The Measurement of Torsional Vibrations

Abstract

An electromagnetic torsional vibration pick-up unit, developed at Sunbury in the Research Laboratories of the Anglo-Iranian Oil Company is described, the output being shown on the screen of a cathode ray oscillograph to which the unit is connected through an integrating amplifier. Calibration curves are given to show the limits of accurate response, and methods for calibrating in service by simple checks are outlined. Torsiograms taken from a two-stroke and a four-stroke Diesel engine illustrate the type of diagram obtained for each cycle of operations. The value of the unit is much increased by including an electrical filter system in the output. The resulting diagrams show any required harmonic component of the swings, and enable a sufficiently accurate analysis to be made on the test bed either of critical speed swings, forced swings on flanks, or major roll amplitudes. The technique for taking diagrams with this filter unit is described in detail. Examples from actual test records are discussed in relation to points of particular interest in connexion with friction dampers, rubber absorber dampers, systems with two modes of vibration, etc.; and finally a brief reference is made to the measurement of linear vibrations.