3—Starting and Stopping Oscillations of an Instron Tensile Testing Instrument

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Abstract
A technique is described for investigating the behaviour of the Instron Tensile Testing Instrument during small intervals of time on starting and stopping. It is shown that, on starting, the carriage speed oscillates about the speed finally attained and that this oscillation dies away in about ¾ second. It is also shown that, during the stopping period, the carriage bounces several times before coming to rest in about ¾ second. This oscillation and bouncing can be considered to be completely negligible when the instrument is used for all normal testing purposes, but they may be of importance when short time intervals are involved. The distances traversed by the carriage during the starting and stopping periods are measured by a glass micrometer scale (engraved with 20 lines/mm) mounted on the carriage. Light passing through this scale falls on a photocell whose output, after suitable amplification, is fed to a cathode ray oscilloscope. The fluctuations in output which indicate the passage of successive scale divisions are recorded by photographing the oscilloscope trace.

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