Method and apparatus for isolating and identifying periodic Doppler signals in a turbine
First Claim
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1. An apparatus for detecting a resonantly vibrating blade in a row of blades secured to a shaft rotating about a rotor axis, in an operating turbine, comprising:
- an acoustic sensor positioned on a stationary member with respect to said shaft to receive sound waves emanating from said rotating blades as said blades rotate about said rotor axis and to provide an output signal representative said received sound waves, said acoustic sensor positioned with respect to said shaft so that said vibrating blade approaches and departs from said acoustic sensor in the course of one rotation of said shaft about said rotor axis;
reference means for obtaining a reference signal indicative of shaft position at least once each time said shaft completes a revolution about said rotor axis and for determining shaft speed;
sampling means for sampling said sensor output signal to obtain samples related to shaft position as said shaft completes a multiplicity of revolutions at a plurality of different shaft speeds;
first memory means for temporarily storing the shaft speed from the reference means and a corresponding plurality of samples synchronized with the shaft position obtained by said sampling means, said plurality of samples together comprising a sample series representing at least one shaft rotation;
ensemble averager means for averaging multiple sample series to develop a plurality of synchronous ensemble averages differentiated by shaft speed;
second memory means for storing the plurality of synchronous ensemble averages differentiated by shaft speed, and an accompanying shaft speed histogram;
Fourier decomposition means for generating a plurality of complex order-normalized spectra differentiated by shaft speed from the synchronous ensemble averages stored in the second memory means, each complex order-normalized spectrum having a real component and an imaginary component;
curve fitter means for curve fitting the plurality of complex order-normalized spectra using the shaft speed histogram as a weighting function to generate a series of generally linear shaft speed functions fit to the real and imaginary Fourier coefficients of the complex order-normalized spectra, wherein for a linear curve fit, the Fourier slope coefficients represent a characteristic Doppler signal and the Fourier intercept coefficients represent periodic background noise; and
synthesis means for constructing a resonant signal characterizing the vibration of the resonantly vibrating blade from the generally linear shaft speed functions generated by the curve fitter means, an instantaneous amplitude thereof being used to identify the resonantly vibrating blade in the monitored row of blades.
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Abstract
An improved method and apparatus for detecting and identifying one or more resonantly vibrating blades of a turbine through the use of acoustic sensors imbedded in the stationary casing of the turbine is disclosed. The acoustic sensor signals are processed to separate the characteristic Doppler waveform from the accompanying random noise and periodic noise. Improved signal processing techniques which involve the evaluation of both an information-bearing resonant signal and its Hilbert transform via direct synthesis are disclosed.
92 Citations
38 Claims
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1. An apparatus for detecting a resonantly vibrating blade in a row of blades secured to a shaft rotating about a rotor axis, in an operating turbine, comprising:
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an acoustic sensor positioned on a stationary member with respect to said shaft to receive sound waves emanating from said rotating blades as said blades rotate about said rotor axis and to provide an output signal representative said received sound waves, said acoustic sensor positioned with respect to said shaft so that said vibrating blade approaches and departs from said acoustic sensor in the course of one rotation of said shaft about said rotor axis; reference means for obtaining a reference signal indicative of shaft position at least once each time said shaft completes a revolution about said rotor axis and for determining shaft speed; sampling means for sampling said sensor output signal to obtain samples related to shaft position as said shaft completes a multiplicity of revolutions at a plurality of different shaft speeds; first memory means for temporarily storing the shaft speed from the reference means and a corresponding plurality of samples synchronized with the shaft position obtained by said sampling means, said plurality of samples together comprising a sample series representing at least one shaft rotation; ensemble averager means for averaging multiple sample series to develop a plurality of synchronous ensemble averages differentiated by shaft speed; second memory means for storing the plurality of synchronous ensemble averages differentiated by shaft speed, and an accompanying shaft speed histogram; Fourier decomposition means for generating a plurality of complex order-normalized spectra differentiated by shaft speed from the synchronous ensemble averages stored in the second memory means, each complex order-normalized spectrum having a real component and an imaginary component; curve fitter means for curve fitting the plurality of complex order-normalized spectra using the shaft speed histogram as a weighting function to generate a series of generally linear shaft speed functions fit to the real and imaginary Fourier coefficients of the complex order-normalized spectra, wherein for a linear curve fit, the Fourier slope coefficients represent a characteristic Doppler signal and the Fourier intercept coefficients represent periodic background noise; and synthesis means for constructing a resonant signal characterizing the vibration of the resonantly vibrating blade from the generally linear shaft speed functions generated by the curve fitter means, an instantaneous amplitude thereof being used to identify the resonantly vibrating blade in the monitored row of blades. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus for detecting a resonantly vibrating blade in a row of blades secured to a shaft rotating about a rotor axis from data acquired at more than two different operating shaft rotational speeds, in an operating turbine, comprising:
