Non-coherent light interferometry as a thickness gauge

This paper describes the development and evaluation of an automated measurement system for assessing at-line and on-line polyester thickness uniformity. The instrument is based on non-coherent light interferometry and includes a dual-interferometer, single mode optical fibers, sample coupling optics, custom electronics, data acquisition system, transport mechanism, data outputs, and a computer. The principles of operation and measurement system performance are discussed. The use of the measurement data for measuring machine parameters in addition to thickness uniformity will be shown. Experiments were performed on an extruder machine to determine the suitability of the instrument and the optical probe design for on-line measurements. An automated measurement system was also developed for assessing at-line web thickness uniformity. The instrumentation for the at-line measurements was the same as the on-line system except a sample transport system was added.