Electronic furnace control system

Claim 1

An electronic furnace control system for forced air gas or oil fired furnaces including a plenum chamber, a burner mechanism connected to a source of fuel, a valve controlling the flow of fuel to the burner mechanism, a solenoid operating the valve, a motor driven fan for circulating air, a furnace operating circuit connected with the fan motor and solenoid, a thermostat for controlling operating of the furnace operating circuit, said electronic furnace control system comprising: a normally open fan relay circuit connected with the furnace operating circuit, a relay latching circuit connected with the fan relay circuit, a delayed electronic pulse-emitting timing circuit including a pulse emitter which emits a single delayed pulse signal after the timing circuit has been energized, a relay switching circuit connected with the furnace operating circuit and pulse-emitting timing circuit and being operable to energize the later when the solenoid is energized by the thermostat, a gated control circuit connected with the fan relay circuit and relay latching circuit and being operable to receive the pulse signal from the pulse emitter and to energize the fan relay circuit and relay latching circuit, said relay latching circuit being operable to latch the fan relay circuit in closed condition while the furnace operating circuit has been closed by the thermostat, an electronic temperature sensing circuit being operable to sense the temperature in the plenum chamber and providing a changing voltage signal in response to changes in temperature in the plenum chamber, the voltage signal provided by the electronic temperature sensing circuit decreasing in magnitude as the temperature in the plenum chamber increases and increasing in magnitude as the temperature in the plenum chamber decreases, a comparator and amplifying circuit receiving the output voltage from the sensing circuit and amplifying said voltage when it exceeds a predetermined magnitude, said comparator and amplifier circuit including adjustable circuit means for sensing temperature changes in an increasing order of magnitude and including an adjustable electronic hysteresis circuit means for seNsing temperature changes in the decreasing order of magnitude, whereby the electronic furnace control may be adjusted to control operation of the furnace within an optimum temperature range, a normally closed solenoid relay circuit connected with a solenoid and with the comparator and amplifying circuit said solenoid circuit receiving the recurrent amplified output voltage from the comparator and amplifying circuit and being operable to de-energize the solenoid, said solenoid relay circuit being closed to energize the solenoid when the temperature in the plenum chamber falls below a predetermined level, and while the furnace operating circuit is closed by the thermostat, a delayed pulse-emitting reset timing circuit connected with the relay switching circuit, the fan relay circuit and relay latching circuit, and being operable to emit a delayed pulse signal to de-energize and reset the fan relay circuit and relay latching circuit when the furnace thermostat has opened the furnace operating circuit.