WO1999025070A2

WO1999025070A2 - Multi-frequency remote location, communication, command and control system and method

Info

Publication number: WO1999025070A2
Application number: PCT/CA1998/001030
Authority: WO
Inventors: John Dyck; Horst Gotowik; Gerald Faltekval; Richard Bentley; James Janke; Joseph Micahel Green; Bradley Cyril Ingham
Original assignee: Fracmaster Ltd.
Priority date: 1997-11-07
Filing date: 1998-11-06
Publication date: 1999-05-20
Also published as: ID22201A; WO1999025070A3; CA2220480A1; AU1016699A

Abstract

A communication system for use with a device located within a containment vessel, comprises a control unit having means providing two-way packet radio frequency communication; a command unit for attachment to a device in a vessel and having means for providing bidirectional low frequency electromagnetic communication; and a translator unit for converting control unit radio frequency transmissions to corresponding low frequency electromagnetic signals and for transmitting the corresponding low frequency electromagnetic signals and for converting command unit low frequency electromagnetic signals to corresponding radio frequency signals and transmitting the corresponding radio frequency signals. The command and translator units utilize 'near field' electromagnetic fields to effect location, two-way communication, command and control beween units through the wall of a pipeline, storage tank or other containment vessel to effect efficient location and control of devices deployed within conducting ferromagnetic containment vessels such as steel pipelines or storage vessels is difficult without intrusion into the vessel by wires and probes.

Description

MULTI-FREQUENCY REMOTE LOCATION, COMMUNICAΗON, COMMAND AND CONTROL SYSTEM AND METHOD

The present invention generally relates to a method and an apparatus for locating, communicating with and controlling devices located in a pipeline, storage tank or other containment vessel and, more specifically, to such method and apparatus which utilize "near field" electromagnetic fields to effect location and two-way communication 5 between remote command units through the wall of a pipeline, storage tank or other containment vessel.

Background of the Invention

It is often necessary to transmit location, communications, command and control

10 signals between units located within a conducting ferromagnetic containment vessel and an external unit used for location, communications, command and control purposes outside the containment unit, without intruding into the containment vessel itself. This can be especially advantageous when a liquid or gaseous medium is enclosed within the containment vessel, and the unit inside the vessel can move and change its location.

15 One example of a device requiring a location, communications, command and control unit is a pipeline packer or isolation tool used to isolate sections of pipe for repair or replacement. The packer is propelled to a designated location using the flow of product in the pipeline with the packer being tracked and precisely located. Upon reaching the desired location, fluid flow in the line is terminated and the packer is

20 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 that 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

25 pipeline to activate each function. In addition, these devices may generate data that then must be communicated to the outside.

In the past, various devices and methods have been used in an effort to locate and communicate signals through the conducting ferromagnetic walls of containment vessels and pipelines. Some of these techniques relied upon radioactive sources, sonic

30 frequencies, or wires that may intrude into the containment 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 been made to transmit electromagnetic signals in the

35 frequency range of 22 Hertz using simple battery powered relaxation oscillators. These methods have enjoyed limited range and success in locating pipeline pigs, but the inherent limitations of the art has prevented their use for generalized location, communications, command and control functions associated with pipeline devices such as isolation tools. In addition, these devices suffer from very limited range distances and are limited to one way transmission of signals and have never been used for two-way communication of data signals.

It would be advantageous to provide a location and communication system that could transmit and receive both location as well as communications, command and control signals between the exterior surface unit and the remote command unit inside the containment vessel or pipeline. It also would be advantageous if this system could adapt to local conditions and automatically transmit its information at the highest possible speeds, and to do so in a manner that allowed location of the remote command unit at greater range distances than is currently possible and to uniquely identify each remote command unit in a field of several remote command units.

Summary of the Invention

A general object of the present invention to provide a multi-frequency remote location, communications, command and control system that is useful for transmitting and receiving signals and data to and from a multiplicity of devices located within conductive ferromagnetic containment vessels, such as pipelines or storage tanks, without intruding into the containment vessel and without removing the devices from the vessel.

It is also an object of the present invention to provide a multi-frequency location and communication system that can send and receive both location and data signals at relatively high rates of speed approaching the theoretical limit over relatively long range distances and narrow bandwidths. Without limiting the generality of the above object, it is also an object of the present invention to operate with all manner of soil, clay, mineral or other conductive overburden covering a containment vessel, including sea water covering a sub-sea pipeline or other containment vessel.

It is a further object of the present invention to provide a multi-frequency location and communication system that can operate at different frequencies in order to adapt and take advantage of local conditions offering the least amount of traffic or extraneous interference. It is a further object of the present invention to provide a multi-frequency location and communication system that can establish the pipeline wall thickness by using measurements of signal strengths at the different frequencies used for location and communication. It is a further object of the present invention to provide a spread spectrum signal transmission format in order to permit location signals to be received at maximum range distances and to co-mingle these signals with other location signals at multiple frequencies so as to transmit a unique identification signal in order to uniquely identify each remote command unit inside the containment vessel from other units in close proximity with the first unit.

Whereas previous art in pipeline tool location has been limited in range and signal availability, the present invention extends the operating range at which location signals may be detected. This permits effective location, even when an external translator unit is not placed directly over the pipeline, or when extended range distances are required at greater pipeline burial depth, such as at river crossings. In addition, the present invention is equally effective for use inside containment vessels that are surrounded by earth, seawater or other conductive minerals such as clay or wet soil.

The location, communications, command and control functions disclosed are also used to precisely locate and identify each such device contained within the pipeline when more than one tool are in close proximity too each other. This information ensures that the right device is at the right location for the required operation within the pipeline. In addition, the invention utilizes multiple frequency signals, the measurement of which permits an accurate estimate of the containment vessel thickness to be determined. The present invention comprises a location, communication, command and control system comprising three main components including a remote command unit secured to a device located inside a containment vessel; a translator unit located outside the containment vessel at a desired location proximate the containment vessel; and a wireless control unit for use by an operator outside the containment vessel. The remote and translator units are capable of transmission and reception of electromagnetic "near field" location and data communication signals. The remote command unit is capable of also transmitting multiple electromagnetic "near field" location signals at several simultaneous frequencies together with unique identification signals for the individual unit. The translator unit is equipped to transmit and receive electromagnetic "near field" signals containing data through both a serial data interface as well as a packet radio, half duplex, synthesized single audio channel, operating at a fixed frequency as a radio modem unit that is capable of communicating with several other translator units without mutual interference. In addition, the translator unit is capable of relaying data from its packet radio modem to the remote command unit inside the vessel using "near field" electromagnetic fields capable of penetrating the conductive ferromagnetic containment vessel, such as a pipeline or a storage tank. The translator unit described herein is capable of receiving and identifying unique identification signals from the remote command unit for use in determining the location of a remote command unit inside the containment vessel.

The control unit is for use by an operator for transmitting commands to one or more remote command units via the translator unit and for displaying data transmitted by one or more remote command units. According to the present invention there is provided a multi-frequency location and communication system comprising a multiplicity of remote command units, a multiplicity of external translator units, and a control unit capable of communicating with a multiplicity of remote command units through a multiplicity of translator units without mutual interference between remote command units in close proximity within the containment vessel or pipeline.

Some of the many advantages associated with the location, communication, command and control 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 conducting ferromagnetic containment units such as pipelines or storage tanks. Second, the system can send and receive signals at high rates of speed over relatively large distances.

Third, 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. Fourth, the system can transmit and receive signals capable of uniquely identifying a remote command unit inside the containment vessel in a multiplicity of remote command units in close proximity with each other, and to produce location signals that can be used to locate each remote command unit with precision at greater distances than the current art would allow. Fifth, the system can transmit and receive signals on a multiplicity of signals that permit the translator unit to establish the thickness of the containment vessel.

Seventh, a preferred embodiment of the invention allows the precise location of the remote command unit inside the containment vessel and which positive identification of individual remote command units in a field of remote command units in close proximity to each other and permits the detection of location signals at relatively long- range distances without error. In sub-sea pipeline applications, the remote command unit inside the containment vessel or pipeline can communicate with a sub-sea instrument sled external to the containment vessel or pipeline and suspended over the sub-sea pipeline from a surface ship.

