Note: Descriptions are shown in the official language in which they were submitted.
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HYBRID POWER MODULE WITH FAULT DETECTION
BACKGROUND
The present invention relates generally to industrial process field devices,
and
more particularly to a hybrid power module for powering a wireless industrial
process
field device.
The term "field device" covers a broad range of process management devices
that
measure and control parameters such as pressure, temperature, and flow rate.
Many field
devices are transmitters which act as communication relays between a
transducer for
sensing or actuating an industrial process variable, and a remote control or
monitoring
device such as a computer in a control room. The output signal of a sensor,
for example,
is generally insufficient to communicate effectively with a remote control or
monitoring
device. A transmitter bridges this gap by receiving communication from the
sensor,
converting this signal to a form more effective for longer distance
communication (for
example, a modulated 4-20 mA current loop signal, or a wireless protocol
signal), and
transmitting the converted signal to the remote control or monitoring device.
Field devices are used to monitor and control a variety of parameters of
industrial
processes, including pressure, temperature, viscosity, and flow rate. Other
field devices
actuate valves, pumps, and other hardware of industrial processes. Each field
device
typically comprises a sealed enclosure containing actuators and/or sensors,
electronics for
receiving and processing sensor and control signals, and electronics for
transmitting
processed sensor signals so that each field device and industrial process
parameter may be
monitored remotely. Large scale industrial manufacturing facilities typically
employ
many field devices distributed across a wide area. These field devices usually
communicate with a common control or monitoring device, allowing industrial
processes
to be centrally monitored and controlled.
Field devices increasingly use wireless transceivers to communicate with
centralized control or monitoring systems. Wireless devices extend the reach
of control
or process monitoring systems beyond that of wired devices to locations where
wiring
may be difficult and expensive to provide. In some cases wireless field
devices may be
powered by direct electrical connection to power utilities such as 120V AC
utilities, or
powered data. More often, however, power utilities are not located nearby or
cannot
readily be installed in hazardous locations where instrumentation and
transducers must
operate. Accordingly, field devices are often locally powered by power sources
with
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limited capacity, either stored, as in the case of a long-life battery, or
produced, as in the
case of a solar panel. Batteries are expected to last more than five years and
preferably
last as long as the life of the product. Because local power sources have
limited
capacities, the use of lower power electronics and RF radios is frequently
essential for
many wireless field devices.
Many field device designs enclose an attached battery under a cover of the
sealed
enclosure of the field device. Other field devices utilize power from external
sources
such as solar panels, energy harvesters such as vibrational or thermo-electric
scavengers,
or a nearby utility grid connection. Each method of powering a wireless field
device
conventionally requires a different wiring terminal interface. Field devices
which run
partly or entirely on battery power typically incorporate terminal blocks
which provide
contact points to an attached battery. Field devices which run on grid power,
by contrast,
include terminal blocks which provide wired connections for grid power
(typically via
screw terminals), and which condition grid power for use by the field device.
Terminal
blocks are often removable, allowing a single field device to be configured
for different
power sources by swapping in one or another source-specific terminal block.
Solar
panels, vibrational energy scavenging systems, and other types of local power
modules
may all use different terminal blocks.
Wireless transmitter field devices broadcast periodic signals corresponding to
sensed parameters. Battery-powered transmitters are typically expected operate
for five
or more years between battery replacements. Depending on the application,
existing
systems can operate for this period of time while transmitting as often as
once every four
seconds. Faster update rates are desirable for many industrial applications,
but necessitate
greater power draw which significantly reduces battery life.
Energy harvesting systems such as solar panels and vibrational or
thermoelectric
scavengers produce power highly dependent on location and application.
Vibrational
scavengers can be highly efficient energy sources in areas with high amplitude
continuous
vibration, for instance, but may not be practical or sufficient in areas with
low amplitude
or intermittent vibration. Furthermore, while batteries and supercapacitors
ordinarily
continue to provide power while discharging, energy harvesting systems may
experience
unpredictable drops in power production, resulting in fluctuating levels of
power
depending on environmental conditions. Solar panels, for instance, produce no
power in
the dark, and vibrational scavengers produce no power when attached structures
(e.g.
motors) are still.
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SUMMARY
The present invention is directed toward a wireless field device assembly
comprising a process sensor, a housing, a power module, and a processor. The
process
sensor is configured to monitor a process variable and produce a sensor
signal. The
housing encloses an interior space of the wireless field device. The power
module
comprises an energy storage device and a connection to a local power source,
and is
configured to be housed in the wireless field device. The processor is located
within the
interior space, and is powered by the power module. The processor produces a
fault
signal value used to differentiate between energy storage device faults, local
power
source faults, and no-fault states.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representative diagram of a process monitoring and control system
including featuring a wireless field device.
FIG. 2a is a schematic block diagram of the wireless field device of FIG. 1.
FIG. 2b is a schematic block diagram of an alternative wireless field device
according to the present invention.
FIG. 3 is an exploded perspective view of the wireless field device of FIG. 1.
FIGS. 4a and 4b are exploded perspective views of a power module of the
wireless field device of FIG. 1, from two angles.
