cable
2 has a main power line 23 including two or more conductors. In one
embodiment, the main
power line 23 includes four main power cables routed directly through the
integral core 140
as, for example, shown by the main power cables designated as 84A - 84D in
Fig. 27. In
these. embodiments, cables 84A - 84D may also perform a stiffening function as
well as a
main power distribution function. Due to the high coupling coefficient and the
geometry of
this particular coupler, it may be possible to eliminate the high frequency
data/power
distribution lines and power conversion circuits in some embodiments. Thus, in
these
embodiments, the main power line 23 is coupled directly to the couplers 16 by
passing one or
more main power cables through the integral core 140. For example, main power
cables 84A
- 84D may transmit four alternating polarity main power signals. Thus, the
wire winding
direction of, for example, wire C may be accomplished by simply routing a main
power line
CA 02617233 2008-01-29
23 composed of four alternating polarity conductors through the integral core
140 (e.g.,
between the extending sections 142A-142D and/or windings 146A-146D as shown by
the main
power cables 84A-84D in Fig. 27). In this embodiment, signal C in Fig. 28 may
be the signal
derived directly from the main power line.
The direction of current flow in the main power conductors 84A-84C preferably
alternates for each consecutive conductor around the integral core, thus
producing the winding
direction CCCC or its inverse. With this coupling arrangement, main power from
the main
power line 23 (as distributed on main power conductors 84A-84C) may then be
distributed
directly from the main power line 23 into the wet units without an
intermediate secondary
power distribution line and AC-AC converter. However, this method is less
preferred for
many embodiments because the integral cores are relatively heavy.
Figs. 30-34 show yet another embodiment of a coupler particularly useful where
the
coils in the wet unit rotate with respect to the underwater cable. A coupler
300 includes a
generally cylindrical housing 301 having a number of parallel bores. A central
bore 302
accommodates electrical power and data lines. A plurality of circumferentially
spaced bores
303, preferably about three, house cable stress members. A plurality of coil
cavities,
preferably about six, are circumferentially spaced and preferably disposed in
pairs between the
stress members. In a preferred embodiment, each coil cavity 304 comprises a
dead-end bore
with a coil 305 disposed therein. Although a symmetrical arrangement of bores
is preferred,
other arrangements can be used to accommodate underwater cable designs.
The coupler housing 301 preferably fits snugly inside the cable jacket 306.
Longitudinal
grooves 307 along the outside of the coupler 300 permit cable-ballasting fluid
to flow past the
coupler. A race 308, separable into two halves, is fastened around the jacket
306 and the
coupler housing 301. A wet unit 309 is preferably rotatably attached to the
cable by means of
a collar 310 that mates with and rides in the race 308. Hinged joints 311 and
a latch 312
which may have a quick-disconnect pin allow the collar to be separated at the
latch pin,
allowing the collar and the wet unit 309 to be removed from the cable and the
race 308.
As shown in Fig. 31, each coil cavity 304 in the housing 301 preferably has an
open
end 313 and a blind end 314 and houses a coil assembly 305. The coil assembly
305, as
shown in Fig. 32, includes a magnetic core 315, which preferably comprises a
ferrite rod,
although other magnetic materials can be used. The magnetic core 315 has a
high relative
permittivity, which is preferably above about 6000 and most preferably about
6500 or more.
In the preferred embodiment, the magnetic core 315 comprises a ferrite rod
housed in a sheath
316, which is preferably slightly longer than the magnetic core 315. Bumpers,
such as
46
CA 02617233 2008-01-29
elastomeric end bumpers 317, retain the core 315 in the longitudinal 1, .
ition and cushion the
coil assembly 305 from shock. The sheath 316 includes a plurality of pairs of
circumferential
ridges 318, preferably about 4. A sheath support ring 319 is retained between
the ridges of
each pair. The support rings 319 are preferably made of an elastic material
with an outermost
diameter slightly greater than the inside diameter of the coil cavity 304. The
support rings
319 keep the core 315 centered in the cavity 304, cushion the core 315 from
bending, and
protect the core 315 from transverse shock loads. An end cap 320, preferably
waterproof,
confines the coil assembly 305 in the cavity 304. The bumpers 317 may contact
an interior
side of the end cap 320 and the blind end 314. An 0-ring 321 mounted in a
circumferential
groove in the end cap 320 seals the cavity 304 from fluid intrusion. External
wires 322A-B
connect the coil windings to the underwater cable's power, outbound data, and
inbound data
lines. The external wires 322A-B preferably extend through end cap 320 and
connect to the
coil windings 331A-B at connections 334. A strain relief 323 may extend from
the exterior
side of the end cap 320 to lessen wire damage. The end cap 320 is preferably
provided with
an extraction loop 324 to facilitate removal of the coil assembly 305 from the
cavity 304.
Referring to Fig. 32, each coil assembly 305 preferably includes a plurality
of windings
331A-B, 332A-B at spaced locations 325, 326 along core 315. A circumferential
channel 327
may be formed between the pairs of ridges 318 at each end of the sheath 316.
Each channel
327 acts as a bobbin to hold the windings 331A-B, 332A-B in place. An A coil
winding 331
A, 332A and a B coil winding 331B, 332B are wound within each channel 327. The
A coil
windings 331A, 332A couple outbound power and/or data to the wet units 309.
The B coil
windings 331B, 332B couple data from the wet unit 309 to the inbound data
lines within the
cable. The B coil windings 331B, 332B may also be used to couple outbound data
to the
devices when operating in backup communications mode, as discussed more fully
below.
The windings may be connected in any suitable manner. For example as shown
schematically in Fig. 33, the A coil windings on core 305 are electrically
connected in a
series-aiding arrangement, as indicated by the dot convention. The A windings
of each core
are connected in parallel with the A windings of the other cores. The B
windings of each
core, on the other hand, are connected in a series-opposing arrangement to
minimize the
mutual inductance between the A and B windings and thereby minimize crosstalk.
The B
windings of each core are connected in series with the B windings of the other
cores .
Referring to Figs. 33A and 33B, the reduction of crosstalk is illustrated by
the flux
paths produced by each set of windings. In Fig. 33A, the series-aiding A coil
windings 33IA,
332A on a coupler 315 produce a flux that links the series-aiding A coil
windings 331A',
47
CA 02617233 2008-01-29
332A' in a similar proximate core 329 in the wet unit along a path 340. Thus,
the ends of the
cores 315, 329 act as pole faces 343, 344 for the A winding flux path. As
shown in Fig 33B,
the series-opposing B coil windings 331B, 332B on the coupler core 315 produce
a flux that
links the series-opposing B coil windings 331B', 332B' in the wet suit core
329 along paths
341 and 342. In addition to the pole faces 343, 344 at the ends of the cores,
a third pole face
is formed between the windings 331A and 331B for the B winding flux path.
Because the flux
produced by the A windings is in the same direction through the cores, no net
voltage is
induced in the series-opposing B windings. Conversely, because the flux
produced by the B
windings is oppositely directed on each half of the cores, no net voltage is
induced in the
series-aiding A windings. In this way, crosstalk between the inbound and
outbound lines is
minimized. It is clear that one set of windings results in two pole faces,
that two sets of
windings result in three pole faces as in Figs. 33B, that three sets of
windings result in four
pole faces as in Fig. 28, and generally that N sets of windings result in N+ 1
pole faces.
Referring again to Fig. 33, a tuning capacitance 328 may be connected in
parallel with
the A coil circuit to tune a resonant circuit formed with the capacitance of
the outbound data
line and the inductance of the A coil circuit. Tuning the resonant circuit
enhances the power
transfer to the wet unit. In a most preferred embodiment for use with a 200 m
underwater
cable segment accommodating two wet units, the net inductance of the A
windings is about
0.246 mH and the tuning capacitance is about 25.1 nF to transfer about 1.5 W
of power to
each wet unit at 64 kHz. A net inductance of about 3.09 mH is preferred for
the B windings
to effectively transmit data inbound to the survey vessel at 32 kbps.
Referring to Fig. 30, only one coil assembly 329 is positioned in the wet unit
309 near
the coupler 300. Preferably, the coil assembly 329 in the wet unit is similar
to each of the
coil assemblies 305 in the coupler. The core of the wet unit is disposed in
parallel with the
core 315 in the coupler 300 with the two winding positions separated in a
radial direction with
little and, preferably, no longitudinal offset. In this way, inductive
coupling between the
windings of the coupler 300 and the windings of the wet unit 309 is enhanced.
In the particular geometry of the coupler 300 of Fig. 30, the coupling between
the
coupler and the wet unit 309 varies as the wet unit 309 rotates about the
cable. Maximum
coupling is achieved when the axis of the core 329 of the wet unit 309 is
equidistant from two
neighboring coupler cores 305 and not radially aligned with a stress member
bore 304, as
indicated by a first radius 335 in Fig. 30. Minimum coupling occurs when the
cable rotates
relative to the wet unit 309, indicated in phantom, to a position in which the
core 305 of the
wet unit 309 lies on the same radius 336 as the stress member bore 303.
