GB558299A - Improvements in or relating to electrical temperature indicators - Google Patents

Abstract

558,299. Temperature-variable resistances; resistance measurements. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., WOLFSON, H., AMBROSE, D. M., and SHEPARD, S. C. June 26, 1942, No. 8820. [Class 37] A circuit arrangement for measuring temperature or currents comprises a thermistor and means including a current meter for measuring or indicating the resistance of the element. As shown in Fig. 1, a directly heated thermistor T is connected in series with a battery B, a constant or adjustable resistance R and a direct current instrument M which may be calibrated in terms of temperature. In an alternative arrangement the thermistor forms one arm of a Wheatstone bridge. Alternatively two thermistors, one of negative and one of positive temperature coefficient, may form two arms of the bridge. For measuring currents a thermistor of the indirectly heated type is employed and the current to be measured or a predetermined proportion thereof is passed through the heating coil. Fig. 3 shows a directly heated thermistor for use as a thermometer and particularly for immersion in a liquid. A bead 1, which may be similar to that described in Specification 545,679, is sealed into the tip of a glass tube 2, the bead being mounted on fine wires 7, 8 welded to lead-out conductors 3, 4. The glass is fused closely around the bead 1 to make good thermal contact. Fig. 4 shows another form of thermometer for use in the open air or in a non- reducing gas. A directly heated thermistor bead 1 is mounted on the leads 3, 4 which are supported on a glass base 9. This also carries a wire gauze screen 10 which serves as a mechanical shield without appreciably impeding the circulation of air. Indirectly heated thermistors may be similarly mounted. A pair of directly heated thermistor beads with temperature coefficients of opposite sign may be sealed into the tip of the tube 2, Fig. 3, or one each in a pair of closely adjacent tips, and connected in adjacent arms of a Wheatstone bridge. Similarly two beads may be mounted close together inside the screen 10, Fig. 4. Specification 540,844 also is referred to.