Boots – shoes – and leggings
Patent
1996-06-17
1998-05-19
Cosimano, Edward R.
Boots, shoes, and leggings
324772, 340679, 361 23, 361 31, 361 87, 364481, 364483, 364550, G01R 19165
Patent
active
057544506
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the detection of faults in the working of electric motor driven equipment.
BACKGROUND OF THE INVENTION
The term "motor driven equipment" is used herein to refer to any piece of equipment consisting of an electric motor, together with one or more devices driven by the electric motor and imposing a load on the motor shaft. Examples of motor driven equipment include a compressor in a refrigeration or cooling/heating device, a fan in air moving equipment and a pump driving a fluid through a pipe.
For compressors, pumps, fans and other motor driven equipment it is of vital importance to be able to carry out early identification of incipient performance problems or faults for such concerns as security, health, production, etc.
Fault detection devices can be roughly divided into two classes: those not requiring direct contact with the equipment, and those that do. The former includes so-called "passive" approaches wherein direct contact is not required while the latter includes devices based on, e.g., vibration analysis for mechanical failures and gas detectors for leaks. Such intrusive devices have inherent weaknesses that often stem from the need for physical contact or closeness to the equipment. Thus vibration sensors must be positioned correctly with respect to the (possibly unknown) directions of vibrations, while gas sensor locations are limited to non-ventilated spaces and are not effective for equipment placed for example, on a roof.
Fault detection devices not requiring direct contact are known in the prior art. An example of an approach which does not require direct contact with the equipment is that of Motor Current Signature Analysis, described in U.S. Pat. No. 4,965,513 to Haynes et al. This method, referred to herein as "MCSA", works as follows:
It is known that the characteristics of the electric current powering an electric motor which in turn operates a piece of equipment reflect the mechanical load of the equipment on the motor shaft. Therefore, the current values may be analyzed with standard spectral analysis, such as by applying the discrete Fourier Transform to a demodulated current signal and computing the power spectrum of the signal. Thus one attempts to obtain a "current signature" which will be different if the equipment is undergoing a change in mechanical behavior due to an incipient breakdown.
Since MCSA requires only values characterizing the electricity it is inherently a passive, non-intrusive approach, not requiring direct contact with the equipment and hence offering the convenience resulting from this fact.
The spectral analysis of the current, serving as the basis for a current signature whose changes reflect changes in the mechanical behavior of the equipment, is the basis for a number of inventions known in the prior art including those described in U.S. Pat. Nos. 4,123,009 to Kilpinen and 4,380,172 to Imam et al.
The MCSA method consists of storing a (possibly long) sequence of current values in a computer memory and applying the Discrete Fourier Transform with an appropriately chosen window function to the sequence. Of course the actual choice of the window function is based more on experimentation and knowing what one is seeking, than on definitive rules. Indeed the non-definitive nature of the choice renders the MCSA method difficult to implement independently of the intervention of an expert.
As a preliminary step in MCSA one will normally demodulate the signal with respect to the line current frequency for an A.C. power source. From the Discrete Fourier Transform we find the power spectrum, a positive real function of the frequency. Attempts will be made to associate various peaks in the spectrum with mechanical features of the equipment/motor combination.
Significant amplitude values are now stored in memory for data collected when operation was normal. The values will normally correspond to slip and r.p.m. values of the motor as well as to other mechanically-related features. For data collected at a later t
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Gelman Efim
Solomon Alan David
Cosimano Edward R.
Diagnostics Temed Ltd.
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