48
CA 02617233 2008-01-29
If room is available in the wet unit 309, the coupler 300, or both, additional
cores may
be installed to further increase the minimum coupling coefficient. For
example, as shown in
the embodiment of Fig. 34, a pair of similar cores 330 in the wet unit 309
improves coupling
over the embodiment of Fig 30.
Part III: Data Communication Structure Generally
Conventionally, communications between the electrical devices 18 and the dry-
end
electronics 5 has occurred via one or more communication lines extending
substantially
through the entire length of the underwater cable 2. However, this
configuration may be
unsatisfactory when electric power is distributed on the same lines as data.
For example,
seawater leakage may detune the entire communication channel and cable losses
may make
communication and power transfer difficult over extended distances.
Accordingly, power
transfer and communications are difficult or impossible using conventional
configurations.
Another aspect of the present invention concerns improving the responsiveness
and
reliability of the communication channels including the data/power
distribution lines between
the survey vessel 8 and the electrical devices 18. Referring to Figs. 3-6, the
underwater cable
2 may include a communication system with a control processor 21 controlling
the
communications to and from one or more communication channels. As shown in
Figs. 3-6,
each communication channel may include a plurality of repeaters 25 for
transmitting/receiving
data. For example, each communication channel may comprise a first group of
repeaters
selectively disposed along the underwater cable 2. The communication channel
may be
variously configured to include any number of repeaters positioned at any
number of suitable
locations within the underwater cable 2. In preferred embodiments, the
underwater cable
includes a plurality of repeaters spaced along the underwater cable and
positioned at about
equal distances from each other.
Where the underwater cable 2 includes streamer electronics modules (SEM's) 14,
the
repeaters may be disposed inside and/or outside of the SEM's, but are
preferably respectively
disposed within the SEM's. The repeaters may be alternately arranged with the
data/power
distribution lines to form a data communication channel. In this arrangement,
the data
communication channel is segmented by the repeaters. Further, the repeaters
are interspersed
at spaced locations along the underwater cable and serve to relay data between
the electrical
devices 18 and the control processor 21 on the survey vessel 8. In preferred
embodiments any
number of couplers 16, 32 may be disposed along each segment of the
communication channel
to couple electrical signals on the data/power distribution lines to an
electrical device 18
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CA 02617233 2008-01-29
located proximate to a coupler. For example, each segment of the communication
channel
may include one, two, three, four, five, six, seven, eight, nine, ten, or more
couplers. When
the repeaters are disposed in the SEM's, the segments of the data
communication channel may
be coextensive with the cable segments. In many preferred embodiments, each
communication
segment includes two spaced couplers disposed between consecutive repeaters.
More than two
couplers may be included between successive repeaters. The two couplers couple
data and/or
power from the data and/or power distribution lines to an associated
electrical device 18.
It has been found that buffering provided by one or more repeaters 25 limits
the effect
of the loss of an electrical device along a particular communication channel
segment to the
deeming of that segment of the data communication channel alone. Accordingly,
power
and/or data transmission to electrical devices 18 along other communication
channel segments
can continue. Further, the retransmission of message signals at a
predetermined level by the
repeater at an end of the detuned segment may be sufficient to overcome the
detuning effects
and allow reliable communications to electrical devices located along the
underwater cable 2
aft of a detuned segment.
In some of the preferred embodiments, the repeaters 25 include encoder,
decoder,
and/or data link control circuits 154. (See Figs. 35-36.) The circuits 154 may
be variously
configured. For example, in some embodiments, the circuits 154 may sample data
received
from receivers 152, 153 and retransmit the sampled data in synchronism with
one or more
system clock signals. The system clock signal may be derived from data on a
separate line or
from data on the inbound and/or outbound data distribution lines. If a clock
signal is to be
derived from data on the inbound and/or outbound data distribution lines, the
clock signal may
be derived with or without recovering data bit information. For example, by
inputting either
the inbound data or the outbound data into an edge detector and then into a
phase locked loop
(PLL), a clock may be recovered from the transmitted data signal. The
recovered system
clock may be utilized to recover bit information by demodulating the data and
then
remodulating the data prior to transmission to an output driver circuit.
Alternatively, the
system clock may be utilized to simply sample data received from the receiver
and to
retransmit the data in synchronism with the system clock without demodulation.
In some of the preferred embodiments, the outbound data received by repeater
25 is
sampled to recover a system clock which is then utilized to demodulate the
outbound data to
recover outbound data bit information. The outbound data is then preferably
remodulated
using the system clock. Bit recovery may also be performed in a like manner on
the inbound
data. Further, the repeaters 25 may sample the inbound data from receiver 153
using a
CA 02617233 2008-01-29
recovered inbound data clock, and then retransmit the inbound data in
synchronism with the
system clock recovered from the outbound data.
In some embodiments, the repeaters 25 may also include additional circuitry
for
performing various link control functions such as error detection and/or
correction as well as
link management functions. Further, it may be desirable to incorporate a
microcomputer or
other suitable control circuits into the repeaters 25. In these embodiments,
it may be desirable
to perform bit recovery to provide, for example, error correction and/or
detection for each
segment of the data communication channel. Disposing data link control
circuits in each
repeater may be advantageous in applications where it is desirable to provide
error detection
and/or correction for individual data/power distribution lines. However, in
configurations
which have a separate communication channel between the dry-end electronics 5
and the
electrical devices 18, repeaters which include data link control are often
less preferred because
of the additional latency introduced by the packetization, error correction
and/or error
detection process occurring at each repeater.
Repeaters 25 which include the encode/decode and/or data link control
circuitry may be
variously configured. For example, the repeaters 25 may be configured to
operate as a full
duplex and/or a half duplex communication channel over one or more signal
distribution lines
(e.g., one or more twisted pair connections). Fig. 35 shows an exemplary
embodiment of
repeater 25 configured for communication over a single line, while Fig. 36
shows an
exemplary embodiment of repeater 25 configured for full-duplex communicating
over two
lines. Where half duplex communications are utilized, the repeater is
preferably configured to
operate over a single line. Where full duplex communications are utilized, the
repeater is
preferably configured to operate over two or more distribution lines.
Referring to Fig. 35, an embodiment of repeater 25 configured for half-duplex
communications is shown. The repeater 25 includes an inbound driver 150 for
driving data
and/or power on a first adjacent inbound/outbound data/power distribution line
and a receiver
152 for receiving data from the first adjacent inbound/outbound data/power
distribution line.
Similarly, an outbound driver 151 may be included for driving data and/or
power on a second
adjacent inbound/outbound data/power distribution line and a receiver 153 may
be included for
receiving data from the second adjacent inbound/outbound data/power
distribution line.
Fig. 36 is similar to Fig. 35 except that in Fig. 36 the drivers 150, 151 of
repeater 25
are coupled to and configured for full-duplex communications. In some of the
preferred
embodiments of the power distribution and/or data communication system 20, the
system is
operated as a full-duplex system and includes an inbound data communication
channel
51
CA 02617233 2008-01-29
including a plurality of inbound repeaters alternately disposed with a
plurality of inbound data
distribution lines and an outbound data communication channel including a
plurality of
outbound repeaters alternately arranged with a plurality of outbound data
distribution lines.
Each data communication channel couples the control processor 21 to the
electrical devices 18.
In some of the preferred embodiments, the data/power distribution lines and
the outbound data
distribution lines are the same lines.
In the embodiments shown in Figs. 35 and 36, power from the underwater power
conversion circuits may be transferred on a separate power distribution line
or may be
combined with the data and transferred via any of drivers 151 and/or 150 in a
similar manner
as discussed above with respect to the power conversion circuits. In
embodiments having a
separate power distribution line, the underwater power conversion circuit 50
may include an
oscillator to supply a power carrier clock for supplying power at the power
carrier clock
frequency to one or more data/power distribution lines. Where power and data
are to be
transferred on the same line, it may be desirable to incorporate the second
power circuit 52
into one or more of the driver circuits 150, 151.
In some of the preferred embodiments, the power and data are transferred by
outbound
data driver 151. One example of such an embodiment is shown in Fig. 4. In this
embodiment, power transfer may be maintained by transmitting idle signals when
no data is
being transferred. The electrical devices 18 extract electric power from the
data signals and
idle signals to provide operational power and to provide power for charging
any batteries.
As discussed above, the repeaters 25 may operate to provide a simple buffering
function
by reshaping the signals output from the repeater to have predetermined
voltage levels. In
these simple buffering arrangements, receivers 152, 153 are preferably coupled
directly to the
respective drivers 151, 150. In the simple buffering configuration, the
repeaters 25 may not
include any encoder/decoder and/or link control circuits 154. The simple
buffering
configuration may be advantageous in that the repeaters operate to control
detnning of the
power/data distribution lines while introducing very little latency between
the survey vessel 8
and the electrical devices 18. However, the simple buffering arrangement may
be less
preferred due to the skew along the underwater cable as discussed below.