FIG. 5 is an illustrative graph of voltage received by the wireless field
device of
FIG. 1 as a function of time.
FIG. 6 is a flowchart of a fault detection method for the wireless field
device of
FIG. 1.
DETAILED DESCRIPTION
The present invention is a power module for an industrial wireless transmitter
or
actuator. This power module includes both an energy storage device such as a
battery or
a supercapacitor, and power conditioning circuitry for an external power
harvesting
energy source. Voltage readings from this power module are used to identify
fault modes
of the power harvesting energy source and the energy storage device.
FIG. 1 depicts process measurement or control point 10, comprising wireless
field
device 12 (with antenna 14), transducer 16, process connection 18, process
piping 20,
local power source 22, and power connection 24. Wireless field device 12
connects via
antenna 14 to control or monitoring system 26.
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Process piping 20 carries flow F of process fluid. Wireless field device 12
may be
a process transmitter configured to receive, process, and transmit signals
from one or
more sensors configured to measure parameters of this process fluid.
Alternatively, field
device 12 may be a wireless controller configured to command a process
actuator such as
a valve or pump in response to signals from control or monitoring system 28.
Transducer
16 is one such sensor or actuator in contact with fluid flow F via process
connection 18.
Process connection 18 may be a parallel or in-line connection to fluid flow F,
depending
on the particular industrial application and the parameter measured or
actuated by
transducer 16. Although only one transducer 16 is shown in FIG. 1, some
embodiments
of process measurement or control point 10 may include multiple sensors and/or
actuators
connected to wireless field device 12.
In some embodiments, transducer 16 is a sensor which provides sensor readings
to
field device 12 for processing and transmission to control or monitoring
system 26. In
other embodiments, transducer 16 is an actuator which actuates a change on the
process
fluid in response to signals received from control or monitoring system 26 by
field device
12. Although further description hereinafter will focus on the embodiment
wherein
transducer 16 comprises a sensor, a person skilled in the art will understand
that the
invention could equally be applied to actuator systems.
Transducer 16 is secured to process piping 20 via process connection 18, and
measures one or more parameters of the process fluid, such as flow rate,
viscosity,
temperature, or pressure. In the depicted embodiment transducer 16 is housed
inside field
device 12, but alternative embodiments may have transducers located separately
from
field device 12 and connected to field device 12 by wire. A sensor signal from
transducer
16 is sent (e.g. as an analog voltage value or a digital signal) to processing
and
transmission electronics within field device 12 (see FIGs. 2a and 2b). The
particular form
of transducer 16 may vary depending on the parameter sensed; in some cases
process
connection 18 may be configured to such that transducer 16 extends into
process flow F,
within process piping 20. Field device 12 receives and digitizes (if
necessary) process
signals from transducer 16, and transmits process messages containing process
information to control or monitoring system 26 via antenna 14. Antenna 14 is
shown as a
single antenna, but may comprise a plurality of diverse antennas in a single
array. Field
device 12 may transmit signals directly to control or monitoring system 26, or
may
transmit signals via an intermediate mesh or hub-and-spoke network. In some
embodiments, field device 12 may utilize WirelessHART protocol (IEC 62591).
Control
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or monitoring system 28 may be a centralized system which receives sensor data
from
and/or broadcasts actuator data to a plurality of field devices in wireless
field device
network 26. Control or monitoring system may be located on-site with wireless
field
device network 26, or may be located at a remote control room.
Field device 12 includes electronics which process and transmit signals from
transducer 16 (or to transducer 16, in the case of an actuator system), as
discussed in
greater detail below. Both signal processing and signal transmission require
energy,
which is supplied by a power module as described below with respect to FIGs.
2a and 2b.
This power module includes both an internal energy storage device such as a
battery or a
supercapacitor, and a hookup to local power source 22 over power connection
24. Local
power source 22 may, for instance, be a solar cell, an energy harvester such
as a
vibrational or thermo-electric scavenger, or a utility power grid. Although
FIG. 1 depicts
local power source 22 as a an external power source situated outside of field
device 12,
some embodiments of local power source 22 may fit inside field device 12, as
described
below with respect to FIG. 2b.
FIGs 2a and 2b depict embodiments of field device 12 wherein local power
source
22 is external (FIG. 2a) and internal (FIG. 2b) to field device 12. The
embodiments of
FIGs 2a and 2b differ only in the composition of power module 120, embodied in
FIG. 2a
as power module 120a, and in FIG. 2b as power module 120b. The designation
"power
module 120" is used herein to refer equivalently power module 120a and power
module
120b, where the distinction between embodiments is not relevant.
FIGs. 2a and 2b focus on the embodiment of field device 12 which receives and
transmits sensor signals to control or monitoring system 28, rather than the
embodiment
which actuates process machinery based on signals from control or monitoring
system 28.
As discussed above, power module 120 could be applied to either type of
system, as well
as field devices which perform both functions.
FIG. 2a is a schematic block diagram of field device 12, illustrating one
embodiment of antenna 14, transducer 16, casing or housing 100, transceiver
102, signal
processor 104, digital signal conditioner 106, analog/digital converter 108,
analog signal
conditioner 110, power supply control 112, cover 116, terminal block 118, and
power
module 120a. Power module 120a comprises energy storage device 122, connection
board 124, power conditioner 126, terminal screws 128, and cable conduit 130.
