Importance

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Abstract

A system for controlling the temperature at a location which is heated by a heater. The heater is intermittently energized by a source of electrical power in response to control signals from a temperature control circuit. The temperature control circuit includes a comparator-amplifier having one input coupled to a sensed temperature signal. The other input to the comparator-amplifier is a set point temperature level. The sensed temperature signal is produced by a bridge circuit including a temperature sensor at the location which is being heated. The comparator-amplifier includes a feedback network to establish a pulse output of a certain frequency when the two inputs are equal. In order to expand the operating band of the comparator-amplifier, an a-c voltage is introduced superimposed on the set point input. Over the operating band the output pulses from the comparator-amplifier are inversely proportional to the sensed temperature signal, and these pulses are used to control the application of electrical power to the heater.

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First Claim