GB2374147A

GB2374147A - Method for monitoring the performance of an electromechanical machine

Info

Publication number: GB2374147A
Application number: GB0108380A
Authority: GB
Inventors: Angus Robertson
Original assignee: PLANNED MAINTENANCE ENGINEERIN
Current assignee: PLANNED MAINTENANCE ENGINEERIN
Priority date: 2001-04-03
Filing date: 2001-04-03
Publication date: 2002-10-09
Also published as: GB0108380D0

Abstract

A method and apparatus for monitoring the performance of an electromechanical machine to warn of a malfunction of the machine takes initial simultaneous measurements of a plurality of parameters characterising the electromechanical behaviour of the machine during the normal operation of the machine, where each parameter characterises a different aspect of the electromechanical behaviour of the machine. The measurements are used to determine and store parameter limits. Simultaneous measurements of the plurality of parameters characterising the electromechanical behaviour of the machine are taken during a monitoring period. The measurements taken during the monitoring period are compared with the stored parameter limits and if they are outside a predetermined normal range of the stored parameter limits, the measurements are stored and an output signal is generated. Optionally the operation of the machine may be modified based on the output signal.

Description

APPARATUS AND METHOD FOR MONITORING THE PERFORMANCE OF AN ELECTROMECHANICAL MACHINE The present invention generally relates to a method and apparatus for monitoring the performance of an electromechanical machine to warn of a malfunction of the machine.

Electromechanical machinery is operated in many situations where the reliability of the machine is important. Further, from a commercial perspective, the reduction of the downtime of a machine for repair or maintenance is desirable.

The inventor of the present invention has identified that, in order to provide a planned maintenance programme for electromechanical machines, it is desirable to determine the electromechanical behaviour of the machine as viewed from several different perspectives i. e. by taking measurements of parameters which characterise different aspects of the electromechanical behaviour of the machine. By taking measurements of a plurality of parameters simultaneously, a more complete picture of the electromechanical behaviour of the machine is available. This"picture"can be used to determine and store parameter limits for warning of the possible malfunction of the machine. Thus when measurements are taken during a monitoring phase, if it is determined that one or more of the parameters is outside the stored parameter limits e. g. above or below a threshold, or the rate of change is greater than the threshold, an output signal is generated e. g. a warning or control signal, and the measurements are stored for analysis.

In this way the present invention provides a means by which a rich picture of the electromechanical behaviour of a machine during a normal phase of operation can be stored and analysed to determine the reason for the change in behaviour. In a preferred embodiment the parameters comprise vibration, temperature and electrical input to the machine which comprises of at least one of power, current and voltage. The parameters can also include an acoustic output of the machine.

The analysis of the machine can take place locally to the machine or remotely. Remote analysis can be provided by any suitable communication link between the local machine monitor and a remote analysing station. The local monitor can be arranged to periodically send stored measurements to the remote analysing station for analysis of the data. Also, the remote analysing station can access the local monitor to cause it to take real time measurements for the real time analysis of the electromechanical behaviour of the machine.

The analysis of the measurements is preferably performed by correlating the parameters to determine if there is an electromechanical malfunction. The correlation analysis enables the possible cause of the malfunction to be identified. The analysis can not just identify a malfunction, but also predict a possible malfunction allowing for proactive maintenance.

In order to avoid erroneous measurements during a start-up phase of operation of the machine, the storage of measurements of the parameters can be programmed to be delayed during the start-up phase of the machine. The start-up phase of the machine can be a preset time period or can be determined automatically from the measurements of the parameters e. g. measurements of the electrical input to a machine can indicate when a machine has been started and when it has stabilised. Thus preferably the storage of the measurements is delayed until the machine reaches a steady state of operation which can either be from start-up or due to a change of operation of the machine.

In one embodiment measurements of the parameters are not just stored when an event is detected, but they are also stored periodically. This enables a more complete picture of the electromechanical behaviour of the machine to be observed from the stored measurements.

The signal generated when an event is detected can be used to output a warning to a local operator e. g. a visible or audio warning, or a warning to a remote monitor.

Alternatively or in addition, the output signal can be used to automatically control the operation of the machine. In its simplest form this can comprise shutting down the machine when a malfunction is detected, but this could comprise any modification to the operation of the machine.

The monitoring apparatus of the present invention can be used in conjunction with a central analysing station which receives and analyses measurements from a plurality of monitoring devices.