A first exemplary embodiment of the encoder/decoder and/or link control
circuits 154
for use with the power distribution and/or data communication system 20 is
shown in Fig. 37.
In the illustrated embodiment, only encode/decode circuits are included in the
repeaters with
the data link control circuits omitted entirely. Of course, data link control
circuits (e.g.,
HDLC circuits) may still be utilized in each electrical device 30, 31 and in
the dry-end
52
CA 02617233 2008-01-29
electronics 5.
The decode circuits 173 for the inbound data and the decode circuits 170 for
the
outbound data may include circuitry such as a phase locked loop for recovering
a clock and
logic circuits for utilizing the clock to recover a plurality of data bits.
Similarly, the encode
circuits for the inbound data 172 and for the outbound data 171 may include
circuitry for
modulating data onto a clock carrier frequency. As will be discussed in more
detail below, in
some embodiments it may be desirable to derive a carrier frequency CLK 174
from the
outbound data using decode circuit 170 and then utilize this clock to
synchronize the inbound
and outbound data via encode circuits 171, 172.
The decode circuits 170, 173 may be the same or different depending on the
modulation
scheme utilized on the inbound data channels and the outbound data channels.
In some of the
preferred embodiments, the decode circuits 170 may be configured for 4 kbps
BPSK while the
decode circuits 173 may be configured for 32 kbps Manchester coding.
The repeaters 25 discussed above may be utilized in any of the embodiments of
the
power distribution and/or data communication system 20. A repeater optimized
for use with
the power distribution and/or data communication system 20 shown in Fig. 6
preferably
includes circuitry to interface to both primary and secondary data
communication channels. In
this embodiment of repeater 25, it is often desirable to include data link
control in each
repeater to packetize and depacketize data transferred to and received from
the dry-end
electronics 5 using the primary data channel.
For example, Fig. 38 shows an exemplary embodiment of a repeater 25 configured
for
operation with the embodiment of the power distribution and/or data
communication system 20
shown in Fig. 6. Referring to Fig. 38, the repeater circuit 25 has a primary
data channel and
a secondary data/power distribution channel. The secondary data/power
distribution channel
may include one or more encoders, decoders and associated drivers and
receivers as well as
underwater cable power conversion circuits in a similar manner as discussed
above.
However, incoming and outgoing data are preferably packetized and depacketized
by CPU
and/or data link control circuits 175 for transmission over a primary data
channel such as an
underwater cable fiber optic network. The repeater 25 may include one or more
drivers,
receivers, encoders, and/or decoders 180-187 to facilitate communications over
the primary
data channel. Further, the CPU and/or data link control circuits 175 may be
adapted to
digitize signals from one or more hydrophones (not shown) along, for example,
each adjacent
cable segment. Further, as discussed with respect to Fig. 40, where drivers
151 are adapted
to transmit both data and power, it may be preferable to incorporate the
drivers 151 into the
53
CA 02617233 2008-01-29
power conversion circuits.
Part IV: Synchronization of Inbound/Outbound Data
A typical problem encountered when introducing bit and/or clock recovery
circuits in
the repeaters 25 is that additional latency time may be introduced. This
latency time often
may result from the carrier recovery loops in the decoders exhibiting a time
delay with respect
to the data. When a wet unit starts to respond, the unit may be required to
send a long
preamble which has a length dependent on the number of decoders between the
electrical
device and the dry-end electronics 5. Further, electrical devices 18 at the
aft end of the
underwater cable 2 may be required to utilize a long preamble of at least 3-4
bit times for
each repeater between the electrical device and the control processor 21.
Accordingly, a long
latency time may exist before the control processor 21 receives a response to
a previously
initiated request.
This problem may be overcome by utilizing a continuously active synchronous
transfer
protocol. This protocol may be particularly efficient where data
communications between the
survey vessel 8 and the electrical devices 18 comprises control and data
messages having a
relatively short message length. A continuously active synchronous transfer
protocol may help
to reduce the amount of the bandwidth of the communication channel dedicated
to start-up and
synchronization bits. In some embodiments of the continuously active
synchronous protocol,
the inbound and outbound data communication channels are maintained
continuously active by,
for example, the continuous transmission of idle signals when no data is
present.
In a full-duplex synchronized system, the control processor 21 preferably
maintains the
outbound data and/or power line continuously active by sending, for example,
instructions to
one or more of the electrical devices 18 or null/idle signals. Similarly, the
inbound link may
be continuously active sending either messages or an idle pattern. The idle
pattern for the
inbound link may be generated by the last repeater in the inbound link, by the
terminating
circuit 34, by a random or non-random signal generator, and/or by noise
generated on the aft
most segment of the data communication channel. In some of the preferred
embodiments, the
idle signals are generated by noise on the aft most segment of the data
communication channel
which is then amplified and propagated by the last repeater. Power may be
distributed on the
same line as the data or on a separate line with or without a power tree
structure. However,
in some of the preferred embodiments, the power tree structure is overlaid on
the
synchronized repeater structure in a complementary fashion such that the
outbound data and
the power transfer utilize the same distribution line.
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CA 02617233 2008-01-29
One problem with in.glementing a synchronous communication protocol in a long
underwater cable is that varying amounts of skew between the electrical
devices 18 along the
underwater cable 2 add to timing uncertainties. For example, electrical
devices 18 near the
survey vessel 8 may receive messages and respond quickly. However, as the
electrical
devices 18 become more remote from the survey vessel 8, the electrical devices
18 may
experience varying amounts of delay. Accordingly, a response from an
electrical device
disposed near the aft end of the underwater cable 2 may become skewed with
respect to
responses from electrical devices 18 near the survey vessel 8. The amount of
skew may
increase with increasing cable length. This can be particularly problematic
where it is
desirable to utilize a single architecture to accommodate varying cable
lengths. Varying
amounts of skew may also necessitate a reduction in the bandwidth of the data
channel in
order to achieve reliable data and power transfers while allowing for varying
cable lengths and
varying amounts of skew.
In some of the preferred embodiments, the above problems may be overcome by
utilizing a clock derived from decoding data and/or a carrier along a first
data and/or power
distribution line to synchronize data and/or a carrier along the same or a
different data and/or
power distribution line. For example, referring to Fig. 4, it may be desirable
to utilize a
carrier clock derived from data on the outbound data and/or power distribution
lines 38A-38C
to synchronize inbound data on the inbound data distribution lines 39A-39C. In
exemplary
embodiments, a synchronizing clock may be supplied by any of the components in
the
underwater power distribution and/or data communication system 20 but
preferably originates
from the dry-end electronics 5 or from electronics disposed toward the aft end
of the
underwater cable 2.
Fig. 39 shows a simplified block diagram illustrating one of the preferred
embodiments
of the synchronized timing relationships between the various functional blocks
of a full duplex
communication system having inbound data synchronized with outbound data. In
some of the
preferred embodiments, a timing acquisition aiding circuitry may be included
in the repeaters
25 and in the electrical devices 18 to fix the inbound data and/or carrier
clock to have an exact
timing relationship with respect to the outbound data and/or carrier clock.
Referring to the
embodiment illustrated in Fig. 39, the carrier clock derived from the outbound
data by
decoder 170 may be utilized by encoder 172 to synchronize inbound data. This
synchronization may occur in both the repeaters 25 and in the electrical
devices 18. Further,
the carrier clock may also be utilized to synchronize data encoded by encoder
171 and
distributed to aft cable segments. In this manner, each of the repeaters and
each of the
CA 02617233 2008-01-29
electrical devices 18 may be locked in an exact timing relationship so that
there is no need to
acquire timing when a response from an electrical device 18 is to be sent.
The particular nature of the timing relationship may vary depending on the
modulation
scheme utilized and on the particular circuits utilized to implement the
synchronization. In the
preferred embodiments, the inbound data/carrier clock is typically delayed by
a quarter carrier
cycle from the outbound data/carrier clock. The synchronized design has the
advantage of
maximizing the inbound data bandwidth while minimizing any delay regardless of
the number
of repeaters along the underwater cable 2.
In embodiments employing the synchronized design, each encoder coupled to the
inbound data distribution line (including those in the electrical devices 18)
preferably has a
carrier phase which is slaved to a carrier clock on a corresponding outbound
data distribution
line. Each repeater 25 and each of the electrical devices 18 coupled to a
particular data and/or
power distribution line are preferably configured to include a carrier
recovery loop and a bit
time recovery loop which are continuously locked. Delay time or skew between
the outbound
signal and inbound signal timing varies depending on the distance from the
repeater along a
particular power/data distribution line but is typically only a fraction of a
bit time (e.g., the
largest delay may be about 3 microseconds in one of the preferred embodiments
where the
distribution lines are limited to about 200m). Any skew on an individual
distribution line may
be accommodated by a small adjustment in the timing recovery circuit which may
typically be
accomplished in a quarter of a bit time.
