GB393603A - Improvements in and relating to methods of and means for measuring the intensity of light - Google Patents

Abstract

393,603. Gauging-apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and RUFF, H. R., Waverley, Featherbed Lane, Overslade, Rugby. Dec. 5, 1931, No. 33789. [Class 106 (ii).] Light from a suitable source is concentrated on an aperture or substance, and the light passing therethrough falls on to a light-sensitive device connected in a bridge circuit containing a variable capacity and an electric discharge device the current from which passes through a measuring instrument to give an indication of the light intensity; the apparatus may be used to determine the width of the aperture. As shown, light from a source 1 is concentrated by a lens system 2 on to a slit 3 to be measured. Light passing the slit falls on a photo-electric cell 4 connected in a bridge circuit containing a variable capacity 5. An alternating current supply is connected across an autotransformer 7, or other transformer, and the voltage at the ccntre of the bridge constitutes the grid voltage of an electric discharge device 6, preferably of the vapour type. A direct current ammeter, or other measuring instrument 9, and a variable resistance 8, may be connected in the anode circuit. The apparatus is used by cutting off all light from the cell 4 and adjusting the capacity 5 so that current is just prevented from flowing in the anode circuit. A standard slit or other article is then placed in position and the resistance 8 is adjusted until the meter 9 gives an appropriate indication; the meter having been previously scaled as desired. The slits or other articles to be measured are then substituted for the standard, and the reading of the meter indicates variations from the standard.