FIG. 2b
is a schematic block diagram of an alternative embodiment of field device 12,
illustrating
antenna 14, transducer 16, casing or housing 100, transceiver 102, signal
processor 104,
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digital signal conditioner 106, analog/digital converter 108, analog signal
conditioner
110, power supply control 112, cover 116, terminal block 118, and power module
120b.
Power module 120b comprises energy storage device 122, connection board 124,
power
conditioner 126, and local power source 22b.
Field device 12 may be exposed to extreme temperatures and hazardous
environments. Field device 12 therefore includes casing or housing 100 to
enclose and
protect electronics in interior region I. Casing or housing 100 is a rigid,
durable body
which may be sealed against the environment to protect transceiver 102, signal
processor
104, digital signal conditioner 106, analog/digital converter 108, analog
signal
conditioner 110, and power supply control 112 from degradation or damage.
Casing or
housing 100 interfaces with cover 116 to enclose receptacle R, which protects
and houses
removable components such as power module 120. Casing or housing 100 and cover
116
may likewise form an environmental seal, thereby protecting components located
in
receptacle R from harmful environmental effects. In some embodiments the seal
between
casing or housing 100 and cover 116 may adequately protect components in
interior
region I (i.e. transceiver 102, signal processor 104, digital signal
conditioner 106,
analog/digital converter 108, analog signal conditioner 110, and power supply
control
112), such that casing or housing 100 need not fully enclose interior region
I, since the
combination of casing or housing 100 and cover 116 will shield these
components from
environmental damage, so long as cover 116 is attached.
According to one embodiment, transceiver 102 is a signal transmitter/receiver
which transmits and receives wireless signals via antenna 14. Signal processor
104 is a
logic-capable data processor such as a microprocessor. Digital signal
conditioner 106
comprises a digital filter which operates on digitized sensor signals, and
which may be
configurable by signal processor 104 in response to diagnostic programs or
instructions
from central control or monitoring system 28. Digital signal conditioner 106
may, for
instance, operate to filter noise or extract signals of interest from the raw
digitized signal
provided by analog/digital converter 108. Analog/digital converter 108 is an
analog-to-
digital converter capable of digitizing analog sensor signals from transducer
16. In some
embodiments (such as in actuator systems) analog/digital converter 108 may
alternatively
or additionally comprise a digital-to-analog converter capable of converting
digital
signals from signal processor 104 into analog signals for transmission to
transducer 16.
Analog signal conditioner 110 is a conventional analog signal conditioner,
which may for
instance perform band-pass filtering to isolate one or more regions of
interest from
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signals received from transducer 16. Power supply control 112 is a
conventional power
routing device configured to draw power from terminal block 118, and report
the voltage
received from terminal block 118 to signal processor 104 (for instance via
analog signal
conditioner 110) as a means for monitoring power quality and imminent power
failure.
Signal processor 104 uses this voltage information to flag fault modes of
local power
source 22 and energy storage device 122, as described in further detail below
with respect
to FIGs. 5 and 6. Power supply control 112 receives electrical power from
internal or
external sources via terminal block 118, and supplies this power as needed to
transceiver
102, signal processor 104, digital signal conditioner 106, analog/digital
converter, analog
signal conditioner 110, and any other powered components of field device 12.
During operation, analog signal conditioner 110 receives and filters process
signals from transducer 16. Transducer 16 may be situated inside field device
12, as
depicted in FIG. 1, or may be located externally and connected to analog
signal
conditioner 110 by wire. Filtered process signals are digitized by
analog/digital converter
108, and further filtered by digital signal conditioner 106 prior to
processing by signal
processor 104. Some embodiments of field device 12 may dispense with one or
both of
digital signal conditioner 105 and analog signal conditioner 110, particularly
if signals
from transducer 16 are preconditioned. Similarly, analog/digital converter 108
is
unnecessary in embodiments wherein transducer 16 provides a digital signal.
Although
transceiver 102, signal processor 104, digital signal conditioner 106,
analog/digital
converter 108, and analog signal conditioner 110 have been described as
distinct
components, the functions of some or all of these components may in some
embodiments
be performed by shared hardware such as a common microprocessor. Field device
12
may also include a local operator interface (not shown) with, for instance, a
screen and/or
input keys allowing an operator to interact directly with field device 12.
Like other
powered components of field device 12, such a local operator interface would
draw power
from power supply control 112.
Powered components of field device 12 receive power from power supply control
112. Power supply control 112 in turn draws power from power module 120
through
terminal block 118. Terminal block 118 is a power routing component configured
to
mate with and draw power from power module 120. Depending on the internal
electronics of field device 12, terminal block 118 may accept AC or DC power.
In some
embodiments, terminal block 118 may serve to anchor power module within
receptacle R.
Terminal block 118 may permanently affixed to field device 12, or may be a
modular
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component which can be swapped out as needed, to provide an interface with
alternative
power sources.
