Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02220480 1997-11-07
MULTI-FREQUENCY REMOTE COMMUNICATION SYSTEM
FIELD OF THE INVENTION
This invention relates to remote 2-way data
communication between units through the wall of a pipeline,
storage tank or other containment vessel.
BACKGROUND OF THE INVENTION
It is often necessary to transmit signals and to send
data between control units on the outside of metal containment
vessels such as pipelines or storage tanks and pipeline tools
or other devices operating inside such containment vessels,
without intruding into the containment vessel itself. This can
be especially advantageous when a liquid or gaseous medium is
enclosed within the containment vessel.
One example of a device requiring a communication
system as disclosed by the present invention is a pipeline
packer or isolation tool used to isolate sections of pipe for
repair or replacement. The packer is propelled to the
designated location using the flow of product in the pipeline
with the packer being tracked using known techniques. Upon
reaching the desired location, fluid flow in the line is
terminated and the packer is activated by a signal from the
operator to form a seal against the inner pipeline wall. On
completion of the repair, the operator transmits another signal
to release the packer which is then moved away by resuming the
flow of pipeline product for removal. Some isolation devices
can perform multiple functions while contained within the
pipeline and thus require a series of control signals to be
transmitted from an operator outside the pipeline to activate
each function. In addition, these devices may generate data
which then must be communicated to the outside.
In the past, various devices and methods have been used
in an effort to transmit signals and data through the metal wall
of a containment vessel such as a pipeline or storage tank.
Some of these techniques relied upon radioactive sources, sonic
frequencies, or wires which may intrude into the containment
CA 02220480 1997-11-07
vessel or pipeline. These methods were hampered by problems
associated with obtaining and containing radioactive sources,
limited range and data speed, and impracticalities associated
with running wires into pipelines or tanks at remote distances.
Some efforts have also been made to send data using a low band
of electromagnetic radiation (EM) in the frequency range of
22hz, however, this method has been used only for sending
signals in one direction to locate and track pipeline pigs and
has never been used for two-way communication of data signals.
This method did not employ dual RF/EM communication and was
severely hampered by the slow speed of data transfer and a
limited transmission range.
It would be advantageous to provide a communications
system that could transmit and receive signals and data at high
rates of speed between devices located within metal containment
vessels such as pipelines or storage tanks and an operator
located some distance away without intruding into the
containment vessel. It would also be advantageous if this
communications system could be programmed to operate at
different frequencies to take advantage of local conditions
offering the least traffic or extraneous interference.
Accordingly, it is a general object of the present
invention to provide a multi-frequency remote communication
system that is useful for transmitting and receiving signals and
data to and from devices located within metal containment units
such as pipelines or storage tanks without intruding into the
containment vessel and without removing the device from the
vessel.
It is a also an object of the present invention to
provide a multi-frequency remote communication system that can
send and r~ceive signals at high rates of speed over relatively
large distances.
It is a further object of the present invention to
provide a multi-frequency re~ote communication system that can
be programmed to operate at different frequencies in order to
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adapt and take advantage of local conditions offering the least
amount of traffic or extraneous interference.
SUMMARY OF THE lNv~N-lION
The present invention comprises a communications system
consisting of three components, a control unit, a translator
unit and a command unit. The control unit is located remote
from the containment vessel and is capable of two-way
communication at radio frequencies (RF) with a translator unit
located on the outside of the containment vessel. The
translator unit is capable of two-way RF communication with the
control unit and two-way electromagnetic (EM) communication at
low frequency through the wall of the containment vessel with
a command unit attached to a device located inside the
containment vessel. The translator unit converts RF signals to
15 EM signals and EM signals back to RF signals.
Signals for controlling a device located inside a
containment vessel are transmitted by RF from the control unit
to the translator unit where they are converted to low frequency
EM signals and transmitted through the wall of the vessel to the
command unit. Signals and data from the command unit are
transmitted by low frequency EM from the command unit through
the wall of the vessel to the translator unit where they are
converted to RF signals and transmitted to the control unit.
