Method for analysing vibration / noise from a running compressor

Abstract

The present invention relates to a method for detecting and analysing a vibration or noise signal generated by a running compressor, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor, the method comprising the steps of detecting the vibration or noise signal in the time domain; translating at least part of the detected vibration or noise signal to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor; calculating a signal power value by summing selected signal values in the frequency domain; calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain; calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and stopping the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times. The present invention further relates to the compressor assembly and a signal processor for performing the method.

Description

[0001] METHOD FOR ANALYSING VIBRATION / NOISE FROM A RUNNING COMPRESSOR

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method for detecting and analysing a vibration or noise signal generated by a running compressor, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor. Stopping of the running compressor may eventually occur. The present invention further relates to a signal processor configured for performing the method, and to a compressor assembly.

[0004] BACKGROUND OF THE INVENTION

[0005] Monitoring and controlling a running compressor in a noiseless and vibrationless manner may be a rather complicated task in that vibration sensors may have to be secured to or integrated with the running compressor.

[0006] Vibration sensors secured to compressors may potentially fall off, whereas integrated vibration sensors may increase the overall production cost of compressors.

[0007] Thus, there is a need for a method that allows easy and reliable monitoring and control of compressors so that they may be operated in an essentially noiseless, vibrationless and safe manner.

[0008] It may be seen as an object of embodiments of the present invention to provide an easy way of monitoring a running compressor.

[0009] It may be seen as a further object of embodiments of the present invention to stop a running compressor if the monitoring of the running compressor reveals reasons to do so.

[0010] SUMMARY OF THE INVENTION To comply with the above objects the present invention relates, in a first aspect, to a method for detecting and analysing a vibration or noise signal generated by a running compressor, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor, the method comprising the steps of

[0011] - detecting the vibration or noise signal in the time domain,

[0012] - translating at least part of the detected vibration or noise signal to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor,

[0013] - calculating a signal power value by summing selected signal values in the frequency domain,

[0014] - calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain,

[0015] - calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and

[0016] - altering the operation of the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times.

[0017] Thus, the first aspect of the present invention relates to a method for detecting and analysing a vibration or noise signal generated by a running compressor, i.e. an operating compressor. The vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor. The compressor element may be any element of the compressor including the motor of the compressor, the pump of the compressor etc. The motor of the compressor may be a brushless DC motor / synchronous permanent magnet motor, whereas the pump of the compressor may be a piston type compressor pump which is operatively connected to the motor. When deciding whether or not to alter the operation of the compressor, the harmonics-to-signal ratio from each sub-harmonic may be compared to a harmonic-to-signal ratio of the compressor's running frequency harmonics. Thus, the comparison is a unit-free ratio to ratio comparison.

[0018] The comparison may be repeated until a desired detection accuracy is achieved. The 1 / 2, 1 / 3 and the 1 / 4 harmonics vs. the running frequency harmonics (reference) may be used. However, the 1 / 5, 1 / 7 and even further harmonics may also be used.

[0019] Altering the operation of the compressor may involve changing the running speed of the compressor, i.e. the rotational speed of the compressor, such as stopping the compressor, i.e. bring the compressor to a complete stillstand.

[0020] The vibration or noise signal in the time domain may be detected using in principle any suitable transducer or sensor, such as a MEMS vibration transducer and / or a MEMS acceleration transducer and / or a MEMS microphone. The vibration or noise signal may be detected at a position outside the compressor housing.

[0021] A signal processor may be provided for translating at least part of the detected vibration or noise signal to the frequency domain, calculating the signal power value, calculating the harmonics power value and calculating the harmonics-to- signal ratio. The signal processor may be an embedded signal processor.

[0022] The translation of at least part of the detected vibration or noise signal to the frequency domain may be performed using Fast Fourier Transform (FFT). It should though be noted that other translation schemes might also be applicable. The FFT translation of the vibration or noise signal from the time domain to the frequency domain will reveal, in the frequency domain, at least the running frequency (fundamental frequency) as well as at least one sub-harmonics thereof, such as the 1 / 2, 1 / 3, 1 / 4, 1 / 7 or other sub-multiple harmonics.

[0023] Preferably, the step of calculating the signal power value is performed by summing all signal values in the frequency domain, i.e. summing the signal values of the frequency spectrum comprising the running frequency and the signal values of the selected sub-harmonics within a given frequency range. This given frequency range may be the full half-band spectrum. For example, if the signal is sampled each 5 milliseconds, the half-band frequency bins goes from 0 to 100 Hz. In another example DC (0 Hz) may be excluded. Here the given frequency range may be from the second frequency bin and upwards, such as to 100 Hz.

