Determining narrowband envelope alarm limit based on machine vibration spectra
First Claim
1. A method for constructing an alarm limit envelope for spectral analysis of vibration data collected from a machine, said constructing based on a single measured machine vibration spectrum, the alarm limit envelope representing maximum vibration levels for which measured vibration levels within a measured vibration spectrum are considered normal, the method comprising the steps of:
- measuring vibration generated by the machine over time to produce a time series of vibration data measurements;
transforming the time series of vibration data measurements from the time domain to the frequency domain to produce the single measured vibration spectrum consisting of a set of data points, where each data point includes a vibration amplitude level and a corresponding vibration frequency;
dividing said measured vibration spectrum into a plurality of frequency windows which are subsets of the data points having consecutive vibration frequencies, where each window includes a vibration peak which is a data point having the largest vibration amplitude within the window; and
calculating an alarm limit value for each window, each of said alarm limit values representing a maximum vibration level above which an amplitude level of any single data point having a vibration frequency within the window is considered abnormal,wherein the alarm limit values for all windows within the measured vibration spectrum collectively comprise an alarm limit envelope.
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Abstract
The disclosed invention senses a machine'"'"'s vibration spectrum, converts the vibration signal into a frequency-domain vibration spectrum, and analyzes the vibration spectrum to generate a narrowband alarm limit envelope against which the vibration spectrum of a previously uncharacterized machine may be compared. The limit envelope is generated from the test vibration spectrum of the machine which is the subject of the test, thus providing a performance benchmark against which to compare the vibration level of the previously uncharacterized machine. A limit envelope is also generated from a test vibration spectrum which has been designated as a reference or baseline spectrum. Further, a limit envelope is generated based upon a mean spectrum which is generated by combining several test vibration spectra. A limit envelope is also generated based upon mean and standard deviation spectra when a statistically significant number of test spectra are available.
86 Citations
19 Claims
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1. A method for constructing an alarm limit envelope for spectral analysis of vibration data collected from a machine, said constructing based on a single measured machine vibration spectrum, the alarm limit envelope representing maximum vibration levels for which measured vibration levels within a measured vibration spectrum are considered normal, the method comprising the steps of:
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measuring vibration generated by the machine over time to produce a time series of vibration data measurements; transforming the time series of vibration data measurements from the time domain to the frequency domain to produce the single measured vibration spectrum consisting of a set of data points, where each data point includes a vibration amplitude level and a corresponding vibration frequency; dividing said measured vibration spectrum into a plurality of frequency windows which are subsets of the data points having consecutive vibration frequencies, where each window includes a vibration peak which is a data point having the largest vibration amplitude within the window; and calculating an alarm limit value for each window, each of said alarm limit values representing a maximum vibration level above which an amplitude level of any single data point having a vibration frequency within the window is considered abnormal, wherein the alarm limit values for all windows within the measured vibration spectrum collectively comprise an alarm limit envelope. - View Dependent Claims (3, 4, 7, 8, 9, 10)
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2. A method for constructing an alarm limit envelope based on a plurality of machine vibration spectra, the alarm limit envelope representing maximum machine vibration levels for which measured vibration levels within a measured machine vibration spectrum are considered normal, the method comprising the steps of:
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providing a plurality of vibration spectra corresponding to vibration generated by at least one machine; determining a mean vibration spectrum based on said plurality of vibration spectra, the mean vibration spectrum consisting of a set of data points, where each data point includes a vibration amplitude level and a corresponding vibration frequency, wherein each amplitude corresponding to a particular frequency in the mean vibration spectrum is a statistical mean of all corresponding amplitude levels of said plurality of vibration spectra; dividing said mean vibration spectrum into a plurality of frequency windows which are subsets of the data points having consecutive vibration frequencies, where each window includes a mean vibration peak which is a data point having the largest vibration amplitude within the window; and calculating an alarm limit value for each window, each of said alarm limit values representing a maximum vibration level above which an amplitude level of any single data point having a vibration frequency within the window is considered abnormal wherein the alarm limit values for all windows within the mean vibration spectrum collectively comprise an alarm limit envelope. - View Dependent Claims (5, 6, 11, 12, 13, 14, 15)
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16. A machine vibration monitoring system for measuring and analyzing mechanical vibration levels of a machine to determine an operational condition of the machine, where the vibration levels are represented by a frequency-domain vibration spectrum, the system comprising:
a computer for analyzing the frequency-domain vibration spectrum, for determining an alarm limit envelope based on the frequency-domain vibration spectrum where the alarm limit envelope represents a maximum vibration level above which the vibration levels of the machine are considered abnormal, and for determining whether the machine'"'"'s vibration levels exceed the alarm limit envelope, the computer comprising; a computer processor for dividing the vibration spectrum into a plurality of frequency windows that are subsets of data points having consecutive vibration frequencies, where each window includes a vibration peak which is a data point having the largest vibration amplitude within the window, calculating an alarm limit value for each window, the alarm limit value representing a maximum vibration level above which an amplitude level of any single data point having a vibration frequency within the window is considered abnormal, and assembling the alarm limit values for all windows within the vibration spectrum to construct the alarm limit envelope; computer memory connected to the computer processor for storing the vibration spectrum and the alarm limit envelope; a user interface connected to the computer processor for providing operator control system functions; and a display connected to the computer processor for providing visual representations used in controlling system functions, and for viewing the vibration spectrum and the alarm limit envelope. - View Dependent Claims (17, 18, 19)
Specification