Design and development of a torsiograph having a serrated-condenser pick-up unit

Abstract

The instrument that forms the subject for this report has a condenser pick-up unit to which a carrier wave is applied : it measures, directly, instantaneous angular displacements due to shaft twist. The pick-up originated in a surface-strain gauge (embodying serrated-condenser elements) which had been the subject of some preliminary experimental work. Two main types of torsiograph are contrasted in relation to their application and the present torsiograph is described. Results of calibration tests with different serrations and air-gaps are given, together with a general account of experience gained during a total of some 10 hours running with the instrument fitted to a Merlin II engine. Some typical records are included but not the results of the torsional vibration investigation - which will form the subject of a separate report. Calibration resultg are given from which the serrations appropriate to particular applications can be decided. The torsiograph gives very satisfactory results when due care is taken with electronic equipment. The natural frequency of the instrument is such that torsional vibrations having a frequency as high as 80,000 cycles per minute can be recorded with ease. The instrument provides a means of making continuous observations of torsional vibration at a moderately remote station and it can be adapted for making observations in flight.