Noninvasive method and apparatus for determining resonance information for rotating machinery components and for anticipating component failure from changes therein

An apparatus for measuring resonance information for at least one rotating element of a rotary machine, said machine's rotating elements:

• comprising a shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said apparatus comprising:
• an alternator, driven by said rotary machine, providing an AC rotation-frequency signal having a fundamental frequency;
• and
• signal-processing means for deriving from said AC rotation-frequency signal further signals representative of frequency components that are contained within said AC rotation-frequency signal and modulate said fundamental frequency, said signal-processing means including spectral analysis means for performing a Fourier Transform spectral analysis on said further signals and deriving therefrom additional signals representative of frequency characteristics for said resonant vibration mode.

An apparatus for measuring resonance information for at least one rotating element of a rotary machine, said machine's rotating elements:

• comprising a shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said apparatus comprising:
• a sensor providing rotation signals representative of said frequency of angular rotation, where said sensor does not require for its use modification of the structure of the rotary machine and is capable of being located at any accessible point along the shaft of said machine;
• means for deriving from said rotation signals signal-components thereof representative of said modulation of said fundamental frequency of angular rotation being caused by oscillatory motions of at least one of said rotating elements;
• and
• signal-processing means for deriving from said signal-components a signal spectrum containing further signals representative of frequency and amplitude characteristics for said resonant mode, said signal-processing means including spectral analysis means for performing a Fourier Transform spectral analysis on said further signals and deriving therefrom additional signals representative of frequency characteristics for said resonant vibration mode.

An apparatus for measuring resonance information for at least one rotating element of a rotary machine, said machine's rotating elements:

• comprising a shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said apparatus comprising:
• a sensor providing a train of N sensor-pulses in each complete 360.degree.-rotation of said shaft, where:
• N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses have an instantaneous frequency associated therewith;
• and
• means for deriving from said train of sensor-pulses digital signals representative of a modulation of said fundamental frequency of angular rotation being caused by oscillatory motions of at least one of said rotating elements, said means comprising:
• f/v pulse-conversion means for deriving from said train of sensor-pulses, or from a signal derived from said train, an analog voltage signal whose amplitude is representative of said instantaneous frequency of said sensor-pulses;
• an analog-to-digital converter for deriving from said analog voltage signal digital signals representative of said instantaneous frequency of said sensor-pulses;
• means for deriving from said digital signals a signal spectrum representative of frequency components present in said instantaneous frequency of said sensor-pulses, said signal spectrum containing signals representative of frequency and amplitude characteristics for said resonant mode, said means comprising spectral-analysis means for performing a Discrete Fourier Transform spectral analysis on said digital signals in a manner that lessens spectral amplitudes of interference at shaft harmonic frequencies, said spectral-analysis means comprising electronic circuitry having:
• means for receiving said digital signals from said analog-to-digital converter and for providing, from said digital signals, DFT-signals representative of a Discrete Fourier Transform of a data record constituting a number of consecutive data segments, each said data segment constituting a set of consecutive said digital signals;
• and
• means for setting:
• the duration of each said data segment to a time interval containing exactly one complete rotation of said shaft;
• the number of said digital signals contained in each said data segment to an integer;
• and
• said number of data segments constituting said data record to an integer.

An apparatus for measuring resonance information for at least one rotating element of a rotary machine, said machine's rotating elements:

