GB728774A - Improvements in ambient-temperature compensated device for measuring the intensity of radiant energy - Google Patents

Abstract

728,774. Electric bolometers. LEEDS & NORTHRUP CO. Nov. 25, 1952 [May 29, 1952], No. 29841/52. Class 40 (3). The structure of an electrical bolometer is formed so that the thermal conductivities of the heat paths compensate for changes in the output of the heat-sensitive element with changes in ambient temperature. As shown, the temperature of an object S, Fig. 1, is determined by focusing radiation from a limited area on a diaphragm 14 by reflection from a concave mirror 12, as checked via an eyepiece 15, and refocusing the part of the image that passes through an aperture 14a on to a target 25 by further reflection from a second concave mirror 13. The target comprises a bifilar temperaturesensitive resistance winding 70, Fig. 4, cemented on to a base 70a and connected to diametric strips 71, 72 on a mounting ring 20, fixed to the housing 21 by three metallic legs 20a, 20b, 20c. The base 70a is also connected to the ring 20 by a wire 73 acting as a shunt heat flow path. The resistance winding 70 is connected in a bridge circuit comprising two equal ratio arms 75, 76 and a resistance winding 74 having the same resistance as the winding 70, and in heat contact with the ring 20. Bridge balance is indicated by zero current in detector D, and unbalance is measured by balancing the output voltage with a voltage from a tapped potentiometer 88, whose slider 88a is attached to a recording pen and chart 91, the ratio of the currents from the bridge supply 82 and the balancing supply 86 being maintained constant. The bridge does not, however, make allowance for variations in radiation and conduction losses from the target area with changes in ambient temperature, and the heat conduction paths are designed to compensate for such variations. A mathematical analysis shows how the dimensions of the thermal shunt wire 73 may be calculated to provide this compensation, which may alternatively be provided by proper dimensioning of the copper leads 71, 72. Specification 692,116 is referred to.