According to the present invention there is provided a
25 multi-frequency remote communication system comprising a control
unit capable of two-way radio frequency communication, a
translator unit capable of both two-way radio frequency
communication and two-way low frequency electromagnetic
communication, and an electronic command unit capable of two way
low frequency electromagnetic communication.
Some of the many advantages associated with the
communication system of the present invention are as follows.
First is that the system is useful for sending and receiving
signals and data to and from devices located within steel
35 containment units such as pipelines or storage tanks. Second,
the system can send and receive signals at high rates of speed
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and over relatively large distances. Third, is that the system
can be programmed to operate at different frequencies in order
to adapt and take advantage of local conditions offering the
least amount of traffic or extraneous interference.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now
be described in greater detail and will be better understood
when read in conjunction with the accompanying drawing, in
which:
Figure 1 is a schematic representation of one
embodiment of the present invention showing possible positioning
of the three communication units;
Figure 2 is an electronic operations block diagram for
the present invention.
DETAILED DESCRIPTION
For the purposes of illustration, the present invention
is described with reference to use in a pipeline. It will be
appreciated, however, that the communications system and the
techniques described herein may be adapted for use with any
suitable containment vessel such as storage tanks, bins, railway
cars, tanker trucks, etc.
Referring to Fig. 1, a pipeline tool 20, is placed
inside a pipeline 5 and moved along by the flow of product in
the pipeline to a desired location.
A multi-frequency remote communication system
includes a control unit 30 located remote from the pipeline 5.
Multi-frequency remote communication system 1 also includes a
translator unit 40 located on the outside surface of the
pipeline wall 10 near the location of pipeline tool 20 deployed
inside pipeline 5. Control unit 30 may be located at a distance
of up 2000 meters (6562 feet) from translator unit 40 depending
on terrain, and may be hand held. Control unit 30 and
translator unit 40 are designed for mutual two-way radio
frequency (RF) communication. Multi-frequency remote
3 5 communication system 1 further includes an electronic command
unit 50 attached to pipeline tool 20 located inside pipeline 5.
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Command unit 50 and translator unit 40 are designed for mutual
two-way electromagnetic (EM) communication at low frequency
through pipeline wall 10. The working distance between
translator unit 40 and command unit 50 can range up to 3.66
meters (12 feet) depending upon the thickness of pipeline wall
10 and the nature of the product within the pipeline 5.
Translator unit 40 also performs two-way translation of
RF signals to low frequency EM signals and of low frequency EM
signals and data to RF signals and data.
Electronic command unit 50 controls pipeline tool 20 by
responding to commands sent by control unit 30 and translator
unit 40.
The operation of one embodiment of the present
invention will now be described in detail with reference once
again to Figure 1. RF signals 35 are transmitted from control
unit 30 to translator unit 40. Translator unit 40 receives RF
signals 35 from control unit 30 and converts them to low
frequency EM signals 45. Translator unit 40 transmits low
frequency EM signals 45 through pipeline wall 10 to electronic
command unit 50 attached to pipeline tool 20 located inside
pipeline 5. Electronic command unit 50 receives low frequency
EM signals from translator unit 40 for controlling pipeline tool
20 and transmits data 46 received from pipeline tool 20, through
the wall of pipeline 10 to translator unit 40 located on the
outside of the pipeline wall. EM signals 46 are received by
translator unit 40 and converted to RF signals 36 which are
transmitted by translator unit 40 to control unit 30. Control
unit 30 receives RF signals 36 from translator unit 40.
The penetrating characteristics of EM frequencies are
significantly increased as the frequency is lowered, however,
at low EM frequencies the ability to carry data at a usable
speed is considerably reduced. Frequencies in the range of 22hz
have greater penetrating ability when compared to frequencies
in the range of 97hz, however, data transmission speed of
frequencies in the range of 22Mhz is severely limited.
