GB1044353A - Temperature control circuit - Google Patents

Abstract

1,044,353. Automatic temperature control systems. FINDLAY, IRVINE Ltd. July 24, 1963 [July 19, 1962; Nov. 21, 1962], Nos. 27862/62 and 44049/62. Heading G3R. An automatic temperature control system suitable for example for the electric heating of roads or floors comprises two temperature-sensing transistors 16, 25 responsive to the temperature to be controlled and arranged so that relay contacts 24 in series with the heating system are controlled according to both the temperature and its rate of change. This latter effect is produced by the transistor 25 which is connected to transistor 16 through a transistor 26, a differentiating circuit comprising capacitor 31, transistor 32 and resistor 33, and a further transistor 34. A biasing circuit comprising resistors 13, 14, 15 and potential divider 12 provides for temperature setting, and the relay coil 22 is controlled by transistor 16 through amplifier transistors 18, 21 so that a rise in temperature causes energization of the coil 22 and the opening of contacts 24, and vice versa. Instead of the current through the coil 22 being continuous as in the circuit shown, the coil may be supplied by way of a bi-stable circuit such as a Schmitt trigger circuit controlled by the voltage across the resistor 17 and triggered by transistor 16.