Power module 120 is a hybrid device which provides power both from energy
storage device 122, and from local power source 22. As illustrated in the
embodiment
shown in FIG. 2a, power module 120b comprises energy storage device 122,
connection
board 124, power conditioner 126, and terminal screws 128. Energy storage
device 122
may be a capacitor, supercapacitor, rechargeable battery, primary (non-
rechargeable)
battery, or any other conventional compact energy storage device. Power
conditioner 126
imay include a capacitor, switching circuits, filtering components, and
voltage and/or
current limiting components. Although FIGs. 2a and 2b depict energy storage
device 122
as a single unitary device, some embodiments of power module 120 may include
multiple
distinct power cells of the same or different types. Connection board 124 is
an internal
circuit board which provides a power connection between energy storage device
122,
terminal screws 128, and power conditioner 126. In many embodiments of field
device
12, particularly those which are expected to operate in extreme environments
and at
extreme temperatures, rechargeable batteries may not be practical. In
appropriate
environments, however, rechargeable embodiments of energy storage device 122
may be
recharged with power from local power source 22. Energy storage device 122 may
be
removable from power module 120.
According to this embodiment, power module 120a includes terminal screws 128.
Terminal screws 128 serve as a terminal interface for power connection 24 by
attaching
exposed loops or other exposed conductive sections of power connection 24 to
power
module 120a. Terminal connection 24 preferably enters receptacle R via cable
conduit
130. Cable conduit 130 may be any sort of opening which allows power
connection 24 to
pass through casing or housing 100 or cover 116, into receptacle R. For
greater
protection of terminal block 118, power module 120, and any other components
located
within receptacle R, cable conduit 130 may include a cable gland which forms a
seal
about terminal connection 24 to shield receptacle R from environmental
hazards.
Power conditioner 126 is a compact device which performs conventional power
conditioning specific to local power source 22. Power conditioner 126 may, for
instance,
limit voltage and/or current so as to protect components of field device 12.
Power
conditioner 126 may also incorporate an AC/DC converter, where appropriate, if
power
source 22 is an AC power source. Power conditioner 126 may be fabricated as a
part of
connection board 124, or may be a separate component attached to connection
board 124.
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Power module 120 provides energy to terminal block 118 from two sources:
energy storage device 122, and local power source 22. As discussed in the
Background
of the present invention, external power sources such as energy scavenging
systems and
solar panels are often limited in the power they can supply. Some embodiments
of local
power source 22 can provide limited but substantially constant power
insufficient to
power signal processor 104, analog and digital signal conditioners 110 and
106,
analog/digital converter 108, and particularly transceiver 102 at all times.
Other
embodiments of local power source 22 may provide greater but unreliable power.
In
either case, power module 120 supplements the power from local power source 22
with
stored power from energy storage device 122 to meet the power requirements of
powered
components of field device 12. Depending on the environment and application of
field
device 12, more or less of the total power consumed by field device 12 may
come from
energy storage device 122 or local power source 22. Where power from local
power
source 22 is relatively scant or unreliable, field device 12 will be powered
primarily from
energy storage device 122, and supplemental power from local power source 22
will
extend the lifetime of energy storage device 122. Where power from local power
source
22 is relatively plentiful and reliable, field device 12 can be powered
primarily from local
power source 22, and supplemental power from energy storage device 122 will
fill in for
any downtimes or sags in power from local power source 22.
As noted above with respect to FIG. 1, local power source 22 may take a
variety
of forms. By way of example, a vibrational scavenger acting as local power
source 22
may satisfy substantially all power requirements of field device 12 while the
motor is
active (e.g. half the time, with a 50% duty cycle). When the motor is
inactive, power
module 120 will instead provide power from energy storage device 122. In
another
embodiment, a thermoelectric energy scavenger acting as local power source 22
might
provide constant but weak power sufficient to power signal processor 104,
digital and
analog signal conditioners 105 and 110, and analog/digital converter 108, but
insufficient
to power transceiver 102 during signal transmissions. In such a case, energy
storage
device 122 could provide supplemental power during transmissions. If local
power
source 22 could only provide even weaker power, energy storage device 122
might be
required to power all components at all times. In such a case, the inclusion
of local power
source 22 could extend the expected lifetime of energy storage device 122,
increasing
time between replacement. In a third embodiment, a direct grid connection
might
constitute local power source 22. In such a case, external power source will
completely
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power all components of field device 12 during ordinary conditions. Should the
grid
experience an outage, or the grid connection fail, energy storage device 122
will act as a
backup power source, allowing field device 12 to continue to operate
uninterrupted.
FIG. 2b depicts an embodiment of field device 12 equipped with power module
120b. Unlike power module 120a, power module 120b does not include terminal
screws
128 or any other means for connecting to an external power source. Instead,
power
module 120b includes local power source 22b, a variant of local power source
22 (see
FIG. 1) sized to fit within receptacle R. Local power source may be, for
instance, a
vibrational scavenger which harvests energy from vibration of field device 12.