The present invention can be implemented in dedicated hardware, using a programmable digital controller suitably programmed, or using a combination of hardware and software. Thus the present invention can be embodied by any suitable carrier medium for carrying machine readable instructions for controlling a programmable controller. The carrier medium can comprise any storage medium such as a floppy disk, CD ROM, magnetic tape, or programmable memory device, or a transient medium such as an electrical, optical or acoustic signal. An example of such a signal is an encoded signal carrying a computer code over a communications network e. g. a TCP/IP signal carrying computer code over an IP network such as the Internet, an intranet, or a local area network.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an arrangement in accordance with one embodiment of the present invention in which a monitoring device is arranged for monitoring the behaviour of a motor ; F :.. une 2 is a schematic diagram of the structure of the monitoring device in the embodiment of Figure 1 ; Figure 3 is a flow diagram illustrating the method of storing the predetermined limits to be used for the detection of the malfunction of the motor in the embodiment of Figure I ; and Figure 4 is a flow diagram illustrating the method of operation of the monitoring device in the embodiment of Figure 1.

Figure 1 illustrates an arrangement in accordance with one embodiment of the present invention wherein a motor 1 is monitored during operation by a monitoring device 7.

The motor I is supplied with a three phase power supply as the electrical input. Each phase of the electrical input is monitored by a respective current transformers 4,5 and 6.

The current transformers 4,5 and 6 each generate a respective current measurement output C 1, C2 and C3 which are input to the monitoring device 7 as measurements of the electrical input to the motor 1. Thus the current transformers 4,5 and 6 provide a measure of the electrical behaviour of the motor 1.

An accelerometer 3 is mounted on the motor 1 at a suitable position to detect vibrations of the motor 1 during operation. The accelerometer 3 generates an output indicative of the vibrations of the motor 1 which is input as an input A to the monitoring device 7.

Thus the accelerometer 3 provides a measure of the vibrational behaviour of the motor 1 during operation.

A thermistor 2 is also mounted on the motor 1 in a suitable position to measure the temperature at a position on the motor 1. Thermistor 2 provides a temperature measure T which is input to the monitoring device 7. Thus the thermistor 2 provides a measure of the thermal behaviour of the motor 1 during operation.

It can thus be seen from Figure 1 that five simultaneous measurements are taken during the operation of the motor 1 and are input to the monitoring device 7 to monitor the electromechanical behaviour of the motor 1.

Figure 2 is a schematic diagram of the monitoring device 7 in the embodiment of Figure 1. The monitoring device 7 comprises a programmable controller having a microprocessor 12 for implementing programme code stored in a programmable read only memory (PROM) 18. A random access memory (RAM) 13 is provided as working memory for use by the microprocessor 12 for the storage of measurements. A multi channel analog to digital converter (ADC) 17 is provided to convert the five inputs Cl, C2, C3, T and A into digital measurements. The multi channel analog to digital converter is controlled to sample the inputs every second.

A display 11 can be connected to the monitoring device 7 to provide a local display to enable measurements of parameters and analysed data to be displayed.

Monitoring device 7 is provided with four different types of interfaces. A serial RS232 interface 10 is provided for a RS232 link to a computer such as a laptop. This enables an engineer to connect in over a serial link to the monitoring device 7.

As another interface, a modem 20 is provided to provide a means of communication over a telecommunications link to the monitoring device 7. Also an ethemet interface 19 is provided for connection to an ethemet 21 to enable remote connection to the monitoring device 7. Thus the interfaces 10,20 and 19 provide for remote monitoring and analysis. The monitoring device 7 is generally provided in the location of the motor 1. The provision of a communications link enables the measurements taken and stored in the memory 13 to be read and analysed at a remote location. The provision of the interfaces in the monitoring device 7 enables a central monitoring and analysing station to communicate with a plurality of monitoring devices 7 and thereby allowing the monitoring of a plurality of motors at different locations.

A digital to analog converter (DAC) 14 is provided to provide an analog output signal for controlling a display panel 22. The display panel 22 provides a local display to give an indication of the functioning of the monitoring device 7. A power light indicates that the device is powered up. A sample light flashes every second a sample is taken by the multi channel analog to digital converter 17. The fault light indicates when a fault is detected.

A digital input/output device 16 is provided to receive digital inputs indicating machine event changes. This enables, for example, the start of the machine to be indicated to the monitoring device. A digital input/output device 16 also generates a digital warning or control output. This can be used locally for controlling the motor 1. It should be further noted that in addition to generating the local fault warning on the display panel 22 and possibly controlling the machine using the digital output, a warning signal can be transmitted using any one of the interfaces 10, 20 or 19 to a remote monitoring station to warn of a fault detection.