Brief Description of the Drawings

These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings in which: Figure 1 is a schematic representation of the main components according to one embodiment of the present invention showing the possible positioning of two remote command units and associated translator units and a control unit used for location, communications, command and control functions; Figure 2 is an electronic operations block diagram of the three main components illustrated in Figure 1 ;

Figure 3 illustrates a sensor coil, according to one embodiment of the present invention, that is used to transmit and receive electromagnetic "near field" signals used for location, communications, command and control functions required by the remote command unit inside the containment vessel; Figure 4 is a side elevational view of a protective stainless steel housing used to house the sensor coil and its electronic circuits and illustrating a pattern of slots cut into the housing for increasing transmitted electromagnetic "near field" signals by increasing the circumferential total resistance of the housing;

Figure 5 illustrates the analog electronic block diagram of an electromagnetic modem incorporated into each translator unit and remote command unit and incorporating a microprocessor having appropriate software for generating linear modulated transmission signals for location, communications, command and control functions and for processing received linear modulated signals; and

Figure 6 is an enlarged front elevational view of the control unit, showing displays, keypad and status lights, according to one embodiment of the present invention. Detailed Description of Preferred Embodiments of the Invention

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 Figure 1 , a control system 10, of the present invention, comprises three main components including a remote command unit 12 secured to each device 14 located inside a pipeline16, a translator unit 18 located outside the containment vessel at a desired location proximate the containment vessel, and a control unit 20 for use by an operator at an appropriate location outside the containment vessel. A separate translator unit 18 is associated with each remote command unit 12.

Each remote command unit and translator unit is capable of transmission and reception of electromagnetic "near field" location and data communication signals. The remote command units are capable of also transmitting multiple electromagnetic "near field" location signals at several simultaneous frequencies together with unique identification signals for the individual unit, as explained later.

The translator units are equipped to transmit and receive electromagnetic "near field" signals containing data through either a serial data interface and/or a packet radio, half duplex, synthesized single audio channel, operating at a predetermined fixed frequency as a radio modem unit that is capable of communicating with the control unit in the presence of several other translator units without mutual interference. In addition, the translator unit is capable of relaying data from its packet radio modem to the remote command unit inside the vessel using "near field" electromagnetic fields capable of penetrating the conductive ferromagnetic containment vessel. The translator unit described herein is capable of receiving and identifying unique identification signals from the remote command unit for use in determining the location of a remote command unit inside the containment vessel.

The control unit is used by an operator for transmitting commands to one or more remote command units via the translator unit and for displaying data received from any of the by one or more remote command units. Figure 6 is a front elevational view of a control unit housing, showing displays, keypad and status lights, according to one embodiment of the invention. The housing encloses electronic circuitry (not shown) for effecting the various functions described herein. Figure 1 illustrates two devices 14 in the form of pipeline tools 14' and 14" placed inside a pipeline 16 and moved along by the flow of product in the pipeline to respective desired locations. The second pipeline tool 14" may be required for a particular pipeline repair operation. For clarity in Figure 1 , only two pipeline tools are illustrated, but a total of up to eight or more individual pipeline tools can be brought into close proximity with each other without mutual signal interference.

Remote command units 12' and 12" are secured to pipeline tools 14' and 14", respectively, and are adapted to communicate with translator units 18' and 18", respectively. For ease of description, the following description refers generally to command unit 12 and translator unit 18. It is to be understood that the description applies to each of command units 12' and 12" and translator units 18' and 18".

Each command unit 12 is provided with a sensor coil 22 which transmits "near field" electromagnetic signals 24 in the form of 1 hertz to 22.5 hertz modulated signals. The "near field" electromagnetic signal can be picked up by a sensor coil 26 in associated translator unit 18 which links to the command unit 12.

The orientation of sensor coil 26 is important for maximizing received signal energy. The orientation of the sensor coil is adjusted by manually adjusting the angular position of the translator unit in which the sensor coil is mounted. Sensor coil 26 is oriented to receive a minimum coupled signal from "near field" electromagnetic field 24. Sensor coil 26 exhibits a sharp null signal at the mid-point of the sensor coil associated with the remote device 12. The orientation of sensor coil 26 associated with translator 18" produces a minimum-coupled signal fortransmission of communications, command and control signals while that of translator 18' produces a maximum-coupled null orientation signal. Sensor coil 26 can also transmit "near field" electromagnetic signals 28 that can be coupled into a sensor coil 22 in remote command unit 12. The transmitted electromagnetic "near field" 24 from the remote command unit and the transmitted electromagnetic "near field" 28 from the translator unit both penetrate the pipeline 16 suffering losses related to the signal frequency and the pipeline thickness T. The translator unit receives "near field" electromagnetic signal 24 from the remote command unit, and relays the signal intelligence via UHF packet radio using a translator antenna 32. The signal travels on a line of sight radio path 34 to an antenna 36 mounted on the control unit. The control unit processes the received UHF packet radio signal and displays information for the operator. The operator can issue and transmit command signals using the control unit. Transmitted commands are radiated as UHF signals from an antenna 32 on the hand held control unit 20 where a line-of-sight radio path 38 is used to propagate the radio signal to the translator unit antenna 32. The translator unit translates the received UHF packet radio signal to "near field" electromagnetic signals and transmits them from the sensor coil 26. The sensor coil sets up a "near field" electromagnetic signal 28 that penetrates the pipeline and where the signal is coupled into the sensor coil 22 associated with the remote command unit 12. In this fashion location, communications command and control signals are conveyed from the remote command unit 12 associated with pipeline tools 14 to translator 18 where the signal is relayed to the hand held control unit 20 controlled by the operator.

UHF packet radio signals transmitted from antenna 32 of control unit 20 to translators 18' and 18" operate on a common UHF frequency channel and do not exhibit any mutual interference. Similarly "near field" electromagnetic signals associated with remote command unit 12' and remote command unit 12" do not interfere with each other. The system 10 is capable of supporting up to eight or more such remote command units in close proximity to each other without interference.

Location Signals

Location signals are transmitted by the remote command units at all times when their associated pipeline tools are in transit to a job site. The location signal consists of the following signal structure: First, a low frequency, direct sequence spread spectrum signal with a sequence length of up to 127 cycles of carrier wave at a frequency between 1 and 3.43 hertz. A total of five frames are used, consisting of an "off' period, a "on" period, and three following periods in which the sequence is transmitted directly, or inverted so as to encode one of eight possible unique data patterns. A total of 635 cycles of carrier define the basic signal structure, which then endlessly repeats itself, allowing the translator unit 18 to receive and detect the "near field" electromagnetic location signals. The basic block can take from 3 to 10 minutes to completely transmit this location signal sequence.

Forfurther clarification, the transmitted carrier is phase modulated using a binary signal structure using in-phase and opposite out-of-phase carrier signals which are modulated by a subset sequence of pseudo-random number (PRN) codes drawn from a minimum sequence length of at least 1027 bits. A portion of this sequence consisting of up to 127 bits is used for this code transmission, depending upon the unique identification of the remote command unit. Thus, a remote command unit identified as "unit #1 " will encode a different portion of the code sequence than will q "unit #2". This ensures that the transmitted signal from remote command unit #1 has no correlation with the signal transmitted from remote command unit #2 which may be in close proximity with unit #1. It is claimed that such a signal has a sharply diminished carrier signal level, making it difficult to observe or detect. The translator unit 18 receives weak "near field" electromagnetic signals that are much smaller than the environmental noise. However, by looking for the unique PRN code, the correlation receiver inside the translator unit 18 builds up the signal level over time while simultaneously averaging out high environmental noise level. In this fashion, a dependable signal can be received at distance up to 35 meters (115 feet). This spread spectrum signal structure supports pipeline tool location at maximum range distances, and is used to locate pipeline tool devices under difficult conditions, such as river crossings and in the ocean.

Superimposed on the low frequency spread spectrum signal are two additional "pinger" signals, one at 11 hertz and another at 22.5 hertz. These two signals are transmitted in sequence, first at 11 hertz and then at 22.5 hertz, each with an interval of approximately 450 milliseconds (5 cycles at 11 hertz, and 10 cycles at 22.5 hertz). Thus, each signal appears at a time interval of approximately 1.2 seconds. A unique identification code is transmitted in each of these two signals, permitting translator units 18 to determine which remote command unit inside the containment vessel is transmitting the location signals. The mid-cycle of the tone burst is phase modulated as one of plus or minus four phase angles between + or - 180 electrical degrees. This modulation method ensures that the tone burst has constant power that can be received by any industry standard pig-tracking receiver.

