Method and apparatus for determining electric motor speed using vibration and flux
First Claim
1. A programmable apparatus for determining the running speed of an ac induction motor, the apparatus comprising:
- a vibration transducer for sensing vibration generated by the motor and producing vibration signals corresponding to the sensed vibration;
a flux sensor for sensing flux generated by the motor and producing flux signals corresponding to the sensed flux;
signal conditioning circuitry for processing the vibration and flux signals to produce processed vibration and flux signals; and
a signal processor operable to receive the processed vibration and flux signals and to determine the running speed of the motor by;
performing a first analysis on at least one of the processed vibration and flux signals according to a first predetermined criterion to determine one or more candidate speeds and whether speed will be determined based on the first analysis or whether a second analysis is required; and
selectively performing a second analysis if required by the first analysis, said second analysis including the steps of comparing the processed vibration signals to the processed flux signals and determining running speed based on said comparison.
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Accused Products
Abstract
A programmable apparatus is used to determine the running speed of an ac induction motor based on vibration and flux measurements. A first analysis is performed on at least one of the vibration and flux signals according to a first criterion to determine candidate speeds and whether speed will be determined based on the first analysis or whether a second analysis is required. A second analysis is selectively performed if required by the first analysis. In the first analysis, vibration signals (for example) are transformed to the frequency domain, such as by Fast Fourier Transform, and vibration amplitude peaks contained in the resulting spectrum are analyzed to identify candidate peaks. If only one candidate peak is identified, the frequency at which the candidate peak occurs is used to determine motor running speed. If two or more candidate peaks are identified and the motor is a two-pole motor, the candidate peak having the maximum amplitude is used to determine running speed. If two or more candidate peaks are identified and the motor has more than two poles, a second analysis is performed by producing a flux spectrum. Peaks at various frequencies within the flux spectrum are compared to the candidate peaks and each candidate peak is scored based on the comparison. The scores are compared to a predetermined score threshold to determine which candidate peak will be used to determine motor running speed. Preferably, each candidate peak is also subjected to testing to determine whether the candidate peak accurately represents the frequency at which the true peak occurs.
30 Citations
27 Claims
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1. A programmable apparatus for determining the running speed of an ac induction motor, the apparatus comprising:
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a vibration transducer for sensing vibration generated by the motor and producing vibration signals corresponding to the sensed vibration; a flux sensor for sensing flux generated by the motor and producing flux signals corresponding to the sensed flux; signal conditioning circuitry for processing the vibration and flux signals to produce processed vibration and flux signals; and a signal processor operable to receive the processed vibration and flux signals and to determine the running speed of the motor by; performing a first analysis on at least one of the processed vibration and flux signals according to a first predetermined criterion to determine one or more candidate speeds and whether speed will be determined based on the first analysis or whether a second analysis is required; and selectively performing a second analysis if required by the first analysis, said second analysis including the steps of comparing the processed vibration signals to the processed flux signals and determining running speed based on said comparison. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for determining the running speed of an ac induction motor comprising the steps of:
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sensing vibration generated by the motor and producing vibration signals corresponding to the sensed vibration; sensing flux generated by the motor and producing flux signals corresponding to the sensed flux; conditioning the vibration and flux signals to produce processed vibration and flux signals; performing a first analysis on at least one of the processed vibration and flux signals according to a first criterion to determine one or more candidate speeds and whether speed will be determined based on the first analysis or whether a second analysis is required; and selectively performing a second analysis if required by the first analysis, said second analysis including the steps of comparing the vibration signals to the flux signals and determining running speed based on said comparison. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A programmable apparatus for determining the running speed of an ac induction motor, the apparatus comprising:
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a structural enclosure; means for attaching said enclosure to the motor; a power source disposed in said enclosure for supplying dc electrical power to the apparatus; a vibration transducer disposed in said enclosure for sensing vibration generated by the motor and producing vibration signals corresponding to the sensed vibration; a flux sensor disposed in said enclosure for sensing flux generated by the motor and producing flux signals corresponding to the sensed flux; and a signal processor disposed in said enclosure for determining the running speed of the motor based on said vibration and flux signals. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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25. A method for determining the running speed of an ac induction motor comprising the steps of:
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attaching an electric motor monitor to the outer frame of an ac induction motor; producing vibration signals with said monitor representing vibrations generated by the motor; producing flux signals with said monitor representing magnetic flux generated by the motor; and processing the vibration and flux signals with said motor monitor to determine the running speed of the motor. - View Dependent Claims (26)
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27. A programmable apparatus for determining the running speed of an induction motor, the apparatus comprising:
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a vibration transducer for sensing vibration generated by the motor and producing vibration signals corresponding to the sensed vibration; a flux sensor for sensing flux generated by the motor and producing flux signals corresponding to the sensed flux; signal conditioning circuitry for processing the vibration and flux signals to produce processed vibration and flux signals; and a signal processor operable to receive the processed vibration and flux signals and to determine the running speed of the motor by; operating on the vibration signals to produce a vibration spectrum including a plurality of vibration amplitude peaks at a plurality of vibration frequencies, said vibration spectrum having a resolution; analyzing the vibration amplitudes to identify candidate vibration amplitude peaks according to a predetermined peak criterion, said candidate peaks being identified as peaks possibly corresponding to the running speed of the motor; if only one candidate peak is identified, using the frequency of the candidate peak to determine the running speed of the motor; and if two or more candidate peaks are identified, using the frequency of the candidate peak having the maximum vibration amplitude to determine the running speed of the motor if the motor is a two-pole motor, and if the motor has more than two poles; operating on the flux signals to produce a flux spectrum including a plurality of flux amplitude peaks at a plurality of flux frequencies corresponding to the running speed of the motor; comparing the candidate vibration peaks to the amplitudes of one or more flux peak frequencies and producing a comparison output; and determining the running speed of the motor based on the comparison output.
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Specification