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The frequency of EM signals 45 and 46 transmitted
through pipeline wall 10 between translator unit 40 and command
unit 50 is programmable within a range between 75hz and 110hz.
At these frequencies, the data handling speed is in the range
of 20 to 30 baud, using 8 data bits, 1 start bit and 1 stop bit.
In a preferred embodiment of the present invention the optimum
operating frequency has been found to be 97.8hz.
The frequency of RF signals 35 and 36 transmitted
between control unit 30 and translator unit 40 is programmable
within a range between 450Mhz and 470Mhz. To determine the most
advantageous frequency for RF signals 35 and 36, the radio
frequency band of the electromagnetic spectrum is monitored and
the frequency having the least amount of traffic and providing
the least amount of extraneous interference is selected.
An example of the operation of multi-frequency remote
communication system 1 will now be described in relation to the
operation and control of a pipeline packer or isolation tool
(tool) of the kind described in our copending International
Application PCT/CA97/00055. Generally, multi-frequency remote
communication system 1 is used to send operating instructions
to and receive data from the tool. The operating instructions
relate to the various amperages, force factorsj and voltages at
which it is desired that the tool operate. Once the tool has
received an instruction via multi-frequency remote communication
system 1 it will request confirmation of the command and will
not carry out any action until confirmation has been received
and a special code is entered. This process of data
transmission and confirmation, back and forth between the tool
and control unit 30, takes place for each command sent to the
tool. In return, the tool sends data, via multi-frequency
remote communication system 1, relating to the remaining battery
voltage, which battery pack is in use, amount of amperage each
motor is drawing, amount of force being applied to pipeline wall
10 and up and downstream pipeline pressure. This type of data
will normally be transmitted by the tool on a continuous basis.
Once the tool reaches programmed force and amperage constants
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it will automatically shut down. During an operation, or at any
time while the tool is holding pipeline pressure, should the
force factor fall below the lower programmed limits, the motors
will automatically restart and return the tool to the proper
force factor. At the same time, the tool will constantly
transmit data relating to is current status and function. An
emergency halt command can be issued through multi-frequency
remote communication system 1 at any time should the operator
deem it necessary.
10 DETAILED EXAMPLE
Isolation tools are normally used in pairs to close off
a section of an active pipeline to allow replacement of a
corroded or damaged section. This saves the time and great
expense of shutting down the complete pipeline. Isolation tools
have been in use generally for a number of years. However, with
the present system, isotools can be instructed to perform tasks
and feed back information. The system is remotely controlled
using radio and electromagnetic coupling as the communications
methods. This also means that the operator need not be close
to the pipeline.
System Overview
The system is divided into three units shown
diagrammatically in Figure 2:
1) Isotool Command Unit 50
2) Base Station Translator 40
3) Hand-held control unit 30
Each isotool has duplicate electromagnetic communi-
cations systems and microcontrollers known as the Main and
Secondary Unset systems 51 and 52 respectively. The electronics
for each are totally separate and there is also a separate
battery pack 59 for the Secondary Unset system. This is a
back-up system and is only meant to be used to unset the isotool
in the event of failure in some part of the Main system. Removal
of a failed isotool when in the pipeline locked in position
would be a very expensive procedure and would requlre draining
of a section of pipeline. During normal operation of the
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isotool the Secondary Unset system is polled to ensure that it
is functioning. Should any problem be detected, the isotool
will be taken out of service and flown down the pipeline until
it can be removed at a convenient point.
Hand-held control unit 30 uses a radio link to
communicate with the translator 40. The translator is used as
a signal repeater between the control unit and the isotool
command unit 50. Because of the severe attenuation of radio
waves through steel piping, electromagnetic coupling is used to
send and receive signals from the isotool.
In a typical set-up there will be two isotools, two
translators and one or two control units. It is possible to
control two isotools with one control unit although this will
probably not be done.
