Location filter

from Wikipedia, the free encyclopedia
Block diagram of a speed sensor based on a CCD spatial filter

Spatial filter ( English spatial filter ) are used for non-contact optical measurement of velocity used and size of moving materials. Unlike the air filters in the laser technology is actually a spatial frequency filter.

The spatial filter is based on the filter effect of grid-like structures, e.g. B. a CCD sensor . A lens images the measurement object on it. The pixels contribute with changing signs to the output signal, which is examined for its frequency components . The speed of movement is the product of the image scale, grating period and measured frequency. Telecentric lenses are used to reduce the influence of the exact working distance .

Since all pixels contribute to the signal, a comparatively low illuminance and a low contrast (at the spatial frequency used) are sufficient. The spatial frequency can be electronically switchable for adaptation to different materials or speed ranges or for measuring size distributions.

literature

  • JT Ator: Image Velocity Sensing with Parallel-Slit Reticles . In: Journal of the Optical Society of America . tape 53 , 1963, pp. 1416-1422 ( abstract ).
  • Yoshihisa Aizu, Toshimitsu Asakura: Spatial Filtering Velocimetry: Fundamentals and Applications . Springer, 2006, ISBN 978-3-540-28186-3 , limited preview in the Google book search.