Measurement of velocity of moving solid particles - involves application of signals to two points and their spacing in time determined

The two test points are provided at a certain distance from each other in the directon of particle movement and signals are applied through light conductors and are detected by photoelectric transducers; their spacing in time is determined by a cross correlation calculator; light conducting glass or plastics fibres are used for light supply to the test points, and to return the reflected light to photocells, in order to obtain a high optical resolution, two single glass fibres are used for guiding the reflected light, and one or several adjacent fibres are used for illumination. The apparatus determines the time for patterns of particles to pass between the two points.