WO1995007451A1

WO1995007451A1 - Detection of faults in the working of electric motor driven equipment

Info

Publication number: WO1995007451A1
Application number: PCT/US1994/009894
Authority: WO
Inventors: Alan David Solomon; Efim Gelman
Original assignee: Diagnostics Temed Ltd.
Priority date: 1993-09-06
Filing date: 1994-09-02
Publication date: 1995-03-16
Also published as: AU7680194A; IL106916A; IL106916A0

Abstract

An apparatus for detecting faults in the working of a motor driven components of a heating, cooling or dehumidifying unit, including a housing in which are located a) a current sensor (110) which is connectable to the power leads of the motors of the unit, the sensor being connected to b) a demodulator (120) being connected to c) a low pass filter (130) which is connected to d) an A-D converter (140) which is connected to e) a micro controller (150) containing an appropriate algorithm program, which is connected to f) a memory (170), both the micro controller (150) and the memory (170) being connected to g) and indicating unit (160), all of the unit being connected in an appropriate manner one after the other.

Description

DETECTION OF FAULTS IN THE WORKING OF ELECTRIC MOTOR DRIVEN

EQUIPMENT

FIELD OF THE INVENTION

The present invention relates to the detection of faults in the working of electric motor driven equip¬ ment.

BACKGROUND OF THE INVENTION

The term "motor driven equipment" is used herein to refer to any piece of equipment consisting of an electric motor, together with one or more devices driven by the electric motor and imposing a load on the motor shaft. Examples of motor driven equipment include a compressor in a refrigeration or cooling/heating de¬ vice, a fan in air moving equipment and a pump driving a fluid through a pipe.

For compressors, pumps, fans and other motor driven equipment it is of vital importance to be able to carry out early identification of incipient performance problems or faults for such concerns as security, health, production, etc.

Fault detection devices can be roughly divided into two classes: those not- requiring direct contact with the equipment, and those that do. The former in¬ cludes so-called "passive" approaches wherein direct contact is not required while the latter includes devices based on, e.g., vibration analysis for mechanical fail¬ ures and gas detectors for leaks. Such intrusive devices have inherent weaknesses that often stem from the need for physical contact or closeness to the equipment. Thus vibration sensors must be positioned correctly with respect to the (possibly unknown) directions of vibra-

SUBSTITU7ΕSHEET(RULE26) tions, while gas sensor locations are limited to non- ventilated spaces and are not effective for equipment placed for example, on a roof.

Fault detection devices not requiring direct contact are known in the prior art. An example of an approach which does not require direct contact with the equipment is that of Motor Current Signature Analysis, described in US Patent 4,965,513 to Haynes et al. This method, referred to herein as "MCSA", works as follows:

It is known that the characteristics of the electric current powering an electric motor which in turn operates a piece of equipment reflect the mechanical load of the equipment on the motor shaft. Therefore, the current values may be analyzed with standard spectral analysis, such as by applying the discrete Fourier Trans¬ form to a demodulated current signal and computing the power spectrum of the signal. Thus one attempts to obtain a "current signature" which will be different if the equipment is undergoing a change in mechanical behav¬ ior due to an incipient breakdown.

Since MCSA requires only values characterizing the electricity it is inherently a passive, non-intrusive approach, not requiring direct contact with the equipment and hence offering the convenience resulting from this fact.

The spectral analysis of the current, serving as the basis for a current signature whose changes re¬ flect changes- in the mechanical behavior of the equip¬ ment, is the basis for a number of inventions known in the prior art including those described in US Patents 4,123,009 to Kilpinen and 4,380,172 to Imam et al.

The MCSA method consists of storing a (possibly long) sequence of current values in a computer memory and applying the Discrete Fourier Transform with an appropri¬ ately chosen window function to the sequence. Of course the actual choice of the window function is based more on experimentation and knowing what one is seeking, than on definitive rules. Indeed the non-definitive nature of the choice renders the MCSA method difficult to implement independently of the intervention of an expert.

As a preliminary step in MCSA one will normally demodulate the signal with respect to the line current frequency for an A.C. power source. From the Discrete Fourier Transform we find the power spectrum, a positive real function of the frequency. Attempts will be made to associate various peaks in the spectrum with mechanical features of the equipment/motor combination.

