Machine fault detection using vibration signal peak detector

• US 5,895,857 A
• Filed: 04/17/1997
• Issued: 04/20/1999
• Est. Priority Date: 11/08/1995
• Status: Expired due to Term

• Current Assignee: Computational Systems Incorporated (Emerson Electric Company)
• Original Assignee: CSI Technology Incorporated (Emerson Electric Company)
• Inventors: Miller, Wojtek, Vanvoorhis, Brent, Robinson, James C.
• Primary Examiner(s): Oda, Christine K.
• Application Number:
  US08/840,844
• Time in Patent Office: 733 Days
• Field of Search: 73/593, 73/660, 73/602, 73/658, 73/659, 340/683, 340/679, 340/680, 702/35, 702/56, 702/171
• US Class Current: 73/660
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G01N 2291/2696 Wheels, Gears, Bearings
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• CPC Class Codes: G01N 29/449 Statistical methods not provided for in G01N29/4409, e.g. averaging, smoothing and interpolation
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01N 29/48 by amplitude comparison

Abstract

A signal processing device for processing a machine vibration signal includes a peak value detector for determining the peak vibration amplitude values during predetermined sample time periods. In one embodiment, the vibration signal is digitally processed prior to receipt by a digital peak value detector. In another embodiment, analog processing and peak value detection of the vibration signal is employed. The peak values are then made available for further processing. In many situations, the peak values will be associated with mechanical faults which will be detected at periodic rates corresponding to the mechanical component defect frequencies without additional signal enhancement. Further enhancement can be acquired by synchronous averaging the peak values with the speed of a rotating element. A signal representing the speed of a rotating element (target element) may be obtained directly from a speed sensor that is measuring the speed of the target element, or if the target element is inaccessible, a corrected pseudo-speed signal can be calculated from the speed of an accessible rotating element that is linked to the target element. Transformation of synchronous amplitudes to the frequency domain by means of a fast Fourier transform reveals information that can be used to assess whether or not a fault is present in the rotating machine element.

Claims

1. A vibration analyzer for analyzing mechanical vibration produced by a machine to produce vibration analysis information corresponding to possible sources of the mechanical vibration, said analyzer comprising:

a vibration transducer for producing a transducer signal corresponding to the mechanical vibration;

an input circuit for receiving and conditioning the transducer signal to produce a vibration signal corresponding to said transducer signal;

a peak value detector for receiving the vibration signal, detecting the peak amplitude values of the vibration signal during each sample time period to produce a time series of peak vibration amplitudes, and outputting the time series of peak vibration amplitudes for further processing; and

means for receiving the time series of peak vibration amplitudes and transforming said time series of peak vibration amplitudes to the frequency domain to produce peak vibration spectra.

2. The analyzer of claim 1, wherein said input circuit comprises:

an auto ranging amplifier for amplifying the transducer signal according to its strength, producing an amplified analog vibration signal;

a sampling circuit for receiving the amplified analog vibration signal and sampling it at a predetermined rate, producing a digitized vibration signal; and

a rectifier for receiving the digitized vibration signal and digitally full wave rectifying it, producing a digitally rectified digital vibration signal that is provided to said peak value detector as the vibration signal.

3. The analyzer of claim 1 wherein said peak value detector comprises:

first peak hold means for holding the peak amplitude values of the vibration signal during a first sample time period T-Δ

T;

second peak hold means for holding the peak amplitude values of the vibration signal during a second sample time period T+Δ

T;

a first analog switch for receiving said vibration signal and alternately providing the vibration signal to the first peak hold means during time T-Δ

T and to the second peak hold means during time T+Δ

T;

a second analog switch for outputting the peak amplitude value held by the first peak hold means during time period T+Δ

T, and outputting the peak amplitude value held by the second peak hold means during time period T-Δ

T; and

reset means for resetting the first peak hold means at time T-Δ

T, and resetting the second peak hold means at time T.

4. The analyzer of claim 3, further comprising clock means for producing a clock signal, wherein said time periods T-Δ

T and T+Δ

T cumulatively comprise one cycle of said clock signal.

5. The analyzer of claim 3 wherein said first peak hold means comprise:

a first capacitor connected to receive said vibration signal during time period T-Δ

T and hold the peak amplitude value as a first capacitor charge;

a first hold buffer connected to said first capacitor for holding the peak amplitude value as represented by said first capacitor charge; and

a third analog switch having an open position and a closed position, connected to receive said vibration signal to pass the vibration signal to said first capacitor when said third analog switch is in the closed position.