This
embodiment is particularly appropriate to applications wherein field device 12
is likely to
be mounted near pumps, motors, or other reliable sources of vibration. Local
power
source 22b may be permanently mounted within power module 120b, or may be
detachably connected to power module 120b via a conductive interface which
serves as a
functional equivalent of terminal screws 128 (see FIG. 2a). Energy storage
device 122,
connection board 124, and power conditioner 126 are substantially functionally
identical
in power module 120a and 120b, but may take slightly different forms (e.g.
different
dimensions or shapes) as needed in power module 120b to accommodate local
power
source 22.
Both embodiments of power module 120 provide hybrid power from energy
storage device 122 and local power source 22 (including 22b). To the extent
that power
from local power source 22 is available, local power source 22 is used
preferentially.
When power from local power source 22 is unavailable or insufficient, power
from
energy storage device 122 is used instead or in addition. Power supply control
112
monitors voltage from power module 120 (via terminal block 118), and thereby
detects
faults in local power source 22 and energy storage device 122.
Although terminal block 118 and power module 120 are depicted as separate
components in FIG. 2, some embodiments may combine the functions of terminal
block
118 and power module 120 into a single removable component which attaches to
field
device 12 within receptacle R, and which is selected to match both the
particular model of
field device 12, and a particular type of local power source 22.
FIG. 3 is an exploded perspective view of field device 12, comprising antenna
14,
casing or housing 100, cover 116, terminal block 118, power module 120, energy
storage
device 122, cable conduit 130, terminal block attachment screws 132, terminal
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attachment screw holes 134, power source attachment 136, and power supply
connector
138.
As discussed above with respect to FIG. 2, power supply control 112 provides
power to all powered components of field device 12. Power supply control 112
receives
electrical power from terminal block 118 via power supply connector 138, an
electrical
contact which interfaces with terminal block 118 when terminal block 118 is
secured in
place. Power supply connector 138 may, for instance, comprise a plurality of
conductive
pins which interface with corresponding recesses or jacks in terminal block
118. As
depicted in FIGs 3, terminal block 118 is secured in contact with power supply
connector
138 by terminal block attachment screws 132. Terminal block attachment screws
132 are
threaded screws which fasten into terminal block attachment holes 134 on
casing or
housing 100, thereby removably anchoring terminal block 118. Although terminal
block
118 is depicted as secured by terminal block attachment screws 132,
alternative
embodiments may use other means to secure terminal block 118, such as by
bayonets or
screws, or by a snap or friction fit. In alternative embodiments, terminal
block 118 may
be a non-removable component permanently affixed to, or mounted in, a wall of
casing or
housing 100 shared by receptacle R and internal space I. Terminal block 118 is
equipped
to receive AC or DC via one or more terminals. These terminals may take the
form of
flat conductive contacts which abut power module 120.
Pursuant to this embodiment, power module 120 is secured to terminal block 118
by means of power source attachment 136. Power source attachment 136 is
depicted as
an electrical contact surrounded by a protruding sleeve on terminal block 118
which
forms a snap or friction fit and an electrical contact with internal power
module 120. In
other embodiments, power source attachment 136 might comprise a hook, screw,
latch, or
any other conventional means for securing internal power module 120 to
terminal block
118, together with any conventional electrical connection. Power source
attachment 136
supports internal power module 120 in the absence of cover 116 (e.g. when
cover 116 is
removed to install or remove components within receptacle R). Cover 116 may,
however,
help to retain internal power module 120 against terminal block 118, as
discussed below
with respect to FIGs. 4a and 4b. Terminal block 118 may, where appropriate,
provide
power conditioning to regulate the voltage or current, and to invert or
rectify power
received from power module 120. Power module 120 provides power from local
power
source 22 and/or energy storage device 122. Power from power module 120 may
originate exclusively from local power source 22 or energy storage device 122,
or may
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come from a combination of both sources. In some embodiments, local power
source 22
may be a rechargeable power source such as a capacitor or rechargeable
battery, and may
be charged from local power source 22.
As discussed above with respect to FIG. 2, energy storage device 122 may be a
conventional battery or supercapacitor. Energy storage device 122 is depicted
as
removably coupled to power module 120 via a snap fit or other conventional
locking
mechanism. In other embodiments, power source 122 may be fully enclosed within
power module 120, and may or may not be removable.
Power module 120 provides a contact point for power connection 24 from which
it receives power from local power source 22. This contact point may comprise
terminal
screws 128 (see FIGs 2a and 4a), or any equivalent attachment means for an
electrical
contact or connection. Connection board 124 is a circuit board with conductive
contacts
at the locations of terminal screws 128. Terminal screws 128 are conductive
fasteners
used to attach one or more wires of power connection 24 to connection board
124. Where
power connection 24 includes hooks or loops, terminal screws 128 and
connection board
124 will interface with these hooks or loops to anchor power connection 24 to
power
module 122. Depending on the form of power connection 24 (which may in turn
depend
on power source 24), terminal screws 128 may be replaced with plug, clips, or
other
attachment means. Although FIG. 3 depicts terminal screws 128 for connecting
power
module 120 to an external embodiment of local power source 22, power module
120 may
instead include an internal local power source 22b (see FIG. 2b). Such a local
power
source 22b could be located within power module 120, or attached to the
exterior of
power module 120 in such a manner as to fit under cover 116.