The second tone burst at 22.5 hertz immediately follows the 11 hertz tone burst. This signal also uniquely encodes the remote command unit's identification number permitting unique identification of one out of eight possible remote command units in close proximity inside the pipeline to be located.

When the translator unit 18 is closer to the pipeline 12, it will directly receive these "near field" electromagnetic "pinger" tone bursts. Since the frequencies of the two bursts are precisely known, a measure of the relative magnitude of the signal level for each tone burst can be measured and used to calculate the thickness of the conducting ferromagnetic containment vessel. Once this factor is known, it is possible to establish a "near field" electromagnetic data link for communications, command and control between the remote command unit 20 and the translator unit 30 which operates at maximum speed and low error rates. This ensures that the remote command unit is responsive and timely in executing commands, retrieving data, and setting new set points inside the pipeline tool.

As illustrated in Figure 1, two individual pipeline tools 14' and 14" can be used to seal two ends of a pipeline that requires repairs. Control over the two pipeline tools 14' and 14" are effected from the hand held control unit 20.

At range distances of up to 5 meters (16 feet), the "near field" electromagnetic signal produced by sensors 22 of the command units is co-axial with the pipeline, with stable and well-behaved geometry.

The receiving sensor coil 26 inside the translator units 18 is highly directional in its response to the "pinger" signals and produces a sharp null when the sensor coil is aligned orthogonally with the "near field" as is illustrated with sensor coil 26 of translator unit 18" in relation to electromagnetic field 24. In this null position, the central axis of the sensor coil 26 points directly toward the remote command unit on the other side of the pipeline 16. By mapping out the direction of the "near field" null signal, it is possible to precisely locate the position of the remote command unit sensor coil to within the order of one centimeter. Thus, it is possible to identify, locate and position the remote command unit inside the pipeline with good accuracy and precision.

When a remote command unit 12 is moving inside pipeline 16, it continuously transmits these location signals 24. A translator unit 18 can be temporarily deployed at a point where station passage of the pipeline tool 14 is monitored and recorded. The invention allows several tools 14 to be deployed inside a pipeline 16 in sequence for complex tasks and field operations, where the location, separation and final position of each of pipeline tools 14 is critical to the assignment.

The sequence of signals used by the components of the present invention, allows a portion of time when the sensor element 22 associated with remote command units 12' and 12" are not transmitting any signals. During this time, the sensor elements 22 may receive signals from the translator units 18' and 18", respectively.

The translator units measure environmental background noise levels when no "near field" electromagnetic signals are present. The translator unit 18' is synchronized to remote command unit 12' and translator unit 18" is synchronized to remote command unit 12", and, thus, commands may be transmitted during this time interval. When the remote command units 12' and 12" receive and detect valid signals from the translator units 18' and 18", the location signals may be partially or totally disabled and the "near field" electromagnetic link optimized for maximum data throughput.

Communication and Control Signals

The translator units 18 are normally located at a range distance "R", as shown in Figure 1, of up to 5 meters (16 feet) between the remote command units 12. The translator unit is capable of supporting convolutional encoded quadrature amplitude modulated (QAM) data transmission at either 11 or 22.5 hertz between the remote command units 12 and the translators units 18 when both pipeline tools 14' and 14" are stopped and not moving. The present invention is capable of supporting data rates approaching the theoretical limit established by bandwidth and environmental noise levels.

It is to be understood that the long sequence, modulated spread spectrum signals described earlier with reference to long range location signals, may be optionally or alternatively used for data transmission. Remote command units 12 and translator units 18 have the ability to disable the location signaling set once the pipeline tools 14' and 14" have been set in position and locked to seal off the pipeline section where repairs are to take place. The quadrature amplitude modulated signals have data transitions synchronized with sub-carrier zero crossings so that each sub-carrier has a whole number of complete sub-carrier cycles, thereby eliminating all discontinuities in the modulated sub-carrier signals. Two sub-carriers, termed an in phase "I" sub-carrier and a quadrature "Q" sub-carrier are summed together and transmitted as a "near field" electromagnetic field. Such a modified modulation method, by which the modulation of the in-phase "I" channel leads the quadrature "Q" channel by a quarter of a carrier cycle, minimizes side-band energy, and improves synchronization of the system in high ambient noise conditions.

The received signal is initially processed for gain stabilization and equalization to minimize inter-symbol interference caused by limited bandwidth of the reception circuits. Software algorithms loaded in microprocessors, described later, in the command and translator units are then used to synchronize and detect the data stream encoded in the "near field" electromagnetic signal. Each sub-carrier can be modulated with a set of signed magnitudes that encode the data. The totality of all possible combinations of the two sub-carriers comprise a symbol set which is selected in such a way as to maximize data transmission rates for given background noise conditions. Allowable points in quadrature signal space decrease with an increase in noise energy. The data that encode the QAM signals are related between sequential transmitted symbols through by convolutional sequential encoded data. Each transmitted symbol depends upon the previously transmitted symbols. A maximum likelihood soft decision decoding microprocessor algorithm is used to decode the complex received signal. The remote command units 12 transmit the "near field" electromagnetic signals 24 and receive "near field" electromagnetic signals 28 at maximum possible data rates approaching the theoretical limits for band limited communication systems at the distance "R", shown in Figure 1 of 5 meters (16 feet) without the necessity of removing conductive material surrounding the pipeline 16 for proper operation of the location, communication, command and control functions of the system 10.

Control unit 20 is capable of transmitting and receiving packet UHF radio signals linked to the remote command units 12 through the translator units 18, as already indicated. The control unit may be located at a distance of up to 2000 meters (6562 feet) or more from translator units 18 depending upon local terrain. Control unit 20 and translator units 18 are designed for mutual two-way linked location, communication, command and control functions, with the translator units 18 performing the functions of a linking data repeater in which control unit 20 is linked to the translator units 18 via UHF packet radio, which, in turn, link to an associated remote command unit 12 inside the pipeline 16 using "near field" electromagnetic signals. The operation of one embodiment of the present invention will now be described in detail with reference once again to Figure 1.

UHF packet radio signals 38 are transmitted from control unit 20 to translator units 18' and 18" which receive the UHF packet radio signals, convert them into "near field" electromagnetic signals 28 and condition the converted signals for transmission through the wall of pipeline 16 and into the remote command units 12' and 12", respectively. The remote command units 12' and 12" are attached to the pipeline tools 14' and 14" located inside the pipeline 16. The remote command units 12' and 12" receive these "near field" electromagnetic signals from the translator units 18' and 18" and decode location, communications, command and control signals for use by the pipeline tools 14' and 14". Commands are verified and executed by the pipeline tools 14' and 14", and then reported. Remote command units 12' and 12" then report their status and data by transmitting a "near field" electromagnetic signals 24 through the pipeline 16 to translator unit 18" and 18" located outside the pipeline wall. Translator units 18' and 18" receive and convert "Near Field" electromagnetic signals 24 to UHF packet radio signals 38 and transmit them to control unit 20 which receives and processes the packet radio signals.

The penetrating characteristics of "near field" electromagnetic signals are significantly increased as the frequency is lowered. This characteristic is used to determine the thickness T of pipeline 16 in Figure 1. Since the location pinger signal set contains both 11 hertz and 22.5 hertz signals, the ratio of their magnitudes can be used to determine the pipeline wall thickness T since the pipeline conductivity and magnetic permeability are known physical constants and are well behaved in practical pipeline systems.

It is instructive to consider Figure 3 to better understand how the "near field" electromagnetic signal is generated and received. Sensor coils 22 and 26 are of the same unit design depicted in Figure 3. Each sensor coil includes core 50 in the form of a ferrite rod with a high magnetic permeability and a low conductivity compared to metallic iron, steel or other transformer cores. A single, tightly wound coil 52 with many turns of insulated copper wire, is wound on the ferrite core rod. This assembly is placed inside an aluminum tube 54 of known size and thickness. An aluminum end plate 54, of similar thickness, is placed on each of the opposite ends of the aluminum tube to completely close off the ferrite rod and coil. A heat shrink-wrap 56 is then applied over the aluminum tube and end plates to completely shield the core from all electrostatic fields and all high frequency magnetic fields.