Significant amplitude values are now stored in memory for data collected when operation was normal. The values will normally correspond to slip and r.p.m. values of the motor as well as to other mechanically-related features. For data collected at a later time we will again find the power spectrum and compare its key fea¬ tures with those stored during the earlier "calibration" stage. By visual observation we determine if differences between the spectra, buttressed by additional input of the current values and known mechanical features, justify concluding that particular performance problems have arisen in the equipment.

The MCSA approach has deficiencies that limit its effectiveness in certain situations. The first is that it requires extensive computing capability for Discrete Fourier Transform evaluation, together with memory sufficient for large vectors; similarly it is a "linear" operation because of the linear nature of the Fourier Transform while the operations taking place in motor-driven equipment are basically nonlinear. In the same vein it is "frequency oriented", with limited capa¬ bility to identify effects with low power that might be associated with current values assumed over brief inter¬ vals of time.

Thus, while the Fourier Transform and Power Spectrum analysis have a strong traditional appeal for periodic processes, they will be inherently limited to the strong signal qualities of the slip and rotor speed in analyzing equipment performance. Finally, as noted above, the need for a window function makes it difficult to implement the method in the form of an autonomous, stand-alone device that does not require human interven¬ tion.

SUBSπTUTΕSHEET(RULE26) SUMMARY OF THE INVENTION

The present invention seeks to provide an improved apparatus and method for detecting faults in the operation of electric motor-driven equipment.

There is thus provided in accordance with a preferred embodiment of the present invention an appara¬ tus for detecting faults in the working of motor driven components of a heating, cooling or dehumidifying unit, including a housing in which are located a) a current sensor which is connectable to the power lead of the motors of the unit, the sensor being connected to b) a demodulator being connected to c) a low pass filter which is connected to d) an A-D converter which is connected to e) a micro controller containing an appropriate algorithm program, which is connected to f) a memory, both the micro controller and the memory being connected to g) an indicating unit, all the units being connected in an appropriate manner one after another.

Further in accordance with a preferred embodi¬ ment of the present invention the current sensor is a current transformer.

Still further in accordance with a preferred embodiment of the present invention the current trans¬ former is of 20 amp.

Additionally in accordance with a preferred embodiment of the present invention the current sensor is a magnetic amplifier.

Further in accordance with a preferred embodi¬ ment of the present invention the current sensor is a shunt.

Still further in accordance with a preferred embodiment of the present invention the demodulator is an active rectifier.

Additionally in accordance with a preferred embodiment of the present invention the filter is a 25 Hz cut-off frequency low pass Butterworth filter. Additionally in accordance with a preferred embodiment of the present invention the A-D converter has at least 6 bits.

Further in accordance with a preferred embodi¬ ment of the present invention the A-D converter has 8 bits.

Still further in accordance with a preferred embodiment of the present invention the indicating unit is a display.

Additionally in accordance with a preferred embodiment of the present invention the indicating unit is an alarm unit.

Further in accordance with a preferred embodi¬ ment of the present invention the indicating unit is located within the housing.

Still further in accordance with a preferred embodiment of the present invention the indicating unit is located outside the housing.

Additionally in accordance with a preferred embodiment of the present invention the unit is an air conditioning one unit and the algorithm is programmed to detect insufficient refrigerant pressure.

Further in accordance with a preferred embodi¬ ment of the present invention the unit is a chiller and the algorithm is programmed to detect clogging of an air filter.

Still further in accordance with a preferred embodiment of the present invention the algorithm is programmed also to detect one or more additional de¬ faults.

There is also provided in accordance with another preferred embodiment of the present invention a method for the detection of faults in the working of a unit (as herein before defined) which method consists in sending a variable voltage signal being proportional to the- time-varying current flowing in the power leads from the motor of the unit, which signal is sent and verified via a demodulator, a low pass filter and an A-D convert¬ er, to a micro controller, which is fed with a suitable algorithm program in which the signal is checked against the signal recorded in a memory, and then sent to the display unit.