An important advantage of the synchronized recovery loops is that each
repeater not
only reforms the data signal but also completely removes any build-up of
timing uncertainties
due to skew. Thus, additional cable segments and/or communication channel
segment may be
added without redesigning any of the components of the power distribution
and/or data
communication system 20.
Figs. 40 and 41 illustrate detailed circuit/block diagrams of the
driver/receivers and
synchronized timing recovery loop circuits in the repeaters 25 while Figs.
42A, 42B, 43 and
44 illustrate detailed circuit/block diagrams of the drivers/receivers and
synchronized recovery
loop circuits in the electrical devices 18.
Referring to Fig. 40, a repeater circuit 25 includes an outbound data
receiving circuit
152 for receiving signals from the outbound data and/or power distribution
lines. In preferred
embodiments, the outbound data receiving circuit 152 provides proper
termination for the
outbound data and/or power distribution lines and reforms the data signal for
input into decode
circuit 170. The outbound data receiving circuit 152 may include a comparator
189 and a
56
CA 02617233 2008-01-29
load adjusting circuit 188. The load adjusting circuit 188 is discussed in
more detail below.
Decode circuit 170 is preferably part of encode/decode and/or link control
circuits 154
(shown in detail in Fig. 41). As discussed above, the circuit 154 may be
variously configured
but preferably includes outbound data decode circuit 170, outbound data encode
circuit 171,
inbound data decode circuit 173, and inbound data encode circuit 172 as shown
in Figs. 40
and 41.
In some of the preferred embodiments, the outbound data decoded by decode
circuit 170
is preferably re-encoded by encode circuit 171 and then output through
outbound data/power
distribution line driver 151. As discussed above with reference to Figs. 7 and
9, where data
and power are coupled to the same lines, it may be desirable to configure the
driver 151 as
part of the underwater cable power conversion circuit 50.
Repeater circuit 25 may also include an inbound data receiving circuit 153 for
receiving
signals from the inbound data and/or power distribution lines. In preferred
embodiments, the
inbound data receiving circuit 153 provides proper termination for the inbound
data and/or
power distribution lines and reforms the data signal for input into decode
circuit 173. The
inbound data receiving circuit 153 preferably includes a band reject filter
for minimizing cross
talk from the outbound data lines or coils to the inbound data lines or coils.
In preferred
embodiments, the inbound data demodulated and/or sampled by decode circuit 173
is
preferably then remodulated and/or re-sampled by encode circuit 172. The
remodulated
and/or re-sampled signal is then output through inbound data driver circuit
150.
Fig. 41 shows a detailed block diagram of one of the preferred embodiments of
the
encoder, decoder, and/or link control circuits 154. Referring to Fig. 41,
outbound data from
receiver 152 is input into a first digital phase locked loop (DPLL) 156. The
first DPLL 156
includes an edge detector 155, phase detector 157, filter 158, and numerically
controlled
oscillator (NCO) 159. The phase detector 157 outputs one or more signals
indicative of
whether the phase output from the NCO 159 is earlier, later, or the same as
the phase of the
signal detected by edge detector 155. The phase detector 157 may be
implemented by an
XOR gate or other suitable circuitry. The filter 158 is utilized to provide
low pass filtering to
screen out any transient abnormalities caused by, for example, noise. The
filter 158 may be
implemented by a divide by N counter or other suitable circuitry. The adjusted
output from
the NCO 159 is then input back into the phase detector 157 to complete the
loop. The output
from the DPLL 156 (designated BPSK CLK) may be configured to be any multiple
of the
carrier frequency but is preferably equal to the carrier frequency (fco) of
the outbound data
received from receiver 152.
57
CA 02617233 2008-01-29
A phase demodulator 160 may be included where it is desirable to recover data
bit
information. Phase demodulator 160 preferably receives outbound data from
receiver 152.
The output of demodulator 160 is preferably input into a second digital phase
locked loop 164
to recover a bit rate clock. The bit rate clock is equal to the data rate of
the outbound data
which, in some of the preferred embodiments, is set to 4 kbps. The second DPLL
164
includes a bit edge detector 155', a phase detector 157', a filter 158', and a
NCO 159' in a
similar arrangement as the first DPLL 156.
The bit rate clock from the second DPLL 164 and the demodulated data from
phase
demodulator 160 are input into sampler 161. Sampler 161 samples the
demodulated data in
synchronization with the bit rate clock. The output from the sampler is non-
return-to-zero
(NRZ) data. The NRZ data is input into a bi-phase modulator 163 and is
utilized to modulate
the BPSK clock from the first DPLL 156. In this manner, the outbound data on a
subsequent
communication channel segment may be transferred in synchronism with a clock
signal
derived from data transferred in the immediately preceding communication
channel segment.
The output from the bi-phase modulator 163 is then preferably output to the
outbound data
driver 151 for transmission across the subsequent cable segment.
The inbound data portion of Fig. 41 shows a sampler/phase demodulator 166 for
sampling the inbound data in conjunction with a Manchester clock (MANCLK)
which is an
even multiple of, or preferably equal to the inbound data carrier frequency
(fci). In the
illustrated embodiment, the inbound data is sampled at the inbound data
carrier frequency
(fci). The Manchester clock MANCLK is generated by a third DPLL 165. The third
DPLL
165 includes a bit edge detector 155", a phase detector 157", a filter 158",
and a NCO 159"
in a similar arrangement as the first DPLL 156.
Sampler 167 inputs the Manchester data from sampler 166 and re-samples this
data in
synchronism with the BPSK CLK output from the first DPLL 156. A divide by N
circuit,
such as a counter, may be used to divide the BPSK CLK signal down to the
inbound data
carrier frequency, which in the preferred embodiment is 32 kHz. Sampler 167
uses the
divided BPSK CLK signal to sample inbound data. In this manner, the inbound
data may be
synchronized with the outbound data without having to demodulate the inbound
data.
Figs. 42A and 42B shows a block diagram of a preferred configuration of the
electrical
devices 18 (e.g., a wet or in-streamer unit 30, 31) for use in embodiments of
the underwater
cable power distribution and/or data communication system 20. Referring to
Figs. 42A and
42B, the electrical device 18 may receive power at a power supply 200 from a
battery, a
combined inbound data/power, outbound data/power, and/or a dedicated power
distribution
58
CA 02617233 2008-01-29
line. In the illustrated embodiment, the power supply 200 receives power from
a combined
outbound data and power distribution line.
Power supply 200 may be variously configured to be any circuit capable of
converting
received power into regulated DC power. In the illustrated embodiment, the
power received
from the outbound data/power distribution lines is preferably AC power. As
discussed above
with regard to Fig. 11, a full-wave bridge rectifier 61 may be utilized to
rectify the AC signal
and a capacitor 64 may be utilized to smooth the rectified signal into a DC
power signal
(Vpwr). A power limiter 201 is preferably included to limit the amount of
power a device can
draw from the cable. A power limiter can also be used to limit the power drawn
from the
batteries. The DC power signal may thereafter be regulated by, for example, a
DC voltage
regulator or other appropriate DC to DC converter 210 to provide operational
power to the
circuits contained in the electrical devices 18.
In some embodiments, it may be desirable for the electrical devices 18 to
include one or
more batteries 212. In some of the preferred embodiments, where batteries are
included, the
batteries are rechargeable via battery charger 211. If batteries are included,
the batteries may
supply operational power in the event that power is not available from the
underwater cable 2.
The batteries 212 may be switched into an operating mode by, for example, a
diode or an
electronic switch. If an electronic switch 221 is utilized, the battery
charger circuits 211
preferably include a low voltage detector which outputs a low voltage signal
to the
microprocessor 204. Microprocessor 204 may then actuate the electronic switch
221
responsive to the low voltage detection signal. Alternatively, the
microprocessor 204 may
detect a low voltage directly via A/D 214. In still other embodiments, the
electronic switch
221 may be controlled directly by the voltage detector 211 in response to, for
example, a low
voltage condition.
In some of the preferred embodiments, the A/D converter 214 receives a voltage
from
the input to the voltage regulators 210 and a separate voltage from the output
of the voltage
regulators 210. In this manner, the microprocessor 204 can monitor the voltage
received from
the underwater cable 2 as well as the voltage supplied from the batteries
(when present and
active). The voltage regulators 210 preferably include a shut-down mode which
may be
utilized to isolate the input from the output when power is inadequate at the
input to the
voltage regulators 210. The microprocessor 204 may control one or more
controlled circuits
205 based on the voltage values detected by the A/D converter 214.
AID converter 214 may be integral with the microprocessor 204 as, for example,
with
the Motorola 68HC 11, or be a separate unit coupled to the microprocessor 204.