The core rod will produce a "near field" electromagnetic field 58 that is directly proportional to the current flowing in the coil winding 52 up to the saturation flux density of core 50. This assembly is then placed inside a non-conducting high strength plastic housing 60 which protects the sensor coil and related electronics from high pressures of fluids and gases inside the pipeline or other containment vessels. This housing is attached to the bulkhead 62 of a pipeline tool 14 using a threaded section 64. The entire housing fits within a larger non-magnetic stainless steel housing 66 which is further depicted in Figure 4. Figure 4 illustrates the circular non-magnetic stainless steel housing 66 that is welded on the pipeline tool bulkhead 62. The housing has a series of elongated slots 70 cut into the housing. Alternating slots 72 are cut into the housing so as to greatly increase the path 74 that an induced secondary current must follow as a result of the strong magnetic field being produced by the sensor coil and ferrite rod system. This slotted housing protects the plastic pressure housing 60, depicted in Figure 3, but does so by reducing the induced secondary currents in the conducting stainless steel housing 66 in Figure 4. In this manner, large linear "near field" electromagnetic fields can be produced by sensor coils that are capable of penetrating the walls of ferromagnetic and conducting pipelines and other containment vessels while transmitting and receiving location, communications, command and control signals.

The sensor coils are also capable of detecting "near field" electromagnetic fields that are captured by ferrite core 50 in Figure 3. The captured magnetic flux induces small but useable signals in coil 52 of the sensor coil. When these signals are amplified and integrated, they are directly related to the currents used to generate the transmitting "near field" electromagnetic field.

Figure 5 illustrates an electronic block diagram of an electromagnetic modem 100 provided in each command unit 12 and translator unit 18 for generating, transmitting, receiving and processing "Near Field" electromagnetic signals. The modem is associated with a sensor coil 22 or 26, depending on whether the modem is used in a command unit or translator unit. However, as indicated in the description of ^cigure 3, the two coils are of identical construction.

The circuits used for transmission of "near field" electromagnetic fields will be described first. A microprocessor 102 is connected to the other systems of the pipeline tool and receives requests from these systems to transmit location, communications, command and control signals to the translator unit outside the containment vessel or pipeline. The microprocessor uses software algorithms and programs that generate a sequence of analog values for the ferrite magnetic flux that is to be set up. These are sent to the digital to analog converter 104 which creates an analog signal. The analog signal is attenuated by resistors R3 and R4 and applied to the positive input of an operational amplifier 106, labeled "PWR AMP" in Figure 5. In the transmission mode, a TX analog switch 108 is closed and an Rx analog switch 110 is open. The output of operational amplifier 106 is applied to the sensor coil and causes a current flow through the coil and into resistor R1. The voltage developed across the resistor R1 is applied to the negative input of operational amplifier 106 and is a form of negative feedback to help stabilize the current in the coil to a value directly related to the analog voltage produced by the microprocessor 102 through the analog to digital converter 104. In this manner, the microprocessor directly controls the magnetic flux produced by the sensor coil. This magnetic flux produced by the sensor coil is the same "near field" electromagnetic signals 22 and 28 in Figure 1.

The microprocessor can encode the location, communication, command and control signals to be transmitted through the pipeline wall using any required linear combination of signals with a frequency sufficiently low so as not to unduly attenuate the "near field" electromagnetic signal transmitted through the walls of the containment vessel or pipeline.

The signal structure for location as well as data communication has already been described in detail. The linear nature of the invention permits the simultaneous transmission of any modulated or unmodulated signal set, including but not limited to spread spectrum location signals, "pinger" location signals at one or more frequencies either sequentially or simultaneously, data signals utilizing quadrature amplitude modulation (QAM) with synchronous detection, frequency and phase modulated data signals using simple or complex frequency shift keying or phase shift keying, and the sequential or simultaneous transmission of signals used in measurements aimed at determining the thickness of containment vessels and pipelines.

The preferred embodiment of the invention uses sufficiently high-speed sample transmission from the microprocessor so as to make total harmonic distortion of carrier waves arbitrarily small. The circuits used for reception of "near field" electromagnetic fields will now be described. Microprocessor 102 in Figure 5 can also close RX switch 108 and open TX switch 106. In this mode, modem 100 can receive location, communications, command and control "near field" electromagnetic signals.

The "near field" electromagnetic signal the outside translator unit is concentrated by the ferrite core in the sensor coil and induces a small voltage across the coil. The signal is applied to the input of a low noise pre-amp 120 which acts as a virtual ground permitting any amount of signal current to flow into amplifier circuit 122. The pre-amp is an operational amplifier with a very large gain. The output of the amplifier is fed back to its input through feedback capacitor 124. Such a circuit has the character of an integrator with a gain determined by frequency and the value of the capacitor 124. The output voltage, therefore, is precisely related to the total magnetic flux captured by the ferrite rod in the sensor coil. The circuit would produce an output directly related to the "near field" electromagnetic signal in a manner independent of frequency. Thus, if two different frequencies were excited at the same magnetic flux density in a translator unit, they would be received at the output of the pre-amp at the same magnitude if the pipeline had no thickness. For pipelines with finite thickness and made from conducting ferromagnetic material such as steel, the higher frequency signal is attenuated a greater amount than the signal at the lower frequency. A comparison of the ratio will directly yield a measure of the pipeline thickness. Pre-amp 120 transmits the received signal to a passive notch filter 126 which is a "twin tee" notch filter tuned to either 50 or 60 hertz, depending upon the civil power system in the area where the pipeline is operated. This notch filter removes power supply "hum" and "pickup" from the incoming signal. The signal is next passed through an active band pass filter 128 that has a bandwidth critically controlled by the design of the amplifier, and tunable to one of two center frequencies; 11 hertz and 22.5 hertz. The filters are used as "anti-alias" filters to prevent high frequency noise from confusing analog to digital converter and attenuator 130.

Attenuator 130 can reduce the incoming signal level from maximum sensitivity in order to permit operation at range distance less than the maximum possible distance. Analog to digital converter and attenuator 130 is controlled by the microprocessor 102 to take channel output samples periodically to establish synchronization, data reception, and location, communication, command and control functions. Microprocessor 102 processes this sequence of samples to determine the data or location signals being sent. In this fashion, the microprocessor can recover the original signal transmitted by the outside translator unit and send it to various components in the pipeline tool.

Reference will now be made to Figure 2 which illustrates the three major components of the control system 10 or the present invention in more detail. An operator can operate any number of pipeline tools from a control unit 20, shown in the block labeled "handheld control unit" in Figure 2. Control unit 20 has buttons and displays to allow the operator to issue commands and to display data and information received from the pipeline tools. Handheld control unit 20 is equipped with an UHF radio modem (not shown) that can transmit and receive packet information via its UHF antenna 32. In this manner, the operator can communicate with a multiplicity of translator units 18 at line of sight distances up to 2000 meters (6562 feet) and beyond. These radio signals intercommunicate with a translator unit 18 shown in Figure 2 in a block entitled "external converter tracker".

The radio signals are received on the UHF antenna 32 where they are received by a radio modem 140 and sent to an electromagnetic EM modem 142 which is identical in construction to modem 100 described in Figure 5. EM modem 142 of translator unit 18 then relays this location, communications, command and control signal through the sensor coil 26. This transmitted signal is received by sensor coil 22 in a remote command unit 12 shown in the block diagram in Figure 2 entitled "isolation tool in pipe section". The signal is received and processed in EM modem 144 which is also identical in construction to previously described modem 100. Modem 144 it is linked to a main processor 146 in the pipeline tool system electronics and not to be confused with the EM modem microprocessor 102 shown in Figure 5.

The operation of the location, communications, command and control system is used for the operation and control of a pipeline packer or isolation tool of the kind described in our co-pending International Application PCT/CA97/00055. Generally, the location, communication, command and control system 10 of Figure 1 is used to send operating instructions to and receive data from the tool. The operating instructions relate to various amperages, force factors, and voltages at which it is desired that the tool operate. Once the tool has received an instruction via the control system 10, it will request confirmation of the command and will not carry out the execution of any action until confirmation has been received and a special authorization code is entered by the operator. This process of data transmission and confirmation, back and forth between the tool and the control unit 20, takes place for each command sent to the tool. In return, the tool sends data, via the system 10, relating to the remaining battery voltage, information as to which battery pack is selected and in use, the amount of amperage each motor is drawing, the amount of force being applied to the pipeline wall, and the upstream and downstream pipeline pressures. This type of data will normally be transmitted by the tool on a continuous basis.

