| 摘要 |
Over two opposite sides of an opening, in each case one transmitter (S1 and S2) and receiver (E7-E12 and, respectively, E1-E6) are arranged or on one side of the opening transmitters (S3-S8) are arranged and on the opposite side receivers (E13-E18) are arranged, adjacent receivers being caused to evaluate pulses received at mutually different times by means of a circuit, not shown, so that beams of adjacent receivers, received at the same time, do not irritate these receivers. This provides the possibility of a closer sequence of the receivers so that a denser grid of beams can be achieved without impairment of the functional reliability, particularly also in the case of beams with a tendency to dispersion. <IMAGE>
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