All the components in the monitoring device 7 are connected over a control and data bus 15.

The monitoring device 7 is a fully programmable controller which can be programmed to perform the monitoring operation.

The method by which parameter limits are determined and stored in the programmable read only memory 18 will now be described with reference to the flow diagram of Figure 3.

In step Si the process starts and in step S2 an engineer positions the sensors on the motor 1. In this embodiment this comprises placing the current transformers 4,5 and 6 on the appropriate phases of the three phase input to the motor 1. Also the accelerometer 3 must be positioned at a suitable position on the motor 1 to monitor the vibrations experienced by the motor 1 which are useful for indicating the mechanical behaviour of the motor 1. Also the thermistor 2 is positioned on the motor 1 at a suitable position to monitor the temperature at a position on the motor 1 which is important to the performance of the motor 1.

In step S3 measurements are taken from the sensors and in step S4 the limits are determined from the measurements and stored in the programmable read only memory (PROM) 18. The limits can be determined by taking measurements over a period of time during a normal operation of the motor 1. The limits can thus comprise deviations from the range of values taken during the normal operation of the motor 1. These can comprise threshold values e. g. an upper and lower current limit, an upper and lower vibration limit and an upper and lower temperature limit. Alternatively, the limits can comprise rate of change limits. During the taking of the measurements over a monitoring phase i. e. during a normal operation of the motor, a rate of change of the measurements of the parameters can be determined within normal operating conditions.

On the basis of this, a threshold rate of change can be determined indicative of an unhealthy rate of change of a parameter.

Once the limits have been determined and stored in the programmable read only memory 18, the process for setting up is finished (step S5). Thus the programmable read only memory 18 stores the programme code for implementation by the microprocessor 12 and parameter data. The parameter data includes fault messages to be generated when fault conditions are determined. Addresses to which the fault messages are to be sent over the communications links, the identity of the machine being monitored, and sensor configurations. The sensor configurations comprise a range of measurements possible for the sensor, the units of measurement, the name of the sensor, the limits comprising high and low values, and a start up time to allow the motor to settle after start up before taking measurements.

The operation of the monitoring device 7 during the monitoring phase will now be described with reference to the flow diagram of Figure 4. In step S 10 the process starts and in step Sil 1 it is determined whether the motor 1 is still in a start up phase. The process waits until the start-up phase has finished. The start-up phase can be determined simply from an input machine event to the digital I/O device 16 and the period can be determined from the stored start-up time period in the programmable read only memory 18. Alternatively, the microprocessor 12 can, following the input of a machine event indicating that the machine has started or following the detection of starting of the motor by the sensors e. g. by detecting a drawing of current by the current transformers 4,5, and 6, perform an analysis of the input measurements in order to determine when the motor 1 reaches a steady state of operation.

Once the start-up phase has finished, the microprocessor 12 controls the multi channel analog to digital converter 17 every second (step Sol 1) to analog to digital convert the measurements Cl, C2, C3, T and A (step SI2). The microprocessor 12 then compares the measurements with the limits stored in the programmable read only memory (PROM) 18 (step S14). If the comparison determines that the measurements are above the maximum permissible limits of the device (indicating that the device has failed) (step S 15), or if the measurements are above the determined limit (indicating a possible malfunction of the motor 1) (step S16), or if the measurements are determined to be below maximum permissible limits (indicating that the sensor has failed) (step S 17), or if the measurements are below the determined limits (indicating a possible malfunction of the motor 1) (step S18), the measurements are stored with the sample time and appropriate fault message in the random access memory 13. In this way the time at which the fault occurred is noted, the values of the sensor measurements at the time of the fault, and the reason for the fault (i. e. above limits, above threshold, below limits, or below threshold) can be stored.

If the user has inhibited the raising of an alarm (step S22) no alarm is raised and measurements are taken in the next sample period (step S12). If however the operator has not inhibited the raising of an alarm, an alarm is generated and sent in step S24. If the alarm is not acknowledged (step S25), the alarm is resent (step S24). Once the alarm is acknowledged, the next measurement will be taken at the appropriate sample time (step S12). The alarm which is generated is output from the digital to analog converter 14 to the display panel 22 to cause the fault light to illuminate.

The alarm which is generated can also be output over the digital input/output device 16 to control the motor 1 e. g. to shut it down. Also, the alarm can be transmitted over any one of the interfaces 10,20 and 19. For example, the micro processor 12 can control the modem 20 to dial up a remote monitoring and analysing station in order to transmit the alarm using address information stored in the programmable read only memory (PROM) 18.. The internet interface 19 can be controlled by the micro processor 12 to transmit the alarm over the ethernet 21 to the address stored in the programmable read only memory (PROM) 18.