Once the tool reaches pre-programmed force and amperage levels, it will autonomously shut down. During an operation, or at any time while the tool is holding pipeline pressure, should the force factor fall below the lower pre-programmed limits, motors , referenced below, will automatically restart and return the tool to the proper force factor, thereby ensuring that the pipeline tool is tightly seated against the pipeline wall. At the same time the tool will continuously transmit data relating to its current status and function. An "emergency halt" command can be issued through the system 10 at any time should the operator deem it necessary.

Returning to Figure 2, it can be seen that the block entitled "Isolation Tool in Pipe Section" contains two main batteries being "Battery A" 148 and "Battery B" 150. These two main battery banks power the tool under normal conditions. Main processor 146 can control motors 152 and 154, which are used to set and release the tool.

A second backup emergency processor 160 is provided for the event that the main processor 146 fails. This processor can access sensors such as a strain gauge 162, a upstream pressure sensor 164 and a downstream pressure sensor 166. It is separately powered by a "battery C" 168 and has its own emergency sensor coil 170 capable of receiving commands separate from the main system. An emergency EM modem 172, identical in construction to modem 100, is provided for receiving and executing emergency release commands by transmitting such command and control signals directly into the emergency processor 160.

DETAILED EXAMPLE

Isolation tools, herein referred to as "isotools", 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 10 of Figure 1, isotools can be instructed to perform tasks on command and feedback critical information from inside the pipeline. The system is remotely controlled using UHF packet radio and electromagnetic coupling as the communication method. This also means that the operator need not be close to the pipeline during critical setting and release operations.

The system 10 of Figure 1 has three main components as shown diagrammatically in Figure 2 and including an Isotool remote command unit 20, a Base station translator 18, and a hand held Control unit 20. Each isotool has duplicate "nearfield" electromagnetic location, communications, command and control units under the control of microprocessors and are known as the "main processor" 146 and "emergency processor" 160 systems in the tool.

The "emergency" system is a secondary system capable of unsetting the tool independently of the "main processor" 146 system. Removal of a failed isotool, when locked in position in the pipeline, would be a very expensive procedure and would require draining a section of the pipeline. During normal operation of the isotool, the "emergency" 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 caught and removed at the next available "pig trap". Hand-held control unit 20 uses an UHF packet radio link to communicate with the translator unit 18. In a typical set-up, there will be two isotools, two translators and one or two control units. It is possible to control up to eight tools with one control unit 20.

ELECTRONIC CONTROL MODULE UNIT FOR THE ISOTOOL For greater clarity in understanding and referring to Figure 2, it is useful to clarify that the isotool itself consists of two main parts connected by an articulated hitch (not shown). Remote command unit 20 illustrated in Figure 1 is mounted on the end of the battery compartment of the isotool. It receives its power from the battery pack to which it is mounted, and can intercommunicate with the electronics control module in the main part of the isotool that contains the main brake clamp and pipeline seal.

The electronics module houses nine printed circuit boards mounted inside an

6.75" diameter aluminum module located with the main part of the isotool. 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 Emergency Unset Motor Controls;

2. Bypass Motor Controls;

3. Main Microprocessor 146;

4. Main EM Modem transmitter circuit; 5. Main EM Modem receiver circuit;

6. Emergency Unset Microprocessor 160;

7. Emergency backup EM Modem transmitter circuit;

8. Emergency backup EM Modem receiver circuit;

9. Motor and Secondary Unset Battery Connector Interface.

These will be further expanded upon in the following discussion.

1. Main and Emergency Unset Motor Controls

This board provides the control electronics for motors 152 and 154 that operate in tandem in a normal functioning tool. The motors are powered from 24-volt DC batteries and are used to open (set) or close (unset) a clamp system that holds and seals the isotool in the pipeline while the repair work is being performed on the pipeline. 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 base-plate metalwork to afford cooling.

An added complication is that power is supplied to both motors from one of two main battery packs - "Battery A" 148 and "Battery B" 150. A separate Emergency unset "Battery C" 168 provides emergency power to unset the tool in the event that it should be necessary. Twelve FETs are used in two H-bridge totem pole configurations on the main and 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 either the main or the emergency unset control can operate these 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.

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 preprogrammed current level. The control circuitry removes 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. Part of the feedback loop is a series of strain gauges 162 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 pre-programmed strain value is maintained by activating the set motors when 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.

Motors 152 and 154 are also used for the standard unset operation. 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 microprocessor circuitry 146 is disabled when the emergency unset is activated.

Because there is only one motor operating during emergency operations, it takes a greater time to unset the tool. However, as the emergency microprocessor 160 is a "last chance" action to release the tool in order to avoid jamming the pipeline, this is not regarded as a serious limitation.

2. Bypass Motor Control Board

There are three bypass motors in the isotool of this example. These are small motors that operate 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 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 equalized there are pressure sensors 164 and 166 mounted in the tool on the upstream and downstream side respectively. Once the bypass valves are open, the sensor readings are sent back to the control unit 20 at frequent intervals so the operator can monitor progress.

The bypass motor control circuitry consists of an H-bridge for each motor (incorporating a total of 12 FETs). Each motor is individually controlled and its current is 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 microprocessor 146 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 motor may require. Because the motors are low current units, 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 microprocessor control unit 146 to indicate 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 equalized 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 pig trap further down the pipeline where the isotool can be removed from the pipeline.

3. Main Microprocessor Board The main microprocessor board 146 is not to be confused with the dedicated microprocessor 102 of Figure 5. The unit under discussion here is used to coordinate and control all required tasks inside the isotool. It performs the following functions:

1. Sends the commands to the set/unset motors and 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; and

5. Looks after all the location, communications, command and control exchanges with the EM modem microprocessor unit;

Also located on this printed circuit board are a 5 volt regulated power supply for all the main system logic circuitry, a real time clock so that commands or information can be time stamped, hardware interval sleep timers with programmable jumpers used to select the sleep intervals for circuitry that is not required, and Calibration and offset potentiometers for pressure sensors.

The microprocessor has two modes of operation: sleep mode and normal mode. Due to the length of time that the isotool may spend in the pipeline traveling between jobs, it is advantageous to be able to put the whole tool to sleep in order to save battery power. Sleep mode is entered either by a operator command from issued the hand-held control unit 20 or automatically after an extended period of receiving no messages. In sleep mode, a hardware timer is activated and then the power to all other circuitry and boards is shut down. The current drawn in this mode is in the order of 2 to 4 milliamps. Hardware jumpers determine the length of the sleep period that can last for up to 35 hours. At the end of the sleep period, power is reapplied to the microprocessors 146 and 160 in Figure 2. This then wakes up and queries the EM modem receiver unit that determines whether there is a message directed to it. After a period of time has elapsed, if no messages have been received, the unit hardware time is reactivated, and the unit returns to the sleep mode. Should a message be received, the microprocessor remains awake and sends an acknowledgment. The tool is then ready to accept location, communications, command and control signals and begin to work. It will remain awake for as long as it is receiving messages from control unit 20.

A watchdog timer is incorporated into microprocessor 146. If the software stops running, the watchdog will reset the microprocessor and the program restarts. Mechanical shock to the tool which causes a connector to momentarily interrupt its connection is one possible reason for the software to "hang-up" and "freeze". If a watchdog timer reset is detected by microprocessor 146, the operating program restarts itself and resumes normal operation of the isotool.

4. Main Electromagnetic Transmitter Board.

This card is responsible for producing the carrier, modulation and linear excitation for the sensor coil 22. Incoming and outgoing data are translated to the main microprocessor 146. Figure 5 illustrates the transmitter elements of the EM Modems of Figure 2.

5. Main Electromagnetic Receiver Board.

This board is responsible for receiving "near field" electromagnetic signals from the sensor coil 22, and processing software algorithms to recover encoded data for location, communication, command and control of the isotool. The receiver unit can process and receive signals that are either sequential or simultaneous in format. The receiving microprocessor recovers the transmitted data with a low error rate and forwards the received signals to the main microprocessor 146. The EM Modems in Figure 2 incorporate this Board.

6. Secondary Unset Microprocessor Board.

The secondary unset microprocessor board, termed the "emergency microprocessor" 160 in Figure 2, is identical to the "main microprocessor" 146, 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 microprocessor" 146. Once awake, the secondary unset microprocessor board is polled by the control unit periodically to determine the unit status.

