Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-02-02
2001-05-22
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S593000, C073S660000, C073S661000
Reexamination Certificate
active
06234021
ABSTRACT:
TECHNICAL FIELD
The present invention is generally directed to the detection and monitoring of sound and vibration signals. The invention is more particularly directed to autoranging of sonic and ultrasonic signals in selected frequency bands to provide for enhanced audible detection and monitoring capabilities.
BACKGROUND OF THE INVENTION
The normal frequency range for human hearing is roughly 20 to 20,000 Hz. Vibration signals having frequencies of above about 20,000 Hz are in the ultrasonic range. Many industrial processes, including almost all sources of friction, create some ultrasonic vibrational noise. For example, leaks in pipes, machinery defects, and electrical arcing produce ultrasonic signals having frequencies too high for the human ear to detect.
In the past, ultrasonic sensors have been used in industrial settings to sense these ultrasonic signals and to detect abnormally high levels of ultrasonic sound which may indicate a mechanical fault in a machine. To monitor the ultrasonic signals produced by operating machinery, an operator would use an ultrasonic sensor to obtain a reading indicating the strength of the ultrasonic signals near the machine. If the ultrasonic signal levels generated by one machine were abnormally large, the operator would investigate further to determine if a problem existed with the noisy machine. If the ultrasonic signal levels were approximately equal to those produced by a properly functioning machine, the operator would assume the machine was properly functioning and simply proceed to the next machine.
Since ultrasonic signals generally cannot be heard by the human ear, ultrasonic sensing devices typically incorporate a heterodyne circuit to generate an audio signal that is a lower-frequency representation of the ultrasonic signal. The typical ultrasonic sensing device includes headphones or earphones to present the audio signal, which has a frequency within the range of human hearing, to the operator. Thus, when the ultrasonic sensing device detects an ultrasonic signal, the operator can hear an audio representation of the ultrasonic signal in the headphones.
As discussed above, machine elements such as bearings, valves, and gears, even those operating normally, produce vibration signals at both audible and ultrasonic frequencies. When trying to detect a machine fault using an ultrasonic sensing device, an operator listens for an abnormal signal, such as an impact sound, against a background of noise produced by the machinery. (For the purposes of this description, the term “background noise” is understood to include the noise that is present even in the absence of a fault condition, such as the noise generated by the normal operation of the machinery.) Many machine faults can be classified as impacts. For example, a bearing with a chip in a race, or a cracked gear tooth will produce an impact signal of only a few milliseconds or less in duration. The severity of the fault, the load conditions of the machine, as well as the amplitude of the normal background noise will determine the signal to noise ratio of the impact signal versus the background noise.
Given the noisy industrial environment and the brief, often transitory, nature of many fault signals that an operator is trying to hear, many important fault signals are not heard. To maximize the utility of the detector, it should be optimized to enhance the ability of the user to detect fault signals.
SUMMARY OF THE INVENTION
In the present invention, a preferred detector of vibration is optimized to enhance user detection of signals by mechanical and electrical tuning and amplitude autoranging. Mechanical and electrical tuning help the user to focus on vibration frequencies of interest, those that contain useful information in a particular situation. Amplitude autoranging guards against a common problem of manually adjusting the gain too high in an effort to hear better, only to defeat the ability to hear short duration impacts at all. If the gain is too high, the user may think he is hearing well, when in fact, the amplifier gain is adjusted so high that the impact signals are beyond clipping, and the background noise has been amplified to such a degree that the impact signals are acoustically masked. When this occurs, the impact signals may go unnoticed by the user.
The present invention addresses these and other problems by providing a device for detecting an emission source of a dynamic signal against a background of noise, where the vibration signal is a dynamic pressure or vibration signal produced by a machine or other mechanical system under test and has one or more frequency components. A sensor senses the dynamic signal and produces a sensor signal corresponding to the dynamic signal. The sensor has mechanical frequency selection means for mechanically resonating at desired frequencies and for mechanically attenuating frequency components of the dynamic signal having frequencies outside the desired frequencies. The mechanical frequency selection means thus produce mechanically-tuned sensor signals. Electrical frequency selection means electrically attenuate frequency components of the mechanically-tuned sensor signal having frequencies outside the desired frequencies. The electrical frequency selection means thus produce an electrically-tuned sensor signal.
The device has at least one amplifier with gain for producing an amplified signal corresponding to the electrically-tuned sensor signal. Amplitude characteristic determination means determine an amplitude characteristic corresponding to the dynamic signal's amplitude. The amplitude characteristic determination means also generate an amplitude indication based on the amplitude characteristic. Automatic gain adjustment means receive the amplitude indication and adjust the gain of the amplifier based at least in part on the amplitude indication.
In preferred embodiments of the invention, the mechanical frequency selection means include a resonator that contacts the machine or mechanical system being tested and vibrates at particular resonant frequencies in response to a vibration signal. A transducer, which is in contact with the resonator, produces electrical signals corresponding to the resonant frequencies of the resonator. A magnetic mount, which is designed to be integral with the resonator, contacts the mechanical system and holds the resonator in contact with the mechanical system.
The electrical frequency selection means of some embodiments incorporate frequency switching means that enable a user of the device to choose one of several selected frequency components of the sensor signal. Based upon the selected frequency component, the electrical frequency selection means produce a frequency selection indication. Filter selection means receive the frequency selection indication and select one of several filters based on the frequency selection indication. Each of these filters is tuned to one of the selected frequency components, such that the selected filter receives the mechanically-tuned sensor signal and electrically attenuates frequencies other than one of the selected frequency components to which the filter is tuned.
Thus, the present invention enhances the detectability of vibration signals by adjusting the frequency and the amplitude of the vibration signals to ranges that are optimum for detection under the particular circumstances.
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patent: 510
Johnson William S.
Piety Kenneth R.
Robinson James C.
Vanvoorhis James Brent
CSI Technology, Inc.
Larkin Daniel S.
Luedeka Neely & Graham P.C.
Miller Rose M.
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