A Fiber Optical Sensor for Non-Contact Vibration Measurements

Vibration tests are fundamental to study the dynamic behavior of equipments and to verify their capability to withstand mechanical stresses. Typically, piezoelectric accelerometers are employed to measure the device response; however, applications exist where even the tiniest accelerometers introduce unacceptable perturbations and therefore it is necessary to use non-contact sensors. This paper describes an intensity based optical sensor for the evaluation of accelerations from non-contact displacement measurements. Plastic optical fibers are used to collect the reflected light from several points on the vibrating surface, allowing the reconstruction of the vibration distribution. Two compensation techniques to reduce systematic effects due to the target reflectivity are also described and compared: one is based on the spectral analysis of the received optical signal and the other takes advantage of a reference displacement sensor. Experimental results in real conditions during vibration tests have demonstrated the capability to measure sub-micrometer vibration amplitudes up to about 40 kHz.