Fibre optic displacement sensor for the measurement of amplitude and frequency of vibration

This paper reports the principle of operation, design aspects, experimentation and performance of an extrinsic fibre optic displacement sensor for the measurement of amplitude and frequency of vibration. The device consists of fibre optic transmitter, fibre optic probe, mini-shaker, power amplifier, dynamic signal analyser and photodiode detector. The fibre optic probe consists of two well-polished PMMA (polymethyl methacrylate) fibres cemented together along some distance over the length. The sensor is capable of measuring vibration amplitudes ranging from 0.008 to 0.74 mm within a frequency range of 75 to 275 Hz. The sensitivity of the device is found to be 0.893 V/mm over 0.6 to 2.1 mm range and -0.226V/mm over 2.9 to 5.9 mm range. The simplicity of the design, high degree of sensitivity, dynamic range and the low cost of the fabrication make it suitable for real field applications. With the emerging fly-by-light concept, the fibre optic probe solves many sensing problems in aircrafts. Moreover, accuracy and reliability are the excellent pay-offs of this fibre optic sensor.