| 摘要 |
PCT No. PCT/DE94/00714 Sec. 371 Date Apr. 15, 1996 Sec. 102(e) Date Apr. 15, 1996 PCT Filed Jun. 18, 1994 PCT Pub. No. WO95/01561 PCT Pub. Date Jan. 12, 1995An arrangement for indicating a change in a reflective element of a radiation-permeable medium having a detection side disposed opposite the reflective element. The arrangement includes two measured sections each having a radiation source for generating radiation for transmission through the radiation-permeable medium; a sensor-active surface on the reflective element for reflecting at least a portion of the generated radiation through the detection side; and a radiation receiver for receiving the reflected radiation which has an output for producing a detection signal representing received radiation. The arrangement further includes a switch arrangement for periodically actuating respective ones of the measured sections in a successive, repeating switching sequence according to a predetermined frequency; an adjusting device for adjusting the detection signal so that, in a rest state of the sensor-active surface of each measured section, a part of the detection signal corresponding to each measured section has an average amplitude value equal to an average amplitude value of parts of the detection signal corresponding to other ones of the measured sections; a filter circuit for producing a filtered detection signal; and an evaluation device having an input for receiving the filtered detection signal and producing an output signal in dependence of a difference between parts of the filtered detection signal corresponding to respective ones of the measured sections.
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