1) Isotool Command Unit
Usually two isotools are inserted into a pipeline when
some repair work is necessary. Each isotool drags a large
battery pack behind it which provides all its power. They flow
along in the pipeline fluid (whatever it may be) until the
faulty section of pipeline is reached. At that time the fluid
flow is halted. The exact position of the isotool in the
pipeline can be determined by receiving an electromagnetic
pulsing signal from the unit allowing exact placement. As
mentioned above, the isotool has two independent electronic
systems. Each electronics system consists of nine printed
circuit boards mounted in a 6.75" diameter module. Connectors
carry the power and signals between the boards. A functional
description of each board follows below.
In the stack, the boards are arranged in the following
order from bottom to top:
1) Main and Secondary Unset Motor Controls.
2) Bypass Motor Controls.
3) Main Microcontroller.
4) Main Electromagnetic Transmitter.
5) Main Electromagnetic Receiver.
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6) Secondary Unset Microcontroller.
7) Secondary Unset Electromagnetic Transmitter.
8) Secondary Unset Electromagnetic Receiver.
9) Motor and Secondary Unset Battery Connector
Interface.
1) Main and Secondary Unset Motor Control Board
This board has the control electronics for two motors
80 and 90 which operate in tandem in a normal functioning tool.
The motors are powered from 24 Volts DC and are used to open
(set) or close (unset) a clamp system which holds and seals the
isotool in the pipeline while the repair work is being
performed. The switches used to control the motors are FETs and
require heat sinks. For this reason this board is placed at the
bottom of the stack to allow the FETs to be fastened to the
baseplate metalwork to afford cooling.
An added complication is that power is supplied to the
both motors from one of two main battery packs - Battery 65 and
Battery 66. A separate Secondary Unset battery 59 provides
power to unset the tool in an emergency should it be necessary.
Twelve FETs are used in two H-bridge configurations on the Main
and Secondary Unset Motors 80 and 90. These consist of two
battery selection FETs on the high side and one on the low side
at either end of each motor. Another two FETs are used on the
Secondary Unset Motor (only one motor is used for an emergency
unset) to select power from the Secondary Unset battery
circuitry. There are fuses on each main battery feed and these
are mounted on this printed circuit board.
The Main and Secondary Unset control circuits are
completely separate except around the Secondary Unset motor
control. As this can be operated by either the Main or
Secondary Unset control circuits, FETs from both circuits
converge here. Interlock circuitry is used to prevent both
control circuits from trying to operate the Secondary Unset
motor control at the same time. The Secondary Unset control
circuitry has priority.
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The current drawn by both motors is monitored for two
reasons. Firstly as part of a feedback loop to determine when
the motors have stalled or reached a programmed current level.
The control circuitry removes the power from both motors in
either of these scenarios. Secondly to detect if there is a
short circuit across the motor which produces a hardware trip
in the control circuitry. Calibration and offset controls for
the motor current monitoring are also on this board.
Also part of the feedback loop is a series of strain
gauges 100 to measure how much pressure is being exerted by the
isotool sealing clamps on the pipeline wall. A strain gauge trip
value can also be programmed to turn off the power to the motors
when the desired strain value is reached. Once the tool is set,
the programmed strain gauge setting is maintained by activating
the set motors if the value falls below the required level.
This ensures that even with any settling of the tool or sealing
material the clamp should not become loose or slip inside the
pipeline. There could be a serious accident if this happened.
The two motors 80 and 90 are also used for the standard
Unset. The motor current sensors determine when the unit is
fully unset and removes power from the motors. If a Secondary
Unset is being performed, only one motor is used. As mentioned
earlier, the Main set/unset control circuitry 51 is disabled
when the Secondary Unset is activated. Because there is only
one motor operating, it takes a greater time to unset the tool.
However, as the Secondary Unset 52 is a last chance action to
release the tool so that it does not jam in the pipeline, this
is a small price to pay.
