Abstract: A heater including a sensing device for sensing an ambient temperature, a temperature input device for providing a user selectable input temperature both connected to a first circuit to control the heater. The first control circuit includes positive feedback and negative feedback to electrically define a temperature range. The first circuit provides an on/off time duty cycle output wherein the on to off time of the duty cycle is relative to the relationship between the temperature range and the sensed ambient temperature. A second circuit is connected to receive the duty cycle output from the first circuit and is further connected to an alternating current power source to provide a second output signal during the zero crossing of the alternating current power source and when the duty cycle output is present. A driver circuit is connected to receive this second signal and activates the heater when the second signal is active by providing a third signal to a triac which regulates power to the heater.

Abstract: In a flare system for waste gases, apparatus is provided for controlling the flow of purge gas into the flare gas line, as required, and not on a continuing basis. Sensor means are provided for detecting a change in temperature in the flare gas line, and means are provided for controlling the flow of purge gas whenever the temperature in the flare gas line changes to a lower value. No purge gas flow is required when the temperature is constant or when the temperature is rising.