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Apparatus and method for surface inspection with test and reference channel comparison

  • US 4,845,356 A
  • Filed: 01/27/1988
  • Issued: 07/04/1989
  • Est. Priority Date: 01/30/1987
  • Status: Expired due to Term
First Claim
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1. Apparatus for comparing a test surface with a reference surface comprisingdetector means;

  • a test channel means for receiving radiation from the test surface;

    reference channel means for receiving radiation from the reference surface;

    selector means to pass radiation from the test channel means and the reference channel means to the detector means,varying means being provided to vary the radiation passed to or from at least one of the test channel means or reference channel meanscycle means being provided to cycle the selector means between a first state in which more radiation from the test channel than the reference channel is passed to the detector means and a second state in which more radiation from the reference channel than the test channel is passed to the detector means;

    control means being provided to control the radiation varying means to provide a zero or minimum variation of radiation received by the detector means as the selector means is cycled by the cycle means.

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