Shaft position indicator for use with journal bearings
J J Hunter, Cecil Hughes · British Journal of Applied Physics · 1961
A description is given of equipment using transistors and designed for the indication and measurement of the position of the shaft within the bush of a journal bearing system. Shaft movements cause variations in the impedance of inductive transducers, unbalancing the a.c. bridge of which they are part. The bridge output, in the form of an amplitude-modulated carrier, is supplied to an a.c. amplifier and then demodulated to recover a voltage proportional to shaft displacemet. By monitoring the bearing on two diameters at right angles and supplying the demodulator outputs to the X- and Y-plates of a cathode-ray oscilloscope, a polar plot of shaft movement is possible and the form of vibration can be observed directly. Although designed for use on a bearing of about 1 in. diameter, the equipment is easily adjustable for other bearing sizes and can give useful information with shaft speeds up to 20 000 rev/min. Circuit details are given and discussed and an assessment is made of the accuracies of the various units.