As discussed
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CA 02617233 2008-01-29
in more detail below, the AID converter 214 may be utilized by the
microprocessor 204 to
initiate various actions by one or more controlled circuits 205 disposed
within the electrical
devices 18.
A power-on reset circuit 213 may be utilized to reset the electrical device
should
operational power be lost from the underwater cable 2 and should the batteries
be not present
or present and inoperative.
The electrical devices 18 may also include outbound data receive circuits 201
and
inbound data driver circuits 203 coupled to encode/decode circuits 202. The
outbound data
receive circuits 201 may include a voltage divider 62 and a comparator 63
which may operate
to reform the outbound data signals prior to decoding by the encode/decode
circuits 202.
The inbound data driver circuits 203 may be variously configured to include
any suitable
driver circuit capable of driving an inbound data signal across any number of
suitable coupling
arrangements between the electrical device 18 and the underwater cable 2. In
the preferred
embodiments, the driver circuit 203 is configured to drive an inbound data
coupling
transformer which inductively couples the wet unit 30 to the underwater cable
2.
The inbound data coupling transformer may include a secondary side comprising
the coil
disposed in the outer sheath 15 of the underwater cable 2 and a primary side
comprising the
coil disposed in the electrical device 18. In some embodiments, the inbound
data coupling
transformer may have a leakage inductance of about 70% or more, for example,
about 94% or
more (i.e., a coupling coefficient of about 0.3 or less, for example, about
0.06 or less). In
this environment, the inbound driver 203 driving the primary side of the
inbound coupling
transformer may drive an inductive load where about 94% or more of the load is
the leakage
inductance. The inbound driver circuit 203 preferably drives the primary of
the inbound data
coupling transformer with a signal which enables the desired data signal
(e.g., a Manchester
signal) to be reproduced on the secondary side of the transformer.
The operation of the inbound driver circuit 203 may be seen with reference to
Fig. 43.
In operation, transistors 216 and 218 are normally both in the ON state with
the output current
lout negative. A negative to positive transition of the inbound signal on the
inbound data lines
in the underwater cable 2 is initiated by momentarily turning OFF transistor
216 and turning
ON transistor 220. Transistor 216 may be turned OFF for a period equal to half
of the
resonance period of capacitor 222 and inductor 231 (e.g., about 1/4 a bit
time). Since the
current in the inductor cannot change instantaneously, the current flows into
capacitor 222
during the next quarter of the resonance cycle. The current then reverses and
flows from the
capacitor 222 to the inductor 231 in the opposite direction. This produces a
negative to
CA 02617233 2008-01-29
positive transition of the inbound signal on the inbound data distribution
lines. Transistor 220
is OFF and transistors 217 and 219 are both in the ON state with the current
lout positive.
Similarly, a positive to negative transition of the inbound signal on the
inbound data
distribution lines in the underwater cable 2 is initiated by momentarily
turning OFF transistor
217 and turning on transistor 220. Transistor 219 may be turned OFF for a
period equal to
half of the resonance period of capacitor 222 and inductor 231 (e.g., one
fourth of a bit
period). Since the current in the inductor cannot change instantaneously, the
current flows
into capacitor 222 during the next quarter of the resonance cycle. The current
then reverses
and flows from the capacitor 222 to the inductor 231 in the opposite
direction. This produces
a positive to negative transition of the inbound signal on the inbound data
distribution lines.
The resonance period of the driver circuit 203 is determined by the resonance
circuit
formed by the inductor 231 and the capacitor 222. The illustrated driver
circuit is particularly
advantageous because the energy is stored in the capacitor 222 while the
current is changing
directions such that energy dissipation is miniri2ed. Energy is alternately
transferred between
the inductor and the capacitors to conserve energy.
In some embodiments, the inbound data coupling transformer has a relatively
low
coupling coefficient and has a secondary coupled to a relatively low load
impedance.
Consequently, the inbound driver circuit 203 may be required to generate a
relatively large
current in the primary of transformer 230 (e.g., 3.6 amps or more). In the
illustrated
embodiment of the driver circuit 203, virtually the entire current flowing in
the circuit (e.g.,
3.6 amps) may be reversed in direction with only a minimum of dissipation.
This is a
remarkable result since the inbound driver circuit 203 may draw from V9 only a
small fraction
of the current flowing in the transformer 230. In the circuit illustrated in
Fig. 43, the inbound
data driver circuit 203 only requires an input of a fraction of an amp (e.g.,
0.24 amps from a
1OV supply). In exemplary embodiments, a 3.6 amp current flowing in the
primary side of
the inbound data coupling transformer may generate a 1.1 V peak/peak signal on
the inbound
data, line even where the leakage inductance of the transformer is large. A
current source,
such as a switchmode current source 229, supplies the operating current Idc
(e.g., 3.6 amps or
more) from source V9 at an efficiency of about 85% or greater.
Operation of the control logic 224-228 can be seen with reference to Figs.
36A, 36B.
The Manchester data (DATOUT) from the encode/decode circuits 202 is input into
an inverted
input of AND gate 224, into an input of AND gate 225, into an inverting buffer
226 and into
a buffer 227. A commutation drive signal CDRV is input into the inverted
inputs of AND
gates 224 and 225 and into buffer 228.
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CA 02617233 2008-01-29
The signals output from AND gates 224 and 225 and buffers 226-228 drive the
gates of
MOS power transistors 216-220. As shown in Fig. 43, the DRV+ signal is pulsed
positive
for 1/4 a bit time (Tb) whenever it is desirable for the inbound data signal
appearing on the
inbound data distribution lines in the underwater cable to make a negative to
positive
transition. Similarly, the DRV- signal is pulsed positive for 1/4 a bit time
(Th) whenever it is
desirable for the inbound data signal appearing on the inbound data
distribution lines in the
underwater cable 2 to make a positive to negative transition.
The illustrated MOS power transistors 216-220 and the driver circuit control
logic 224-
228 are exemplary of one embodiment of the invention and may be replaced with
any suitable
alternative arrangement. For example, a, bipolar transistor with a diode
connected between the
emitter and collector may be substituted for the MOS power transistors 216-
220. Further, in
some embodiments, the input to the gate drivers 224-228 may be controlled
directly by
microprocessor 204 or with other suitable control logic to produce the DRV+
and DRV-
signals shown in Fig. 43.
Driver circuit 203 operates to couple inbound data from the electrical devices
18 to the
underwater cable 2 after encoding by the encode/decode circuits 202. The
inbound data drive
circuits 203 may be configured to drive the inbound data signals with
sufficient power to cause
the couplers 16, 32 to substantially overpower any signal imparted on the
inbound data
distribution lines by the driver circuits 150 disposed in the repeaters 25
(See Fig. 40.) In
some of the preferred embodiments, the inbound data channel of the repeaters
is continuously
active sending, for example, idle signals. The idle signals may originate as
noise amplified by
the aft most repeater. When an electrical device 18 is commanded by the
control processor 21
(Figs. 3-6) to respond, the electrical device 18 may be configured to simply
"blast" a response
onto the inbound data distribution lines by overpowering any existing signal
being sent by a
repeater circuit 25. The control processor 21 preferably time multiplexes
requests to the
electrical devices 18 such that the electrical devices 18 do not improperly
conflict with each
other.
During periods where no responses are being transmitted by the electrical
devices 18,
synchronization of the phase locked loops 165 (see Fig. 41) in the decode
circuits 173 of
repeaters 25 may be maintained by the idle signals. However, as discussed
above, since the
electrical devices 18 are synchronized with the repeaters, the electrical
devices 18 may simply
transmit a response onto the inbound data distribution line with sufficient
force to mask any
data/idle signals being transmitted by driver circuit 150 of a repeater
coupled to an aft end of
the inbound data distribution line. In this manner, a preamble may not be
required to be
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CA 02617233 2008-01-29
added to the response sent on the inbound data distribution line by the
electrical devices 18 to
synchronize the phase locked loops in the repeaters. Accordingly, latency time
is substantially
reduced.
The encode/decode circuits 202 perform a similar function as the encode/decode
and/or
link control circuit 154 described above. The encode/decode circuits 202 may
be coupled to
microprocessor circuits 204 directly or through one or more data link control
circuits 206. If
a data link control circuit 206 is utilized, in some of the preferred
embodiments, the data link
control circuit 206 is preferably a high level data link control (HDLC)
integrated circuit part
number MT8952, manufactured by Mitel. In these embodiments, data link control
may be
provided at the control processor 21 and at each of the electrical devices 18.
The microprocessor circuits 204 are preferably coupled to one or more circuits
such as
memory 220 and/or one or more controlled circuits 205. The microprocessor
circuits 204
may include one or more microprocessors or other logic circuits such as a
Motorola 68HC 11
and/or Motorola 56002. Depending on the particular application, type, and
location of the
electrical device 18, the microprocessor circuits 204 may be configured to
control one or more
functions in the controlled circuits 205.