As described above with respect to the embodiment shown in FIG. 2, cover 116
meets casing or housing 100 in a seal, thereby protecting components within
receptacle R
(e.g. terminal block 118 and power module 120). Power module 120 fits snugly
inside
receptacle R, under cover 116 and in contact with terminal block 118. Local
power
source 22 is connected to power module 120 via power connection 24 (see FIG.
2), which
extends through cable conduit 130 into receptacle R, and affixes to terminal
screws 128
(or analogous fasteners). As described above, power module 120 includes power
conditioner 126, which conditions power from local power source 22 and energy
storage
device 122 for use by powered components of field device 12. The voltage of
power
provided by power module 120 varies as a function of the condition of local
power source
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22 and energy storage device 122, as described below with respect to FIGs. 5
and 6,
below. This variation in voltage is used to detect and flag faults in both
power sources.
FIGS. 4a and 4b are exploded perspective views of one embodiment of power
module 120 from two different angles. Power module 120 includes energy storage
device
122, connection board 124, terminal screws 128, casing front 202, casing back
204,
terminal posts 206, energy storage device attachment 208, friction fit
connection 210,
support 212, and anchoring ring 214.
In this embodiment, power module casing 200 is a rigid protective enclosure
which surrounds and protects connection board 124, and which supports terminal
screws
128 and energy storage device 122 snugly within receptacle R of field device
12. As
noted above, connection board 124 is a circuit board which provides electrical
connections to energy storage device 122 and terminal screws 128, and which
may house
or mount power conditioner 126 (see FIGs 2a and 2b).
Terminal posts 206 are
conductive posts which extend from connection board 124 through friction fit
connection
210 of casing front 202 to form an electrical connection with power source
attachment
136 of terminal block 118 (see FIG. 3). Friction fit connection 210 is a
connecting
portion of casing front 202 which extends into and mechanically attaches to
power source
attachment 136, thereby securing power module 120 to terminal block 118.
Friction fit
connection 210 may comprise one or more snap rings or similar components to
form a
snug connection to power source attachment 136.
According to this embodiment, energy storage device attachment 208 is a
conventional snap-in battery housing, or an equivalent means for securing
energy storage
device 122. Energy storage device attachment 208 is anchored to casing back
204, and
provides both mechanical retention and an electrical connection for energy
storage device
122. As discussed above, energy storage device 122 may be a specialized energy
cell, an
off-the-shelf battery, a supercapacitor, or any similar energy storage device.
The size and
shape of energy storage device attachment 208 may vary depending on the type
of energy
storage device 122 selected. Energy storage device attachment 208 provides
electrical
contacts between energy storage device 122 and connection board 124.
Casing back 204 includes support 212, a substantially rigid portion extending
away from connection board 124 to meet with cover 116 (see FIG. 3), so as to
provide a
snug fit within receptacle R. This fit helps to hold friction fit connection
210 in place at
power source attachment 136. In the depicted embodiment, support 212 includes
anchoring ring 214, a raised circular ridge on the outermost surface of casing
back 204.
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Anchoring ring 214 is sized to interface with a complementary ring or wave
spring on the
interior (not shown) of cover 116, thereby securing power module 120 against
vibration,
between terminal block 118 and cover 116. Terminal screws 128 extend through
back
casing 204 into connection board 124, thereby providing an electrical
interface for power
connection 24 to local power source 22. For embodiments of field device 12
wherein
local power source 22 is enclosed within receptacle R (see local power source
22b,
described above with respect to FIG. 2b), terminal screws 128 may be omitted
in favor of
a direct connection between connection board 124 and local power source 22 (if
local
power source 22 is included within power module 120), or a detachable hookup
for local
power source 22 conceptually similar to energy storage device attachment 208
(if local
power source 22 is detachably affixed to power module 120). Alternatively,
terminal
screws 128 or similar attachment means may be used to connect connection board
124 to
an entirely separate local power source 22 housed between casing back 204 and
cover
116. In this last embodiment, support 212 could be reduced to provide space
for local
power source 22.
Whether local power source 22 is housed within receptacle R or not, power
module 120 provides an electrical connection which draws power preferentially
from
power source 22, and supplementally from energy storage device 122 when power
from
local power source 22 is unavailable or insufficient to satisfy the power
needs of wireless
device 12. Although particular applications or installation locations may
result in either
of power source 22 or energy storage device 122 providing the bulk of the
power required
by field device 12, field device 12 preferably draws power from local power
source 22,
when available, before depleting energy storage device 122. Power from each
source is
conditioned as needed by power conditioner 126, inverting or rectifying power
from local
power source 22 and energy storage device 122, as needed. In this way, power
module
122 is able to provide continuous power for field device 12 despite varying
availability of
power from external power source 22, while extending the lifetime of energy
storage
device 122.
FIG. 5 is a graph of voltage received from power module 120 as a function of
time. FIG. 5 is intended to serve only as an illustrative example of possible
voltage
fluctuation during operation of field device 12, and thereby to illustrate the
operation of
fault detection system discussed in further detail below with respect to FIG.
6. FIG. 5 is
not to scale, and the particular details of the shape of the voltage curve of
FIG. 5 are of no
intrinsic significance to the functioning of power module 120 of field device
12.