There is also provided in accordance with another preferred embodiment of the present invention fault detection apparatus for detecting faults in the working of motor driven equipment including current sensing apparatus connectable to the power input of the motor and producing a current signal, signal correction apparatus receiving as input the current signal and operative to demodulate the current signal, filter the current signal to retain low frequencies thereof, and convert the current signal from analog to digital form and producing a corrected signal, a memory, a controller in operative connection with the memory, receiving the corrected signal and having a calibration state and an operation state and operative, when in the calibration state, to compute the calibration norm of the corrected signal based partly on data contained in the memory and to store the calibration norm in the memory and opera¬ tive, when in the operation state, to compute the opera¬ tion norm of t e corrected signal based partly on data contained in the memory and to compare the operation norm with the stored calibration norm and to produce a func¬ tion signal indicating the functioning of the motor driven equipment, and an indicating unit receiving as input the function signal and producing an output indica¬ tion of the functioning of the motor- driven equipment.

Further in accordance with a preferred embodi¬ ment of the present invention the current sensing appara¬ tus includes a magnetic amplifier.

Still further in accordance with a preferred embodiment of the present invention the current sensing apparatus includes a shunt.

Additionally in accordance with a preferred embodiment of the present invention the demodulating apparatus includes an active rectifier.

Further in accordance with a preferred embodi¬ ment of the present invention the low pass filter in¬ cludes a Butterworth filter.

Still further in accordance with a preferred embodiment of the present invention the A-D conversion apparatus has at least 6 bits.

Additionally in accordance with a preferred embodiment of the present invention the A-D conversion apparatus has at least 8 bits.

Further in accordance with a preferred embodi¬ ment of the present invention the motor driven equipment includes an air conditioning unit and the controller is operative to detect insufficient refrigerant pressure.

Still further in accordance with a preferred embodiment of the present invention the motor driven equipment includes a chiller and the controller is opera¬ tive to detect clogging of an air_, filter.

Additionally in accordance with a preferred embodiment of the present invention the controller is also operative to detect at least one additional defect.

Further in accordance with a preferred embodi¬ ment of the present invention the motor driven equipment includes a heat pump.

Still further in accordance with a preferred embodiment of the present invention the heat pump has a plurality of modes of heating and the controller is operative to detect the mode of heating of the heat pump.

Additionally in accordance with a preferred embodiment of the present invention the motor driven equipment includes a fluid pump.

Further in accordance with a preferred embodi¬ ment of the present invention the controller is operative to detect the rate of flow of the fluid.

Still further in accordance with a preferred embodiment of the present invention the controller is operative to detect faults in the pump.

Additionally in accordance with a preferred embodiment of the present invention the controller is also operative to control the operation of the pump.

Further in accordance with a preferred embodi¬ ment of the present invention the fault detection appara¬ tus also includes a container being fed by the pump, and the controller is operative to detect the level of liquid in the container.

Still further in accordance with a preferred embodiment of the present invention the motor driven equipment includes a fan.

Additionally in accordance with a preferred embodiment of the present invention the motor driven equipment includes refrigeration equipment.

Further in accordance with a preferred embodi¬ ment of the present invention the refrigeration equipment includes evaporator coils and the controller is operative to detect the growth of frost on the evaporator coils.

Still further in accordance with a preferred embodiment of the present invention the motor driven equipment includes a rotating member and the controller is operative to detect the rate of rotation of the rotat¬ ing member.

Additionally in accordance with a preferred embodiment of the present invention the indicating unit includes a display.

Further in accordance with a preferred embodi¬ ment of the present invention the indicating unit in¬ cludes an alarm.

There is also provided in accordance with another preferred embodiment of the present invention a fault detection method for detecting faults in the work- ing of motor driven equipment including sensing the current in the power input of the motor and producing a current signal, demodulating the current signal, filter¬ ing the current signal to retain low frequencies thereof, and converting the current signal from analog to digital form and producing a corrected signal, receiving the corrected signal, retrieving at least one stored correct¬ ed signal from the memory and comparing the corrected signal with the stored corrected signal and producing a function signal indicating the functioning of the motor driven equipment, receiving the corrected signal and having a calibration state and an operation state and, when in the calibration state, computing the calibration norm of the corrected signal based partly on stored data and storing the calibration norm and, when in the opera¬ tion state, computing the operation norm of the correct¬ ed signal based partly on stored data and to comparing the operation norm with the stored calibration norm and producing a function signal indicating the functioning of the motor driven equipment, and receiving the function signal and producing an output indication of the func¬ tioning of the motor driven equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which:

Fig. 1 is a simplified block diagram of an apparatus for detecting faults in the operation of elec¬ tric motor-driven equipment constructed and operative in accordance with a preferred embodiment of the present invention;

Figs. 2A - 2D together constitute an electric circuit diagram of a portion of the apparatus of Fig. 1;

Fig. 3 is a flow chart illustrating a portion of the method performed by the apparatus of Fig. 1;

Fig. 4 is a flow chart illustrating an alterna¬ tive embodiment of the method performed by the apparatus of Fig 1; and

Figs. 5A - 5F together constitute an electronic circuit diagram of an alternative embodiment of a portion of the apparatus of Fig. 1.

Attached herewith are the following Appen¬ dices which aid in the understanding and appreciation of one preferred embodiment of the invention shown and described herein:

Appendix A is a list of the various parts in the circuit diagram of Figs. 2A - 2D;

Appendix B is a list of the various parts in the circuit diagram of Figs. 5A - 5F; and

Appendix C is a computer listing of a preferred software implementation of the method of Fig. 4. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a method and to an apparatus for detecting faults in the working of motor driven components of heating, cooling or dehumidi- fying units, e.g. an air conditioning unit, a chiller, a fan coil, refrigerating unit, etc. (Hereinafter called "unit"). The unit will be described herein in particular as an air conditioning unit. However it is not restrict¬ ed thereto. Such air conditioning may be either a small one used in private homes or a large one used in indus¬ trial plants, large halls, and the like.

It is appreciated that the method and apparatus described herein may in fact be used for detecting faults in any motor driven equipment as defined above and need not be limited to use with a unit as defined above.

In the working of air conditioning many faults occur, for example: a) insufficient refrigerant pressure; b) air-filter clogging; c) water in the system; d) the reverse valve does not operate; e) the refrigerant filter is clogged; f) the condenser fan fails; g) the compressor itself does not work; h) water freezes in the capillary tube.

It is very often difficult to check and distin¬ guish between such faults and thus a technician has to be called. It has therefore been desirable to design a method and/or a device which would show one or more of such faults as early as possible upon its onset, indicate whether indeed a technician has to be called and aid the technician in identifying the problem. Said device should be simple, relatively cheap and easy to connect to a commercially available air conditioning unit.

Reference is now made to Fig. 1 which illus-

SUBSTtTUTESHEET(RULE26) trates - A apparatus for detecting faults in the operation of electric motor-driven equipment constructed and opera¬ tive in accordance with a preferred embodiment of the present invention. The apparatus of Fig. 1 comprises apparatus for detecting faults in the working of motor driven components of a heating, cooling, or dehumidifying unit, comprising: a) a current sensor 110 which is connectable to the power lead of the motors of the unit, said sensor being connected to b) a demodulator 120 being connected to c) a low pass filter 130 which is connected to d) an A-D converter 140 which is connected to e) a micro-controller 150 containing an appro¬ priate algorithm program, which is connected to f) a memory 170, both the micro-controller and the memory being connected to g) an indicating unit 160; all said units being connected in an appropri¬ ate manner one after another.

The current sensor, being a secondary output, is, for example, a current transformer, advantageously of 20 amp; a magnetic amplifier; a shunt, etc.

Said output is a variable voltage signal pro¬ portional to the time-varying current flowing in the air conditioning power lead.

The demodulator is advantageously an active having a demodulating circuit, a multiplier, etc.

The low pass filters may be, for example, any of those mentioned in the following publications:

1. R.W. Hamming, Digital Filters, Prentice- Hall, Englewood Cliffs, 1983.

2. W. Press, S. Teukolsky, W. Veterling, B. Flannery, Numerical Recipes, Cambridge University Press, Cambridge, 1992. An example of a suitable low pass filter is a Butterworth filter. Said filter, whose frequency is below 25 Hz removes effects associated with, e.g., the 50 Hz line frequency, its harmonics, and other unused sig¬ nals.

The A-D converter should preferably have at least 6 bits. However, advantageously, it has 8 bits or even more.