2) By~ass Motor Control Board
There are three Bypass Motors in the isotool of this
example. These are small motors which control valves. When the
valves are opened, pipeline fluid flows through a small diameter
tube or tubes from one side of the isotool to the other. The
Bypass Motors are opened at the end of a pipeline repair cycle
in readiness for the tool Unset. As the section of pipeline
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that has been replaced is full of air, before releasing the tool
the air has to be replaced with pipeline fluid. To determine
when the pressure has been equalised there are pressure sensors
110 and 120 mounted in the tool on the upstream and downstream
ends thereof. Once the bypass valves are open, the sensor
readings are sent back to the control unit 30 at frequent
intervals so the operator can monitor progress.
The Bypass Motor control circuitry consists of an
H-bridge around each motor. (A total of 12 FETs.) Each motor
is individually controlled and its current monitored. The motor
only takes a matter of a few seconds to open the bypass valves
and completion of the task is detected by an increase in the
motor current. Hardware then trips the control circuitry and
sets a flag to inform the microcontroller that a particular
motor has completed the open or close cycle. As each motor
control circuit is separate, it does not matter that one motor
may take a little longer than another. Because the motors are
low current, the increase in current upon stalling is not too
significant. Should the circuitry not detect that a motor has
stalled, there is a time-out of 10 seconds after which power is
removed from the motor. A signal is sent to the control unit to
the effect that one or more of the Bypass Motors have timed out
and that there could be a problem in the tool.
Each Bypass Motor control system has independent fuses
on the power feed. This means that even if there is a failure
in one set of electronics, the other two Bypass Motors will be
able to complete the task.
Once the pressure has been equalised on both sides of
the isotool, the bypass valves are closed and the tool can be
unset. It is then free to flow with the pipeline fluid to the
location of the next job.
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3) Main Microcontroller Board
The main microcontroller board is the heart of the
isotool command system. It performs the following functions:
1) Sends the commands to the Set/Unset Motors and the
Bypass Valves and monitors the motor currents.
2) Receives data from the strain gauges and the two
fluid pressure sensors.
3) Monitors the voltage of both battery packs.
4) Has a watchdog timer to detect problems with the
running of the software.
5) Looks after all the communications with the control
unit by way of the translator.
Also on the printed circuit boards are:
1) A 5 Volt power supply for all the main system logic
circuitry.
2) A real time clock so that commands or information
can be time stamped.
3) A hardware sleep timer with programmable jumpers to
select sleep intervals.
4) Calibration and offset potentiometers for the
pressure sensors.
The microcontroller has two modes of operation; sleep
mode and normal mode. Due to the length of time that the
isotool may spend in the pipeline travelling between jobs, in
order to save battery power, it is advantageous to be able to
put the whole tool to sleep.
Sleep mode is entered either by a command from the
hand-held control unit or after an extended period of receiving
no messages. In this mode, a hardware timer is activated and
the power to all other circuitry and boards is shut down. The
current drawn in this mode is 2-4mA. Hardware jumpers determine
the length of the sleep period up to 35 hours. At the end of
the sleep period power is reapplied to the microcontroller.
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This then wakes up and turns on the electromagnetic receiver
which listens to see if there is a message directed to it.
After a period of time, perhaps 30 seconds or so, if no message
has been received, the hardware timer is once again activated
and the tool goes back to sleep. Should a message be received,
the microcontroller remains awake and sends an acknowledgement.
The tool is then ready to receive commands and begin work. It
will remain awake for as long as it is receiving messages from
the control unit.
A watchdog timer is incorporated into the
microcontroller. If the software stops running, the watchdog
will reset the microcontroller to restart it again. Mechanical
shock to the tool causing a connector to very briefly lose
contact is one possible reason for the software to freeze. If
a watchdog reset is detected by the microcontroller, this fact
will be sent to the control unit after it has finished rebooting
the system so that normal operations can be resumed.