The controlled circuits 205 may be variously configured to include one or more
functions. For example, the controlled circuits 205 may include one or more of
the following
functions: a) compass/heading, b) pitch/roll, c) acceleration, angular rates,
magnetic field,
optical ranging/bearing, flotation, position detection sensors such as hall
effect sensors to
monitor, for example, the position of the vanes, d) motors, e) depth sensors,
and f) acoustic
ranging devices. In some of the preferred embodiments, the compass function
forms a first
electrical device, the leveling related functions (motors, depth sensors,
position detectors,
pitch/roll detection) form a second electrical device, and the acoustic
ranging functions form a
third electrical device. Further, in some of the preferred embodiments, only
the electrical
device which includes the leveling function is equipped with batteries 212.
Fig. 45 shows a detailed block diagram of the encode/decode and/or clock
recovery
circuits 202 for one of the preferred embodiments of the electrical devices of
the invention.
The outbound data decode circuits of Fig. 45 are similar to the outbound data
decode circuits
of Fig. 41 and designated with similar numbers. For example, the operation of
the circuits
155A-161A and 164A is substantially the same as the operation of the circuits
155-161 and
164 as discussed above with regard to Fig. 45. Details of the operation of
these circuits are
not repeated with regard to the operation of the electrical devices 18.
In the circuit illustrated in Fig. 45, the bit rate clock from the second DPLL
164A, the
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CA 02617233 2008-01-29
outbound non-return to zero (NRZ) data from sampler 161A, and the BPSK clock
from the
first DPLL 156A are output to the data link control circuit 203.
The inbound data portion of Fig. 45 shows a modulator 168 for modulating the
inbound
NRZ data from the data link control circuit 203 and a sampler 169 for sampling
the inbound
data. A divide by N circuit, such as a counter, divides the BPSK CLK signal
down to the
inbound carrier frequency, which in the preferred embodiment is 32 kHz. The
divided BPSK
CLK signal is input into sampler 169. Sampler 169 uses the divided BPSK CLK
signal to
sample inbound data. In this manner, the inbound data may be synchronized with
the
outbound data in each of the electrical devices 18.
Sampler 169 outputs a Manchester inbound data signal to inbound driver 203
(shown in
Figs. 42A, 42B) and to an edge detector 170. The edge detector 170 outputs a
commutation
drive signal (CDRV) to inbound driver 203.
Part V: Communicating with Underwater Cable Power Off
There are operating conditions of underwater cables where it may be preferable
to
communicate with in-streamer and wet units when main underwater cable power is
OFF. To
operate without power supplied from the cable, the in-streamer and wet units
preferably
include backup batteries. Because battery power is limited, a low power
communications
mode is preferred. One aspect of a low power communications mode preferably
includes
bypassing the repeaters along the outbound data lines, the inbound date lines,
or both.
For example, referring to Fig. 40, one embodiment of the backup communications
mode
includes bypass switches 53 to bypass a repeater along the inbound data lines.
The switches
53 are preferably magnetic latching relays, as they conserve power and have
very low contact
resistance. Control circuit 52 sets the switches to the bypass state when the
main streamer
power switches OFF. In the position indicated in Fig. 40, switches 53 are in
the primary
communications mode. Switches 53 preferably provide redundant contacts, as
illustrated, to
further increase reliability.
When control circuit 52 moves the switches 53 to a bypass position, the
inbound data
line becomes a continuous line throughout the cable, bypassing the repeaters.
The inbound
data windings of the couplers are connected across the inbound data line.
A conventional communication system may be used to communicate along the
inbound.
data line running the entire length of the cable in a backup mode. For
example, U.S. Patent
No. 4,912,684 discloses a conventional communications system which may
function as the
backup communications system of the present invention.
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CA 02617233 2008-01-29
Another aspect of a backup communications mode includes circuitry within the
individual devices to communicate over the continuous line. In the illustrated
embodiment, the
inbound data line preferably operates in half-duplex mode when the main cable
power is OFF.
As a consequence, the inbound data coils in the wet units and in streamer
devices preferably
include circuits capable of receiving data from the survey vessel. Figs 42A
and 42B illustrate
backup communications circuits 202', primary communications circuits 202, and
switches S1
and S2, which switch between primary and backup communications mode in an
electrical
device. Microprocessor 204 preferably controls switches S1 and S2. When the
main cable
power is OFF, Vpwr approaches zero, and microprocessor 204 actuates switches S
l, S2 to
switch in backup communications circuit 202'. Backup communications circuits
202'
preferably include encode and decode circuits configured to encode inbound
data and decode
outbound data using conventional modulation techniques, for example, frequency
modulation
(FM) or phase modulation (PM). In the backup mode, the devices may communicate
at a
lower bit rate (e.g. 4kbps) than in the primary communications mode. In this
manner, the
electrical devices are able to communicate with the survey vessel when the
main cable power
is OFF and conserve battery power.
Part VI: Fault Tolerant Structures
A common failure mode of the underwater cable power distribution and/or data
communication system 20 is the loss of one or more electrical devices 18 along
the underwater
cable 2. Efficient power distribution to the electrical devices 18 from the
underwater cable 2
is preferably conducted using tuned power transfer circuits. However, it was
found that the
loss of one or more electrical devices 18 from along the underwater cable 2
often decreased
the bandwidth of the tuned power transfer circuits making outbound data
communication
difficult in combined dataipower embodiments.
In accordance with the present invention, the reliability problems associated
with this
failure mode may be reduced by segmenting the data/power distribution lines as
discussed
above and/or by incorporating a load adjusting circuit 188 (see Fig. 46) into
the underwater
cable power distribution and/or data communication system 20. The load
adjusting circuit 188
may be disposed at any location along one or more data/power distribution
lines as, for
example, in one or more in-streamer electrical devices 18, in the repeater
driver circuits, or in
the repeater receiver circuits, in the couplers, and/or in the terminators 34,
44.
A second common failure mode of the underwater cable power distribution and/or
communication system is the intrusion of seawater which applies a shorting
load to the power
CA 02617233 2008-01-29
distribution and/or data communication lines. The shorting load may decrease
the bandwidth
of the tuned circuit in the driver 50, making outbound data communication
difficult in
combined data/power embodiments.
In accordance with the present invention, the reliability problems associated
with this
failure mode may be reduced by incorporating a load adjusting circuit 188'
(see Fig. 46) into
the underwater power distribution and/or data communication system. The load
adjusting
circuit 188' is preferably disposed in the driver circuit as shown in Figs. 9
and 40.
In one of the preferred embodiments, the load compensating circuit 188, 188'
includes
two oppositely connected Zener diodes coupled across the power distribution
line at or near
the receiver 152. Of course, other locations are also suitable. By oppositely
connected, it is
meant that the Zener diodes are connected in series across the data/power
distribution lines in
a cathode to cathode or in an anode to anode configuration. For example, in
Fig. 40, the load
adjusting circuit 188, 188' is shown as two cathode connected Zener diodes
connected across
the outbound data and/or power distribution lines.
Other configurations of the load adjusting circuit are also possible. For
example, the
circuit may include one or more voltage sensors which monitor the voltage on
the power
distribution line and which switch in various amounts of resistance in
response to a change in
the voltage level. The load adjusting circuits operate to control the change
in bandwidth of the
power transfer circuits due to, for example, loss of one or more inductively
coupled loads
along the underwater cable. Also, the system is simpler to deploy, not
requiring a load from
a wet unit 30 at unused locations.
In preferred embodiments, it may be desirable to size the load adjustment
circuit (e.g.,
the Zener diodes) such that the voltage rise associated with a misalignment of
the coils in the
coupler within the tolerance range (e.g., the pole face length/width) does not
trigger the load
adjustment circuit to activate. Activation of some embodiments of the load
adjustment circuit
may cause a loss of power transfer efficiency along the data/power
distribution lines.
Accordingly, the load adjustment circuit 188, 188' may be designed to engage
just above the
voltage rise that may be attributed to one or more couplers being misaligned
within the
coupler tolerance.
When a fault along the dataipower distribution line occurs, load may be
removed.
When load is removed, the voltage along the power distribution line typically
rises because the
Q of the distributed filter rises. The load adjusting circuit is preferably
configured to, add
dissipation to the circuit to keep the Q of the circuit relatively constant so
that the bandwidth
of the distributed filter does not change.
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CA 02617233 2008-01-29
In preferred embodiments, the load adjusting circuit 188, lho may enable the Q
to
increase about 10% or more before the load adjustment takes place and reduces
the peaks of
the waveform. This is particularly important where power and data are
distributed on the
same line. Where data and power are distributed on the same line, it may be
desirable to
maintain the load resistance near design nominal for the distributed filter to
operate with the
proper data bandwidth. If the voltage on the power distribution line increases
above a nominal
design value, the bandwidth of the filter may contract and the data waveform
may become
distorted. Accordingly, it may be difficult to demodulate the data at the next
repeater, and
hence the communication channel may be interrupted.
