Abstract
Direct thickness measurements (also called “caliper” sensors) provide an actual thickness measurement of paper web. There are two methods used to provide this. The first is to measure the distance between two product contacting sensing “elements”. The other is to assume the distance between two sensor heads is fixed and to measure the distance to each head from a product to their support. Of the two methods the first will typically provide the highest degree of accuracy and repeatability but needs to either physically touch the material to keep the sensing element at a fixed standoff distance. The contacting sensor sometimes causes the marking, damage and dirt spike problems to products especially for lightweight papers on high-speed machines and supercalender applications. Also the contacting head of Caliper sensor itself has abrasion and dirt build-up problems as a maintenance issue.
So the second method has been developed for a long time, but non contacting methods typically have accuracy problems as a scanning on-line sensor because of the assumed fixed head separation. Honeywell has solved this issue by physically compensating the separation in the two sensing heads and introduced the Non Contacting Laser Caliper. The method for looking at the distance of each sensing head to the sheet and assuming a fixed distance between the two sensing heads is using laser triangulation and Z sensors. This paper presents the new developed Honeywell NC Laser Caliper.
