Measuring or identification system for measuring change

摘要

A sensor-active region is provided with at least two measuring paths, a radiation source and receiver (16). A circuit (23, 30) activates each path in a determined switching sequence. An adjusting unit sets the radiation output of each source, such that with a dry sensor-region, each source generates a part of the detection signal. The average amplitude of the part is equal to those of the parts assigned to the other radiation sources of groups of the detection signal. The detection signal (SD) is supplied to an evaluation circuit (41) to produce a control and/or measurement signal (S41) to establish the different parts assigned to individual sources.