CA2673163A1

CA2673163A1 - Method and apparatus for monitoring the performance of a compressor

Info

Publication number: CA2673163A1
Application number: CA002673163A
Authority: CA
Inventors: Jackey Lee
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-07-23
Filing date: 2009-07-21
Publication date: 2010-01-23
Also published as: US20100021314A1

Abstract

A method of monitoring the operation of a compressor includes sensing a parameter on a housing of the compressor from a device placed on the housing, generating a representative sensor signal in response to the sensed parameter, transmitting from the device a data signal related to the representative sensor signal, and receiving the data signal at a location remote from the housing. Other methods and an apparatus for monitoring the compressor are further disclosed.

Description

METHOD AND APPARATUS FOR MONITORING
THE PERFORMANCE OF A COMPRESSOR
BACKGROUND OF THE INVENTION
1. Field of the Invention This disclosure relates generally to devices used to monitor apparatus, and more particularly to systems and related methods for monitoring the operation of compressors used in pipeline operations, oil refineries, chemical plants, petrochemical plants and in other industries.

2. Discussion of Related Art In the gas transmission industry, it has become ziecessary to operate large reciprocating type compressors that drive the movement of gas within a pipeline continuously without interruption, with the goal of achieving one hundred percent efficiency. Engine driven compressors may operate at high speeds (e.g., 500-1000 rpm), and are therefore subject to failing due to normal wear and tear. In addition, since pipeline compressors often operate unattended for protracted periods of time in remote locations, it is imperative that compressors be monitored to ensure they are operating properly.
Pipeline compressors often operate unattended for protracted periods in remote locations and may require a host of instrumentation to ensure failsafe operation. Periodically, the efficiency of the compressors may be measured to determine the operation of the compressor, as well as to measure performance characteristics of the compressor.
To measure efficiency of the compressor, it may be necessary to determine the work performed by the compressor. Prior techniques have involved the calculation of indicated horsepower through the measurement of pressure in the cylinder head or at the discharge and suction sides of the compressor. Problems may exist with such methods, however, in that pressure sensors may be expensive, inherently produce signal errors, and have limited durability, thereby resulting in lost time and efficiency during replacement of failed pressure sensors. Accurate measurement of compressor cylinder pressure may be hampered by the acoustic distortion introduced by the measurement channel between the cylinder and the installed pressure sensor. This distortion is particularly severe on high-speed compressors.
Moreover, measurement of cylinder pressure and the resulting calculated work may not include the frictional costs of the piston riding on the cylinder walls. For large compressors in the range of 2000 HP to 10,000 HP, or above, these losses can be significant.
One approach to measuring work performed by a compressor is disclosed in U.S.
Patent No. 7,186,094, which is incorporated herein by reference for all purposes. U.S. Patent No. 7,186,094 discloses an apparatus and method for monitoring key parameters of a reciprocating member of a reciprocating piston compressor. Specifically, an apparatus for directly measuring rod strain on a compressor is disclosed in this patent. The data acquired may then be used to calculate power and work performed by the compressor. U.
S. Patent No.
7,186,094 also discloses that other parameters of the reciprocating members, such as the temperature of the cross-head bushing, may be measured.
SUMMARY OF THE INVENTION
One aspect of the disclosure is directed to a method of monitoring the operation of a compressor. In one embodiment, the compressor has a housing and a reciprocating member disposed within the housing. In a certain embodiment, the method comprises:
sensing a parameter on the housing from a device placed on the housing; generating a representative sensor signal in response to the sensed parameter; transmitting from the device a data signal related to the representative sensor signal; and receiving the data signal at a location remote from the housing.
Embodiments of the method may include, when sensing a parameter, monitoring a load on the housing. Transmitting a signal may comprise manipulating the representative sensor signal. Generating a representative signal may comprise generating a voltage signal, and transmitting from the device a data signal may comprise manipulating the voltage signal to a frequency signal. Sensing a parameter may comprise mounting a plurality of strain gauges on a load cell mounted on the housing. The method may further coniprise calculating a load on the housing and/or calculating the power used by the compressor. In one embodiment, the compressor may have a pressure inlet and a pressure outlet, and the method further includes sensing the pressure at the pressure inlet and outlet.
Another aspect of the disclosure is directed to a method of monitoring a machine. In one embodiment, the machine has a housing and a reciprocating member disposed within the housing. In a certain embodiment, the method comprises: sensing at least one parameter on the housing of the machine from a device placed on the housing; generating a representative sensor signal in response to the at least one sensed parameter; transmitting from the device on the housing a data signal related to the representative senor signal; and receiving the data signal at a location remote from the housing.
Embodiments of the method may include, when sensing at least one parameter, monitoring a load on the housing. Transmitting a signal may comprise manipulating the representative sensor signal. Sensing at least one parameter may comprise mounting a plurality of strain gauges on a load cell mounted on the housing. The method may further comprise calculating a load on the housing and/or calculating the power used by the compressor. In one embodiment, the compressor may have a pressure inlet and a pressure outlet, and the method further includes sensing the pressure at the pressure inlet and outlet.
Receiving the data signal may further comprise manipulating the data signal.
Transmitting may be performed by a transmitter. Sensing at least one parameter may be performed by at least one sensor.
Yet another aspect of the disclosure may be directed to a compressor comprising a housing, a reciprocating member disposed in the housing, a motor coupled to the reciprocating member, and an apparatus. In one embodiment, the apparatus includes a mobile assembly attachable to the housing. The mobile assembly has a sensor, a transmitter and a power source. The sensor is operable to measure a parameter of the housing and generate a representative sensor signal. The representative sensor signal is input to the transmitter, with the transmitter being operable to transmit a data signal related to the representative sensor signal. The power source is operable to power the transmitter and sensor. The apparatus further includes a stationary assembly having a receiver operable to receive the data signal from the transmitter.