Under normal operating conditions, the power to operate the secondary unset system is drawn from either of the main battery packs. However, should these fail, power will be supplied from the secondary unset "Battery C" 168. Any logic circuitry related to the secondary unset system is powered by the 5-volt power supply on this board. The only command that the secondary unset microprocessor board sends out is to the main and secondary unset motor control board to initiate a secondary unset. This command has priority over the main set/unset circuitry and disables power to these sub-systems. This is done for the reason, that the arrangement will override any hardware or software fault condition that is trying to activate an unauthorized set or unset operation. As mentioned earlier, this is used to release the isotool from the pipeline in the event of failure of the main electronics system.

7. Secondary Unset Electromagnetic Transmitter Board

This card is responsible for modulating and transmitting the modulated signal on sensor coil 170. Encoded "near field" electromagnetic signals from the transmitter unit encodes a different ID so that the source of transmitted signals inside the pipeline is unambiguous and clear. The EM Modem 172 incorporates this board.

8. Secondary Unset Electromagnetic Receiver Board.

This card is responsible for receiving EM modem signals that bear emergency location, communication, command and control signals for the isotool secondary unset microprocessor. The EM Modem 172 incorporates this board.

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 three by-pass valve motors, Main and Secondary unset motors, Strain Gauge and Pipeline Fluid Pressure Sensors Circuitry and

Secondary unset Battery Pack. Another connector board mounted to the main part of the tool mates up to this board. TRANSLATOR

The translator unit is identified as "external converter tracker" 18 in Figures 1 and 2. This unit has the ability to receive and display data traffic linked to the isotool in the pipeline. The unit is also used to detect and display location information required locating isotools and other generic "pingers" on pigs inside the pipeline. The data traffic can be linked to a portable computer system via a serial data port 180. Individual isotool ID numbers are displayed on a display unit 182.

The microprocessorthat controls the EM modem receives serial packet data from the UHF packet radio transceiver and re-formats the data for transmission into the isotool. The UHF packet radio is designed to utilize a single narrow-band FM channel in the region 450 to 470 MHZ of the UHF radio spectrum.

The translator unit can intercommunicate with both the main and secondary EM modems in the isotool via the sensor coils 22 and 170, respectively.

The translator unit can be carried or placed on the ground in the vicinity of the pipeline where the isotool is placed to isolate the pipeline. The translator keeps interrogating sleep mode isotool until a response is received. The translator unit is battery operated, and can be float charged from a 12-volt vehicle connector plugged into the cigarette lighter of the vehicle. 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 inside pipeline wall and this means that the tool could soon slip. The translator would then activate the warning systems. A message is also sent to the control unit.

HAND-HELD CONTROL UNIT

As already indicated, the control unit 20 allows the operator to send messages to the remote command units 12 inside the pipeline attached to the isotools by way of translator units 18. The control unit can control up to eight individual tools equipped with the remote command unit 12 in the pipeline or containment vessel. The control unit 20 is mounted in a case, and consists of the following components:

1. 450 to 470 MHZ UHF narrow band FM packet radio modem;

2. Two 4 line by 20 character LCD (liquid crystal display) which is back-lit and used for data presentation;

3. Four LED's to indicate communications status;

4. Microprocessor, real time clock and data logging module;

5. a Keypad;

6. A 12 volt DC, 2.5 amp-hr Nickel Metal Hydride battery pack with charger circuitry; and

7. Connectors for RS-232 and Power/Battery Charger.

There are two printed circuit cards in the hand-held control unit 20. A radio board, together with the radio power supplies, digital interface circuitry and electro-luminescent LCD back lighted power unit is mounted behind the LCD's. The rest of the circuitry is mounted on a printed circuit board with the battery pack laying behind the PCB in the lower part of the case. Flexible antenna 36 is mounted from the top edge of the control unit 20.

Transmission power of the radio is 2 watts and uses narrow band frequency modulation (NBFM). The default frequency is 464.6375 MHZ that is a dedicated data channel throughout Canada, as defined by Industry Canada. However, the radio frequency is programmable to any channel within the 450 to 470 MHZ range should interference be experienced on this channel. Each Province and Territory also has at least one other frequency that can be used specifically for critical industrial data communications projects. When the complete system is in operation, control unit 20 is in constant radio communications with the translator units 18. Commands are sent to the translator unit to be relayed to the isotool remote command unit inside the pipeline and status information from the remote command unit is sent back to the control unit via the translator unit outside the pipeline. Green LED's on the control unit indicate the quality of the communications links. A "steady - on" LED means that the communications link is good and that the messages are being received without errors. Should there be some uncorrected errors in the messages, the LED relevant to that link may go out briefly.

Total operating time with the battery pack can be approximately 14 hours between recharges. Battery voltage is continuously monitored and when the capacity is down to 10% of 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 the battery is achieved by connecting a cable to a recharge connector on the control unit. Suitable power sources are a cigarette lighter at 12-volts DC available with most vehicles in the vicinity of a job site. The battery charging circuit protects the unit against overcharging and overheating of the battery. Recharging is totally automatic and does not affect operation of the control unit. Once the battery is fully charged, the charger circuitry goes into a trickle charge mode thereby maintaining the battery charge at full scale. 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 20 to the isotool command unit 12, via the translator 18, require entry of a four digit supervisor authentication code before the command is sent and executed. Even switching off the control unit requires such a supervisor authorization code.

Access to programmed menus to change trip values or radio frequency used for the packet radio channel requires use of the supervisor code.

During the set and unset procedures, readings will be received from the isotool relating to the 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 authorization code and time stamp. The stored data can be downloaded to a laptop computer through the RS-232 port on the unit. If the data-logging module become full, it will begin to overwrite the existing data, starting with the oldest data first.

All the variables relating to the commands for the isotool command unit are stored in the control unit. Each time an isotool wakes up to begin a project, it is sent the stored values of all of the trip functions. These stored values are also sent if the isotool starts up after a watchdog software reset. The trip values relate to items such as: maximum set motor current (exceeding this value causes the logic circuit to cut the power to the motors); maximum unset motor current (after an unset is in progress. This is used to detect when the tool has fully unset and retracted the braking clamp at which point the motor stalls); and maximum and delta strain gauge readings for the set motors to maintain set. The delta value is the fall in strain gauge readings before the set motor is reapplied. COMMUNICATIONS OVERVIEW

The ability of an isotool to operate hinges on the ability of the remote command unit inside the pipeline to transmit and receive "near field" electromagnetic signals through steel pipelines up to approximately 0.5" thick pipeline walls. Signals are rapidly attenuated as frequencies increase, so that it is desirable to operate at the lowest possible carrier frequency.

The above described embodiments of the present invention are intended 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 invention. The only limitations to the scope of the present invention are set out in the following appended claims.

Claims

We Claim:

1. A communication system for use with a device located within a containment vessel, comprising: a control unit having means providing two-way packet radio frequency communication; a command unit for attachment to a device in a vessel and having means for providing bidirectional low frequency electromagnetic communication; and a translator unit for converting control unit radio frequency transmissions to corresponding low frequency electromagnetic signals and for transmitting said corresponding low frequency electromagnetic signals and for converting command unit low frequency electromagnetic signals to corresponding radio frequency signals and transmitting said corresponding radio frequency signals.

2. A communication system as defined in claim 1, said translator unit having: a packet radio transceiver for bidirectional communication with said control unit; an electromagnetic modem connected to said transceiver for receiving and transmitting signals thereto; and a sensor coil for generating electrical signals in response to detected "near field" electromagnetic signals and responsive to signals from said electromagnetic modem for transmitting "near field" electromagnetic signals.

3. A communication system as defined in claim 2, said electromagnetic modem including: a microprocessor; a transmit circuit including said sensor coil, a transmit switch controlled by said microprocessor, a digital to analog converter connected to an output of said microprocessor, an amplifier having one input for the output of said digital to analog converter, and a second input for receiving a voltage signal across a resistor connected to said sensor coil; and a receive circuit including said sensor coil, a receive switch controlled by said microprocessor, an amplifier for amplifying the output of said sensor coil, an analog to digital converter for digitizing said sensor coil output and applying a digitized coil signal input to said microprocessor.

4. A communication system as defined in claim 2, said translator sensor coil being further operable to transmit "near field" electromagnetic signals that can be coupled into a sensor coil of a second command unit.

