APPARATUS AND METHOD FOR ELIMINATING INTERFERENCE ERRORS IN DUAL-BEAM INFRARED REFLECTION MEASUREMENTS ON A DIFFUSELY REFLECTING SURFACE BY GEOMETRICAL ELIMINATION OF INTERFERENCE-PRODUCING SPECULARLY-REFLECTED RADIATION COMPONENTS

摘要

Interference error elimination is provided for infrared reflection measurement of a film having a diffusely reflecting surface by apparatus and method which utilizes geometrical arrangement of apparatus components for geometrical selection of only diffusely reflected radiation components and elimination of specularly reflected radiation components that would produce interference error. A specific application of this measurement technique is in connection with a two-layer, sheet-form product having a film of infrared-radiation-transmissive material formed on a substrate or base layer with the interface surface being diffuse. A radiation source forms and directs two beams of infrared radiation of discrete wavelengths in angularly incident relationship toward an exposed, specular surface of the film producing reflective-components at both the specular surface and the diffuse interface surface. Only diffusely reflected components of incident beams of radiation are detected by a radiation-responsive sensor which is disposed in a particular geometrical arrangement such that only the diffusely reflected beam components are incident to a radiation receptor surface of the sensor. Thus, interference errors are eliminated as the specularly reflected beam components will not be incident to the radiation sensors receptor-surface.