B6.4 - Optical Measurement of the Thickness of an Individual Layer in a Plastic Multilayer Compound

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B6 - Dimensional Measurement
W. Weber, D. Plohmann - Sensorik-Bayern GmbH, Regensburg (Germany), M. Huber, H. Steigerwald - Strategische Partnerschaft für Sensorik e.V., Regensburg (Germany)
321 - 322


In plastic multilayer compounds the functionality of the system is often provided by a single functional layer. The materials used for these functional layers often are comparatively expensive, which makes it desirable to have these layers as thin as possible.
The pipe extrusion method is the standard manufacturing technique for production of multilayer plastic pipes. To be safe, the functional layer is deposited with significantly higher thickness than actually required. This procedure causes a significantly higher material and financial effort. Currently no available sensor can selectively measure the thickness of the single layers. Here, we present an optical solution to this problem. It is based on the absorption principle. While plastics cannot be distinguished using standard, their absorption spectra often are significantly different. The corresponding absorption spectra mainly depend on the molecular consistency of the substance. The operating frequency is chosen in a way that the absorption of the functional layer is significantly higher than the absorption of the other layers at that frequency.
Certain operating frequencies may require the use of extraordinary optical sources like quantum cascade or distributed feedback laser sources for this technique to work. Our solution is designed for the quality management process of conventional multilayer compounds like floor heating pipes. Thickness deviations of the monitored layer can be detected during the pipe extrusion process, therefore making it no longer necessary to apply excessively thick layers of the expensive functional material without compromising the quality of the product.