F - Mech Eng,Light,Heat,Weapons – 24 – H
Patent
F - Mech Eng,Light,Heat,Weapons
24
H
341/21
F24H 9/20 (2006.01) F23N 1/00 (2006.01) F23N 5/24 (2006.01)
Patent
CA 1218728
Case No. R110-9843-US APPLICATION OF DALE A. MUELLER FURNACE CONTROL APPARATUS HAVING A CIRCULATOR FAILURE DETECTION CIRCUIT FOR A DOWNFLOW FURNACE ABSTRACT A furnace control apparatus for a downflow forced warm air furnace uses a microprocessor and a thermostat to initiate and control the start-up of the furnace and to monitor the subsequent furnace operation to prevent an abnormal operation thereof. During the initial start-up operation, the microprocessor receives an input signal from the thermostat indicative of the need for a furnace operation and produces an output signal for controlling, in combination with the thermostat which responds to the temperature of the space to be heated, an actuation of a gas valve to supply gas to the furnace. A flame detector is used to provide another input signal to the microprocessor representative of the presence of a burner flame following the opening of a gas valve. Subsequently, an analog temperature sensor in an air supply duct is used to supply another input signal through an analog-to-digital converter to the microprocessor representative of the air temperature in the duct. The microprocessor stores the value of the air temperature following the start-up of the burner and subsequently turns on an air circulator. Following the energization of the air circulator, the microprocessor determines via a fixed logic sequence whether the delivered air temperature rises a minimum amount above the stored initial temperature after a preset time period as an indication of a circulator failure. Additionally, the analog temperature sensor is used by the microprocessor to determine if the delivered air temperature ultimately above a predetermined high or maximum limit an an indication of a restriction in an air return duct. In either case of the delivered air temperature not meeting aforesaid criteria, the microprocessor deactuates the gas valve to interrupt the flow of gas to the burner to protect the heating system. Thus, the thermostat provides a means for con- trolling the furnace in response to the heat requirement of the space to be heated while the circulator failure detector uses the mircoprocessor in conjunction with an analog temperature sensor to monitor the safe operation of the furnace. -2-
456669
Honeywell Inc.
Smart & Biggar
LandOfFree
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