Abstract: In the power controller disclosed herein, a load is energized from an a.c. line through a triac. When the triac is triggered on an a.c. half-cycle of one polarity, a capacitor is charged while the load is energized. The capacitor is interconnected with the gate circuit of the triac through an SCR and the charging circuit for the capacitor is arranged so as to trigger the SCR on the a.c. half-cycle following a half-cycle during which the capacitor was charged. Thus, the triac is selectively triggered on alternating half-cycles and integral cycle energization of the load is obtained.

Abstract: A temperature controller for use with an electrical heater for precisely maintaining the temperature within a system at a selected set point, and employing an improved bridge circuit. A temperature sensitive resistor forms one of the two variable arms of the bridge circuit. The resistor varies in value as a function of temperature exhibiting a temperature coefficient of resistance which is not constant but which varies, decreasing with increasing temperature. The other variable arm, the setting arm, is in the form of a network, including a linear setting resistor and a pair of fixed resistors arranged in a series-shunt circuit. The setting resistor is linearly calibrated in terms of temperature, the series-shunt arrangement providing a composite resistance-set point temperature characteristic which closely corresponds to that of the sensing arm.