System and methodology for vibration analysis and condition monitoring

• US 20050209814A1
• Filed: 01/12/2005
• Published: 09/22/2005
• Est. Priority Date: 06/07/2002
• Status: Active Grant

• Current Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Original Assignee: ExxonMobil Research & Engineering Company (Exxon Mobil Corporation)
• Inventors: Song, Limin
• Granted Patent: US 7,133,801 B2
• Time in Patent Office: Days
• US Class Current: 702/145
• CPC Class Codes: G01P 3/44 for measuring angular speed G01P3/56 takes precedence

Abstract

A system and methodology for the continuous condition monitoring of rotating equipment. The present invention comprises a method that employs adaptive signal processing techniques to determine the RPM of a rotating machine from the time-based vibration data. According to a preferred embodiment of the present invention, RPM is determined based upon the input of a digitized time-based sample sequence of vibration data acquired directly from a vibration transducer mounted on the machine for on-line real-time measurement of the machine RPM. Alternatively, the input to the “virtual RPM sensor” could come from a database or file where the sample sequences of the vibration signal are stored for off-line measurement of the machine RPM. Once RPM is determined, online vibration analysis for a given RPM or set of RPMs may be performed. The present invention extracts characteristic vibration features from vibration data and uses these extracted values to provide condition detection and diagnoses of machine faults.

Claims

1. A method for monitoring machine faults comprising the steps of:

(a) determining one or more base vibration features associated with said machine;

(b) acquiring time-based vibration data samples from a vibration transducer in physical contact with said machine;

(c) determining a machine operating speed estimate for said machine using a continuous vibration model;

(d) acquiring vibration data for said machine occurring at said machine operating speed;

(e) determining whether one or more faults exists within said machine based upon a comparison of said base vibration features with said vibration data occurring at said machine operating speed.

2. The method of claim 1 wherein said determination of or absence of one or more faults is reported to an operator on a periodic basis.

3. The method of claim 1 wherein said machine speed is reported to an operator on a periodic basis.

4. The method of claim 1 wherein said base vibration features comprise vibration features at a plurality of machine speeds.

5. The method of claim 4 wherein said step of determining whether one or more faults exists comprises a comparison of base vibration features against vibration data at a plurality of machine speeds.

6. The method of claim 1 wherein said step of determining said one or more base features associated with a machine further comprises the steps of determining symptom frequencies and symptom levels associated with said machine.

7. The method of claim 1 wherein said step of determining machine speed further comprises the steps of:

(a) selecting a discrete range of operating speeds through which to conduct a search;

(b) dividing the time-based vibration data sample into a plurality of sub-records of sample length P;

(c) obtaining the coefficients of a digital comb filter based upon P;

(d) convoluting the time-based vibration data samples using the digital comb filter in the time-domain;

(e) computing the total vibration power and the coherent vibration power;

(f) computing a vibration power error function;

(g) selecting the optimal P that minimizes the error function by comparing the error functions of all sub-record lengths within said selected discrete range of operating speeds; and

(h) estimating the machine speed RPM based upon said selected optimal P.

8. The method of claim 7 wherein the step of determining machine operating speed further comprises the steps of:

(i) selecting a machine speed step length for searching RPM;

(j) selecting a search range of machine speed based on the result of an optimal P obtained through the said estimating step;

(k) using a continuous vibration model of K'"'"'s vibration harmonics to represent the coherent vibration, in which each harmonic is a vibration component with a frequency as a multiple of RPM, and the number of harmonics are selected to include all possible vibration components in the filtered vibration samples to be processed;

(l) using a DFT to obtain the coefficients of said continuous vibration model from the filtered time-based vibration data samples;

(m) computing the coherent vibration power from said continuous vibration model;

(n) computing the error function; and

obtaining a machine operating speed measurement that minimizes the cost function.

9. A method for monitoring machine faults comprising the steps of:

acquiring time-based vibration data samples associated with said machine;

using said time-based vibration data samples to extract a current RPM value for said machine;

extracting vibration features corresponding to said extracted RPM value for said machine;

measuring the degree of machine fault symptoms based upon said extracted vibration features and said time-based vibration data samples.

10. The method of claim 9 further including the step of performing condition diagnosis for said machine based upon said degree of machine fault symptoms.

11. The method of claim 9 wherein said vibration data is measured at ordered multiples of machine RPM.

12. The method of claim 9 wherein said vibration data is measured at non-ordered multiples of machine RPM.

13. The method of claim 9 wherein said monitored machine fault is a shaft imbalance.

14. The method of claim 9 wherein said monitored machine fault is a bearing problem.

15. A system for detecting faults within a machine comprising:

(a) means for determining one or more base vibration features associated with said machine;

(b) means for acquiring time-based vibration data samples from a vibration transducer in physical contact with said machine;

(c) means for determining a machine operating speed estimate for said machine using a continuous vibration model;

(d) means for acquiring vibration data for said machine occurring at said machine operating speed; and

(e) means for determining whether one or more faults exists within said machine based upon a comparison of said base vibration features with said vibration data occurring at said machine operating speed.

16. The system of claim 15 wherein said means for determining a machine operating speed comprises:

(a) means for selecting a discrete range of operating speeds through which to conduct a search;

(b) means for dividing said time-based vibration data sample into a plurality of sub-records of sample length P;

(c) means for obtaining the coefficients of a digital comb filter based upon P;

(d) means for convoluting the time-based vibration data samples using the digital comb filter in the time-domain;

(e) means for computing the total vibration power and the coherent vibration power;

(f) means for computing a vibration power error function;

(g) means for selecting the optimal P that minimizes the error function by comparing the error functions of all sub-record lengths within said selected discrete range of operating speeds; and

(h) means for estimating the machine speed RPM based upon said selected optimal P.

17. The system of claim 15 wherein said detected faults are reported to an operator on a periodic basis.

18. The system of claim 15 wherein said machine speed is reported to an operator on a periodic basis.

19. The system of claim 15 wherein said base vibration features comprise vibration features at a plurality of machine speeds.

20. The system of claim 15 wherein said machine is shut down in the presence of one or more detected faults.