It is indispensable for the reliability of the attributes derived from the acoustic emission that the noise emissions stemming to the operation of the machine, which are not directly related to the machining process, are stationary and separable from the process noise.
Fig. 10-5 shows an assortment of relevant emission sources in grinding machines. Measurement results are applied to the frequency ranges shown at the measurement locations of grinding and workpiece spindles, grinding and workpiece spindle headstocks and the tailstock since there appear the strongest process emissions.
Hydraulic noise and electrical disturbances generally exhibit amplitudes that do not significantly influence the grinding spectrum [MEYE91]. One dominant source of disturbance on the other hand is characterised by main spindles with ball bearings. By means of cage noise, rollover frequencies etc., disturbance spectra emerge that permit a reliable measurement at the spindle housings in exceptional cases only. In this case, flawless signals can often only be captured directly on the rotating spindle with contactlessly transmitting AE sensors or fluid sensors. Disturbances can also appear because of the flow of cooling lubricant. However, their intensity reduces significantly above 15 to 20 kHz, such that here a high-pass filtering leads to a sufficient isolation of the process signal.