GB886287A - Voltage or current-sensitive controlling device - Google Patents

Abstract

886,287. Current and voltage measuring. STANDARD TELEPHONES & CABLES Ltd. June 13, 1958 [June 20, 1957], No. 19507/57. Class 37. In a current or voltage - sensitive bridge network, a non-linear resistor 7 is connected in series with a second resistor 10 to one input terminal C, and constitutes one arm, of the bridge; and an amplifier 12, 13, having a differential output connected across the second resistor, has two inputs with respect to a common terminal which are connected to the respective output terminals A, B of the bridge, the common terminal being connected to the other input terminal 20 of the bridge. The base electrodes of transistors 12, 13 are connected to bridge vertices A, B ; the emitter electrodes are commonly connected to the positive side of the bridge input over resistor 11; and the collector electrodes are connected through coils 14, 15 across resistor 10 which is in series with a thermistor 7. The arm AC contains a temperature compensating network constituted by a thermistor 22 shunted by resistor 23. The bridge is initially balanced by adjusting rheostats 6 and 24. Any subsequent fluctuation of the D.C. supply voltage S will produce unequal currents in coils 14, 15 due to unequal bias voltages at A and B ; the coils may be part of a controlling device to maintain S at a given value ; alternatively they may constitute the differential coils of an ammeter. In another embodiment, Fig. 3 (not shown), the transistor collector currents may be amplified by a further pair of transistors; the coils 14, 15 being connected to the collectors of these latter transistors. A capacitor may be shunted across resistor 10 to improve the response of the circuit.