| 摘要 |
1,222,677. Photo-electric distance measuring. ELTRO G.m.b.H. & CO. GES. FUR STRAHLUNGSTECHNIK. 14 June, 1968 [28 June, 1967], No. 28351/68. Heading H4D. [Also in Division G1] The amplification factor of a photomultiplier, e.g. in a laser distance measuring device is varied in dependence upon the intensity of the background radiation. The photomultiplier 4 receiving reflected laser pulses through a field stop 1, lens 2 and filter 3 produces corresponding pulses together with noise proportional to the intensity of background radiation. A pulse counter 7 determines the frequency of noise pulses of sufficient amplitude to cause a false indication if they arrive at an appropriate time. The signal from the counter 7 controls a setting member 9 for the photomultiplier H.T. transformer 10 so that the photomultiplier gain is always such that there is a predetermined probability of a false indication occurring, and the sensitivity of the apparatus is always at the maximum permitted by the prevailing background radiation. The probability of false indication is selected by a potentiometer 11 and the selected level indicated by meter 8. In a modification Fig. 2 (not shown) the inputs to counter 7 is derived from a separate photodiode instead of the photomultiplier 4.
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