• comprising a shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said apparatus comprising:
• a sensor providing a train of N sensor-pulses in each complete 360.degree.-rotation of said shaft, where:
• N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses have an instantaneous frequency associated therewith;
• and
• means for deriving from said train of sensor-pulses digital signals representative of a modulation of said fundamental frequency of angular rotation being caused by oscillatory motions of at least one of said rotating elements, said means comprising:
• f/v pulse-conversion means for deriving from said train of sensor-pulses, or from a signal derived from said train, an analog voltage signal whose amplitude is representative of said instantaneous frequency of said sensor-pulses;
• an analog-to-digital converter for deriving from said analog voltage signal digital signals representative of said instantaneous frequency of said sensor-pulses, said analog-to-digital converter having a clock-signal input port;
• means for deriving from said digital signals a signal spectrum representative of frequency components present in said instantaneous frequency of said sensor-pulses, said signal spectrum containing signals representative of frequency and amplitude characteristics for said resonant mode, said means comprising spectral-analysis means for performing a Fast Fourier Transform spectral analysis on said digital signals in a manner that lessens spectral amplitudes of interference at shaft harmonic frequencies, said spectral-analysis means comprising electronic circuitry having:
• means for receiving said digital signals from said analog-to-digital converter and for providing, from said digital signals, FFT-signals representative of a Fast Fourier Transform of a data record constituting a number of consecutive data segments, each said data segment constituting a set of consecutive said digital signals;
• a multiplier-divider having means for:
• receiving said train of sensor pulses having N sensor-pulses for each complete 360.degree.-rotation of said shaft;
• multiplying said pulses by a first factor, providing a product, and dividing said product by a second factor, providing a quotient, said first and second factors being such that said quotient is an integral power of two, M;
• and
• providing a further pulse train containing M pulses for each complete 360.degree.-rotation of said shaft;
• and
• means for feeding said further pulse train to said clock-signal input port of said analog-to-digital converter, whereby:
• the duration of each said data segment is set to a time interval containing exactly one complete rotation of said shaft;
• the number of said digital signals in each data segment is set to exactly an integral power of two, M;
• and
• said number of data segments constituting said data record is set to exactly an integral power of two, M'.

An apparatus for measuring resonance information for at least one rotating element of a rotary machine, said machine's rotating elements:

• comprising a shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said apparatus comprising:
• a sensor providing a train of N sensor-pulses in each complete 360.degree.-rotation of said shaft, where:
• N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses have an instantaneous frequency associated therewith;
• and
• means for deriving from said train of sensor-pulses digital signals representative of a modulation of said fundamental frequency of angular rotation being caused by oscillatory motions of at least one of said rotating elements, said means comprising:
• a low-pass pulse filter for receiving said train of sensor-pulses, or a signal derived therefrom, said filter having a cutoff frequency that is lower than half of a clocking frequency and is higher than a highest frequency-component of interest present in said train of sensor-pulses or signal derived therefrom, said filter providing as its output an anti-aliased pulse train;
• means for receiving said train of sensor-pulses or signal derived therefrom and removing from said train of sensor pulses or signal derived therefrom signal components representative of said modulation of said fundamental frequency of angular rotation, thereby providing an unmodulated pulse train;
• and
• analog-to-digital conversion means for providing as an output digital signals representative of said instantaneous frequency of said sensor-pulses, without an intermediate frequency-to-voltage conversion before digitization, said analog-to-digital conversion means having a clock-signal input for receiving said unmodulated pulse train as a clocking signal for said conversion and having an analog signal input for receiving said anti-aliased pulse train;
• and
• means for deriving from said digital signals resonance-information signals representative of frequency and amplitude characteristics for said resonant mode, said means comprising means for subjecting said digital signals to Fourier Transform spectral analysis, providing a signal spectrum representative of frequency components present in said instantaneous frequency of said sensor-pulses.

A machine system comprising:

• a rotary machine, said machine having a shaft rotating at an angular rotation frequency, said shaft having rotating elements attached thereto and rotated thereby, said shaft and said elements having resonant vibration modes, and said shaft's angular rotation frequency being a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• shutdown means for shutting said machine down upon receipt of a shutdown signal and/or alarm means for providing an alarm upon receipt of a shutdown signal;
• a sensor for providing signals representative of said angular rotation frequency of said shaft;
• signal-processing means for detecting from said signals signal-components thereof representative of said modulation of said fundamental frequency of angular rotation by said oscillatory vibrations, and for deriving from said signal-components resonant-frequency signals representative of frequency and amplitude characteristics for said resonant modes;
• a comparator
• for comparing a first signal representative of an initial value or resonance information for at least one of said shaft and/or rotating elements with a second signal representative of at least one subsequent value of said resonance information;
• and
• for providing an output signal representative of whether said first and second signals have a predetermined relationship indicating a shift in said resonance information;
• and
• means for sending said output signal as a shutdown signal to said shutdown means and/or to said alarm means.