A load control circuit 188, 188', which includes Zener diodes, may be
particularly
advantageous because when all electrical devices 18 are operational, the
diodes do not conduct
and therefore do not consume precious power resources. Further, the Zener
diodes are
simple, easy to implement, and do not add significant weight to the underwater
cable 2.
Part VII: Hierarchical Load Shedding
The main power line 23 in the underwater cable 2 powers a plurality of spaced
electrical
devices 18. Each of these electrical devices 18 may be designed to draw a
predetermined
current as determined by an overall power budget for the underwater cable 2.
However, when
a fault occurs along any one of the plurality of data/power distribution lines
or in the electrical
devices 18 coupled thereto, the current drawn from the data/power distribution
lines may
exceed the maximum allocated predetermined load. In extreme cases, the voltage
on the main
power line becomes degraded and the entire underwater cable becomes
inoperative. In less
extreme cases, and especially where power and data are coupled to a single
data/power
distribution line, data transfer through the plurality of repeaters may become
inoperative over
the faulty cable segment.
Accordingly, in many embodiments, it may be desirable to configure the second
power
circuit 52 of each power conversion circuit 50 (Fig. 8) as a current limited
power source. In
this way, power supplied to a power distribution line on a particular cable
segment never
exceeds the maximum allocated current. A fault along the cable segment simply
causes the
voltage along the cable segment to drop while the current remains
substantially constant.
This drop in voltage may have an adverse effect on the electrical devices 18.
Power
transferred to the electrical device 18 may be reduced to the point where all
of the electrical
devices 18 cannot operate. However, by employing a hierarchical load shedding
technique, it
may be possible to maintain some electrical devices 18 and/or electrical
device functions while
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CA 02617233 2008-01-29
disconnecting or shedding others. If some electrical devices and/or electrical
device functions
are to be shed, the loads associated with these functions are preferably shed
in reverse order
of the particular function's criticality to the underwater cable 2 and power
distribution and/or
data communication system 20.
Hierarchical load shedding may be controlled by any suitable circuit
throughout the
system including the control processor 21, the repeaters 25, and/or the
electrical devices 18.
Further, the hierarchical load shedding within each of these circuits may be
variously
configured. For example, in some embodiments, it may be desirable to shed one
or more
loads depending on the voltage level of one or more data/power distribution
lines within the
underwater cable 2. In other embodiments, it may be desirable to shed one or
more loads
based on other factors such as the loss of communications to the electrical
devices 18.
Each electrical device 18 may be considered a load individually or may itself
contain
one or more loads. For example, each electrical device may include one or more
functions
such as indicated by the controlled circuits of Figs. 42A, 42B. A load may be
interpreted as
being whatever electrical load is associated with one, a plurality, or all of
the functions of an
associated electrical device 18.
Further, the control for the load shedding may occur autonomously in each
electrical
device based on the presence, absence, and/or level of a signal (e.g., a power
signal and/or
data communication signal) in, for example, the underwater cable 2 and/or
electrical devices
18. Additionally, the control and/or fault detection for initiating the load
shedding may be co-
located or distributed at a plurality of locations throughout the underwater
cable.
For example, fault detection circuitry (e.g., a voltage detector and/or A/D
converter)
may be located in the individual electrical devices 18 and/or in the repeaters
while control for
the load shedding may be in the electrical devices, in the repeaters, and/or
the control
processor 21. Although control of the hierarchical load shedding may be
controlled by a
single processor (e.g., the control processor 21), in some of the preferred
embodiments, the
control for the hierarchical load shedding is distributed to the plurality of
electrical devices 18
(e.g., programmed into microprocessors 204) which each act autonomously. This
distributed
control for the load shedding function has been found to provide enhanced
reliability.
A first exemplary embodiment of a hierarchical load shedding function
implemented in
the underwater cable power distribution and/or data communication system 20 is
illustrated in
flow chart form in Fig. 47. Referring to Fig. 47, step 250 determines if the
electrical device
18 is already in the low power mode. If power and/or data communications to
the electrical
device are at normal levels, step 251 is entered. In steps 251 and 252, the
power level and/or
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CA 02617233 2008-01-29
data communications are continuously monitored to determine if a fault
condition exists.
When a fault condition is detected, step 253 is executed. In step 253, a
single load (e.g., one
of loads a-e) is removed by, for example, powering down the circuitry that
controls and/or
performs the functions associated with that load. This may be an entire
electrical device 18 or
portions of circuitry located within an electrical device 18. The particular
load selected is
preferably chosen in a hierarchical order, with some of the preferred orders
being, for
example, a) acoustic ranging, b) compass, c) depth setting to set a new depth,
d) depth
reporting to report the current depth, and e) depth control to maintain the
current depth. In
this embodiment, the least important/critical functions are removed first.
After a load (e.g., device or function within a device) has been removed, in
embodiments where the load shedding control is distributed, the electrical
device waits for
other electrical devices 18 to also remove their loads (step 254). The
electrical device may
wait for a predetermined period of time and/or a variable period of time based
on stability of
a received voltage for a given period of time. Thereafter, the electrical
device 18 then checks
to determine if the fault condition is still active. If the fault condition is
no longer present, the
electrical device 18 sets the low power mode active (step 257) and returns to
start. However,
if the fault is still detected (step 256), the electrical device continues
again at step 253 until all
loads associated with a particular electrical device have been powered down.
If all loads have been powered down and the fault is still present (step 256),
a depth
control electrical device or bird preferably will maintain a substantially
constant depth
(possibly using only battery power) (step 259), set the low power mode active
(step 257), and
return to the start step. Other electrical devices 18 without a depth control
function preferably
will set the low power mode active (step 257) and return directly to the start
step.
When the low power mode is active, in steps 260-261 the electrical devices 18
will
preferably continue to monitor the underwater cable 2 to determine if the
fault condition is still
active. Where a voltage level is utilized to determine a fault condition, it
is desirable to set
the voltage level of clearing a fault to be higher than the voltage level for
detecting a fault.
These different voltage levels provide a hysteresis so that the system does
not continuously
oscillate between a fault present and a fault not present condition.
If the fault condition has been corrected, in step 262, loads are added in a
reverse
hierarchical order (one load per iteration) until the fault condition is
cleared. By reverse
hierarchical order it is meant that loads are preferably restored in the
reverse order in which
they were removed. In many cases, this order will be with the most important
loads restored
first (e.g., in order of loads e-a).
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CA 02617233 2008-01-29
After adding a load, in a distributed control configuration, the controller
waits for the
other controllers to add loads in step 263. In step 264, a check is made to
determine if all
loads have been added. If all loads have been added, the low power mode is set
inactive (step
265) and control is returned to the start step. If more loads remain inactive,
step 260 is again
initiated and the process continues as discussed above.
In step 256, the fault condition may simply be a determination to verify that
communications with the control processor 21 are enabled. In other
embodiments, the fault
condition may be determined if the voltage received from the underwater cable
2 is below a
fixed value (preferably programmable). In still other embodiments, the fault
condition
detection in step 256 may be based on a plurality of predetermined voltage
threshold values
(preferably programmable) with a different predetermined voltage level
associated with each
load identified in step 253. For example, on the first iteration, the
electrical loads associated
with the acoustic ranging function may be removed if the voltage received from
the
underwater cable is below a first predetermined voltage level, e.g., 9.5
volts. On the second
iteration, the electrical loads associated with the compass function may be
removed if the
voltage received from the underwater cable is below a second predetermined
voltage level,
e.g., 9 volts. On the third iteration, the electrical loads associated with
the depth setting and
recording functions may be removed if the voltage received from the underwater
cable is
below a third predetermined voltage level, e.g., 8.5 volts. Step 258 then
determines if there
are any loads left to shed for a particular voltage level.
In alternate embodiments, the fault condition may be determined if the voltage
received
from the underwater cable 2 is below a predetermined value (preferably
programmable) and
rather than removing the loads individually as discussed above, all loads may
be removed
simultaneously in step 253. In this embodiment, if the voltage received from
the underwater
cable is below a predetermined voltage value (e.g., 9.5V, 9.OV, or 8.5V), then
all loads are
removed in step 253 simultaneously. The electrical devices may then return to
the start mode
and idle waiting for commands to be received from the repeaters 25 (when load
shedding
intelligence, e.g., a CPU is located in the repeaters) and/or control
processor 21. The
commands can then be utilized to selectively enable one or more loads on a
faulty cable
segment depending on the severity of the fault and the particular function
required at that
individual instance. In this manner, the control processor and/or repeater may
manage a
degraded mode operation where individual loads are time multiplexed to
accommodate the
faulty condition.