4) Main Electromaqnetic Transmitter Board
This card is responsible for modulating, demodulating,
and transmitting the modulated signal to the coil 91. The
incoming and outgoing modulated signals are transmitted and
received by use of a modem. Transmission of the modulated
signal is accomplished with two totem-pole drivers. One on each
side of the transmit coil 91. These drivers are put in a
tristated mode when transmission is not taking place. More
information on the EM communications is provided below with
reference to Communications Overview.
5) Main Electromaqnetic Receiver Board
This is responsible for receiving electromagnetic
signals generated by the translator. The received signal is
amplified, filtered and then sent to the Main Electromagnetic
Transmitter Board. The receive section filters out signals that
are not between 85Hz and 110Hz. The demodulation of this signal
takes place on the Main Electromagnetic Transmitter Board by the
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.
modem. This modem with its automatic gain control produces
serial data that is sent to the Main Microcontroller. When the
microcontroller wakes up from sleep mode, after initialisation
it then turns on the Main Electromagnetic Receiver 130 to listen
for messages. More information on the EM communications is
provided below with reference to Communications Overview.
6) Secondary Unset Microcontroller Board
The Secondary Unset Microcontroller Board is identical
to the Main Microcontroller Board except that there are no
adjustments for sensors on the board. It has its own independent
Sleep Mode timer and behaves in the same way as the Main
Microcontroller Board. Once awake, the Secondary Unset
Microcontroller Board is polled by the control unit
periodically.
Under normal operating conditions, the power to operate
the Secondary Unset system is drawn from either of the main
battery packs. However, should they fail, it will be powered
from the Secondary Unset battery. The microcontroller monitors
the voltage of this battery. Any logic circuitry related to the
20 -Secondary Unset system is powered by the 5 Volt power supply on
this board. The only command that the Secondary Unset
Microcontroller Board sends out is to the Main and Secondary
Unset Motor Controls Board to initiate a Secondary Unset. This
command has priority over the Main Set/Unset circuitry and
disables power to it and this is in case there is some hardware
or software fault that is trying to activate a set or unset.
As mentioned earlier this is used to release the isotool from
the pipeline in the event of failure of the Main electronics
system in some way.
7) Secondary Unset Electromaqnetic Transmitter Board
This card is responsible for modulating, demodulating,
and transmitting the modulated signal to the coil 93. The
incoming and outgoing modulated signals are transmitted and
received by use of a modem. Transmission of the modulated
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signal is accomplished with two totem-pole drivers. One on each
side of the transmit coil 93. These drivers are put in a
tristated mode when transmission is not taking place. Because
the main control system and backup system have different ID's,
only the system with the proper ID will respond after having
received a valid packet. Never will they respond at the same
time. For more information on the EM communications read the
Communications Overview.
8) Secondary Unset Electromaqnetic Receiver Board
This is responsible for receiving electromagnetic
signals generated by the translator. The Secondary Unset
Electromagnetic Receiver 150 is a second receiver that reads
everything that the main receiver card does except it routes the
messages to the Secondary Unset Microcontroller. It is up to
this microcontroller to determine by the destination ID if the
signal is for itself or for the main receiver. It shares the
same coupling coil 92 as the Main Receiver Coil 92. The Main
and Secondary Unset units have different IDs and so the
microcontroller will only respond when the message is meant for
it. For more information on the EM communications, reference
is made to the Communications Overview below.
9) Motor and Secondary Unset Battery Connector Interface Board
At the top of the stack of circuit boards in the
module, this board has four connectors. These are interfaces for
the following:
1) The three bypass motors.
2) Main and Secondary Unset Motors.
3) Strain Gauge and Downstream Fluid Pressure Sensor
Circuitry.
4) Secondary Unset Battery Pack.
Another connector board mounted to the main part of the
tool mates up to this board.