DESCRIPTION OF THE DRAWINGS
For a better understanding of the present disclosure, reference is made to the drawing figures which are incorporated herein by reference and in which:
FIG. 1 is a schematic view of a compressor and a monitoring system of the disclosure;
and FIG. 2 is a partial view of a compressor and the monitoring system shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
This disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or ofbeing carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including,"
"coniprising," or "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
Directly measured parameters of components of a compressor are not readily available because of the difficulties in directly accessing internal components of the compressor and transmitting the key sensor data from the internal reciprocating member. The rapid movement and resulting forces on a monitoring sensor and associated devices make direct monitoring very difficult and expensive when using a sensor mounted on any of the internal components of the compressor. For example, directly measured brake horsepower may not be readily available on compressors, such as those used in the gas pipeline industry.
Typically compressors are controlled based on indirect measurements, such as torque inferred from fuel flow, suction pressure, discharge pressure, swept volume and clearance. This may lead to inaccuracies in the measurement of the load on the engine, limits the ability to take full advantage of the flexibility available and can result in overloading the compressor and parts, such as the frame, crankshaft, rods and bearings. Prior methods and apparatus, such as the approach disclosed in U.S. Patent No. 7,186,094, teach a system for directly measuring parameters of a reciprocating motor or compressor port. More specifically, as disclosed in the 7,186,094 patent, an apparatus for directly measuring rod strain on a compressor is provided The data acquired may then be used to calculate power and work performed by the compressor. Similarly, other parameters of the reciprocating members, such as the temperature of the cross-head bushing may be measured. The resulting information can be used to control and limit potential operating conditions leading to part overloading, reducing the likelihood of potentially catastrophic failures.
However, although the approach disclosed in U.S. Patent No. 7,186,094 provides an improvement over prior art methods and apparatus, applying sensors to the reciprocating member still provides design challenges. Specifically, since the reciprocating member (i.e., the piston) is an internal component that operates at a rapid rate, a tremendous amount of wear and tear associated with normal operation of the compressor may compromise the reliability of such an approach. It is also much more difficult, more expensive and less practical to install sensors on internal compressor parts rather than on external areas of the compressor. The methods and apparatus of the instant disclosure improve on monitoring the performance and safety of the compressor. Specifically, the methods and apparatus provide a means for measuring parameters of the reciprocating member without having to attach a device to the reciprocating member. Instead, a device may be attached to a housing (sometimes referred to as an "external casing") of the reciprocating member.
In one embodiment, the device may be one or more strain sensors. The strain sensors may be configured to measure parameters of the compressor and generate signals that are sent to a computer or data analyzer to analyze the information to optimize the performance and safety of the compressor.
Using the presented methods and apparatus make it possible to operate the compressor at maximized efficiency, and in combination with other measurements, such as compressor temperature or enthalpy rise, fuel flow, crank shaft angle and other parameters, to locate capacity and performance problems more accurately.
In one embodiment, the strain sensors may be comprised of full bridge strain gauges that are mounted externally on the housing that surrounds the piston assembly.
The strain sensors may be configured to measure compressive, tensile and bending strain on the external wall of the housing. In a certain embodiment, data obtained by the bending strain gauge may be required to analyze data obtained by the tensile and conipression strain gauges in order to calculate the work performed by the compressor. The strain sensors may embody load cells that are mounted on a device that is located on an external surface of the housing. These sensors may be configured to isolate strain due to bending forces thereby allowing accurate calculation of strain due solely to axial loading. Each load cell may generate a representative strain gauge signal that is transmitted to a computer via a transmitter/receiver system. The strain sensors, also known as load cells, are temperature compensated in order to offset fals signals generated from thermal drift.
With reference to FIG. 1, a reciprocating piston compressor is generally designated at 10. As shown, a motor 12 is configured to supply fuel from a line 14 that is connected to the same source as the gas to be compressed by the compressor 10, although fuel could alternately be provided by other means. The compressor 10 is constructed in the typical manner to include a crankshaft 16 rotated by the motor 12. This crankshaft 14 may be connected to a slider 18, which is in turn may be connected to a connecting rod 20 and a piston rod 22. As shown, the piston rod 22 is configured to drive a piston 24.
The rotation of the crankshaft 16 causes the piston 24 to reciprocate within a cylinder 26. A
typical compressor 10 may employ the shown slider 18 and connecting rod 20, but this arrangement may be modified as is known in the art. As shown schematically in FIG. 1, a housing or external casing 28 is provided to house and protect the components of the compressor 10.
These components are suitably coupled to the housing 28 as is known in the art.

