Comparison between two methods of optical profilometry on micro-PTC

The development of a new prototype of micro-PTC (Parabolic Trough Collector) system requests to study the optical characteristics of the mirrors in use. Two techniques were developed for this purpose. The first one is based on the projection of a Moiré pattern on the mirror surface covered with an opaque material. It provides a reconstruction of the profile from which it is possible to calculate focus position, vertex position and hence the focal length. This method represents a very fast estimation of the macroscopic defects of parabolic collectors, which is useful to determine the quality of the product. The second method is based on the analysis of the reflection of a laser beam, scanning the surface of the parabolic mirror. Despite this latter method is more time consuming, it is a more accurate technique that allows measuring both position and slope of each point of the mirror. In addition, this second method permits to estimate the intercept factor of the concentrator.