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2) Translator
The translator 40 acts as a repeater between control
unit and the isotool. It is equipped with a UHF radio
transmitter/receiver 170 and an electromagnetic transmitter /
receiver system 175 all on one printed circuit board. Messages
are received from and sent to the control unit 30 on the radio
link in the 450-470 Mhz range. A message received from the
control unit at 4800 baud is briefly stored in memory and then
passed to the Electromagnetic Transmitter at approximately 23
baud. The output of the transmitter is passed to the coil 176
which couples the signal to the coil 92 on the isotool inside
the pipeline. Similarly, a response message from the isotool
is received by the translator at around 23 baud by the
Electromagnetic Receiver and retransmitted to the control unit
at 4800 baud on the UHF radio link. The translator is in
contact with both the Main and Secondary Unset units in the
isotool. Both Main and Secondary Units receive the packets but
the unit who's ID matches that of the destination byte of the
packet will respond.
The translator can be placed in position above the
isotool in the pipeline and used to establish contact with the
isotool. As mentioned earlier, to conserve battery power the
isotool is in sleep mode during its travel down the pipeline,
only waking up for a brief period to determine if there is
contact from the translator. To wake up the isotool, the
translator would transmit repeatedly an all-call message at an
interval which would guarantee that the isotool would get it.
Using the transmitter on the translator for extended periods of
time is not a problem as the batteries can be easily replaced.
Sirens and strobe lights can be fitted on the
translator to warn of imminent failure of the isotool to hold
back the pipeline pressure. The isotool sends a message that
it cannot maintain sufficient setting pressure against the
pipellne wall and this means that the tool could soon slip. The
translator would then activate the warning systems. The message
would also be sent to the control unit.
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3) Hand-held control unit
This is the third part of the system. This allows the
operator to send messages to the command unit in the isotool by
way of the translator.
- Mounted in a case, the hand-held control unit consists
of
1) 450-470 Mhz transmitter/receiver unit.
2) Two 4 line x 20 character LCDs (liquid crystal
display) which are backlit.
3) Four LED's to indicate communications status.
4) Microcontroller, real time clock and data logging
module.
5) Keypad.
6) 12 Volt, 2.5 Ah Nickel Metal Hydride battery pack
with charger circuitry.
7) Connectors for RS-232 and Power/Battery charger.
There are two printed circuit boards in the control
unit. The radio board together with the radio power supply,
digital interface circuitry and electroluminescent LCD back
light power unit is mounted behind the LCD's. The rest of the
circuitry is mounted on a PCB (printed circuit board) with the
battery pack laying behind the PCB in the lower part of the
case. A flexible antenna 55 is mounted from the top edge of the
control unit.
Transmission power of the radio is 2 Watts and uses
NBFM. This means that communications to the translator over
distances exceeding 2 miles could be possible dependent upon the
terrain. The default frequency is 464.6375 Mhz which is a
dedicated data channel throughout the country, as defined by
Industry Canada. However, the radio frequency is programmable
to any channel within the 450-470 Mhz range should interference
be experienced on this channel. Each Province and Territory
also has at least one frequency which can be used specifically
for data communications.
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When the complete system is in operation, the control
unit is in constant communication with the translator. Commands
are sent to the translator to be relayed to the isotool command
unit and status information from the command unit is sent back
to the control unit. The green LED's on the control unit show
the quality of the communications link. A steady - on LED means
that the communications link is good and that the messages are
being received without errors. Should there be some errors in
the messages, the LED relevant to that link may go out briefly.
Total operating time with the battery pack can be 14
hrs dependent upon frequency of transmission and usage of the
back light. Battery voltage is continuously monitored and when
the capacity is down to 10~ reserve, a warning is flashed on the
LCD. More urgent warnings appear on the display as the battery
capacity is reduced. If charging is not initiated, then the
control unit will shut down to protect the operational
reliability of the battery.
