Measuring and testing – Instrument proving or calibrating – Dynamometer
Patent
1996-02-22
1998-05-19
Williams, Hezron E.
Measuring and testing
Instrument proving or calibrating
Dynamometer
73 138, G01C 2500
Patent
active
057537933
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an apparatus for detecting the malfunctioning of an accelerometer in form of a piezoelectric device, where an electric test signal, preferably in form of a square pulse, can be transmitted from a test signal generator to the piezoelectric device by means of a changeover switch capable of performing a change in such a manner that the response signal from the piezoelectric device can be transmitted to an analysis circuit, preferably a frequency-analyzing circuit, so as to be subjected to a malfunction detection.
BACKGROUND ART
In order to obtain a sufficient measuring accuracy of a vibration measurement by means of an accelerometer it is necessary to meet two requirements, viz. the accelerometer must be mounted on a plane surface and the securing torque or force must be suitable. When the securing torque or force is reduced, the resonance frequency drops until no connection exists at all between the accelerometer and the mounting surface. Subsequently, the free resonance frequency of the accelerometer is measured. The optimum resonance frequency results in the maximum amplitude. A measurement of the resonance frequency of the accelerometer and the associated amplitude results in an indication of the mounting state of the accelerometer. When the resonance frequency of the accelerometer is measured after being mounted and said resonance frequency is compared with a value given on a calibration card or chart the following factors apply:
A lower resonance frequency than the indication given on the calibration chart or card indicates that the accelerometer has not been sufficiently tightened up during mounting. When the measured resonance frequency for instance is 1.5 times the indication of the calibration card it means that the accelerometer has not been mounted. When the measured resonance frequency is very close to the indication of the calibration card it means that the accelerometer has been sufficiently well mounted.
When the mounting to the surface is correct, the frequency and the amplitude of the measurement are stored. A change of the frequency during later measurements indicates that something has happened to the mounting. A change of the amplitude without a simultaneous change of the resonance frequency indicates that the sensitivity of the accelerometer has changed.
It is known from EP Publication No. 534,366 to perform a continuous observation of the mounting state of an accelerometer. A test signal is fed to the accelerometer through a capacitor. Such a capacitor should, of course, be avoided. In addition, a rather complicated analysis circuit is required which must be able to distinguish between applied and actual vibration signals. The feeding of test signals and the analysis are carried out simultaneously.
Furthermore U.S. Pat. No. 4,418,567 discloses a sensor equipment for detecting the motor knocking in a car motor. This equipment comprises a control circuit generating gate control signals for a splitting up into measuring and test phases. The test phase includes detection of a possible malfunctioning of the sensor. The splitting up into measuring and test phases is carried out synchronously with the rotation of the motor. The test signal is in fact fed simultaneously with the measuring procedure. The testing is merely carried out at a time where it is known than no measuring signal exists. Accordingly, this equipment is limited to a particular use.
In addition DE Offenlegungsschrift No. 3,542,397 discloses a device for testing an accelerometer in form of a piezoelectric unit. This piezoelectric unit is tested by being mechanically influenced by an additional piezoelectric unit. This additional piezoelectric unit should, however, be avoided.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to provide an apparatus for detecting the malfunctioning of an accelerometer in the form of a piezoelectric device, and which is far more simple and universal in use than previously known.
The apparatus according to the invention is characteri
REFERENCES:
patent: 4418567 (1983-12-01), Boning et al.
patent: 5103667 (1992-04-01), Allen et al.
patent: 5337260 (1994-08-01), Spangler
patent: 5373722 (1994-12-01), Spies et al.
patent: 5375468 (1994-12-01), Ohta et al.
patent: 5438859 (1995-08-01), Yamashita et al.
patent: 5447051 (1995-09-01), Hanks et al.
Jensen Henrik Brill
Lindahl Claus
A/S Bruel & Kjaer
Moller Richard A.
Williams Hezron E.
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