The memory is advantageously battery powered for a case of unexpected line voltage drop. It may be, for example, an on-chip resident memory of a micro con¬ troller, an external CMOS memory, etc.

The micro-controller is preferably an embedded one, such as one from INTEL (U.S.A.) MCS - 51 system.

The indicating unit may be any suitable one. It may be an integral part of the apparatus, i.e. be located within the housing or it may be located at a distance therefrom. It may be a display unit, an alarm unit, etc. It may show various lights or make various sounds, or even a combination of the two. Advantageous¬ ly, for each fault there are at least two separate posi¬ tions, i.e. one indicating the normal situation and one indicating the fault. However, there may also be addi¬ tional positions comprising an intervening signal indi¬ cating that the situation is not normal but there is no urgency to repair it.

The display may have various arrangements for each fault. However, it may also only indicate that there is a fault in any of the various systems.

The present invention will be illustrated with reference to detecting insufficient refrigerant pressure. However, as indicated above, it is not restricted to detecting this fault or any other fault mentioned above. The detection of other faults appearing in said units may be envisaged. It is also appreciated that the detection of faults in any motor driven equipment may be envisaged. If the unit is a chiller the main fault to be detected will be the clogging of the air filter.

The present invention also comprises a method for the detection of faults in the working of a unit as hereinabove defined, which method consists in sending a variable voltage signal being proportional to the time- varying current flowing in the power leads from the motors of the unit, which signal is sent and verified via a demodulator, a low pass filter and an A-D converter, to a micro controller, which may be programmed with a suit¬ able computer program in which the signal is checked against the signal recorded in a memory, and then sent to the display unit.

As described above, the controller is prefera¬ bly implemented in a combination of hardware and soft¬ ware. It is appreciated that the controller may also be implemented purely in hardware or by other means.

The present invention will now be illustrated with reference to the accompanying drawings, without being limited by them. Said drawings comprise:

Fig. 1, which is a block diagram of an appara¬ tus constructed and operative in accordance with a pre¬ ferred embodiment of the present invention;

Figs. 2A - 2D, which together constitute an electric circuit diagram of the apparatus shown in Fig. 1; and

Fig. 3 shows a method which is suitable for checking the defects caused by insufficient refrigerant pressure and for detecting other defects.

The block diagram shown in Fig. 1 works as follows: The current sensor 110 secondary (output), which is a variable voltage signal proportional to the time-varying current flowing in the air conditioner power lead, is connected to the demodulator 120, being an active rectifier, which produces a DC voltage, propor¬ tional to the average value of air conditioner current. The demodulated signal is fed through low pass filter 130, having an upper frequency cutoff below 25 Hz.

The conditioned voltage signal is then trans¬ formed to an 8-bit digital code by the A-to-D converter 140. The micro controller 150, upon occurrence of an appropriate event such as the receipt of an external signal, such as the pressing of an appropriately labeled pushbutton (not shown) , reads this code and stores it in the memory 170, which is advantageously battery powered for a case of unexpected line voltage drop.

The code is regulated by the computer program stored in the micro controller 150.

This program is used as the basis for comparing further readouts (obtained without pressing the pushbut¬ ton) with the first readout. According to the results of this comparison, display 6 outputs a message: either NORMAL or NO REFRIGERANT or OPERATIONAL STAND BY (COM¬ PRESSOR OFF) , in the example of a detecting refrigerant pressure.

Reference is now made to Appendix A, which is a list of the various parts in the electric circuit diagram of Figs. 2A - 2D.

The operation of the method of Fig. 3 may be understood as follows:

Data Input: A sequence of consecutive current values is collected from the electric line powering the air conditioner. These values are denoted by C(l), C(2), C(3), ... , C(N). N is preferably equal to 2048 in the case of the refrigerant checking application.

Data Transformation: We form the sum of the squares of the current values:

SUM(l) = C(1)*C(1) + C(2)*C(2) + ... + C(N)*C(N) where the operation * denotes multiplication.

Representation of Data Collection and Transfor¬ mation Steps and Finding the Average P: We repeat steps 1 and 2 M times, resulting in successive sums:

SUM(2), SUM(3), ... , SUM(M) for M so large that the average

P = [SUM(l) + SUM(2) + ... + SUM(M)]/M is unchanging or changes very little when an additional value of SUM is found and inserted into the average.

