GB1025624A - Electronic temperature regulators - Google Patents

Abstract

1,025,624. Automatic temperature control. R. ROHLF. June 21,1963 [June 22, 1962], No. 24901/63. Heading G3R. An automatic temperature control system comprises a bridge network which includes a variable resistor P1 by means of which a desired temperature may be selected and a resistance thermometer Th which measures the temperature of the controlled apparatus, the bridge output being used to control a two state (ON-OFF) amplifier comprising two transistors T1, T2 subsequently controlling an output stage transistor so as to control the energization of a relay rel. 1 which, by way of its normally open contact, controls the apparatus heating circuit and thus the heating of an element H associated with a negative temperature coefficient resistor Tr connected, in parallel with a fixed resistor R 1 , in a further arm of the bridge, the resistor Tr functioning to bias the bridge to a higher than normal value thus providing the system with a measure of "anticipation". A connection GK from the bridge output to the base of the output transistor T3 provides a safety device in the event of a short circuit of the resistance thermometer Th. A further output stage comprising a fourth transistor and a second relay r.e.1. 2, together with a variable resistor P 2 , may be provided to follow the first output stage, the resistor P 2 being connected in series with the resistor Th. Thus should the apparatus reach a selectable critical value the further output stage becomes operative, for example, to provide an alarm or operate a cooling system.