GB1351740A - Electric heat storage devices - Google Patents

Abstract

1351740 Automatic control of temperature ALLIED IRONFOUNDERS Ltd 21 July 1971 [27 April 19701 20086/70 Heading G3R An electric storage heater connected to a two-rate public supply meter ("white" meter) is controlled by a bridge circuit the datum of which is automatically changed by the white meter whereby the heater will be charged automatically to say 1250‹F. during the night and will not be permitted to fall below 260‹F. during the day. Thus a resistor R10 is by-passed during the night by a switch 11, controlled by contacts on the meter, and is effectively in series with a platinum resistance temperature sensor 5 in one arm of the bridge, during the day. At room temperature the probe 5 has for example a resistance of 15 ohms and when this increases to say 37 ohms at 1250‹F. a transistor 9, the base/emitter circuit of which is connected across the output diagonal of the bridge, is biased to conduct and pass current via an amplifier 3 to a relay 4 which switches off current to the heater (not shown) connected to cables 1. With R10 in series with the probe, the probe circuit has a total resistance of 37 ohms when the probe temperature is 260‹F. so that the control circuit will operate to maintain the heater core at this temperature during the day, which is just enough to maintain the room temperature at 140‹F. Alternatively the temperature sensor may be a thermocouple, in which case a secondary D.C. voltage source may be switched into and out of the bridge circuit instead of R10.