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Sensor for water film on a plate in printing machines

  • US 5,185,644 A
  • Filed: 07/17/1991
  • Issued: 02/09/1993
  • Est. Priority Date: 07/17/1990
  • Status: Expired due to Term
First Claim
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1. A sensor for measuring the thickness of a water film formed on a plate in a printing machine, comprising a narrow-band light source, a photo modulator for alternatively chopping light from the light source into p-polarized and s-polarized beams, a collimator for making rays of the chopped beams parallel to each other with a given cross-sectional area for measurement, a wave-length plate for adjusting wavefront of the collimated parallel rays and directing the parallel rays onto the water film at a selected angle of incidence, and a device for receiving light beams reflected specularly from the plate and for calculating the thickness of a water film formed on the plate.

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