Motor current signature analysis method for diagnosing motor operated devices

• US 4,965,513 A
• Filed: 11/14/1989
• Issued: 10/23/1990
• Est. Priority Date: 09/30/1986
• Status: Expired due to Term

• Current Assignee: Martin Marietta Energy Systems, Inc.
• Original Assignee: Martin Marietta Energy Systems, Inc.
• Inventors: Haynes, Howard D., Eissenberg, David M.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): BURNS, WILLIAM
• Application Number:
  US07/436,139
• Time in Patent Office: 343 Days
• Field of Search: 318/490, 324/158 MG, 364/551, 361/31, 340/648, 73/593, 73/659, 73/168, 73/660
• US Class Current: 73/1.72
• CPC Class Codes: F16K 37/0083 by measuring valve parameters
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines

Abstract

A motor current noise signature analysis method and apparatus for remotely monitoring the operating characteristics of an electric motor-operated device such as a motor-operated valve. Frequency domain signal analysis techniques are applied to a conditioned motor current signal to distinctly identify various operating parameters of the motor driven device from the motor current signature. The signature may be recorded and compared with subsequent signatures to detect operating abnormalities and degradation of the device. This diagnostic method does not require special equipment to be installed on the motor-operated device, and the current sensing may be performed at remote control locations, e.g., where the motor-operated devices are used in accessible or hostile environments.

Claims

1. A method for diagnosing operating characteristics of a device driven by an operating electric motor wherein said device produces noise in a current drawn by said motor, comprising the steps of:

sensing said current drawn by said motor;

determining a frequency range based on a specific operating element whose operating characteristics are to be analyzed;

measuring jamplitudes of various frequencies of said current within said frequency range;

storing said ;

measured frequency amplitudes as a frequency spectrum in a recording device in the form of a frequency domain recording to form a a recording of a frequency spectrum;

comparing said stored frequency domain recording with other frequency domain recordings to detect changes in the operating characteristics of said device; and

comparing said stored frequency domain recording with time domain recordings to determine additional operating characteristics of said device.

2. A method for diagnosing operating characteristics of a device driven by an operating motor that draws an electric current, comprising the steps of:

operating the motor to drive the device;

sensing an electric current drawn by the motor during an operation of the device, to produce a detect signal;

determining a frequency range based on a specific operating element whose operating characteristics are to be analyzed;

generating, at a first time, a first frequency signature, within the frequency range, from the detect signal in the form of a plurality of amplitude values at a plurality of frequency values, the frequency values and associated amplitude values of the first frequency signature corresponding to the frequencies and the associated amplitudes in the detect signal;

generating, at a second time, a second frequency signature from the detect signal, said second frequency signature having a same form as the form of the first frequency signature;

comparing the first and second frequency signatures to determine information as to the operating characteristics of the device;

identifying specific side band frequencies that are indicative of a degradation of an operating characteristic of the device;

comparing the first and second frequency signatures to determine a presence of the specified side band frequencies in the second frequency signature as compared to the first frequency signature; and

determining a degradation condition in an operating characteristic of the device when said presence is detected.

3. A method for diagnosing operating characteristics of a device driven by an operating motor that draws an electric current, comprising the steps of:

operating the motor to drive the device;

sensing an electric current drawn by the motor during an operation of the device, to produce a detect signal;

determining a frequency range based on a specific operating element whose operating characteristics are to be analyzed;

generating, at a first time, a first frequency signature, within the frequency range, from the detect signal in the form of a plurality of amplitude values at a plurality of frequency values, the frequency values and associated amplitude values of the first frequency signature corresponding to the frequencies and the associated amplitudes in the detect signal;

generating, at a second time, a second frequency signature from the detect signal, said second frequency signature having a same form as the form of the first frequency signature;

comparing the first and second frequency signatures to determine information as to the operating characteristics of the device;

identifying at least one side band frequency that is an indication of an operating characteristic of the device; and

analyzing the side band frequency in the first and second frequency signatures to determine information as to the operating characteristic.

4. An apparatus for diagnosing operating characteristics of a device driven by an operating electric motor wherein said device produces noise in a current drawn by said motor, comprising:

means for sensing said current drawn by said motor;

means for specifying a frequency range based on a specific operating element whose operating characteristics are to be analyzed;

spectrum analyzer means for measuring amplitudes of a frequency spectrum of said current;

means for storing said measured frequency spectrum amplitudes in a recording device in the form of a frequency domain recording, to form a recording of a frequency spectrum;

means for comparing said stored frequency domain recording with other frequency domain recordings to detect changes in the operating characteristics of said device,

wherein said comparing means also includes means for comparing said stored frequency domain recordings with time domain recordings to determine additional operating characteristics of said device.