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As discussed above with respect to FIGs. 2a, 2b, 3, 4a, and 4b, power from
power
module 120 may be provided by local power source 22, energy storage device
122, or a
combination of the two. Generally speaking, field device 12 may operate in
three power
modes: a first mode wherein all electric power is supplied by local power
source 22, a
second mode wherein field device 12 operates on a combination of power
produced by
local power source 22 and stored energy from energy storage device 122, and a
third
mode wherein field device 12 operates exclusively on stored energy from energy
storage
device 122. The voltage output of power module 120 is generally highest in the
first
mode (within constraints imposed by power conditioner 126), lowest in the
third mode,
and intermediate in the second mode. More particularly, voltage in the third
mode
typically matches a battery voltage of energy storage device 122, while
voltage in the first
and second modes exceeds this battery or capacitor voltage by an amount
dependent on
the degree of voltage sag of power from local power source 22.
Over time, however, voltage from local power source 22 may fluctuate depending
on power draw and the condition of local power source 22. A sag in voltage
from local
power source 22 may indicate that local power source 22 has fallen offline
(e.g. if local
power source 22 constitutes a solar panel in a dark area), or may indicate
that local power
source 22 is incapable of satisfying the instantaneous power demands of field
device 12
alone, necessitating supplemental power from energy storage device 122. In
addition,
minor voltage fluctuations can occur even while field device 12 is powered
entirely by
local power source 22.
FIG. 5 depicts voltage in ranges corresponding to all three modes, as
indicated
along the y-axis (voltage) of the graph. These modes correspond to time
domains
wherein local power source 22 and energy storage device 122 are capable of
supplying
changing amounts of power.
At time to, field device 12 is powered exclusively from energy storage device
122,
which maintains a substantially steady (but likely slightly diminishing)
voltage;---,' V2. At
time t1, local power source 22 activates, and entirely takes over the powering
of field
device 12, providing a voltage in excess of voltage V3. Voltage V3 corresponds
to a
threshold below which energy storage device 122 contributes to powering field
device 12.
Between times t2 and t3, voltage from local power source 22 sags from above to
below V3. A voltage sag of this kind could be due to increased power draw from
local
power source 22, or to a drop-off in power produced by local power source 22
(e.g. a
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decrease in the light incident on a solar panel, or a reduction in the
amplitude of vibration
at a vibrational harvester).
At time Li, local power source 22 deactivates. Some embodiments of local power
source 22 may frequently activate and deactivate over the course of operation
of an
industrial process. A vibrational scavenger affixed to a 50% duty cycle motor,
for
instance, will deactivate (i.e. produce no power) and reactivate regularly, as
the motor
turns off and on. Other embodiments of local power source 22 might ordinarily
be
expected to provide constant power, with any deactivation indicating a fault
condition.
FIG. 5 shows energy storage device 122 beginning to fail at time t5, causing
voltage received at terminal block 118 to drop further. Voltage fall-off below
voltage V2
may, for instance, correspond to the depletion of a battery or the discharge
of a
supercapacitor, depending on the particular embodiment of energy storage
device 122.
Although FIG. 5 shows voltage rapidly falling off beginning at time, battery
or
supercapacitor failure need not be abrupt. In ordinary circumstances, gradual
depletion of
energy storage device 122 will result in a gradual drop in voltage received at
terminal
block 118 while field device 12 is powered exclusively by energy storage
device 122. As
energy storage device 122 discharges, voltage at terminal block 118 eventually
falls
below voltage V1, a threshold indicating depletion of energy storage device
122.
FIG. 6 is a flowchart of a method 300 for detecting power supply faults based
on
voltage received from power module 120. More particularly, method 300 allows
control
or monitoring system 28 (see FIG. 1) to differentiate between faults in local
power source
22 and faults in energy storage device 122 based on a fault signal value set
by signal
processor 104. Method 300 allows control or monitoring system 28 to
distinguish
between modes 1, 2, and 3 of FIG. 5, and provide alerts to users and
maintenance
personnel, accordingly.
As discussed above with respect to FIGs 2a and 2b, power supply control 112
reports voltage from signal processor 104, indicating the voltage of power
received from
terminal block 118 (and thereby from power module 120). In some cases this
voltage
report may be received by way of analog signal conditioner 110, analog/digital
converter
108, and/or digital signal conditioner 106. Signal processor 104 is set with a
series of
voltage thresholds corresponding to different possible voltage values which
could be
provided by power module 120 during ordinary and faulty operation. (Step 51).
These
voltage thresholds may be programmed or hardwired into signal processor 104
during
manufacture, or may be set in response to signals received from control or
monitoring
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system 28 or another user terminal via transceiver 102. Signal processor 104
monitors
voltage received from power module 120 using power supply control 112. (Step
S2). As
discussed above with respect to FIG. 1, signal processor 104 regularly
transmits process
signals to control or monitoring system 28. These process messages include
process
variable signals which reflect sensor readings from transducer 16. In
addition, each
process message includes a fault signal value from which failure states of
energy storage
device 122 and local power source 22 can be flagged and identified. Although
the
following discussion focuses on an embodiment wherein each process message
includes
both a process variable signal and a fault signal value, alternative
embodiments may
separate these two components, e.g. by transmitting a fault signal value only
occasionally,
or by transmitting fault information separately. In some embodiments,
different signal
processors may be used for proves variable signals and energy fault signal
values.
