In collaboration with the "Fractal" enterprise (Moscow Aviation Institute, Moscow, Russia) I took part in the industrial equipment design for the HDK-Technik GmbH Company (Quedlinburg, Germany). Their special apparatus has to produce a thin tape (about 10...100 (ug/cm2)) with some special physical and chemical properties. My subtask was development of an electronical device to measure the amount of this film wich is rolling up during the technological process. The simplest solution was to measure the increasing diameter of the foil drum using selsyn sensors with a light lever arm touching the film. I developed a board to operate selsyn sensors and to stop the conveyor if the foil has been torn.