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Furnace control with safety circuit and non-volatile memory

  • US 9,500,366 B2
  • Filed: 12/05/2013
  • Issued: 11/22/2016
  • Est. Priority Date: 12/05/2013
  • Status: Active Grant
First Claim
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1. In a fuel-fed furnace of the type which comprisesa burner supplied with fuel and which produces a flame;

  • a heat exchanger in which the flame passes through a combustion air path of a heat exchanger to an exhaust;

    a blower which forces a flow or return air from a comfort space through a comfort air path of said heat exchanger, and thence through a ductwork to supply heated air to said comfort space;

    a source of AC power;

    a controller circuit coupled to said source of AC power and which controllably actuates said burner and said blower to effect a turn-on sequence in response to a call for heat from an associated thermostat, and to effect a shut down sequence when said call for heat is satisfied, said controller circuit including a microcontroller having a plurality of input ports and a plurality of output ports including ports to issue control signals for actuation of said burner and for said blower, said controller circuit further including a non-volatile memory device coupled with said microcontroller and operative to store a fault indication when present;

    at least one temperature actuated limit switch effective to commence said shut-down sequence when the temperature of said heat exchanger exceeds a predetermined limit temperature, and which resets to permit said turn-on sequence after said shut-down sequence;

    the improvement whereinsaid microcontroller is configured to so as to store a history of actuations of said limit switch; and

    wherein said microcontroller is operative upon an actuation of said limit switch to establish a lock-out condition to preclude said furnace from effecting said start-up sequence for a period of time depending upon a stored history of actuations of said limit switch;

    said microcontroller being operative to monitor time remaining in said period of time of said lock-out condition;

    said microcontroller being suitably programmed to process the stored history of actuations of the limit switch;

    whereinsaid controller circuit includes a rechargeable DC supply, sufficient to power said microprocessor for a limited period of time in an absence of power provided from said source of AC power; and

    whereinsaid microcontroller is operative, when absence of AC power occurs, to continue to monitor time remaining in the period of time of the lock-out condition; and

    upon restoration of power to said source of AC power, if time remains in said period of time of the lock-out condition, to continue said lock-out condition until the time that remains in said period of time thereof has expired.

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