Improvements in optical pyrometers of the disappearingfilament type and like instruments

摘要

587,065. Pyrometers photometers. HITCHMAN, D. G. I., and SCHOFIELD, F. H. Oct. 8, 1945, No. 26122. [Classes 97 (i) and 97 (iii)] [Also in Group XXXV] The comparison lamp P of a disappearing filament pyrometer or similar instrument for measuring brightness is arranged in the diagonal of a self-regulating bridge circuit so that the current therethrough is maintained constant notwithstanding variations in the voltage supply B. The arms of the bridge are formed by two identical control lamps L, having voltage-current characteristics as shown in Fig. 2, and two resistances m each equal to the tangent of the angle between the straight portion T1, T2 of the curve in Fig. 2 and the current axis. With this arrangement the current through P will be independent of the supply B so long as the lamps L are operating between the points T1, T2. The resistance s is chosen so that current and voltage corresponding to the point T2 are not exceeded with the battery B giving maximum voltage. The lower limit T1 may be readily judged by inspection if the lamps L are chosen so that the point T1 corresponds with a brightness as near as possible to the visible limit. If, however, the point T1 corresponds with a brightness above the visible limit, the lamps may be inspected through an appropriate absorption screen, or an optical system may be provided to enable the brightness of the lamp L to be measured by comparison with the lamp P. A variable resistance r graduated to read temperature direct may be adjusted until the filament of the lamp P is of the same brightness as the observed object. Alternatively, the resistance may have one of a number of predetermined values corresponding to several ranges of brightness, the filament of the lamp P being then made to disappear by using an optical wedge. The effect of air temperature on the characteristics of the lamps L may be compensated by using resistances m and r with appropriate temperature coefficients of resistance. If the lamps L are not identical, effective equality may be achieved by using appropriate resistances in series and/or parallel. In a modification, only one control lamp is used.