METHOD AND APPARATUS FOR MONITORING AND ANALYZING VIBRATIONS IN ROTARY MACHINES

• US 20120035885A1
• Filed: 02/17/2010
• Published: 02/09/2012
• Est. Priority Date: 02/18/2009
• Status: Active Grant

• Current Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Original Assignee: Optimized Systems and Solutions Ltd (Rolls-Royce Holdings Plc)
• Inventors: Tarassenko, Lionel, King, Dennis, Clifton, David A., King, Steven P., Ault, David J.
• Granted Patent: US 9,874,472 B2
• Time in Patent Office: Days
• US Class Current: 702/183
• CPC Class Codes: G01H 1/006 of the rotor of turbo machines
• CPC Class Codes: G01H 3/08 Analysing frequencies present in complex vibrations, e.g. comparing harmonics present acoustic presence detection G01V1/001
• CPC Class Codes: G01M 13/028 Acoustic or vibration analysis
• CPC Class Codes: G01M 13/045 Acoustic or vibration analysis
• CPC Class Codes: G01M 15/12 by monitoring vibrations
• CPC Class Codes: G01N 2291/2693 Rotor or turbine parts
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

Vibration amplitudes are recorded as a function of rotation speed and of frequency and the data is analyzed to estimate a noise floor amplitude threshold for each of a plurality of different speed and frequency sub-ranges. On the basis of training data known to be normal speed-frequency areas which contain significant spectral content in normal operation are deemed “known significant spectral content”, so that during monitoring of new data points which correspond to significant vibration energy at speeds and frequencies different from the known significant spectral content can be deemed “novel significant spectral content” and form the basis for an alert. The estimation of the noise floor is based on a probabilistic analysis of the data in each speed-frequency area and from this analysis an extreme value distribution expressing the probability that any given sample is noise is obtained.

Claims

1. A method of monitoring vibration amplitude and frequency in a rotary machine, comprising the steps of:

—

receiving measurements of the vibration amplitude and the rotation speed of the machine;

recording as a data point each amplitude measurement as a function of vibration frequency and rotational speed;

storing a plurality of different amplitude thresholds each representing a noise floor for a respective one of a first set of sub-ranges of vibration frequency and rotational speed;

comparing each amplitude measurement to the amplitude threshold for the sub-range of vibration frequency and rotational speed within which it falls; and

determining the measurement as representing noise if it falls below the threshold and as significant spectral content if it is above the threshold.

2. A method according to claim 1 wherein the different amplitude thresholds each representing a noise floor for a respective sub-range of vibration frequency and rotational speed are set in a training process using training data points comprising vibration data from a run of the rotary machine deemed to be normal.

3. A method according to claim 2 wherein the different amplitude thresholds each representing a noise floor for a respective sub-range of vibration frequency and rotational speed are set by fitting an amplitude distribution to the training data points in each sub-range of vibration frequency and rotational speed, calculating an extreme value distribution for said amplitude distribution and setting as said amplitude threshold an amplitude value representing a preset probability of being the maximum amplitude value that would be obtained for noise.

4. A method according to claim 3 wherein the preset probability is a probability above 0.99.

5. A method according to claim 3 wherein the amplitude distribution is a Gamma distribution.

6. A method according to claim 3 wherein the amplitude distribution is fitted after excluding training data points not representing background noise from said data in each subrange of vibration frequency and rotational speed.

7. A method according to claim 3 further comprising:

comparing each amplitude measurement to the extreme value distribution obtained from the training data points to read-off a probability value for that amplitude;

calculating from the probability value a novelty value as;

novelty value=−

log₁₀{1−

P_e(x)}, where P_e(x) is the extreme value distribution as a function of amplitude x; and

outputting said novelty value.

8. A method according to claim 1 further comprising:

storing which of a second set of vibration frequency and rotational speed subranges contained, during a training process using vibration data from a run of the rotary machine deemed to be normal, more than a preset number of training data points whose amplitude was above the noise floor and defining these vibration frequency and rotational speed sub-ranges as known significant spectral content;

comparing each amplitude measurement to the amplitude threshold representing the noise floor for the one of the first number of sub-ranges of vibration frequency and rotational speed within which it falls;

defining as novel significant spectral content any of the second set of vibration frequency and rotational speed sub-ranges not defined as known significant spectral content and which contain more than a second preset number of amplitude measurements exceeding the amplitude threshold representing the noise floor.

9. A method according to claim 8 wherein the second preset number of amplitude measurements is one.

10. A method according to claim 8 wherein the second set of vibration frequency and rotational speed sub-ranges, and said preset number of training data points, are determined in a training process using training data points comprising vibration data from a run of the rotary machine containing abnormal data, such that only those of the second set of vibration frequency and rotational speed sub-ranges containing abnormal training data points are defined as novel significant spectral energy.

11. A method according to claim 8 wherein the first and the second sets of vibration frequency and rotational speed sub-ranges are the same.

12. A method according to claim 1 wherein the frequency range is divided into 30 to 120 sub-ranges and the rotational speed range is divided into 5 to 40 subranges.

13. A method according to claim 1 wherein the frequency range is divided into 50 to 100 sub-ranges and the rotational speed range is divided into 10 to 30 subranges.

14. Apparatus for monitoring vibration amplitude and frequency in a rotary machine, comprising inputs for receiving vibration measurements from a vibration sensor and measurements of the rotation speed of the machine from a tachometer, and a data processing system adapted to execute the method of claim 1.

15. A control system for a rotary machine comprising apparatus according to claim 14.