Arrangement for measuring or detecting a change in a back-scattering element

摘要

In the case of an arrangement for detecting wetting of a wettable outer surface (5) of a panel or wall (1) which is transparent to specific radiation, the effect is obtained by an active sensor region (14) with at least two measuring sections having a radiation source and a radiation detector (16), by a switch arrangement (22, 30) for time-interval active switching of each of the individual measurement sections in a specific switching sequence, by an adjustment arrangement (32) for adjusting a radiation power of the individual radiation sources, measured in such a way that when the active sensor region is not wetted, each radiation source produces a section (37) of the detection signal, the mean amplitude value of which is equal to the mean amplitude value of the sections (38, 39) of the detection signal assigned to the other radiation sources or groups of radiation sources, and by a filter circuit (36), connected downstream of the radiation detector(s), for transferring the detector signal (SD) to an evaluation arrangement (41) for producing a control-value and/or measured-value signal (S41) from which the difference, measured or established in the evaluation arrangement, of the sections of the detection signal assigned to the individual radiation sources, that interfering radiation does not substantially influence, distort and vitiate the measurement or recognition of wetting. <IMAGE>