The cylinder 26 may be provided with an inlet line 30, which is connected to a source of gas, such as the gas line 14. An inlet valve 32 may be provided to control the flow of gas from the inlet line 30 into the cylinder 26. The cylinder 26 may also be provided with an outlet line 34. An outlet valve 36 may be provided to control the flow of gas from the cylinder 26 to the outlet line 34. As is conventional in the art, operation of the valves 32, 36 may be controlled by pressure differentials so that gas is drawn from the inlet line 30 through the inlet valve 32 into the cylinder 26. Once gas enters the cylinder 26, the gas is compressed by the piston 24, with the compressed gas flowing out of the cylinder through the outlet valve 36 to the outlet line 34.
As discussed above, prior art devices, such as the apparatus disclosed in U.S.
Patent No. 7,186,094, may be used in conjunction with the compressor to measure performance parameters of the compressor. The apparatus may include a sensor assembly, such as a rod load monitor or temperature sensor, an encoder, a processor, a transmitter and a power source. The apparatus may be designed to measure one or more parameters of the reciprocating parts of the compressor, such as the crankshaft cross-head or bushing, the connecting rods, slider or piston rods, and transmit data based on the sensed parameters to a receiver.
Contrary to the teachings of U.S. Patent No. 7,186,094, an apparatus of the present disclosure, which is generally designated at 40 in FIG. 1, measures a parameter associated with a non-moving member, such as the housing 28 of the compressor 10. Various parameters may be measured, such as strain or load, axial and transverse loading, temperature, enthalpy, or other parameters considered relevant to monitoring the performance and efficiency of the compressor 10.
In one embodiment, the apparatus includes a mobile assembly generally indicated at 42 and a stationary assembly generally indicated at 44. The mobile assembly 42 includes a sensor 46 that may embody a strain monitor, preferably mounted to the housing 28 of the compressor 10, for measuring the load or strain on the housing when the compressor is in use.
It should be understood that the strain monitor may be mounted to other non-moving parts of the compressor, such as the outer wall of the cylinder 26. The sensor 46 generates a representative sensor signa148. When attached to the housing 28 of the compressor 10, the sensor 46 may generate a strain signal representative of the strain on the housing 28. In other embodiments, a temperature sensor may be employed to measure the temperature of the housing 28. Temperature variations of the housing 28 may indicate certain operating conditions of the compressor 10.