6. The analyzer of claim 5 wherein said second peak hold means comprise:

a second capacitor connected to receive said vibration signal during time period T+Δ

T and hold the peak amplitude value as a second capacitor charge;

a second hold buffer connected to said second capacitor for holding the peak amplitude value as represented by said second capacitor charge; and

a fourth analog switch having an open position and a closed position, connected to receive said vibration signal and to pass the vibration signal to said second capacitor when said fourth analog switch is in the closed position.

7. A fault detection apparatus for receiving machine vibration and speed signals, processing said vibration signal to produce a processed vibration signal, and synchronously averaging the processed vibration signals at the speed indicated by the speed signal to determine the presence of a fault in a rotating element of the machine where the rotating element is rotating at the speed indicated by the speed signal, the apparatus comprising:

a peak value detector for receiving the machine vibration signal, sampling said vibration signal during predetermined sample time periods, and detecting the peak amplitude values of the vibration signal during the sample time periods, producing a time series of peak amplitude values;

clock means for generating at least one clock signal, said peak value detector being responsive to said at least one clock signal to set the length of said sample time periods; and

means for synchronously averaging said time series of peak amplitude values at the speed of said rotating element, producing a time series of synchronously averaged amplitude values.

8. The apparatus of claim 7, further comprising:

an auto ranging amplifier for amplifying the vibration signal according to its strength, producing an amplified vibration signal;

a sampling circuit for receiving the amplified vibration signal and sampling it at a predetermined rate, producing a digitized vibration signal; and

a rectifier for receiving the digitized vibration signal and full wave rectifying it, producing a rectified vibration signal that is provided to said peak value detector.

9. The apparatus of claim 7 wherein said peak value detector comprises:

first peak hold means for holding the peak amplitude value of the vibration signal during a first sample time period T-Δ

T;

second peak hold means for holding the peak amplitude value of the vibration signal during a second sample time period T+Δ

T;

a first analog switch for receiving said rectified vibration signal and alternately providing the vibration signal to the first peak hold means during time T-Δ

T and to the second peak hold means during time T+Δ

T;

a second analog switch for providing to the means for synchronously averaging the peak amplitude held by the first peak hold means during time period T+Δ

T, and providing to the means for synchronously averaging the peak amplitude held by the second peak hold means during time period T-Δ

T; and

reset means for resetting the first peak hold means at time T-Δ

T, and resetting the second peak hold means at time T.

10. The apparatus of claim 9 wherein said time periods T-Δ

T and T+Δ

T cumulatively comprise one cycle of said clock signal.

11. The apparatus of claim 7, further comprising a rectifier for rectifying the vibration signal.

12. The apparatus of claim 7, further comprising a filter for filtering selected frequencies from said vibration signal.

13. The apparatus of claim 7, further comprising an amplifier for amplifying said vibration signal.

14. The apparatus of claim 7, further comprising a pseudo-speed circuit for adjusting the speed signal to reduce errors and to compensate for a rotation ratio between an accessible rotating machine element and a target rotating machine element, producing a pseudo-speed signal corresponding to the speed of the target rotating machine element.

15. The apparatus of claim 14 wherein said pseudo-speed circuit comprises:

a filter for eliminating noise from the speed signal, producing a filtered speed signal;

a computer for receiving the filtered speed signal and adjusting the filtered speed signal to reduce errors and to compensate for said rotation ratio, producing a pseudo-speed signal; and

an output buffer for holding the pseudo-speed signal so that it can be provided to said means for synchronously averaging.

16. The apparatus of claim 7, further comprising fast Fourier transform means for transforming said time series of synchronously averaged amplitude values to the frequency domain.

17. A fault detection system for detecting mechanical faults of machines having one or more rotating elements that generate mechanical vibrations while rotating, including an accessible element and a target element, the system comprising:

a vibration sensor for sensing vibrations generated by at least a target rotating machine element during machine operation, producing a vibration signal containing a plurality of amplitudes and frequencies;

a peak value detector for sampling said vibration signal during predetermined sample time periods and detecting the peak amplitude value of the vibration signal during the sample time periods, producing a time series of peak amplitude values;

clock means for generating at least one clock signal, said peak value detector being responsive to said at least one clock signal to set the length of said sample time periods;

a speed sensor for sensing the speed of an accessible rotating machine element, producing a speed signal;

a pseudo-speed circuit for adjusting the speed signal to reduce errors and to compensate for a rotation ratio between the accessible rotating machine element and the target rotating machine element, producing a pseudo-speed signal; and

means for reading said time series of peak amplitude values, receiving said pseudo-speed signal, and synchronously averaging said time series of peak amplitude values at the speed indicated by said pseudo-speed signal, producing a time series of synchronously averaged amplitude values corresponding to possible sources of the mechanical vibration.