Diagnosing the Coolant State: During an ini¬ tial calibration stage or in the course of research on a particular air conditioner, we determine a value Plow, to be used in this step (below) . Similarly, our research results in a value Phigh. These values are defined as follows: if P < Plow then refrigerant levels are low if Plow < P < Phigh then operation is normal if P > Phigh then something else is wrong with the air conditioner.

The indications appearing in Fig. 3 have the following meanings:

CALIBRATION mode = A logical variable which is "YES" if the calibration button is pressed, and is "NO" if the calibration button is not pressed.

Display = Output via some kind of signal.

ESTIMATION = Average power level for normal operation.

Icond = InPut current signal.

Nmax = Maximum number of current readings to be sampled,

Npts = Present number of current readings in sample.

Pcond = Calculated average power.

START = Inflation step of program - done either at regular time intervals or upon a button being pressed.

Threshold 1 = Lower bound on allowable average power level.

Threshold 2 = Upper bound on allowable average power level. Threshold 3 = Permissible extent of deviation below ESTIMATION, for normal operation.

The program illustrated in Fig. 3 operates as follows: After START the program begins reading the input current signal Icond coming through the sequence: Current Sensor 110, Demodulator 120, Low-Pass Filter 130 and A-to-D convertor 140. The average power Pcond is calcu¬ lated after each readout, until the number of reading Npts reaches the maximum number of readings Nmax.

Now the program checks to see if the calibra¬ tion button is pressed. If the calibration button is pressed (CALIBRATION BUTTONPRESSED = "YES" ) then the calculated average power Pcond is labeled "ESTIMATION" and is written to Memory 7. If it is "NO" then the condi¬ tion to be checked is:

Pcond 4 < THRESHOLD 1 or Pcond >= THRESHOLD 2

If either of these conditions is met then the average power is outside of the working range and we display the message "OTHER FAILURES". If both these expressions are false then another flow of the algorithm is carried out in which we calculate the difference ESTIMATION - THRESHOLD 3 and compare it with average Pcond.

If:

Pcond 4 < ESTIMATION - THRESHOLD 3 then the output message is "NO REFRIGERANT".

If :

Pcond > ESTIMATION - THRESHOLD 3 Then the output message is "NORMAL" signifying normal operation.

The three messages "NO REFRIGERANT", "NORMAL" and "OTHER FAILURES" constitute the possible outputs. Upon outputting one of these , the program reaches com¬ pletion, denoted by "END".

It is appreciated that the particular choice of data transformation described above is one particular example of how an abnormal state of operation is deter- mined and is not meant to be limiting.

Reference is now made to Fig. 4, which is a flow chart illustrating an alternative embodiment of the method performed by the apparatus of Fig 1. The method of Fig. 4 is as follows:

STEP 500: Evaluation of the calibration norm. Evaluation of the norm F during a "calibration" stage when the equipment is known to be operating correctly.

The norm F will generally be a nonlinear function of voltage values v and hence of the current values C. Its evaluation is sequential, not requiring the storage of lengthy sequences of current values, and possibly highly nonlinear. A suitable norm F may be, for example, the Truncated Sum Estimate for N values C sub 1, C sub 2, ... , C sub N given by

N F = SUM {R(alpha, v sub i) abs(v sub i)} i=l where v sub i = voltage corresponding to C sub i

0, for v < alpha R(alpha,v) =

1, for v > alpha

alpha = (v sub MAX)/l.414

for v sub MAX the maximum voltage value among values collected over a large prior sample collected during calibration.

An additional example of the norm F is given by the Histogram Function

N G = SUM {R(alpha,v sub i)} i=l It is appreciated that the examples for the norm F given above are suitable for use with a wide variety of motor driven equipment.

STEP 510: Continuing evaluation of the opera¬ tion norm. Continuing, realtime evaluation of the norm F with progressing time, and continuing comparison of its value with that obtained during the calibration period.

STEP 520: Evaluate performance based on com¬ parison of norms. Determine, based on each comparison of the operation norm with the sorted calibration norm, if there is reason to believe that the performance has degraded.

STEP 530: Signal output device. Send a signal to an output device, as for example a light emitting diode of computer channel, informing it of whether per¬ formance has indeed degraded.