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an acoustic sensor positioned on a stationary member with respect to said shaft to receive sound waves emanating from said rotating blades as said blades rotate about said rotor axis and to provide an output representative of said received sound waves, said acoustic sensor positioned with respect to said shaft so that said vibrating blade approaches and departs from said acoustic sensor in the course of one rotation of said shaft about said rotor axis; reference means for obtaining a reference signal indicative of shaft position at least once each time said shaft completes a revolution about said rotor axis and for determining shaft speed; a sample control circuit for establishing a rate for sampling the sensor output signal over a multiplicity of shaft revolutions; first memory means for temporarily storing a plurality of samples of said sensor output signal the data acquisition means, said plurality of samples together comprising a time history per blade revolution; Fourier decomposition means for generating a multiplicity of complex order-normalized spectra from the time history, each complex spectrum having a real component and an imaginary component, the spectrum reflecting the spectral content of a single most recently completed shaft revolution; first ensemble averager means for forming and accumulating an average complex order-normalized spectrum from the multiplicity of complex order-normalized spectra; an address deviation look-up table cooperating with the reference means for generating an instantaneous speed deviation; multiplier means for multiplying the complex order-normalized spectrum associated with the most recent revolution and the associated instantaneous speed deviation to generate a multiplicity of speed weighted complex order-normalized spectra; second ensemble averager means for forming and accumulating an average speed weighted complex order-normalized spectrum from the multiplicity of speed weighted complex order-normalized spectra; a deviation statistics means for averaging instantaneous shaft speed deviations to generate deviation statistics; curve fitter means for simultaneously fitting a linear function of the shaft speed deviation to the real and the imaginary components of the averaged complex order-normalized spectrum and the averaged speed weighted complex order-normalized spectrum using the deviation statistics, to generate a series of generally linear shaft speed functions and; synthesis means for constructing a resonant signal characterizing the vibration of the resonantly vibrating blade from the generally linear shaft speed functions generated by the curve fitter means, an instantaneous amplitude thereof being used to identify the resonantly vibrating blade in the monitored row of blades. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. An apparatus for detecting a resonantly vibrating blade in a row of blades secured to a shaft rotating about a rotor axis in an operating turbine, from data acquired at more than two different operating shaft rotational speeds, to identify the vibrating blade, comprising:
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an acoustic sensor positioned on a stationary member with respect to said shaft to receive sound waves emanating from said rotating blades as said blades rotate about said rotor axis and to provide an output signal representative of said received sound waves, said acoustic sensor positioned with respect to said shaft so that said vibrating blade approaches and departs from said acoustic sensor in the course of one rotation of said shaft about said rotor axis; reference means for obtaining a reference signal indicative of shaft position at least once each time said shaft completes a revolution about said rotor axis and for determining shaft speed; a sample control circuit for establishing a rate for sampling the output signal sensor over a multiplicity of shaft revolutions; first memory means for temporarily storing a plurality of samples of the sensor output signal, said plurality of samples together comprising an instantaneous angle history; a period detector circuit cooperating with a shaft speed deviation look-up table for generating an instantaneous speed deviation; a deviation statistics module for averaging instantaneous speed deviations to generate deviation statistics; first ensemble averager means for generating an average angle history from the instantaneous angle history; multiplier means for multiplying the instantaneous speed deviation and the instantaneous angle history to generate a speed weighted angle history; second ensemble averager means for generating an average speed weighted angle history from the speed weighted angle history; first Fourier decomposition means for generating an average complex order-normalized spectrum from the average angle history; second Fourier decomposition means for generating an average speed weighted complex order-normalized spectrum from the average speed weighted angle history; curve fitter means for simultaneously fitting a linear function of the shaft speed deviation to the real and the imaginary components of the averaged complex order-normalized spectrum and the averaged speed weighted complex order-normalized spectrum using the deviation statistics, to generate a series of generally linear shaft speed functions; synthesis means for constructing a resonant signal characterizing the vibration of the resonantly vibrating blade from the generally linear shaft speed functions generated by the curve fitter means, an instantaneous amplitude thereof being used to identify the resonantly vibrating blade in the monitored row of blades. - View Dependent Claims (25, 26, 29, 30, 31, 32, 33, 34, 35)
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27. The apparatus of 26 wherein the sample control circuit comprises a multiple pulse per revolution encoder affixed to the shaft.
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28. The apparatus of 26 wherein the sample control circuit comprises a phase locked loop having a phase assertion means for fixing the sample number per shaft revolution.
