GB934654A - Electronic transistor-controlled device for measuring or control of temperatures - Google Patents

Abstract

934,654. Electric bridge measuring circuits. K. G. BERG. Sept. 1, 1960 [Sept. 4, 1959]' No. 30146/60. Class 37. [Also in Groups XXXV and XXXVIII] Apparatus for simultaneously sensing the temperature at a series of locations and indicating the value of the highest, comprises a multiple bridge circuit having common ratio arm resistors 20, 21 (Fig. 3) and a series of thermistors 22, 28 which, together with preset resistors 23, 29 form parallel bridges, each bridge having a PNP transistor 26, 30 in the unbalance diagonal with the emitters joined together so that the thermistor at the highest temperature, say 28, makes the base of transistor 30 more negative than the base of the other transistors, whereby only transistor 30 passes current through instrument G where it is indicated, or operates an alarm. Each preset resistor 23, 29 may be set to make its associated thermistor 22, 28 and transistor 26, 30 take over control at different temperatures. Transistor 31 compensates for variations in transistor characteristics due to changes in the common ambient temperature. By transposing each thermistor and its preset resistor, or by changing the transistor to an NPN type, the circuit is made to respond to the minimum temperature. The two circuits may be combined (Fig. 6) with a changeover switch 39 to enable the maximum or minimum temperature to be ascertained. In a circuit for determining the mean temperature of a number of locations by means of thermistors 40, 41, 42 (Fig. 7), each thermistor forms one arm of a series of parallel bridge branches, the total unbalance voltage producing the emitter current of a transistor 49, indicated on instrument G. The invention may be used for automatic control of the temperature of hot air fed through a conduit 60 (Fig. 8). The air is heated at 62 by hot water entering at 63 and passing through a valve 65, set by a motor 72, controlled by a regulator 70. Normally thermistor 69 and bridge resistors 75, 20, 21 ensure that the flow of hot water maintains a constant temperature at the outflow 68, but if the temperature in the water outlet 66, as sensed by thermistor 74, falls below a limiting value, control of transistor 77 and regulator 70 passes to thermistor 74. In another control arrangement (Fig. 9), the temperature in a room 80 is maintained constant by thermistor 81, but a further thermistor 82 prevents the temperature of the heated air from falling below a predetermined value.