Solid state optic vibration/displacement sensors

Sensitivities, displacement range, acid accuracy of two types of optical vibration sensors, one fiber optic with a light-emitting diode source (LED/FO) and the other with a laser diode source and small (similar to 1 mm) optics (LD/SO) were designed, assembled, tested, and compared. For the configurations adopted, sensitivity of the LED/FO with a 400-mu m aperture was found to be about 1.13 mV/mu m over a 0.2- to 1.0-mm range and -0.37 mV/mu over a 1.5- to 2.5-mm range. LD/SO sensitivities were -2.28 mV/mu m over a 2.0- to 3.0-mm range for the f/2 design and about -1 mV/mu m over a 0.1- to 10-mm range for the f/5 design. Although the LD/small-optics arrangement is capable of yielding greater sensitivities over longer ranges, the tower cost yet still precise and accurate LED/FO configuration is more rugged and therefore better suited to the field and related in situ and embedded applications. (C) 1996 Society of Photo-Optical Instrumentation Engineers.