Heating element control circuit - has temp. sensitive resistor in bridge whose output is added to sawtooth and to reference voltage

摘要

The control circuit, for a heating element, has a temp. sensitive platinum resistor in a Wheatstone bridge whose output diagonal is connected to the input of an operational amplifier with offset adjustment. In addition to the bridge output, the output of a sawtooth generator and a reference voltage are also applied algebraically to the operational amplifier inputs. The amplifier output controls the transistor that operates a relay in the heating circuit. The reference voltage is produced by either one of two potentiometers selected by switch contacts.