With reference to FIG. 2, in a certain embodiment, the sensor 46 may include multiple strain gauges, each indicated at 50, mounted on the outer surface of the housing 28. The strain gauges 50 may be mounted on the housing 28 to sense loads on or movement of the housing. In one embodiment, two pairs of strain gauges 50 may be employed, with each pair consisting of two strain gauges to measure strain in two separate directions on the housing.
As discussed above, the sensor 46 (e.g., strain gauges 50) generates the representative sensor signal 48, which is transmitted to a computer or data analyzer 52. In one embodiment, the sensor 46 may be wired to the computer 52 (FIG. 2) via wire lines.
In certain embodiments, other sensor assemblies may be used with the present apparatus to monitor other parameters of the compressor. For example, as discussed above, a temperature sensor (not shown) may be mounted to the housing to measure the temperature of the compressor housing. For example, an unexpected temperature rise may indicate a potential catastrophic failure of the compressor. Monitoring such a rise in temperature would allow the user to shut down the compressor for repair prior to such a failure.
In one embodiment, the temperature sensor may be connected to the power source, for powering the sensor, and produces a temperature sensor signal which is transmitted to the computer and encoder, as necessary, so that the signal may be transmitted via a transmitter.
The representative sensor signal 48, such as strain gauge signal or temperature signal, may be processed by the computer 52, which may include amplifiers, filters, data storage units, a CPU, gauge bridges, AC/DC and other converters, clocks, calculators, software and other devices as known in the art. For example, the computer 52 may include an encoder 54 to convert analog signals to digital signals as necessary. Preferably the computer 52 may include a low noise amplifier to amplify to a more usable level the output of the sensor signal 48. Similarly, the computer 52 may employ an electronic integrator as a negative feedback element in the amplifier to eliminate or reduce any static levels in the representative signals.
The representative signals typically are output from the sensors as a voltage.
As discussed below, the computer 52 may operate to generate a signal, such as a radio frequency signal, for transmission to a stationary assembly. The computer 52 may include an electronic device, such as a VCO, which outputs a continuous train of fixed width pulses whose frequency is proportional to the rod strain, as measured in voltage by the rod load monitor. Further circuitry may be used, such as for generating a static offset voltage to the VCO so as to establish a stable signal.

The apparatus 40 may also include a transmitter 56, which is coupled to the computer 52. The transmitter 56 transmits a signa158 to a receiver 60 of the stationary assembly 44.
The signa158 may be an analog, digital, optical, or an RF-based signal.
Power for the operation of the various components of the mobile assembly 42 of the apparatus 40 is provided with a power source 64. In one embodiment, the power necessary to operate various electrical components of the apparatus 40 may be supplied through the operation of the compressor itself. In one particular embodiment, the power source 64 may be a battery or other source capable of being mounted to the housing 28 of the compressor 10.
However, a power generator, such as an inductive coil assembly, may be preferred since the power generator would eliminate the need for frequent replacement.
In addition to the receiver 60 and the antenna 62, the stationary assembly 44 may include another computer or data analyzer 66. The antenna 62 may be configured to receive the signa158 from the transmitter 56 of the mobile assembly 42. The signal 58 may then be manipulated as necessary by the computer 66, which can include decoders, clocks, pulse generators, stabilizers, a CPU, software, programs and other devices. The circuitry may be powered by the power source 64 of the mobile assembly 42, such as a battery, by direct wiring to an electrical supply or other source, such as a solar power generator.
The transmitter 56 of the mobile assembly 42 and the receiver 60 of the stationary assembly 44 eliminates the need for a wire connection between the two assemblies for transmission of the signals.
As shown, FIG. 2 illustrates the slider 18, connected to the crankshaft at cross-head bushing or connector (not shown). The slide 18 moves linearly along a channel 70. A back cover 72 of the housing 28 is shown and typically a similar front cover (not shown) encloses the slider 18 and piston rod 22.
The apparatus 40 of the disclosure used in conjunction with the compressor 10 may also include pressure sensors, such as a suction pressure sensor 74 fixed in the inlet line 30 so as to measure the suction pressure of gas entering the compressor 10.
Appropriate pressure sensors are well known and are readily available. Such a sensor 74 may generate a suction pressure signal 76 representative of the suction pressure of the gas entering the compressor 10. The apparatus 40 may further comprise a discharge pressure sensor 78 fixed in the outlet line 34 so as to measure the pressure in this line, which is the discharge pressure of gas leaving the compressor 10. The discharge pressure sensor 78 generates a discharge pressure signal 80 representative of the discharge pressure.