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36. A method of isolating from periodic background noise an acoustic signal characterizing the vibration of a resonantly vibrating blade in a row of turbine blades secured to a shaft rotating about a rotor axis from data acquired at more than two different operating shaft rotational speeds to identify the vibrating blade, comprising the steps of:
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acquiring acoustic pressure wave data from pressure waves emanating from the rotating blades from one or more stationary sensors located proximate the turbine blades; identifying the angular position of the shaft and the shaft speed at least once each time said shaft completes a revolution about said rotor axis; sampling the pressure wave data acquired by the one or more sensor at a predetermined sample rate; temporarily storing in a first memory the shaft speed and a corresponding plurality of samples of the pressure wave data synchronized with the shaft position, said plurality of samples together comprising a sample series representing at least one shaft rotation; averaging multiple sample series to develop a plurality of synchronous ensemble averages differentiated by shaft speed; storing in a second memory the plurality of synchronous ensemble averages differentiated by shaft speed and an accompanying shaft speed histogram; performing a Fourier decomposition on the stored synchronous ensemble averages to generate a plurality of complex order-normalized spectra differentiated by shaft speed, each complex order-normalized spectrum having a real component and an imaginary component; curve fitting the plurality of complex order-normalized spectra using the shaft speed histogram as a weighting function to generate a series of generally linear shaft speed functions fit to the real and imaginary Fourier coefficients of the complex order-normalized spectra, wherein the Fourier slope coefficients represent a characteristic Doppler signal and the Fourier intercept coefficients represent periodic background noise; constructing a resonant signal characterizing the vibration of the resonantly vibrating turbine blade from the generally linear shaft speed functions; and determining an instantaneous amplitude of the constructed resonant signal to identify the vibrating blade in the monitored row of blades.
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37. A method of isolating from periodic background noise an resonant signal characterizing the vibration of a resonantly vibrating turbine blade in a row of turbine blades secured to a shaft rotating about a rotor axis from data acquired at more than two different operating shaft rotational speeds to identify the vibrating blade, comprising the steps of:
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acquiring acoustic pressure wave data from pressure waves emanating from the rotating blades from one or more stationary sensors located proximate the turbine blades; identifying the angular position of the shaft and the shaft speed at least once each time said shaft completes a revolution about said rotor axis; sampling the pressure wave data at a predetermined sample rate; temporarily storing in a first memory a plurality of samples of the data acquired, said plurality of samples together comprising a time history per blade revolution; performing a Fourier decomposition on the time history data to generate a multiplicity of complex order-normalized spectra, each complex spectrum having a real component and an imaginary component, the spectrum reflecting the spectral content of a single most recently completed shaft revolution; forming and accumulating an average complex order-normalized spectrum from the multiplicity of complex order-normalized spectra; generating an instantaneous speed deviation from the angular position and the speed of the shaft using an address deviation look-up table; multiplying the complex order-normalized spectrum associated with the most recent revolution and the associated instantaneous speed deviation to generate a multiplicity of speed weighted complex order-normalized spectra; averaging the multiplicity of speed weighted complex order-normalized spectra to form and accumulate an average speed weighted complex order-normalized spectrum; generating deviation statistics based on instantaneous shaft speed deviations; curve fitting a linear function of the shaft speed deviation to the real and the imaginary components of the averaged complex order-normalized spectrum and the averaged speed weighted complex order-normalized spectrum using the deviation statistics, to generate a series of generally linear shaft speed functions; constructing a resonant signal characterizing the vibration of the resonantly vibrating turbine blade from the generally linear shaft speed functions via Fourier-based synthesis; and determining an instantaneous amplitude of the constructed resonant signal to identify the resonantly vibrating blade in the monitored row of blades.
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38. A method of isolating from periodic background noise an resonant signal characterizing the vibration of a resonantly vibrating blade in a row of turbine blades secured to a shaft rotating about a rotor axis from data acquired at more than two different operating shaft rotational speeds to identify the vibrating blade, comprising the steps of:
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acquiring acoustic pressure wave data from pressure waves emanating from the rotating blades from one or more sensors located proximate the turbine blades; identifying the angular position of the shaft and the speed of the shaft at least once each time said shaft completes a revolution about said rotor axis; sampling the pressure wave data acquired at a predetermined sample rate; temporarily storing in a first memory a plurality of samples of the sampled data, said plurality of samples together comprising an instantaneous angle history; generating an instantaneous speed deviation using a period detector circuit cooperating with a shaft speed deviation look-up table; generating deviation statistics based on instantaneous shaft speed deviations; generating an average angle history from the instantaneous angle history; multiplying the instantaneous speed deviation and the instantaneous angle history to generate a speed weighted angle history; generating an average speed weighted angle history from the speed weighted angle history; generating an average complex order-normalized spectrum by performing a Fourier decomposition on the average angle history; generating an average speed weighted complex order-normalized spectrum by performing a Fourier decomposition on the average speed weighted angle history; fitting a linear function of the shaft speed deviation to the real and the imaginary components of the averaged complex order-normalized spectrum and the averaged speed weighted complex order-normalized spectrum substantially simultaneously using the deviation statistics to generate a series of generally linear shaft speed functions; constructing a resonant signal characterizing the vibration of the resonantly vibrating turbine blade by performing Fourier-based synthesis on the linear shaft speed functions; and determining an amplitude of the constructed resonant signal to identify the resonantly vibrating blade in the monitored row of blades.
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Specification