5. A communication system as defined in claim 2, said sensor coil in said translator unit being highly directional in response to "pinger" signals contained in an electromagnetic signal transmitted by an associated command unit device and producing a sharp null when said sensor coil is aligned orthogonally with a "near field" electromagnetic field containing said electromagnetic signal, the central axis of said sensor coil in said null position pointing toward said associated device when said associated device is located on the other side of a wall of said vessel.

6. A communication system as defined in claim 2, each said sensor coil including: a core in the form of a ferrite rod having a high magnetic permeability and a low conductivity compared to metallic iron, steel or other transformer cores; a single, tightly wound coil having a plurality of turns of insulated wire wound on said ferrite core; a tubular housing containing said ferrite core with said coil thereon; an end plate of similar thickness to that of said housing secured to each end of said housing for encapsulating said ferrite rod and coil within said housing; and a heat shrink-wrap applied over the aluminum tube and end plates for insulating said coil from conductive currents.

7. A communication system as defined in claim 1 , each said command unit and said translator unit having: an electromagnetic modem and an associated sensor coil; each said sensor coil being oriented to receive a maximum coupled signal from "near field" electromagnetic field from the other of said sensor coils and to receive a minimum coupled signal from "near field" electromagnetic field associated with others of said devices, the relative orientation said sensor coils exhibiting a sharp null signal at the mid-point of the sensor coil associated with said device.

8. A communication system for use with a device located within a containment vessel, comprising: at least one control unit having means providing two-way packet radio frequency communication; a command unit for attachment to each device to be controlled within a vessel and having means for providing bidirectional low frequency electromagnetic communication; and a translator unit associated with each said command unit for converting control unit radio frequency transmissions to corresponding low frequency electromagnetic signals and for transmitting said corresponding low frequency electromagnetic signals and for converting command unit low frequency electromagnetic signals to corresponding radio frequency signals and transmitting said corresponding radio frequency signals; each said translator unit having: a packet radio transceiver for bidirectional communication with said control unit; each said command unit and said translator unit having: an electromagnetic modem and an associated sensor coil; each said sensor coil being oriented to receive a maximum coupled signal from "near field" electromagnetic field from the other of said sensor coils and to receive a minimum coupled signal from "near field" electromagnetic field associated with others of said devices, the relative orientation said sensor coils exhibiting a sharp null signal at the mid-point of the sensor coil associated with said device, each said electromagnetic modem including: a microprocessor; a transmit circuit including said sensor coil, a transmit switch controlled by said microprocessor, a digital to analog converter connected to an output of said microprocessor, an amplifier having one input for the output of said digital to analog converter, and a second input for receiving a voltage signal across a resistor connected to said sensor coil; and a receive circuit including said sensor coil, a receive switch controlled by said microprocessor, an amplifier for amplifying the output of said sensor coil, an analog to digital converter for digitizing said sensor coil output and applying a digitized coil signal input to said microprocessor.

9. A command unit for use with an isolation tool in a communication system for tools located within a containment vessel, said command unit comprising: a primary control circuit including: a main microprocessor for issuing commands for setting and unsetting motors and bypass valves associated with said device and monitoring the motor currents; receiving data from strain gauges and upstream and downstream fluid pressure sensors; monitoring power supply voltage, detecting problems with the running of the microprocessor software, processing location, communications, command and control exchanges with the EM modem microprocessor unit; a main electromagnetic modem associated with said main microprocessor for encoding and decoding electromagnetic signals, said modem including a main sensor coil for detecting and emitting electromagnetic signals; and main power supply associated with said main primary control circuit; an emergency circuit including: an emergency microprocessor; a emergency electromagnetic modem associated with said emergency microprocessor for encoding and decoding electromagnetic signals, said emergency modem including an emergency sensor coil for detecting and emitting electromagnetic signals; and; an emergency power supply associated with said emergency circuit.

10. A command unit as defined in claim 9, each said electromagnetic modem including: a microprocessor; a transmit circuit including said sensor coil, a transmit switch controlled by said microprocessor, a digital to analog converter connected to an output of said microprocessor, an amplifier having one input for the output of said digital to analog converter, and a second input for receiving a voltage signal across a resistor connected to said sensor coil; and a receive circuit including said sensor coil, a receive switch controlled by said microprocessor, an amplifier for amplifying the output of said sensor coil, an analog to digital converter for digitizing said sensor coil output and applying a digitized coil signal input to said microprocessor.

11. A command unit as defined in claim 9, each said sensor coil including: a core in the form of a ferrite rod having a high magnetic permeability and a low conductivity compared to metallic iron, steel or other transformer cores; a single, tightly wound coil having a plurality of turns of insulated wire wound on said ferrite core; a tubular housing containing said ferrite core with said coil thereon; an end plate of similar thickness to that of said housing secured to each end of said housing for encapsulating said ferrite rod and coil within said housing; and a heat shrink-wrap applied over the aluminum tube and end plates for shielding said core from electrostatic fields and high frequency magnetic fields.

12. A translator unit for use with an isolation tool in a communication system for tools located within a containment vessel, said command unit comprising: a packet radio transceiver for bidirectional communication with said control unit; an electromagnetic modem connected to said transceiver for receiving and transmitting signals thereto; and a sensor coil for generating electrical signals in response to detected "near field" electromagnetic signals and responsive to signals from said electromagnetic modem for transmitting "near field" electromagnetic signals.

13. A translator unit as defined in claim 12, said electromagnetic modem including: a microprocessor; a transmit circuit including said sensor coil, a transmit switch controlled by said microprocessor, a digital to analog converter connected to an output of said microprocessor, an amplifier having one input for the output of said digital to analog converter, and a second input for receiving a voltage signal across a resistor connected to said sensor coil; and a receive circuit including said sensor coil, a receive switch controlled by said microprocessor, an amplifier for amplifying the output of said sensor coil, an analog to digital converter for digitizing said sensor coil output and applying a digitized coil signal input to said microprocessor.

14. A communication system as defined in claim 12, said translator sensor coil being further operable to transmit "near field" electromagnetic signals that can be coupled into the sensor coil of a second device.

15. A communication system as defined in claim 1 , said control unit being a handheld unit for use by an operator for operating at least one of said devices, said control unit having: a display for displaying data and information respecting each said at least one device; and means for enabling the operator to issue predetermined commands.

16. A communication system as defined in claim 1, said control unit including a 450 to 470 MHZ UHF narrow band FM packet radio modem; a display for data presentation; means for indicating communications status information; a microprocessor, real time clock and a data logging module; a keypad; and a power supply.

17. A communication system as defined in claim 1 , said control unit further having an UHF radio modem for transmitting and receiving packet information via a UHF antenna to and from said translator unit, respectively.

18. A communication system as defined in claim 12, said sensor coil in said translator unit being highly directional in response to "pinger" signals contained in an electromagnetic signal transmitted by an associated device and producing a sharp null when said sensor coil is aligned orthogonally with a "near field" electromagnetic field containing said electromagnetic signal, the central axis of the sensor coil in said null position pointing directly toward said associated device when said associated device is located on the other side of a wall of said vessel.

19. A system according to claim 12, said translator unit being operable as a communications repeater whereby packet radio signals are received and translated and re-transmitted on "near field" electromagnetic field signals to a remote unit located inside a containment vessel and whereby "near field" electromagnetic field signals received from said remote unit inside the containment vessel are received and translated and retransmitted using packet radio signals to a control unit for use by the human operator distant from both the remote unit inside the containment vessel and the translator unit outside the containment vessel.

20. A system according to claim 12, said translator being operable as a communications multiplex repeater in which a linear combination of "near field" electromagnetic field signals are received from a remote unit located within a containment vessel and decoded and are then reformatted and re-transmitted on the packet radio unit to a distant control unit for use by a human operator and wherein received packet radio signals from the distant control unit with the human operator are received, decoded, and are then re-formatted and re-transmitted as "near field" electromagnetic field signals to the remote unit inside the containment vessel.

21. A translator unit as defined in claim 15, said translator repeater functions being implemented microprocessor software.

22. A communication system according to claim 1 , said command unit being operable to transmit sequential or simultaneous linear combinations of location "near field" electromagnetic field signals with precisely controlled linear magnetic field levels for use by a receiver as a measure of containment vessel wall thickness by considering the difference in received field strength levels at the sensor coil receivers.

23. A system as defined in claim 1, said command unit being operable to transmit sequential or simultaneous location "near field" electromagnetic field signals containing contain a sharp null characteristic which yields geometric information related to the precise alignment and location of the remote unit inside the containment vessel.