[0024] The step of calculating the harmonics power value may be performed by summing selected signal values of one or more selected harmonics in the frequency domain within a given frequency range. The selected harmonics in the frequency domain may comprises the 1 / 2, 1 / 3, 1 / 4 and / or the 1 / 7 sub-multiple harmonics. However, other sub-multiple harmonics may also be selected.

[0025] In relation to the harmonics-to-signal ratio the predetermined amount and / or the predetermined number of times are preferably user controllable values, i.e. the predetermined amount and / or the predetermined number is / are provided by a user. These user controllable values may be selected once (static) or they may be updated on-the-fly (dynamic) via some sort of computer interface.

[0026] According to the first aspect, when the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor by the predetermined amount, a detection counter value is increased by one. The predetermined amount may be less than 50%, such as less than 40%, such as less than 30%. Thus, every time the ratio of the running frequency harmonics of the compressor is exceeded by the predetermined amount an integer is added to the detection counter value.

[0027] The compressor may be stopped when the detection counter value exceeds the predetermined number of times. Alternative the speed of the compressor may be altered or changed when the detection counter value exceeds the predetermined number of times. The predetermined number of times may be a variable or a fixed value and it may be in the range of 1-5 depending on for example sensitivity. Thus, the detection counter may be limited to 1 in case of a highly sensitive system where immediate action is desired. At the other end of the scale a detection counter of for example 4 or 5 may be used in order to provide a system being robust against false detections, such as harmonics from cars with combustion engines. The predetermined number of times may also be adjusted on-the-fly by the user, i.e. a user controllable value.

[0028] A user controllable predetermined timer timeout, i.e. a user controllable time range, may be associated with the detection counter value. The detection counter value may be set to zero if the user controllable predetermined timer timeout is exceeded when determining whether the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor with a predetermined amount. The user controllable predetermined timer timeout may be in the range of a few hundred milliseconds to several seconds. Thus, a timeout may be for example 400 milliseconds which reflects the minimum time to compute or run the algorithm. Moreover, detections should occur in rapid successions to be acknowledged. A timeout of 3 or 4 seconds may be applied in systems being more sensitive to sparse detections.

[0029] If the harmonics-to-signal ratio does not exceed the ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times the operation of the compressor is not altered.

[0030] In a second aspect the present invention relates to a compressor assembly comprising a compressor and an arrangement for detecting and analysing a vibration or noise signal generated by the compressor when running, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor, and wherein the arrangement for detecting and analysing the vibration or noise signal generated by the compressor comprises

[0031] - a transducer for detecting the vibration or noise signal in the time domain, a signal processor configured for o translating at least part of the detected vibration or noise signal to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor, o calculating a signal power value by summing selected signal values in the frequency domain, o calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain, o calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and o altering the operation of the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor with a predetermined amount a predetermined number of times.

[0032] Thus, according to the second aspect a compressor assembly suitable for performing the method of the first aspect is provided. The signal processing steps are performed by the signal processor. The signal processor may be an embedded signal processor.

[0033] Again, when deciding whether or not to alter the operation of the compressor, the harmonics-to-signal ratio from each sub-harmonic may be compared to a harmonic-to-signal ratio of the compressor's running frequency harmonics. Thus, the comparison is a unit-free ratio to ratio comparison. The comparison may be repeated until a desired detection accuracy is achieved. The 1 / 2, 1 / 3 and the 1 / 4 harmonics vs. the running frequency harmonics (reference) may be used. However, the 1 / 5, 1 / 7 and even further harmonics may also be used.

[0034] The compressor assembly according to the second aspect may form part of a cooling device of for example a vehicle, such as an electric vehicle.

[0035] Similar to the first aspect, the transducer for detecting the vibration or noise signal in the time domain may in principle be any suitable transducer or sensor, such as a MEMS vibration transducer and / or a MEMS acceleration transducer and / or a MEMS microphone. The vibration or noise signal may be detected at a position outside the compressor housing.

[0036] Moreover, the signal processor is provided for translating at least part of the detected vibration or noise signal to the frequency domain, calculating the signal power value, calculating the harmonics power value and calculating the harmonics-to-signal ratio. With respect to the implementation of the various method steps reference is made to the disclosure of the first aspect of the present invention.