If the measurements are not above the limits, above the threshold, below the limits, or below the threshold, this indicates that no fault has occurred with the motor 1 or with the sensors (i. e. no event has occurred). In order to monitor the regular behaviour of the motor 1, every minute the measurements can be stored in a cyclical manner in the random access memory 13 (step S19 and step S20). In this way the random access memory 13 stores a picture of the electromechanical behaviour of the motor 1 in a recent time period irrespective of whether or not events have occurred.

Thus the random access memory 13 will store measurements for a recent period of time and measurements for a recent number of events.

The analysis of the stored measurements can be carried out locally or remotely.

Although an alarm can be raised when only one of the measurements moves outside a limit e. g. moves outside a threshold range, or exceeds a threshold rate of change, the analysis to investigate the electromechanical behaviour of the motor 1 utilises all of the measurements. Because the measurements are taken simultaneously, this allows the correlation to be identified between changes in measurements of different parameters.

The process of analysis not only allows for faults to be detected, but also enables predications on future behaviour of the electromechanical device to be determined. This is particularly important since it allows for predications on the maintenance programme required in order to avoid failure of the electromechanical apparatus. Thus, the analysis of the data allows for the planned maintenance programme to reduce the down time of machinery and avoid unforeseen failures.

Where the alarm automatically causes the shut down of the machine, an operator can disable the alarm to avoid spurious shut downs of the machine. This interference by the operator is however noted in the stored data. Thus if an operator mistakenly overrides the automatic safety provided by the monitoring device, this fact will be known.

The remote analysing and monitoring station can also access the monitoring device 7 over the communications interfaces 10,20 or 19 to cause the microprocessor 12 to control the multi-channel analogue to digital converter 17 to take real time measurements from the sensors and send the measurements to the remote monitoring and analysing station. This allows the remote monitoring and analysing station after having received an alarm, to access the monitoring device 7 and undertake a real time monitoring process the electromechanical behaviour of the motor 1.

The remote monitoring and analysing station can be connected to the monitoring device 1 over any conventional communication link such as via a telecommunications link using a modem, via a local area network such as the ethernet 21, or via any other suitable communication device.

Although the present invention has been described hereinafter with reference to specific embodiments, the present invention is not limited to these embodiments and modifications which lie within the spirit and scope of the present invention will be apparent to a skilled person in the art.

