GB874141A - Improvements in or relating to electrical temperature measurement apparatus - Google Patents

Abstract

874,141. Temperature measurements. WAYNE KERR LABORATORIES Ltd., FLETCHER, K. A., and GOURIEL, G. G. April 25, 1960 [June 2, 1959], No. 18858/59. Class 40 (1). [Also in Group XXXVI] The time lag occurring in the measurement of temperature by means of a sensitive element which gives an electrical signal representative of the temperature is minimized by .supplying the indicator with the amplified differentiated signal in addition to the signal itself; the amount of the differentiated signal is arranged to be insufficient to cause overshoot. In the Figure a D.C. bridge circuit includes a resistor 10 of spinel in a glass bead, of the type described in Specification 864,587 whose resistance R varies with temperature T according to the law T# - R/(R + K); the resistance of the bridge arm 13 is made equal to K. The resistances of the other arms are made low so that the bridge output varies linearly with temperature. The voltage across 10 is applied to an emitter-follower transistor stage 18 whose output is directly coupled to a transistor amplifier 21. The signal from this stage is differentiated by one of the capacitors 23 or 25 in conjunction with resistor 17 and applied to a meter 16 in addition to the normal unbalance output of the bridge. The initial deflection of the meter is thus made more rapid without any effect on the final steady value. The transistor stages are biased at or near the mid-points of their characteristics so that the differentiating effect is operative whether the initial temperature of the element 10 is above or below the temperature to be measured. The alternative capacitors 23 and 25 are included so that the time constant can be changed to suit the degree of thermal contact between the element and the body to be measured. Thus, a different value can be used when the element is immersed in a liquid than that when it is placed on a solid surface.