[0037] As already mentioned, altering the operation of the compressor may involve changing the running speed of the compressor, i.e. the rotational speed of the compressor, such as stopping the compressor, i.e. bring the compressor to a complete stillstand.

[0038] If the harmonics-to-signal ratio does not exceed the ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times the operation of the compressor is not altered.

[0039] The compressor element may comprise a motor, such as a brushless DC motor / synchronous permanent magnet motor and / or a piston type compressor pump operatively connected to the motor.

[0040] In a third aspect the present invention relates to a signal processor for a compressor assembly comprising a compressor, the signal processor being configured for analysing a vibration or noise signal generated by the compressor when running, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor, and wherein the signal processor is configured for

[0041] - translating at least part of a detected vibration or noise signal in the time domain to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor, calculating a signal power value by summing selected signal values in the frequency domain,

[0042] - calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain,

[0043] - calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and

[0044] - generating an altering signal for altering the operation of the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor with a predetermined amount a predetermined number of times.

[0045] Thus, according to the third aspect a signal processor for performing the method of the first aspect is provided. The signal processor may form an embedded system.

[0046] The signal processor may form part of a compressor assembly also comprising a motor, such as a brushless DC motor / synchronous permanent magnet motor, and a piston type compressor pump operatively connected to the motor. Moreover, the compressor assembly may comprise electronics for driving the motor, and an appropriate transducer for detecting the vibration or noise signal in the time domain. The vibration or noise signal in the time domain may be detected using a MEMS vibration transducer and / or a MEMS acceleration transducer and / or a MEMS microphone. Again, when deciding whether or not to alter the operation of the compressor, the harmonics-to-signal ratio from each sub-harmonic may be compared to a harmonic-to-signal ratio of the compressor's running frequency harmonics. Thus, the comparison is a unit-free ratio to ratio comparison. The comparison may be repeated until a desired detection accuracy is achieved. The 1 / 2, 1 / 3 and the 1 / 4 harmonics vs. the running frequency harmonics (reference) may be used. However, the 1 / 5, 1 / 7 and even further harmonics may also be used. In general, the various aspects of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and / or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0047] BRIEF DESCRIPTION OF THE INVENTION

[0048] The present invention will now be described in further details with reference to the accompanying figures where

[0049] Fig. 1 shows an example of a frequency domain spectrum of a running / operating compressor,

[0050] Fig. 2 shows how to configure a filter mask in order to select a given subharmonic,

[0051] Fig. 3 shows a flowchart of the method according to the present invention, and

[0052] Fig. 4 shows the methods steps with respect to the harmonics-to-signal ratio in more details.

[0053] DETAILED DESCRIPTION OF THE INVENTION

[0054] As already mentioned, the present invention relates to a method for detecting and analysing a vibration or noise signal generated by a running / operating compressor. The vibration or noise signal from the running / operating compressor originates from collisions between a compressor element and a housing of the compressor. The compressor element may, as already mentioned, be any element of the compressor including the motor of the compressor, the pump of the compressor etc.

[0055] The motor of the compressor may be a brushless DC motor / synchronous permanent magnet motor, whereas the pump of the compressor may be a piston type compressor pump which is operatively connected to the motor. Referring now to Fig. 1 an example of a frequency domain spectrum is shown. In Fig. 1 the running frequency corresponds to the 50 Hz component (1), whereas the 25 Hz and 75 Hz frequency components (2, 3) correspond to unwanted subharmonics originating from collisions between a compressor element and a housing of the compressor. The frequency spectrum of Fig. 1 has already been translated from the time domain using for example FFT.

[0056] It should be noted that further sub-harmonics could potentially also be present as disclosed elsewhere in the application. In Fig. 1 though only a single subharmonics (1 / 2) is depicted for simplicity reasons.

[0057] According to the present invention a signal power value is calculated by summing selected signal values in the frequency domain. In the situation depicted in Fig. 1 preferably all signal values in the frequency domain are selected and thus summed.

[0058] Also according to the present invention a harmonics power value is calculated by summing selected signal values of one or more selected harmonics in the frequency domain. In the situation depicted in Fig. 1 the signal values of the 1 / 2 sub-harmonics are selected and thus summed.

[0059] Selecting signal values of one or more selected harmonics in the frequency domain may be provided by proper filtering of the frequency domain spectrum, such as applying a triangular shaped filter mask to the frequency domain spectrum of Fig. 1 that equals unity (100%) at 25 Hz and 75 Hz and equals zero (0%) at 50 Hz, cf. the dashed lines in Fig. 2. It should though be noted that other types of filter masks may also be applicable. In addition, a plurality of filter masks may be applied, such as one filter mask for each sub-harmonics.