Claims

CLAIMS: 1. A method of monitoring the performance of an electromechanical machine to warn of a possible malfunction of the machine, the method comprising: taking initial simultaneous measurements of a plurality of parameters characterising the electromechanical behaviour of the machine during a normal operation of the machine, each parameter characterising a different aspect of the electromechanical behaviour of the machine; using the measurements to determine and store parameter limits for warning of a possible malfunction of the machine; taking simultaneous measurements of said plurality of parameters characterising the electromechanical behaviour of the machine during a monitoring period; comparing the measurements taken during the monitoring period with the stored parameter limits; and if the comparison determines that one or more of the measurements taken during the monitoring period are outside a predetermined normal range of the stored parameter limits, storing the measurements of the parameters and generating an output signal.
2. A method according to claim 1, including storing the measured parameters periodically during the monitoring period.
3. A method according to claim 2, wherein the measurements are stored in a cyclical memory.
4. A method according to any preceding claim, wherein the parameters comprise vibration, temperature and electrical input comprising at least one of power, current and voltage.
5. A method according to claim 4, wherein the parameters include an acoustic output of the machine
6. A method according to any preceding claim, wherein, in response to said output signal, the stored measurements of the parameters are analysed by correlating the parameters to determine if there is an electromechanical malfunction and if so, to identify the possible cause.
7. A method according to claim 6, wherein the analysis includes a rate of change analysis.
8. A method according to claim 6 or claim 7, wherein the measurements of the parameters are taken and stored locally to the machine, the stored measurements are read at a remote location, and the analysis is performed at the remote location.
9. A method according to claim 8, wherein the stored measurements of the parameters are automatically sent to the remote station periodically.
10. A method according to claim 8 or claim 9, wherein the local location can be accessed by the remote location to cause the taking of real time measurements of the parameters and the transmission of the measurements to the remote location.
11. A method according to any preceding claim, wherein, if the comparison determines that one or more of the measurements are outside the predetermined normal range of the stored parameter limits, the storage of the measurements of the parameters is delayed following start-up of the machine, the delay being determined from the measurements of the parameters.
12. A method according to claim 11, wherein, if the comparison determines that one or more of the measurements are outside the predetermined normal range of the stored parameter limits, the storage of the measurements of the parameters is delayed until the machine reaches a steady state of operation.
13. A method according to any preceding claim, wherein a plurality sets of measurements associated with the generation of the most recent output signals are stored
14. A method according to any preceding claim, wherein an operator can disable the output signal.
15. A method of controlling a machine comprising: the method of monitoring the performance of an electromechanical machine to warn of a malfunction of the machine according to any preceding claim; and modifying the operation of the machine on the basis of the generated output signal.
16. Apparatus for monitoring the performance of an electromechanical machine to warn of a malfunction of the machine, the apparatus comprising: receiving means for receiving initial simultaneous measurements of a plurality of parameters characterising the electromechanical behaviour of the machine during a normal operation of the machine and during a monitoring period, each parameter characterising a different aspect of the electromechanical behaviour of the machine; limit storage means for store parameter limits determined from the initial measurements for warning of a possible malfunction of the machine; comparing means for comparing the measurements taken during the monitoring period with the stored parameter limits; and measurement storage means for, if the comparison determines that one or more of the measurements taken during the monitoring period are outside a predetermined normal range of the stored parameter limits, storing the measurements of the parameters and generating an output signal.
17. Apparatus according to claim 16, wherein said measurement storage means is adapted to store the measured parameters periodically during the monitoring period.
18. Apparatus according to claim 17. wherein the measurement storage means is adapted to store the measurements in a cyclical memory.
19. Apparatus according to any one of claims 16 to 18, wherein the parameters comprise vibration, temperature and electrical input comprising at least one of power, current or voltage.
20. Apparatus according to claim 19, wherein the parameters include an acoustic output of the machine
21. Apparatus according to any one of claims 16 to 20, including analysing means for, in response to said output signal, analysing the stored measurements of the parameters by correlating the parameters to determine if there is an electromechanical malfunction.
22. Apparatus according to claim 21, wherein the analysing means is adapted to use a rate of change analysis.
23. Apparatus according to any one of claims 16 to 20, including transmission means for transmitting the stored measurements to a remote location for analysis at the remote location.
24. Apparatus according to claim 23, wherein the transmission means is adapted to automatically transmit the stored measurements of the parameters to the remote station periodically.
25. Apparatus according to claim 23 or claim 24, including access means for allowing the remote location to cause the taking of real time measurements of the parameters and the transmission of the measurements to the remote location.
26. Apparatus according to any one of claims 16 to 25, wherein, if the comparing means determines that one or more of the measurements are outside the predetermined normal range of the stored parameter limits, the measurement storage means is adapted to delay the storage of the measurements of the parameters following start-up of the machine, the delay being determined from the measurements of the parameters.
27. Apparatus according to claim 26, wherein, if the comparing means determines that one or more of the measurements are outside the predetermined normal range of the stored parameter limits, the measurement storage means is adapted to delay the storage of the measurements of the parameters until the machine reaches a steady state of operation.
28. Apparatus according to any one of claims 16 to 27, wherein said measurement storage means is adapted to store a plurality sets of measurements associated with the generation of the most recent output signals.
29. Apparatus according to any one of claims 16 to 28, including operator control means to allow an operator to disable the output signal.
30. Apparatus for controlling a machine comprising: the apparatus for monitoring the performance of an electromechanical machine to warn of a malfunction of the machine according to any one of claims 16 to 29; and means for modifying the operation of the machine on the basis of the generated output signal.
31. Apparatus for monitoring the performance of an electromechanical machine to warn of a malfunction of the machine, the apparatus comprising: an input port for receiving initial simultaneous measurements of a plurality of parameters characterising the electromechanical behaviour of the machine during a normal operation of the machine and during a monitoring period, each parameter characterising a different aspect of the electromechanical behaviour of the machine; a first memory storing parameter limits determined from the initial measurements for warning of a possible malfunction of the machine; a processor programmed to compare the measurements taken during the monitoring period with the stored parameter limits; and a second memory for, if the comparison determines that one or more of the measurements taken during the monitoring period are outside a predetermined normal range of the stored parameter limits, storing the measurements of the parameters and generating an output signal.
32. A carrier medium carrying machine readable instructions for controlling a programmable controller to carry out the method of any one of claims 1 to 15.
33. A carrier medium carrying machine readable instructions for controlling a programmable controller to be configured as the apparatus of any one of claims 16 to 31.