Speed measuring system for slow moving particles in suspension - detects Doppler shift changes in reflected laser beam transmitted by optical fibre

摘要

Light from a semiconductor laser diode (L) passes through an optical input coupling assembly (C) to a conventional optical fibre (F), which may be a single- or multi-mode type. The other end of the fibre, which may have an optical output coupling (L1) is immersed in the fluid. Some of the light reflected from the moving particle (O), passes back along the fibre to the laser diode housing. Within the laser housing is a photosensor. The mixed signal detected by the sensor is electronically processed to detect the Doppler shift and hence the speed of movement of the particle.