[0060] Finally, a harmonics-to-signal ratio is calculated by dividing the harmonics power value with the signal power value. If the harmonics-to-signal ratio exceeds the running frequency of the compressor (50 Hz in Fig. 1) by a predetermined amount a predetermined number of times the operating condition of the compressor is altered, i.e. the speed of rotation of the compressor is altered, such as stopped. Preferably, the predetermined amount and / or the predetermined number of times are user controllable values, i.e. the predetermined amount and / or the predetermined number is / are provided by a user.

[0061] As already discussed, when the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor by the predetermined amount, a detection counter value is increased by one. The predetermined amount may be less than 50%, such as less than 40%, such as less than 30%. Thus, whenever the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor by the predetermined amount an integer is added to the detection counter value.

[0062] In terms of operation the compressor speed may be altered, such as stopped, when the detection counter value exceeds the predetermined number of times. The predetermined number of times may be a variable or a fixed value and it may be in the range of 1-5 depending on for example sensitivity. Thus, the detection counter may be limited to 1 if a highly sensitive system where immediate action is desired. At the other end of the scale a detection counter of for example 4 or 5 may be used in order to provide a system being robust against false detections, such as harmonics from cars with combustion engines. The predetermined number of times may also be adjusted on-the-fly by the user, i.e. a user controllable value.

[0063] As already discussed a user controllable predetermined timer timeout, i.e. a user controllable time range, may be associated with the detection counter value. The detection counter value may be set to zero in case the user controllable predetermined timer timeout is exceeded when determining whether the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor with a predetermined amount. The user controllable predetermined timer timeout may be in the range of a few hundred milliseconds to several seconds. Thus, a timeout may be for example 400 milliseconds which reflects the minimum time to compute or run the algorithm. Moreover, detections should occur in rapid successions to be acknowledged. A timeout of 3 or 4 seconds may be applied in systems being more sensitive to sparse detections. The present invention also relates to a compressor assembly suitable for performing the above method. The signal processing steps are performed by a suitable signal processor, and the compressor assembly may form part of a cooling device of for example a vehicle, such as an electric vehicle.

[0064] The compressor assembly comprises a transducer for detecting a vibration or noise signal in the time domain. This transducer may in principle be any suitable transducer or sensor, such as a MEMS vibration transducer and / or a MEMS acceleration transducer and / or a MEMS microphone. The vibration or noise signal may be detected at a position outside the compressor housing.

[0065] The detected vibration or noise signal originates from collisions between a compressor element and a housing of the compressor, where the compressor element may comprise a motor, such as a brushless DC motor / synchronous permanent magnet motor and / or a piston type compressor pump operatively connected to the motor.

[0066] Moreover, a suitable signal processor is provided for translating at least part of the detected vibration or noise signal from the time domains to the frequency domain, calculating the signal power value, calculating the harmonics power value and calculating the harmonics-to-signal ratio. The signal processor may be an embedded signal processor.

[0067] In response to the signal processor's calculations the operation of the compressor may be altered. As already mentioned, altering the operation of the compressor may involve changing the running speed of the compressor, i.e. the rotational speed of the compressor, such as stopping the compressor, i.e. bring the compressor to a complete stillstand.

[0068] A simplified flowchart of the method according to the present invention is depicted in Fig. 3. As seen in Fig. 3 and as already discussed above the method comprises the following steps: a) detecting a vibration or noise signal from a compressor in the time domain, b) translating at least part of the detected vibration or noise signal to the frequency domain using for example FFT, c) calculating a signal power value by summing for example all signal values in the frequency domain, d) calculating a harmonics power value by summing signal values of one or more selected harmonics in the frequency domain, e) calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and f) altering the operation of the compressor, such as stopping the compressor, if the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times.

[0069] The individual method steps have already been disclosed above, but in order to complete method step f) it is noted that altering the operation of the compressor may involve changing the rotational speed of the compressor, such as bringing the compressor to a complete stillstand. It is also noted that the predetermined amount and / or the predetermined number of times are preferably user controllable values, i.e. the predetermined amount and / or the predetermined number is / are provided by a user.