The apparatus 40 is designed to reduce dependence on pressure sensors provided on the inlet and outlet lines 30, 34 of the compressor 10. However, the apparatus 40 maybe used in conjunction with such sensors. The pressure and strain data may be used in conjunction or as comparative data. For example, the function of the remaining sensors, such as a crank angle indicator, may be to provide the remaining data necessary to determine the work performed by the compressor.
Other sensors, such as a fuel consumption flow rate sensor may be used as well.
The apparatus may also include a rod location sensor 82 as is known in the art. The rod location sensor 82 serves a similar function as the crank angle indicator and will not be described in detail. The rod location sensor 82 provides a generated rod location signal 84 representative of the location of the rod in its travel along its function path such that the user has an indication of the location of the rod.
The representative signals from the stationary assembly 44, pressure sensors 74, 78, crank angle encoder and/or rod member location sensor 82 are sent by respective lines to a sensor controller 86. The stationary assembly 44 is connected to the controller 86 by line 88.
The pressure sensors 74, 78 are connected to the controller 86 by line 90. The rod member location sensor 82 is connected to the controller 86 by line 92. The sensor controller 86 is designed to receive the representative signals from the various indicators.
The controller 86 may include amplifiers, band pass filters, data storage units, a CPU, gauge bridges, A/D
converters and other devices as are known in the art. For example, the processor may convert analog signals to digital signals as necessary. The controller 86 may include a calculator, timing and other circuitry, converter soflware, storage capacity and cumulative mathematical calculations.
The sensor controller 86 may include many members and be located on or off-site or partially off-site. That is, the controller 86 is not limited to a single physical location. The controller 86 may compute or monitor certain parameters on-site while transmitting these or other parameters to an off-site control room. On-site monitoring and control may, for example, include emergency shut-down control in the case of an actual or impending failure.
The controller 86 may be used to control the compressor operation. Typically, at least some of the controller function is remote to the compressor site.
The sensor controller 86 may function as the central processing unit carrying out the logic functions of the apparatus 40. The controller 86 may comprise a single computer or a multiplicity of computers or other calculator devices. The controller 86 may be located on site or remote from the compressor 10. It is anticipated that the controller 86 may most likely be remote from the compressor 10 and will receive data from a plurality of compressors spread over a wide geographic area. The controller 86 may contain a microprocessor, digital input and output subsystems, memory capacity in which is stored various mathematical and analytical programs and software and constant data regarding the compressor being analyzed.
One of the primary functions of the controller 86 is to compute, using the representative data signals, the work performed by the compressor 10 during a predetermined time interval. The controller 86 may include the necessary formulas for repetitive calculations of performance parameters. Preferably the controller 86, in conjunction with the rod load monitor, other sensors and transmitter/receiver pair, permits continuous real-time monitoring of the compressor. Real-time and continuous work calculations can then be performed and monitored.
Other calculations may be made as well, such as the computation of work and power based on pressure measurements. The measurements and results of the calculation can then be used for optimization of the efficiency and use of the compressor 10. That is, the resulting data from the computer 86 may be used to regulate the operation of the compressor 10 to maximize the efficiency of the unit. Where several compressor units are being monitored simultaneously, the compressors can each be regulated to maximize the efficiency of the pipeline operation as a whole. The compressor utilization, health and integrity is then used by the compressor controllers (either human or software based) to affect operation in an optimized fashion. The optimization and regulation of the compressor units can be done manually, by remote transmission or direct manipulation, or automatically through the use of computer optimization software.
Optimization can also include automatic shut-downs where the measured parameters indicate a failure or danger of catastrophic failure. For example, the temperature sensor may be an indicator of impending failure. A sharp temperature rise may indicate a need to turn off the compressor.
In one embodiment, the controller may include many members and be located on or off-site or partially off-site with respect to the compressor. Specifically, the controller may not be limited to a single physical location. The controller may compute or monitor certain parameters on-site while transmitting these or other parameters to an off-site control room.
On-site monitoring and control may, for example, include emergency shut-down control in the case of an actual or impending failure. The controller will be used to control the compressor operation. Typically at least some of the controller function is remote to the compressor site. The unit controller may function as the central processing unit carrying out the logic functions of the device. The controller may comprise a single computer or multiple computers or other calculator devices. The controller may be located on site or remote from the compressor. The controller may contain a microprocessor, digital input and output subsystems, memory capacity in which is stored various mathematical and analytical programs and software and constant data regarding the compressor being analyzed. One of the primary functions of the controller is to compute, using the representative data signals, the work performed by the compressor during a predetermined time interval. The controller may include the necessary formulas for repetitive calculations of performance parameters.
Preferably the controller, in conjunction with the rod load monitor, other sensors and transmitter/receiver pair, permits continuous real-time monitoring of the compressor. Real-time and continuous work calculations can then be performed and monitored.
Having thus described several aspects of at least one embodiment of this disclosure, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure.
Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. A method of monitoring the operation of a compressor, the compressor having a housing and a reciprocating member disposed within the housing, the method comprising:
sensing a parameter on the housing from a device placed on the housing;
generating a representative sensor signal in response to the sensed parameter;