24. A system as defined in claim 29, wherein said command unit being operable to select a spread spectrum carrier code as a fixed length code drawn as a subset from a long sequence linear pseudo-random number (PRN) generator in such manner that cross correlation between selected codes is small over all code intervals with all other codes in the selected set used with other remote units in the containment vessel, and being implemented in microprocessor software for the purpose of separating several such simultaneous signals from different units inside the containment vessel.

25. A system as defined in claim 1 wherein said translator unit being connected to control unit via and an interconnected data link cable.

26. A system as defined in claim 1 , said command unit being operable to transmit location signals that uniquely identify the remote transmitter unit "pinger" from a field of up to eight other units in close proximity with each other within the containment vessel or pipeline while simultaneously operating the location signals.

27. A system as defined in claim 1 , said command unit and said translator being capable of operating with modified synchronous quadrature amplitude modulated (QAM) narrow band signal structure capable of transmitting data using convolutional sequential encoding that encode several bits of data within each signaling symbol and which recovers synchronization and data thus transmitted signals using "near field" electromagnetic field signals.

28. A system as defined in claim 1 , said command unit and said translator unit being operable with a linear combination of two or more multiplex quadrature amplitude modulated (QAM) "near field" electromagnetic field signals as implemented using microprocessor software otherwise associated with electronic hardware.

29. A system as defined in claim 1 , wherein "near field" electromagnetic field signals are utilized in a narrow band frequency modulated format for use with remote units inside the containment vessel or pipeline and a translator unit in motion.

30. A system as defined in claim 1, each said command and translator having microprocessor software for transmitting and receiving said the "near field" electromagnetic field signals and which can operate with large variations of signal amplitude related to the relative motion of the translator unit with respect to the remote unit within the containment vessel or pipeline.

31. A system as defined in claim 1, wherein said "near field" electromagnetic field signals being utilized from a remote device in motion in which a previously positioned translator can be used to precisely determine "station passage" of a remote device.

32. A system as defined in claim 30 wherein a remote unit inside the containment vessel and translator unit outside the device being operable to use said "near field" electromagnetic field signals to produce a spectrum measurement of occupied noise bandwidth at the location of the remote and translator units, so as to present this information to the distant operator.

33. A system as defined in claim 1 , wherein transmitter and receiver functions are cross-connected to perform "built in test and evaluation" (BITE) functions and ensure the full functionality of the location, communication, command and control system by utilizing microprocessor software in the remote unit, the translator unit, and the distant control unit to replace electronic hardware normally associated with such test and monitoring instruments.

34. A sensor coil for use with an electromagnetic modem in an isolation tool in a communication system for tools located within a containment vessel, said coil comprising: a core in the form of a ferrite rod having a high magnetic permeability and a low conductivity compared to metallic iron, steel or other transformer cores; a single, tightly wound coil having a plurality of turns of insulated wire wound on said ferrite core; a tubular housing containing said ferrite core with said coil thereon; an end plate of similar thickness to that of said housing secured to each end of said housing for encapsulating said ferrite rod and coil within said housing; and a heat shrink-wrap applied over the aluminum tube and end plates for insulating said coil from conductive currents.

35. A method of non-obtrusively locating and communicating with a device located within a containment vessel from outside said vessel, said method comprising the steps of: continuously transmitting "near field" electromagnetic signals from said device within said vessel; monitoring "near field" electromagnetic fields for signals modulated therein from a predetermined location outside and proximate said vessel; recovering data encoded into said signals.

36. A method as defined in claim 35, said step of transmitting including generating "near field" electromagnetic field signals including generating a linear combination of a plurality of independent signals, each of said plurality of independent signals representing predetermined data and respecting said device, and transmitting said independent signals as a single "near field" electromagnetic field signal.

37. A method as defined in claim 35, wherein said step of receiving said "near field" electromagnetic field signals including recovering a linear combination of several independent signals from their original form after transmission as a single "near field" electromagnetic field signal.

38. A method as defined in claim 35, wherein said step of generating "near field" electromagnetic field signals including generating said signals using microprocessor software including carrier frequency, modulation, clock synchronization, automatic gain control, equalization, detection, soft decision decoding of received data, and other required functions normally associated with electronic hardware.

39. A method as defined in claim 35, said step of receiving "near field" electromagnetic field signals including using microprocessor software for separating linear combinations of signals including carrier frequency channel filtering and separation, multiplexing and de-multiplexing functions, and other required functions normally associated with electronic multiplex and de-multiplex hardware.

40. A method of non-obtrusively locating and communicating with a device located within a containment vessel from outside said vessel, comprising: generating a low frequency, direct sequence spread spectrum signal with a sequence length of up to 127 cycles of carrier wave at a frequency between 1 and 3.43 hertz, using a total of five frames, consisting of an "OFF" period, an "ON" period, and three following periods; transmitting said sequence either directly or inverted so as to encode one of eight possible unique data patterns; a total of 635 cycles of said carrier wave defining a basic signal structure, which repeats endlessly, allowing a translator unit to receive and detect the "near field" electromagnetic location signals; including phase modulating said carrier wave using a binary signal structure with in-phase and opposite out-of-phase carrier signals which are modulated by a subset sequence of pseudo-random number (PRN) codes drawn from a minimum sequence length of at least 1027 bits; a portion of said sequence length, of up to 127 bits, being used for this code transmission, depending upon a unique identification of a remote unit, such that a particular remote unit encodes a predetermined portion of said code sequence so that the transmitted signal from said particular unit has no correlation with a signal transmitted from another of said remote units, which may be in close physical proximity with said particular unit; encoding a unique identification code into each of two "pinger" signals, including a first pinger signal at 11 hertz and a second pinger signal at 22.5 hertz, to permit a translator to determine the identity of the unit inside the containment vessel which is transmitting the location signals; superimposing each of said pinger signals on said low frequency spread spectrum signal; transmitting said first and second pinger signals in sequence, first at 11 hertz and then at 22.5 hertz, each with an interval of approximately 450 milliseconds (5 cycles at 11 hertz, and 10 cycles at 22.5 hertz); phase modulating the mid-cycle of a tone burst signal as one of plus or minus four phase angles between + or - 180 electrical degrees so as to ensure that the tone burst has constant power that can be received by any industry standard pig-tracking receiver.

41. A method as defined in claim 40, wherein: said second tone burst at 22.5 hertz immediately following said tone burst 11 hertz; said signal also uniquely encoding the identification number of a command unit permitting unique identification of one out of eight possible remote units in close proximity inside the pipeline to be located; further including: measuring the relative magnitude of the signal level for each said tone burst; and using the measured relative magnitude for calculating the thickness of the conducting ferromagnetic containment vessel and for establishing a "near field" electromagnetic data link for communications, command and control between the remote unit and the translator unit which operates at maximum speed and low error rates.

42. A method as defined in claim 40, further including the steps of: disabling transmission of the location signaling set once the pipeline tools have been set in position and locked to seal off a pipeline section where repairs are to be performed; synchronizing said quadrature amplitude modulated signals with sub-carrier zero crossings so that each sub-carrier has a whole number of complete sub-carrier cycles, thereby eliminating all discontinuities in the modulated sub-carrier signals, said two sub-carriers, termed in phase "I" sub-carrier and the quadrature "Q" sub- carrier being summed together and transmitted as a "near field" electromagnetic field so as to provide a modified modulation method by which the modulation of the in-phase "I" channel leads the quadrature "Q" channel by a quarter of a carrier cycle which minimizes side-band energy and improves synchronization of the system in high ambient noise conditions; each sub-carrier being modulated with a set of signed magnitudes that encode the data, the totality of all possible combinations of the two sub-carriers comprise a symbol set which is selected in such a way as to maximize data transmission rates for given background noise conditions, allowable points in quadrature signal space decreasing with an increase in noise energy; data that encode the QAM signals being related between sequential transmitted symbols through by means of convolutional sequential encoded data. each transmitted symbol depending upon a previously transmitted symbols, using a maximum likelihood soft decision decoding microprocessor algorithm for decoding the complex received signal.

43. A vessel wall thickness indicator incorporated in the translator unit whereby "near field" electromagnetic field signals incorporated are implemented in microprocessor software to solve and display the containment vessel wall thickness as a measure of the received relative strength of two "near field" electromagnetic field signals at two or more frequencies.