18. The system of claim 17, further comprising:

an auto ranging amplifier for amplifying the vibration signal according to its strength, producing an amplified vibration signal;

a sampling circuit for receiving the amplified vibration signal and sampling it at a predetermined rate, producing a digitized vibration signal; and

a rectifier for receiving the digitized vibration signal and full wave rectifying it, producing a rectified vibration signal that is provided to said peak value detector.

19. The system of claim 17 wherein said peak value detector comprises:

first peak hold means for holding the peak amplitude value of the vibration signal during a first sample time period T-Δ

T;

second peak hold means for holding the peak amplitude value of the vibration signal during a second sample time period T+Δ

T;

a first analog switch for receiving said vibration signal and alternately providing the vibration signal to the first peak hold means during time T-Δ

T and to the second peak hold means during time T+Δ

T;

a second analog switch for providing to the means for reading the peak amplitude value held by the first peak hold means during time period T+Δ

T, and providing to the means for reading the peak amplitude value held by the second peak hold means during time period T-Δ

T; and

reset means for resetting the first peak hold means at time T-Δ

T, and resetting the second peak hold means at time T.

20. The system of claim 19 wherein said time periods T-Δ

T and T+Δ

T cumulatively comprise one cycle of said clock signal.

21. The system of claim 17, further comprising a rectifier for rectifying the vibration signal.

22. The system of claim 17, further comprising a filter for filtering selected frequencies from said vibration signal.

23. The system of claim 17, further comprising an amplifier for amplifying said vibration signal.

24. The fault detection system of claim 17 wherein said speed sensor comprises a tachometer.

25. The fault detection system of claim 17 wherein said pseudo-speed circuit comprises:

a filter for eliminating noise from the speed signal, producing a filtered speed signal;

a microcomputer for receiving the filtered speed signal and adjusting the filtered speed signal to reduce errors and to compensate for said rotation ratio, producing a pseudo-speed signal; and

an output buffer for holding the pseudo-speed signal so that it can be read by a peripheral device.

26. A method of processing, for further analysis, a vibration signal generated by a vibration sensor attached to a machine, the method comprising the steps of:

determining the peak amplitude value of the vibration signal with a peak value detector during sample time periods, producing a time series of peak vibration amplitudes;

transforming said time series of peak vibration amplitudes to the frequency domain to produce peak vibration spectra; and

outputting the peak vibration spectra for further processing.

27. The method of claim 26, further comprising the steps of:

auto range amplifying the vibration signal according to the strength of the vibration signal, producing an amplified vibration signal;

sampling the amplified vibration signal at a predetermined rate to produce a digitized vibration signal; and

rectifying the digitized vibration signal, producing a rectified digital vibration signal that is provided to the peak value detector.

30. The method of claim 26, further comprising the step of analyzing said peak vibration spectra for possible machine faults.

28. A method of detecting faults in a machine having rotating machine elements, said elements including at least an accessible element and a target element, said method comprising the steps of:

producing a vibration signal containing amplitudes and frequencies, said vibration signal being representative of vibrations generated by at least the target rotating machine element;

sampling said vibration signal during predetermined sample periods of time;

determining the peak amplitude value of said vibration signal during each sample period of time to produce a time series of peak amplitude values;

producing a speed signal with a speed sensor, said speed signal being representative of the speed of the target element as sensed by said speed sensor;

synchronously averaging said time series of peak amplitude values at the speed indicated by said speed signal, producing a time series of synchronously averaged amplitude values; and

transforming the time series of synchronously averaged amplitude values to the frequency domain to determine the presence of a fault in the target element.

29. The method of claim 28, further comprising the step of adjusting the speed signal to reduce errors and to compensate for a rotation ratio between the first rotating machine element and the target rotating machine element, producing a pseudo-speed signal representing the speed of the target element.