GB1435325A - Thermostatic control arrangement for a heater automatic temperature control s - Google Patents

Abstract

1435325 Automatic temperature control TEXAS INSTRUMENTS Ltd 24 May 1973 24839/73 Heading G3R When a thermostat, designed to switch a room heater on and off in accordance with the ambient air temperature, is mounted on the heater, errors arise from the fact that the temperature sensor receives directly-conducted heat from the heater at a variable rate depending on the proportion of time that the heater is switched on. The invention proposes to eliminate such errors by providing an auxiliary heater which supplies to the sensor an amount of heat inversely dependent on the proportion of each switching cycle that the main heater is on. The auxiliary heater and main heater are required, in combination, to provide an average rate of heat input which is the same from cycle to cycle. In Fig. 2, a bridge circuit, including as one arm the sensor 8, controls a pulse generator PG and a triac 5, triggered at zero-voltage instants of the applied pulse train, effects an appropriate mark/ space ratio of on/off periods of the main heater element 3. Thermally coupled to the sensor 8 is the auxiliary heater 6, which is switched on whenever the main heater is switched off, and vice versa. The sensor receives heat at the same rate from heater 6 when it is on as from heater 3 when it is on, so that the rate of supply of directly-conducted heat is substantially constant, so eliminating the error which would otherwise be caused by the variable heat input from the main heater 3. The circuit components 12 to 15 in Fig. 2 may be constituted by an integrated circuit (20) Fig. 3, (not shown).