GB877012A - Electronic temperature control circuit - Google Patents

Abstract

877,012. Automatic temperature-control systems. REGULATOR A.G. Jan. 16, 1959 [Jan. 17, 1958], No. 1679/59. Class 38 (4). In an automatic temperature-control system, heating of a space is controlled by a transistor amplifier having a thermistor in its input circuit, both the thermistor and an amplifier transistor being temperature responsive to influence the control system in the same sense. In Fig. 1 air supplied through a conduit 13 to a room 11 is heated by a hot-water heat exchanger 15. A thermistor 27 responsive to the temperature of the room produces a direct voltage which is amplified by a transistor 25 the output of which energizes a relay 19. The arrangement is such that a rise in room temperature affects both thermistor and transistor in such a sense as to increase the energization of relay 19 until, at a temperature determined by the setting of a rheostat 35, relay 19 operates a solenoid valve 17 to cut off the supply of hot water to heat exchanger 15. Thereafter room temperature is maintained constant by intermittent operation of relay 19. Modifications are described in which (a) resistor 35 is either outside the room or omitted altogether; (b) a thermistor 27 is either arranged in a bridge circuit or replaced by a resistor which is not temperature responsive ; or (c) a further transistor also responsive to room temperature provides a second stage of amplification.