GB789000A - Improvements in or relating to resistor thermometers - Google Patents

Abstract

789,000. Electric temperature measuring systems. RESEARCH INTERESTS, Ltd., and WEISHEIT, G. April 30, 1954 [April 30, 1953; Nov. 28, 1953], No. 12621/54. Class 40 (1). A D.C. bridge circuit for measuring temperature comprises two temperature-sensitive elements 19, 27 (Fig. 1), with negative temperature coefficients, constricted as described in Specification 790,764, located in adjacent arms of the bridge, and a valve 12 connected across the measuring diagonal, the grid connected to one corner and the cathode to the opposite corner of the bridge, whereby the valve anode current, indicated on a meter 17, is proportional to the difference between the temperatures of the elements 19, 27. To measure an absolute temperature the element 19 is replaced by a fixed reference resistor 21, the range of absolute temperatures measured being determined by choice of resistors 23-26. Calibration of the bridge is checked by replacing elements 19, 27 by fixed resistors 21, 28, and the bridge connections are such that a drop in anode voltage, due to ageing of the battery 7, is compensated by a fall in bias voltage on the grid of valve 12 to maintain a constant anode current. The meter 17 may be biased by an adjustable spring torque, or by a bias winding carrying a compensating current, to restrict its deflection to the linear part of the valve anode current characteristic.