In still other alternate embodiments, once all loads have been removed in the
single step
CA 02617233 2008-01-29
253, the program then proceeds to set the low power mode active and enter the
low power
mode of the program. In step 261, each load may then be replaced in a
hierarchical order
with the most critical loads being replaced first. For example, in exemplary
embodiments, on
the first iteration, the electrical loads associated with the depth setting,
recording, and control
functions may be activated if the voltage received from the underwater cable
is above a first
predetermined and/or programmable voltage level, e.g., 8.5 volts. On the
second iteration,
the electrical loads associated with the compass function may be activated if
the voltage
received from the underwater cable 2 is above a second predetermined and/or
programmable
voltage level, e.g., 9 volts. On the third iteration, the electrical loads
associated with the
acoustic ranging function may be activated if the voltage received from the
underwater cable is
above a third predetermined and/or programmable voltage level, e.g., 9.5
volts.
Other alternate modes may also be implemented to enable hierarchical load
shedding.
Control for these modes may be entirely within the electrical devices,
repeaters, and/or control
processor. Alternatively, control for the hierarchical load shedding may be
distributed
between one or more of the repeaters, electrical devices and/or control
processor. For
example, one of the preferred embodiments of hierarchical load shedding is
illustrated by the
state diagrams in Figs. 48 and 49. Fig. 48 illustrates the hierarchical load
shedding associated
with devices, such as a dedicated depth-control device, or bird, a dedicated
compass/heading
device, or a dedicated acoustic device, each of which may have multiple
functions to be shed
hierarchically.
Referring to Fig. 48, from reset state 270, the electrical device may enter an
idle state
271. In the idle state 271, communications with the device are enabled. If the
voltage
detected by the electrical device using, for example, the A/D converter 214 in
Fig. 42A, 42B
is less than VLO, for example 7 volts, and the battery is dead, the electrical
device enters
shutdown state 272 and performs a clean shutdown of ongoing processes before
powering off
to a dead state. From the dead state, if the voltage Vpwr supplied by the main
power line and
detected by the electrical device exceeds VH,, the device again enters the
idle state 271. VH1 is
preferably about 9.5 volts for an acoustic device, about 9.0 volts for a
compass/heading
device, and 8.5 volts for a depth control device, or bird. In the idle state,
communications
between the electrical device and the control processor 21 are preferably
enabled.
From the idle state 271, if the device receives a command signal (CMI)), the
device
may enter a mains-powered active state 273 if Vpwr is greater than or equal to
V. The
device may enter a battery-powered active state 274 if a command is received
and Vpwr is
less than VLO. A command signal may originate from control processor 21 or
from the
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CA 02617233 2008-01-29
repeaters. If the device is in either the mains powered active state 273 or
the battery-powered
active state 274, and the device receives a CMD signal, the device may reenter
the idle state
271.
In mains-powered active state 273, if the electrical device detects that Vpwr
is less than
Vu,, the device may enter battery-powered active state 274. The hysteresis
between VLO and
VHI prevents the device from oscillating between battery-powered active and
mains-powered
active states.
In battery-powered active state 274, the electrical device may continuously
monitor
battery voltage level. If the battery voltage falls below a predetermined
level, for example,
about 7 volts, the device enters shutdown mode 272 before entering the dead
state. As
indicated above, the control processor 21 or the repeaters may instruct the
device to enter the
idle state 271 by sending a command signal (CHID).
If a device performs multiple functions, a device may shed one or more of
those
functions. For example, as shown in Fig. 47 loads can be shed hierarchically.
The hierarchical order of the load shedding may be controlled by the differing
voltage
levels set for each electrical device for entering an off/idle, state and/or
for returning to an
idle/active state. For example, when the power supplied to the electrical
devices 18 is below,
for example, 9.5 volts, the acoustic function and/or device may be the only
load to enter or
remain in the off and/or idle state (e.g., the acoustic device may reactivate
at 9.5 volts). In
alternate embodiments, the acoustic device may be the first device to enter an
off or idle state
at, for example, 9.5 volts. If the voltage supplied to the electrical devices
18 is below, for
example, 9 volts, the acoustic device and the compass may be in an off or idle
state.
Similarly, if the voltage supplied to the electrical devices 18 is below, for
example, 8.5 volts,
the bird may enter the battery back-up state and the acoustic device and the
compass may be
in an idle or inactive state.
Referring to one of the preferred embodiments illustrated in Figs. 47-49, when
the
voltage is below 7 volts all of the electrical devices enter an idle state
where only
communications with the dry-end electronics 5 is maintained with other loads
in the electrical
devices 18 turned off. If the voltage is still below 7 volts, all of the
electrical devices enter
the Off state. From the Off state, in the illustrated embodiments, the
leveling devices or birds
re-enter the idle state when the voltage rises above 8.5 volts, the compass
devices re-enter the
idle state when the voltage rises above 9 volts, and the acoustic devices re-
enter the idle state
when the voltage rises above 9.5 volts. In this manner, the electrical devices
in the illustrated
embodiments may reactivate themselves autonomously responsive to programmable
voltage
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CA 02617233 2008-01-29
levels keyed to the criticality of each electrical device function.
One feature of the embodiments of the electrical devices 18 shown in Fig. 49
is that the
electrical devices perform the hierarchical load shedding autonomously. For
example, each of
the load shedding programs and state diagrams indicated by Figs. 47-49 may be
performed by
microprocessor 204 without communication with other wet units and/or the
control processor
21.
The term hierarchical load shedding is intended to broadly cover
configurations where
the load on the power line in the underwater cable is reduced in a specified
order in response
to one or more fault conditions as discussed herein.
Control of the communications modes may take place in the individual
electrical
devices. For example, in Fig. 49, if there is a power failure in the
underwater cable or a
shutdown of external power to the devices, Vpwr in Figs. 42A, 42B goes to
zero. The
devices enter state 280 and enable backup communications mode, as discussed
above. When
power is restored, the devices enter primary communications mode, indicated by
state 281.
In alternate embodiments, the repeaters may include a CPU, voltage sensors,
and other
control circuits configured to enable the control processor 21 and/or repeater
to switch
additional current to the affected data/power distribution lines in the event
of a fault. For
example, each repeater may include a redundant driver circuit which can
optionally be
switched into operation by the control processor 21 and/or by the individual
repeaters in
response to a fault on a particular distribution line. In this manner, instead
of selectively
reducing the load along a particular cable segment, power may be selectively
increased to
compensate for the fault.
A remarkable result of combining various aspects of embodiments of the present
invention is that power may be reliably transferred to the wet units 30 with
an overall power
transfer efficiency of about 60% or more. This remarkable result allows wet
units to be
powered entirely from the underwater cable and has eliminated the necessity of
supplying
operational power using batteries in practical underwater streamer cable
applications. Further,
substantial improvements have been made in the reliability of the underwater
cable power
distribution and communication system 20. Additionally, the latency of data
transferred from
the electrical devices 18 even while employing repeaters has been minimized.
While the present invention has been shown in conjunction with a towed seismic
streamer cable, it will be understood that it could be used in other
instrumented underwater
cables, such as any towed hydrophone cable, whether for geophysical,
scientific, or military
use, or with untowed, bottom-referenced cables. In any of these applications,
the underwater
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CA 02617233 2008-01-29
cable may be oriented horizontaily, vertically, or at any angle between
horizontal and vertical.
While several exemplary power distribution and communication systems and
elements
embodying the present inventions have been shown, it will be understood, of
course, that the
inventions are not limited to these embodiments. Modifications may be made by
those skilled
in the art, particularly in light of the foregoing teachings. For example, in
some
embodiments, it may be desirable to distribute power to the electrical devices
18 on both the
inbound and outbound data distribution lines. In this manner, the total amount
of power
distributed on any one line may be reduced. Further, elements from the various
embodiments
may be combined with and/or substituted for corresponding elements of another
embodiment.
Additionally, alternate embodiments of the inventions may include more or less
components
than those in the illustrated embodiments. For example, each of the
embodiments shown may
utilize one or more of the features, circuits, and/or functions of the other
embodiments. It is,
therefore, intended that the appended claims cover any such modifications in
any combination
which incorporate the features of this invention or encompass the spirit and
scope of the
invention.
It should be understood that the invention encompasses all possible
combinations and
subcombinations of the elements herein described. For example, each of the
embodiments
shown or described may utilize one or more of the features, components, and/or
functions of
the other embodiments. Further, the specification is divided into Parts I-VII
to facilitate
understanding of the invention. However, many aspects of the invention span
more than one
of the Parts. For example, the repeaters in an underwater cable may include
structures which
distribute power, synchronize data, and respond to faults. As a result, the
repeaters appear in
Part I: Power Distribution/Communication Structure, Part IV: Synchronization
of
Inbound/Outbound data, and Part VI: Fault Tolerant Structures. Other aspects
of the
invention span one or more of the Parts. The various aspects of the invention
may be
interrelated and are not limited to one or more of the Parts of the
specification.
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