transmitting from the device a data signal related to the representative sensor signal;
and receiving the data signal at a location remote from the housing.

2. The method of claim 1, wherein sensing a parameter comprises monitoring a load on the housing.

3. The method of claim 1, wherein transmitting a signal comprises manipulating the representative sensor signal.

4. The method of claim 3, wherein generating a representative signal comprises generating a voltage signal, and wherein transmitting from the device a data signal comprises manipulating the voltage signal to a frequency signal.

5. The method of claim 1, wherein sensing a parameter comprises mounting a plurality of strain gauges on a load cell mounted on the housing.

6. The method of claim 1, further comprising calculating a load on the housing.

7. The method of claim 1, further comprising calculating the power used by the compressor.

8. The method of claim 1, wherein the compressor has a pressure inlet and a pressure outlet, and wherein the method further comprises sensing the pressure at the pressure inlet and outlet.

9. A method of monitoring a machine, the machine having a housing and a reciprocating member disposed within the housing, the method comprising:

sensing at least one parameter on the housing of the machine from a device placed on the housing;
generating a representative sensor signal in response to the at least one sensed parameter;
transmitting from the device on the housing a data signal related to the representative senor signal; and receiving the data signal at a location remote from the housing.

10. The method of claim 9, wherein sensing at least one parameter further comprises monitoring a load on the housing.

11. The method of claim 9, wherein transmitting a signal further comprises manipulating the representative sensor signal.

12. The method of claim 9, wherein sensing at least one parameter comprises mounting a plurality of strain gauges on a load cell mounted on the housing of the machine.

13. The method of claim 9, further comprising calculating a load on the housing.

14. The method of claim 9, wherein receiving the data signal further comprises manipulating the data signal.

15. The method of claim 9, wherein the transmitting a signal is performed by a transmitter.

16. The method of claim 9, wherein the sensing at least one parameter is performed by at least one sensor.

17. The method of claim 9, wherein the compressor has a pressure inlet and a pressure outlet, and wherein the method further comprises sensing the pressure at the pressure inlet and outlet.

18. A compressor comprising:
a housing;
a reciprocating member disposed in the housing;
a motor coupled to the reciprocating member; and an apparatus comprising a mobile assembly attachable to the housing, the mobile assembly having a sensor, a transmitter and a power source, the sensor being operable to measure a parameter of the housing and generate a representative sensor signal, the representative sensor signal being input to the transmitter, the transmitter being operable to transmit a data signal related to the representative sensor signal, and the power source being operable to power the transmitter and sensor, and a stationary assembly having a receiver operable to receive the data signal from the transmitter.