GB941471A - Improvements in or relating to electro-optical detectors - Google Patents

Abstract

941,471. Photo-electric measurement of temperature. BLACK AUTOMATIC CONTROLS Ltd. June 14, 1960 [March 19, 1959],No. 9517/59. Heading G1A. A detector for indicating or measuring a change in a physical quantity such as temperature or pressure comprises a pair of apertured light obturators spaced apart along the light beam between a light source and a light responsive element together with fluid pressure means responsive to changes in the physical quantity for displacing at least one of the obturators with respect to the light beam so as to expose or obturate the light responsive element. In an arrangement, Fig. 1, for detecting the relative difference in temperature of the air within and without an enclosure 1, bulbs 6, 8 are connected by capillary tubes 5,7 with bellows members 2, 3 connected to laminar obturators 9,10 having apertures 11,12 normally aligned with a light-source 16 and a photo-cell 17. Relative change between the internal and external temperatures produces relative movement between the members 9,10 so that light is prevented from reaching the cell 17 which is arranged to operate an indicating device. A beam of relatively large cross-section may be employed so that a rough quantitative indication may be derived. In a modification, Fig. 2 (not shown), for indicating a rise in temperature, a bulb exposed to the temperature changes to be detected operates a bellows having a knife-edge connection with a pivoted T- shaped lever having a horizontal arm carrying the apertured obturators 9,10. The connection between the bellows and the lever may be modified to provide response to a fall in temperature. The Provisional Specification describes a modification, in which the optical system 16, 17 may be replaced by a pair of coaxial, relatively free air jets which are variably obturated by the edges of the apertures 11,12 in the plates 9,10 respectively before impinging on a pressure sensitive element.