Reference is now made to Figs. 5A - 5F, which together constitute an electronic circuit diagram of an alternative embodiment of a portion of the apparatus of Fig. 1.

Reference is now made to Appendix B, which is a list of the various parts in the circuit diagram of Figs. 5A - 5F. Taken together with Appendix B, the circuit diagram of Figs. 5A - 5F is self-explanatory.

Reference is now made to Appendix C, which is a computer listing of a preferred software implementation of the method of Fig. 4. The program may be loaded and run with the INTEL (U.S.A.) MCS - 51 microcontroller referred to above by loading it into program memory with a standard universal programmer such as, for example, an ALL-03A.

It is appreciated that the software components of the present invention may, if desired, be implemented in ROM (read-only memory) form. The software components may, generally, be implemented in hardware, if desired, using conventional techniques.

It is appreciated that the particular embodi¬ ment described in the Appendices is intended only to provide an extremely detailed disclosure of the present invention and is not intended to be limiting.

It is appreciated that various features of the invention which are, for clarity, described in the con¬ texts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, de¬ scribed in the context of a single embodiment may also be provided separately or in any suitable subcombination.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow:

Item Quantity Reference Part

28 U6 27C256(PLCC) in socket

SN74LS02D

MC74F373DW

LM324D

TL7705ACD

CRYSTAL 16 MHz

APPENDIX C

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1. An apparatus for detecting faults in the work¬ ing of motor driven components of a heating, cooling or dehumidifying unit, comprising a housing in which are located: a) a current sensor which is connectable to the power lead of the motors of the unit, said sensor being connected to b) a demodulator being connected to c) a low pass filter which is connected to d) an A-D converter which is connected to e) a micro controller containing an appropriate algorithm program, which is connected to f) a memory, both the micro controller and the memory being connected to g) an indicating unit; all said units being connected in an appropriate manner one after another.

2. An apparatus according to claim 1, wherein the current sensor is a current transformer.

3. An apparatus according to claim 2, wherein the current transformer is of 20 amp.

4. An apparatus according to claim 1, wherein the current sensor is a magnetic amplifier.

5. An apparatus according to claim 1, wherein the current sensor is a shunt.

6. An apparatus according to any of claims 1 to 5, wherein the demodulator is an active rectifier.

Claims

7. An apparatus according to any of claims 1 to 6, wherein the filter is a 25 Hz cut-off frequency low pass Butterworth filter.

8. An apparatus according to any of claims 1 to 7, wherein the A-D converter has at least 6 bits.

9. An apparatus according to claim 8, wherein the A-D converter has 8 bits.

10. An apparatus according to any of claims 1 to 9, wherein the indicating unit is a display.

11. An apparatus according to any of claims 1 to 9, wherein the indicating unit is an alarm unit.

12. An apparatus according to any of claims 1 to 11, wherein the indicating unit is located within the housing.

13. An apparatus according to any of claims 1 to 11, wherein the indicating unit is located outside the housing.

14. An apparatus according to any of claims 1 to

13, wherein the unit is an air conditioning one unit and the algorithm is programmed to detect insufficient re¬ frigerant pressure.

15. An apparatus according to any of claims 1 to

14, wherein the unit is a chiller and the algorithm is programmed to detect clogging of an air filter.

16. An apparatus according to claims 14 or 15, wherein the algorithm is programmed also to detect one or more additional defaults. 17. A method for the detection of faults in the working of a unit (as herein before defined) which method consists in sending a variable voltage signal being proportional to the time-varying current flowing in the power leads from the motor of the unit, which signal is sent and verified via a demodulator, a low pass filter and an A-D converter, to a micro controller, which is fed with a suitable algorithm program in which the signal is checked against the signal recorded in a memory, and then sent to the display unit.

18. Fault detection apparatus for detecting faults in the working of motor driven equipment comprising: current sensing apparatus connectable to the power input of the motor and producing a current signal; signal correction apparatus receiving as input said current signal and operative to demodulate said current signal, filter said current signal to retain low frequencies thereof, and convert said current signal from analog to digital form and producing a corrected signal; a memory; a controller in operative connection with said memory, receiving said corrected signal and having a calibration state and an operation state and operative, when in the calibration state, to compute the calibration norm of said corrected signal based partly on data con¬ tained in said memory and to store said calibration norm in said memory and operative, when in the operation state, to compute the operation norm of said corrected signal based partly on data contained^' in said memory and to compare said operation norm with said stored calibra¬ tion norm and to produce a function signal indicating the functioning of said motor driven equipment; and an indicating unit receiving as input said function signal and producing an output indication of the functioning of said motor driven equipment.