Based on comparison of the monitored voltage with the voltage thresholds,
signal
processor 104 sets a fault signal value in each process message reflecting the
present
voltage provided by power module 120. (Step S3). For the purposes of the
present
explanation, high voltages will be presumed to correspond to high fault signal
value
values, and low voltages to low fault signal value values, although this need
not be the
case in all embodiments. Field device 12 transmits the process message
containing this
fault signal value wireless by means of transceiver 102. (Step S4).
Control or monitoring system 28 regularly receives process messages from
individual field devices (including field device 12) within wireless field
device network
26. Upon receiving a process message with a fault signal value from field
device 12,
control or monitoring system 28 ascertains whether the value of this fault
signal value is
less than an energy storage device fault condition threshold. (Step S5). This
fault
condition threshold is a preset number corresponding at least approximately to
voltage Vi
of FIG. 5, a voltage less than voltage V2 ordinarily provided by energy
storage device
122. FIG. 5 is not drawn to scale; in some embodiments voltage Vi may be only
slightly
lower than voltage V2. If the fault signal value received by monitoring or
control system
28 is less than this energy storage device fault condition threshold,
monitoring or control
system 28 reports an energy storage device fault (e.g. battery depletion), and
sends a
corresponding alert notifying users or maintenance personnel so that energy
storage
device 122 can be replaced or repaired. The energy storage device fault
condition
threshold may be set to an appropriate value depending on the particular
environment and
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application, to notify users and maintenance personnel of imminent energy
storage device
failure sufficiently in advance of complete failure.
If the fault signal value is greater than the energy storage device fault
condition
threshold, monitoring or control system 28 ascertains whether the fault signal
value is
nevertheless less than a local power source fault condition threshold
approximately
corresponding to a voltage value between V2 and V3 (see FIG. 5). (Step S7). If
not,
monitoring or control system 28 reports no fault. (Step S8). If so, monitoring
or control
system 28 reports a local power source fault. (Step S9). A fault signal value
lower than
the local power source fault condition threshold, but greater than the energy
storage
device fault condition threshold, indicates that local power source 22 is
incapable of
supplying all power utilized by field device 12. Depending on the application
and
environment of field device 12, the local power source fault condition
threshold may be
selected to correspond with voltage V3 (such that a fault is reported whenever
local power
source 22 is unable to completely power field device 12), with voltage V2
(such that a
fault is reported only when local power source is unable to supply any power
to field
device 12), or with any intermediate voltage.
Fault conditions may be archived for maintenance purposes; not all reported
fault
conditions need be accompanied by a fault alert. In particular, some
embodiments of
process measurement or control point 10 may sometimes lose local power source
22
during ordinary operation, as noted above. Upon reporting a local power source
fault,
control or monitoring system 28 determines whether occasional loss of local
power
source 22 is expected for field device 12. (Step S10). This determination may
be based
on a history of voltage received by field device 12, on configuration
information provided
by a user, or on any other appropriate factors. If occasional or periodic
losses of local
power source 22 are expected, control or monitoring system 28 may not transmit
any alert
indicating a fault at local power source 22. If occasional or periodic losses
of local power
source 22 are not expected, however, control or monitoring system 28 will
preferably
transmit a local power source fault alert notifying users and maintenance
personnel so
that local power source 22 can be replaced or repaired. In some cases,
reporting a local
power source fault may trigger a timer or increment a counter, such that a
sufficient
number of fault reports or a sufficient time spent at low voltage will trigger
a local power
source fault alert, even for systems wherein intermittent losses of local
power source 22
are expected.
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The preceding description has focused on monitoring or control system 28 as
the
source of fault reports and alerts. In alternative embodiments, however,
signal processor
104 of field device 12 may be capable of performing method steps S5-811 of
method
300, and may transmit only a fault alert or fault report to monitoring or
control system 28.
Regardless of whether field device 12 or control or monitoring system 28
produces these
fault reports and fault alerts, method 100 allows power faults in power from
power
module 120 to be detected and identified using voltage received at power
supply control
112. Power module 120 provides increased energy storage device longevity over
conventional systems with only batteries or supercapacitors, and provides
greater
reliability than systems utilizing only local energy sources such as energy
harvesting
systems. All of these functions are accomplished with a power module
configured to fit
into receptacle R, with no need for additional external components, or
protection for such
components to survive harsh environments.
While the invention has been described with reference to an exemplary
embodiment(s), it will be understood by those skilled in the art that various
changes may
be made and equivalents may be substituted for elements thereof without
departing from
the scope of the invention. In addition, many modifications may be made to
adapt a
particular situation or material to the teachings of the invention without
departing from
the essential scope thereof. Therefore, it is intended that the invention not
be limited to
the particular embodiment(s) disclosed, but that the invention will include
all
embodiments falling within the scope of the appended claims.
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