SE438047B - MISCELLANEOUS FAULTS OR DEFECTS IN MACHINE PARTS WHICH MOVE THE MIDDLE PICK-UP FOR CONVERSION OF MECHANICAL VIBRATIONS TO ELECTRICAL SIGNALS - Google Patents

Description

7ao41ss-4 from or is the same as the natural frequency of the pick-up in a mixture or multiplying means, from which signals are generated with a sum and difference frequency; which later signals fed to a low-pass filter, after which the signals with difference the frequency remains ooh thereafter (possibly after amplification carried to an indicating instrument or to an analyzer.

An embodiment of the invention is shown schematically in attached figure. In this it represents the piezoelectric the pick-up l the component to which the vibrations from the machine part is led during the examination. These vibrations converted into electrical signals which are amplified in amplifier 2, after which these signals are fed into a mixer or multiplying means 3. Oscillations are now also fed into the means 3 from a tunable oscillator Ä, whose frequency is slightly higher than the resonant frequency of the pick-up.

In the mixing or multiplying means 3 is generated in a known manner signals with the difference frequency fo-ft and with the sum frequency fo + ft, where fo and ft represent the resonant frequencies of the oscillator Ä resp. pick-upen l.

The signals with difference and sum frequencies are then fed into a low-pass filter 5, the output of which is connected to a peak value detector 6. The sensed signals are reproduced in one indicating instrument 7, from which the magnitude of the errors or the defects can be continuously interpreted or measured; An advantage of the system according to the invention is that the frequency is a low frequency, whereby e.g. can place lower demands on the "analyzing" apparatus, i.e. the peak value detector 6 and the instrument 7, which is not possible when working in the high frequency range. A non-critical low pass filters were used to separate the difference frequency from the signal obtained from the mixing or multiplying the means 3. The amplitude of the difference frequency is thus characteristic of the magnitude of the fault of the machine part, such as a layer being examined. An additional benefit is n: that the resonant frequency of the pick-up l is no longer critical since the oscillator H can be tuned to any .._ .. ø - «----.___._, .._ .. ...___- ev,, _ 780-4165-4 desired frequency. The system is also due to its selective nature insensitive to interference signals intercepted by the pick-up or off the amplifier. The system is also more reliable because one can use one slowly working peak value detector.

Claims (3)

7804165-4 PATENT REQUIREMENTS 1. System for detecting faults or defects in moving machine parts, e.g. layer, using a pick-up, in particular a piezoelectric pick-up, for converting the mechanical vibrations into electrical signals, characterized in that these signals are combined with the signal from an oscillator (Ä), which generates oscillations with a frequency different from or equal to the natural frequency of the pick-up (1), in a mixing or multiplying means (3), in which signals with a sum and difference frequency are generated, the latter signals are fed to a low-pass filter (5) after which the signals with difference frequency remain and are fed to an indicating instrument (7) or an analyzer. 2. A system according to claim 1, characterized in that the natural frequency of the oscillator (R) is slightly higher than the natural frequency of the pick-up (1). 3. A system according to claim 1 or 2, characterized in that the oscillations with difference frequency are fed to a slow-cooperating upper value detector (6).