Fibre optic sensor for speed measurement

Gogoasa, Ion (1996) Fibre optic sensor for speed measurement. Research Master thesis, Victoria University of Technology.


Determination of speed is an important requirement in a wide variety of technical and industrial applications. The measurement of speed has evolved from pure mechanical to magnetoelectric and radio frequency (RF) based devices. There is however a demand for low-cost sensors capable of operating in potentially hazardous environments in which optical fibre sensors are more suited. In this thesis the development of a non-intrusive speed measurement sensor, based on optical technology is described. The optical fibre sensor described herein gives an almost instantaneous indication of the speed and is compared to a commercial speed sensor (Cateye, 1993) which relies on a magnet attached to a rotating surface yielding an averaged speed reading over several revolutions. The optical speed sensor requires incoherent light, conveniently provided by two low cost 780 nm CD-type laser diodes. The light was directed through a pair of spatially displaced fibres illuminating the moving surface. Some of the back-scattered light from the moving surface was collected by a second pair of fibres leading to two photodiodes (where the light information was converted into an electrical signal). An analogue to digital converter in conjunction with a PC (386SX-33) was used to digitise the signals from the photodiodes. The numeric data was then used to compute the speed of the moving surface using a cross-correlation technique. The optical fibre speed sensor was tested successfully on a large number of surfaces at speeds up to 30 km/h. It showed excellent agreement (better than 3%) with the commercial speed sensor. The absolute accuracy (about 9% at 30 km/h) is limited only by the quality of the analogue to digital converters and indirectly by the data processing capability of the PC.

Additional Information

Master of Science

Item type Thesis (Research Master thesis)
Subjects Current > FOR Classification > 0205 Optical Physics
Current > FOR Classification > 0915 Interdisciplinary Engineering
Historical > Faculty/School/Research Centre/Department > School of Engineering and Science
Keywords optical fiber detectors, speed measurement systems, techniques, theoretical analysis
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