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Methods are apparatus for monitoring the diffuse reflectivity of a surface

  • US 4,988,206 A
  • Filed: 04/26/1988
  • Issued: 01/29/1991
  • Est. Priority Date: 07/04/1986
  • Status: Expired due to Fees
First Claim
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1. A method of monitoring the diffuse reflectivity of a portion of a surface (3), the method comprising:

  • exposing the surface portion to a beam of radiation (9);

    sensing the intensity of a part of the diffuse radiation, reflected by the surface portion, at two sensing positions situated such that the intensity of the diffusely reflected radiation, sensed at each sensing position, is substantially invariant within a working range of distances (D) between the sensing position and the surface portion, the size and position of the surface portion within the plane of the surface being substantially constant within the working range of distances; and

    determining from each sensed intensity a value representative of the diffuse reflectivity of the surface portion;

    the method further comprising;

    arranging the sensing positions in symmetrical locations to either side of the beam of radiation; and

    averaging the intensities sensed at the sensing positions to obtain a diffuse reflectivity value for the surface portion which is substantially invariant to folds and creases in the surface portion.

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