Charging of the battery is achieved by connecting a
cable to a recharge connector on the control unit. Suitable
power sources are a car battery via the cigarette lighter or an
8 to 16 volt power supply. Included in the battery charger
input circuitry is over-voltage and reverse polarity protection
of the battery. Overheating of the battery is protected by a
thermal trip in the battery pack. Battery charging is totally
automatic and does not affect operation of the control unit.
Once the battery is fully charged, the charger circuitry goes
into trickle charge mode thereby maintaining the battery charge
at full. During the time that the control unit is connected to
an external power source, power is not drawn from the battery
pack.
To prevent accidents or keys being pushed
unintentionally all command functions from the control unit to
the isotool command unit, via the translator, require entry of
a four digit supervisor code before the command is sent. Even
switching off the control unit requires supervisor code entry.
Access to menus to change trip values or radio frequency used
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to communicate with the translator also require entry of
supervlsor code.
During the Set and Unset Procedures, readings will be
received from the isotool relating to Main and Secondary Unset
motor currents along with strain gauge values. Readings from
the upstream and downstream pressure sensors are also being
continuously received. Any commands sent to the isotool will
be stored in the data logging module along with the supervisor
code and time stamped. The stored data can be downloaded to a
lap-top computer through the RS-232 port. If the data logging
module becomes full, it will begin to overwrite the existing
data.
All the variables as relating to the commands for the
isotool command unit are stored in the control unit. Each time
the isotool wakes up to begin a project, it is sent the stored
values of all the trip functions. These stored values are also
sent if the isotool starts up after watchdog reset. The trip
values relate to items such as the following:
1) Maximum Set motor current. Exceeding this value
causes the logic circuit to cut the power to the motors.
2) Maximum Unset motor current, after an unset is in
progress. This is to detect when the tool is fully unset and
the motor has stalled.
3) Maximum and delta strain gauge readings for the set
motors to maintain the set. The delta value is the fall in
strain gauge readings before the' set motor is reapplied.
Csm~-ln;cation~ Overview
The isotool's ability to operate hinges on the ability
of the command unit to transmit and receive through a 0.5 inch
or less pipe wall. Tool transmitters normally operate at a
frequency of about 30Hz. Most equipment operates from 120V
60Hz. The higher frequency starts to greatly attenuate at
frequencies greater than 120Hz. It is for this reason the
communication frequency was chosen at about 97.5Hz as a center
frequency. This frequency can be changed depending on the
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application. The mark frequency is 106Hz and the space
frequency is 89Hz. The UHF link communicates at 4800 baud and
operates between 45OMhz to 47OMhz.
UHF E.M.
Handheld ~ ~ Translator ~ ~ Command Unit
Controller
A packet originates from the handheld controller and is sent by
a UHF radio to the translator. The translator then determines
if the packet is for itself. If so, it responds to the packet,
else it transmits the packet to the isotool. The electro-
magnetic transmit section works by sending a serial packet
generated by the translator microprocessor's UART and modulating
it. The modulated signal is then sent to a dual totempole
driver system to switch current into the transmit coil and
control the direction of the current in the coil. A
electromagnetic field is produced by current going through the
coil. The field produced passes by the receive coil 177 and
induces a voltage across the coil. The amount of signal
produced is relational to the distance from the transmit coil
as well as the strength of the transmit coil. This incoming
signal is amplified and filtered so that only frequencies
between 85Hz and llOHz will be able to pass through. The
aforementioned mark and space frequencies are within this range.
This system can be altered to use different frequencies for
different applications. The received signal is demodulated to
produce serial data which can then be interpreted by the serial
UART internal to the Main and Secondary Unset Microprocessor.
The response packet back follows the same method for modulation
detection and UHF response back to the hand-held control unit.
The above described embodiments of the present
invention are meant to be illustrative of the preferred
embodiments of the present invention and are not intended to
limit the scope of the present invention. Various
modifications, which would be readily apparent to one skilled
in the art, are intended to be within the scope of the present
CA 02220480 1997-11-07
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invention. The only limitations to the scope of the present
invention are set out in the following appended claims.
