Method of and instrument for objective measurement of atmospheric cloudiness

摘要

983,931. Photo-electric measurement of fog or mist. DEUTSCHE AKADEMIE DER WISSENSCHAFTEN ZU BERLIN. June 9, 1961, No. 20931/61. Heading G1A. In an arrangement for measuring atmospheric visibility by switching to an annular photo-cell 9 having a blue-sensitive layer a reference ray from a high-pressure mercury lamp 1 modulated at 100 c/s alternately by rotatable prism 2 with back-scattered light collected by parabolic mirror 11, the reference ray is directed to the photo-cell via a rotatable analyzing filter 7, an attenuator 8 and a polarizing reflecting surface of diaphragm 10, the photo-cell output is amplified in unit 12 which incorporates a 100 c/s filter, rectified in unit 13 and switched alternately to capacitors C1, C2, and the output of differential amplifier 15 actuates a relay to so rotate filter 7 by motor 16 that the photo-cell output is constant; the extent of filter rotation is indicated at 17 and repeated remotely on indicator 20 by the output of motordriven wiper of a potentiometer 18. A cam 14 provides for the necessary timed operation of switches K 1 ... K 4 . Replacing attenuator 8 by one of a different density permits the test range of the apparatus to be changed. The whole arrangement may be fitted to a universal head to afford training in horizontal and vertical planes.