SETT OCH ANORDNING ATT UTFORA OPTISK ROKDETEKTERING

摘要

A light beam of known intensity is transmitted from a sender unit (1) and after passage through an air space, is picked up and its intensity measured by a receiver unit (3). An alarm is activated when the intensity of the picked-up light radiation is less than that of the transmitted radiation by a specific amount. The sender (1) and receiver (3) are connected to a comparison unit (9) which at specific time intervals compares the light effect detected by the receiver (3) with the original value, and if necessary, controls the sender (1) so that the value is built up again.