ABNORMAL NOISE DETECTOR FOR INSPECTING GEAR UNITS

An abnormal noise detector for detecting abnormal noises produced by a gear unit with an eccentrically mounted gear is disclosed. A first embodiment comprises a microphone placed in the vicinity of a gear unit to be tested, a bandpass filter connected to the microphone which passes only a band of frequencies centered around an integral multiple of the normal fundamental frequency of the noise produced by the meshing of the gears of the gear unit, an amplitude detector which detects the amplitude of the signal from the bandpass filter, a frequency deviation detector which detects the frequency deviation of the signal from the bandpass filter, and recorders for recording the values of the signals from the amplitude detector and the frequency deviation detector as a function of time. A second embodiment comprises a microphone, a digital frequency analyzer and a central processing unit for determining whether abnormalities exist in the data produced by the digital frequency analyzer.