[0070] If method step f) is not complied with, i.e. if the harmonics-to-signal ratio does not exceed the ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times, the operation of the compressor is not altered. When deciding whether or not to alter the operation of the compressor, the harmonics-to-signal ratio from each sub-harmonic may be compared to a harmonic-to-signal ratio of the compressor's running frequency harmonics. Thus, the comparison is a unit-free ratio to ratio comparison. The comparison may be repeated until a desired detection accuracy is achieved. The 1 / 2, 1 / 3 and the1 / 4 harmonics vs. the running frequency harmonics (reference) may be used. However, the 1 / 5, 1 / 7 and even further harmonics may also be used. The method step f) of Fig. 3 is illustrated in Fig. 4 where the decisions with respect to the predetermined amount and the predetermined number of times are shown. Firstly, if the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor by the predetermined amount an integer is added to a detection counter value. Secondly, if the detection counter value exceeds the predetermined number of times the operation of the compressor is altered, such as stopped, in order to avoid collisions between a compressor element and a housing of the compressor.

[0071] Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary, the embodiments are merely intended to explain the wording of the appended claims, without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.

Claims

CLAIMS1. A method for detecting and analysing a vibration or noise signal generated by a running compressor, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor, the method comprising the steps of- detecting the vibration or noise signal in the time domain,- translating at least part of the detected vibration or noise signal to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor,- calculating a signal power value by summing selected signal values in the frequency domain,- calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain,- calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and- altering the operation of the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor by a predetermined amount a predetermined number of times.

2. A method according to claim 1, wherein the vibration or noise signal in the time domain is detected using a MEMS vibration transducer and / or a MEMS acceleration transducer and / or a MEMS microphone.

3. A method according to claim 1 or 2, wherein the translation of at least part of the detected vibration or noise signal to the frequency domain is performed using FFT.

4. A method according to any of the preceding claims, wherein the step of calculating the signal power value is performed by summing all signal values in the frequency domain.

5. A method according to any of the preceding claims, wherein the selected harmonics in the frequency domain comprises the 1 / 2, 1 / 3 and / or the 1 / 4 submultiple harmonics.

6. A method according to any of the preceding claims, wherein the predetermined amount and / or the predetermined number of times are user controllable values.

7. A method according to any of the preceding claims, wherein, when the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor by a predetermined amount, a detection counter value is increased by one.

8. A method according to claim 7, wherein the compressor is stopped when the detection counter value exceeds the predetermined number of times.

9. A method according to claims 7 or 8, wherein the detection counter value is set to zero if a user controllable predetermined timer timeout is exceeded when determining whether the harmonics-to-signal ratio exceeds the ratio of the running frequency harmonics of the compressor with a predetermined amount.

10. A compressor assembly comprising a compressor and an arrangement for detecting and analysing a vibration or noise signal generated by the compressor when running, wherein the vibration or noise signal from the running compressor originates from collisions between a compressor element and a housing of the compressor, and wherein the arrangement for detecting and analysing the vibration or noise signal generated by the compressor comprises- a transducer for detecting the vibration or noise signal in the time domain, a signal processor configured foro translating at least part of the detected vibration or noise signal to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor, o calculating a signal power value by summing selected signal values in the frequency domain, o calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain, o calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and o altering the operation of the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor with a predetermined amount a predetermined number of times.

11. A compressor assembly according to claim 10, wherein the transducer for detecting the vibration or noise signal in the time domain comprises a MEMS vibration transducer and / or a MEMS acceleration transducer and / or a MEMS microphone.

12. A compressor assembly according to claims 10 or 11, wherein the signal processor forms an embedded system.

13. A compressor assembly according to any of claims 10-12, wherein the compressor element comprises a motor, such as a brushless DC motor / synchronous permanent magnet motor and / or a piston type compressor pump operatively connected to the motor.

14. A signal processor for a compressor assembly comprising a compressor, the signal processor being configured for analysing a vibration or noise signal generated by the compressor when running, wherein the vibration or noise signal from the running compressor originates from collisions between acompressor element and a housing of the compressor, and wherein the signal processor is configured for- translating at least part of a detected vibration or noise signal in the time domain to the frequency domain, wherein the frequency domain comprises a running frequency of the compressor,- calculating a signal power value by summing selected signal values in the frequency domain,- calculating a harmonics power value by summing selected signal values of one or more selected harmonics in the frequency domain,- calculating a harmonics-to-signal ratio by dividing the harmonics power value with the signal power value, and- generating an altering signal for altering the operation of the compressor if the harmonics-to-signal ratio exceeds a ratio of the running frequency harmonics of the compressor with a predetermined amount a predetermined number of times.

15. A signal processor according to claim 14, wherein the signal processor forms an embedded system.

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