19. Fault detection apparatus according to claim 18, wherein the current sensing apparatus comprises a current transformer.

20. Fault detection apparatus according to claim 18, wherein the current sensing apparatus comprises a magnetic amplifier.

21. Fault detection apparatus according to claim 18, wherein the current sensing apparatus comprises a shunt.

22. Fault detection apparatus according to any of claims 18 - 21, wherein the demodulating apparatus com¬ prises an active rectifier.

23. Fault detection apparatus according to any of claims 13 - 22, wherein the low pass filter comprises a Butterworth filter.

24. Fault detection apparatus according to any of claims 18 - 23, wherein the A-D conversion apparatus has at least 6 bits.

25. Fault detection apparatus according to claim 24, wherein the A-D conversion apparatus has at least 8 bits.

26. Fault detection apparatus according to any of claims 18 - 25, wherein the motor driven equipment com¬ prises an air conditioning unit and the controller is operative to detect insufficient refrigerant pressure.

27. Fault detection apparatus according to any of claims 18 - 26, wherein the motor driven equipment com¬ prises a chiller and the controller is operative to detect clogging of an air filter.

28. Fault detection apparatus according to any of claims 26 - 27, wherein the controller is also operative to detect at least one additional defect.

29. Fault detection apparatus according to any of claims 18 - 19 wherein the motor driven equipment com¬ prises a heat pump.

30. Fault detection apparatus according to claim 29 wherein the heat pump has a plurality of modes of heating and the controller is operative to detect the mode of heating of the heat pump.

31. Fault detection apparatus according to any of claims 18 - 19 wherein the motor driven equipment com¬ prises a fluid pump.

32. Fault detection apparatus according to claim 31 wherein the controller is operative to detect the rate of flow of the fluid.

33. Fault detection apparatus according to any of claims 31 - 32 wherein the controller is operative to detect faults in the pump.

34. Fault detection apparatus according to any of claims 32 - 33 wherein the controller is also operative to control the operation of the pump.

35. Fault detection apparatus according to any of claims 32 - 34 and also comprising a container being fed by the pump, wherein the controller is operative to detect the level of liquid in the container.

36. Fault detection apparatus according to any of claims 18 - 19 wherein the motor driven equipment com¬ prises a fan.

37. Fault detection apparatus according to any of claims 18 - 19 wherein the motor driven equipment com¬ prises refrigeration equipment.

38. Fault detection apparatus according to claim 37 wherein the refrigeration equipment comprises evaporator coils and wherein the controller is operative to detect the growth of frost on the evaporator coils.

39. Fault detection apparatus according to any of claims 18 - 19 wherein the motor driven equipment com¬ prises a rotating member and wherein the controller is operative to detect the rate of rotation of the rotating member.

40. Fault detection apparatus according to any of claims 18 - 39, wherein the indicating unit comprises a display.

41. Fault detection apparatus according to any of claims 18 - 40, wherein the indicating unit comprises an alarm.

42. A fault detection method for detecting faults in the working of motor driven equipment comprising: sensing the current in the power input of the motor and producing a current signal; demodulating said current signal, filtering said current signal to retain low frequencies thereof, and converting said current signal from analog to digital form and producing a corrected signal; receiving said corrected signal, retrieving at least one stored corrected signal from said memory and comparing said corrected signal with said stored correct¬ ed signal and producing a function signal indicating the functioning of said motor driven equipment; receiving said corrected signal and having a calibration state and an operation state and, when in the calibration state, computing the calibration norm of said corrected signal based partly on stored data and storing said calibration norm and, when in the operation state, computing the operation norm of said corrected signal based partly on stored data and to comparing said opera¬ tion norm with said stored calibration norm and producing a function signal indicating the functioning of said motor driven equipment; and receiving said function signal and producing an output indication of the functioning of said motor driven equipment.