A method for measuring resonance information for at least one rotating element of a rotary machine, said rotary machine's rotating elements:

• comprising a rotating shaft and one or more nonshaft rotating elements;
• having at least one resonant mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation that is modulated by oscillatory vibrations of at least one of said rotating elements;
• said method comprising:
• (1) obtaining from a sensor monitoring said machine a rotation signal representative of said shaft's frequency of angular rotation, said sensor being one that provides a train of sensor-pulses, where:
• there are N sensor-pulses for each 360.degree. rotation of said shaft, where N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses, or the spacings therebetween, have an instantaneous frequency associated therewith;
• (2) electronically deriving from said rotation signal further signals representative of said modulation of said fundamental frequency of angular rotation by said oscillatory vibrations of at least one of said rotating elements;
• (3) feeding said further signals to a electronic device for performing Fourier Transform spectral analysis, providing a signal spectrum representative of instantaneous frequency components present in said pulse train, or in the spacing thereof, and deriving therefrom resonance-information signals representative of frequency and amplitude characteristics for said resonant vibration mode.

A method for measuring resonance information for at least one rotating element of a rotary, machine, said machine's rotating elements;

• comprising a rotating shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said method comprising:
• (1) driving from said shaft an alternator providing an AC rotation-frequency signal having a fundamental frequency;
• and
• (2) extracting from said AC rotation-frequency signal signals representative of frequency components therein that modulate said fundamental frequency.

A method for measuring resonance information for at least one rotating element of a rotary machine, said machine's rotating elements:

• comprising a shaft and one or more nonshaft rotating elements;
• having at least one resonant vibration mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;
• said method comprising:
• (1) registering from a sensor rotation signals representative of said frequency of angular rotation, where said sensor does not require modification of the structure of the rotary machine and is capable of being located at any accessible point along the shaft of said machine;
• (2) deriving from said rotation signals signal-components thereof representative of said modulation of said fundamental frequency of angular rotation being caused by oscillatory motions of at least one of said rotating elements;
• and
• (3) deriving from said signal-components a signal spectrum containing further signals representative of frequency and amplitude characteristics for said resonant mode, performing a Fourier Transform spectral analysis on said further signals, and deriving therefrom additional signals representative of frequency characteristics for said resonant vibration mode.

A method for measuring resonance information for at least one rotating element of a rotary machine, said rotary machine's rotating elements:

• comprising a rotating shaft and one or more nonshaft rotating elements;
• having at least one resonant mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation that is modulated by oscillatory vibrations of at least one of said rotating elements;
• said method comprising:
• (1) obtaining a rotation signal representative of said shaft's frequency of angular rotation, from a sensor that provides a train of sensor-pulses, where:
• there are N sensor pulses for each 360.degree. rotation of said shaft, where N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses have an instantaneous frequency associated therewith;
• (2) electronically deriving from said rotation signal further signals representative of said modulation of said fundamental frequency of angular rotation by said oscillatory vibrations, by:
• (a) feeding said train of sensor-pulses to a frequency-to-voltage converter which:
• (A) feeds to an input port of an integrator a predetermined quantity of charge for each of said sensor-pulses, whereby said integrator registers a predetermined voltage increment for each angular-rotation increment;
• (B) allows charge to leak from said integrator through an output resistor in accordance with a predetermined time constant, providing a sawtooth wave as output voltage signal;
• (C) feeding said output voltage signal to a low-pass filter;
• and
• (D) smoothing said sawtooth wave by said filter, providing an analog voltage signal whose amplitude is representative of instantaneous frequency of said sensor-pulses;
• (b) feeding said analog voltage signal to an analog-to-digital converter, which provides at its output digital signals representative of instantaneous frequency of said sensor-pulses, as said further signals;
• (3) feeding said further signals to an electronic device for performing spectral analysis, providing a signal spectrum representative of frequency components present in said pulse train or in the spacing thereof, and deriving therefrom resonance-information signals representative of frequency and amplitude characteristics for said resonant vibration mode.

A method for measuring resonance information for at least one rotating element of a rotary machine, said rotary machine's rotating elements:

• comprising a rotating shaft and one or more nonshaft rotating elements;
• having at least one resonant mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation that is modulated by oscillatory vibrations of at least one of said rotating elements;
• said method comprising:
• (1) obtaining a rotation signal representative of said shaft's frequency of angular rotation, from a sensor that provides a train of sensor-pulses, where:
• there are N sensor-pulses for each 360.degree. rotation of said shaft, where N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses have an instantaneous frequency associated therewith;
• (2) electronically deriving from said rotation signal further signals representative of said modulation of said fundamental frequency of angular rotation by said oscillatory vibrations, by:
• (a) feeding said train of sensor-pulses to a frequency-to-voltage converter which provides an analog voltage signal whose amplitude is representative of instantaneous frequency of said sensor-pulses;
• (b) feeding said analog voltage signal to an analog-to-digital converter, which provides at its output digital signals representative of instantaneous frequency of said sensor-pulses, as said further signals;
• (3) feeding said further signals to an electronic device for performing Discrete Fourier Transform spectral analysis, providing a signal spectrum representative of frequency components present in said pulse train or in the spacing thereof, and deriving therefrom resonance-information signals representative of frequency and amplitude characteristics for said resonant vibration mode, where said device performs said spectral analysis in a manner that lessens spectral amplitudes of interference at shaft harmonic frequencies, by:
• (a) providing a data record constituting a number of consecutive data segments, each said data segment constituting a set of consecutive said digital signals
• (b) making the duration of each said data segment a time interval containing exactly one complete rotation of said shaft;
• (c) making the number of said digital signals contained in said data segment an integer;
• (d) making said number of data segments constituting said data record an integer;
• and
• (e) subjecting said digital signals constituting said data record to a Discrete Fourier Transform analysis.

A method for measuring resonance information for at least one rotating element of a rotary machine, said rotary machine's rotating elements:

• comprising a rotating shaft and one or more nonshaft rotating elements;
• having at least one resonant mode;
• and
• rotating about an axis at a fundamental frequency of angular rotation that is modulated by oscillatory vibrations of at least one of said rotating elements;
• said method comprising:
• (1) obtaining a rotation signal representative of said shaft's frequency of angular rotation, from a sensor that provides a train of sensor-pulses, where:
• there are N sensor-pulses for each 360.degree. rotation of said shaft, where N is a positive integer;
• each of said N sensor-pulses is representative of an angular-rotation increment by said shaft;
• and
• said pulses have an instantaneous frequency associated therewith;
• (2) electronically deriving from said rotation signal further signals representative of said modulation of said fundamental frequency of angular rotation by said oscillatory vibrations, by:
• (a) feeding said train of sensor-pulses, or a signal derived therefrom, to a low-pass filter whose cutoff frequency is lower than half a clocking frequency and is higher than a highest frequency component of interest present in said train of sensor-pulses, providing an anti-aliased pulse train;
• (b) feeding said anti-aliased pulse train to an analog-to-digital converter, which provides at its output digital signals representative of instantaneous frequency of said sensor-pulses, as said further signals, said analog-to-digital converter having a clock-signal input port to which a clocking signal is fed;
• (c) feeding said train of sensor-pulses, or a signal derived therefrom, to a means for removing therefrom signal-components representative of said modulation of said fundamental frequency of angular rotation, thereby providing an unmodulated pulse train;
• (d) feeding said unmodulated pulse train to said clock-signal input port of said analog-to-digital converter as said clocking signal, and clocking said analog-to-digital converter therewith (for purposes of step 2b);
• (3) feeding said further signals to an electronic device for performing Fourier Transform spectral analysis, providing a signal spectrum representative of instantaneous frequency components present in said pulse train or in the spacing thereof, and deriving therefrom resonance-information signals representative of frequency and amplitude characteristics for said resonant vibration mode.

A method of operating a machine system and anticipating occurrence of resonance phenomena therein, said system comprising a rotary machine, said machine comprising a rotating shaft and rotating elements attached to said shaft and rotated thereby, said shaft and said rotating elements having resonant vibration modes, and said shaft's angular rotation frequency being a fundamental frequency of angular rotation modulated by oscillatory vibrations of at least one of said rotating elements;

• said method comprising:
• (1) obtaining a signal representative of said shaft's frequency of angular rotation;
• (2) deriving from said signal further signals representative of said modulation of said frequency by oscillations of at least one said rotating element and/or shaft;
• (3) processing said further signals by detecting therefrom signal-components thereof representative of said modulation of said fundamental frequency of angular rotation by said oscillatory vibrations and deriving from said signal-components resonance-information signals representative of amplitude and frequency characteristics for at least one said resonant vibration mode;
• (4) storing said resonance-information signals;
• (5) periodically fetching from storage and comparing current and historic values of said resonance-information signals;
• (6) providing an output alarm signal if said current values differ from said historic values by more than a predetermined threshold value;
• and
• (7) sounding an alarm and/or shutting down said system if said output alarm signal is provided.