Furnace control apparatus and method
First Claim
1. Apparatus for controlling the energization of a main blower fan motor and an induced draft fan motor based on low voltage AC input signals comprising transformer means for providing a selected low voltage AC power supply from a line voltage AC power source having a selected frequency, means for providing a 5 volt DC power supply.microprocessor means having input ports including an interrupt IRQ port and output ports and having a real time clock, the microprocessor means powered by the 5 volt DC power supply, low voltage input signal lines connected to the input ports and adapted to provide the low voltage AC input signals to the input ports,relays having contacts relatively movable into and out of engagement with one another is response to selected low voltage AC input signals to the input ports of the microprocessor means, the contacts adapted to energize high power lines coupled to the main blower fan motor and the induced draft fan motor,the low voltage AC power supply of the transformer means having an AC voltage common connected to the IRQ port, means to detect the falling edge of the AC voltage common wave at the IRQ port and, after a delay of a quarter of an AC wave length, to read the signals at the input ports,and, in response to the signals at the input ports, means to energize the relay contacts from an output signal at the microprocessor means based on the real time clock so that the output signal is asynchronous relative to the AC power line frequency.
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Accused Products
Abstract
An electric control for gas furnaces which controls a two speed main blower fan and an induction draft fan based on inputs from a room thermostat, a high limit and an ignition control including a gas valve. The control has a circuit board having a power supply for providing 24 volts DC current source to drive DC relays and a 5 volt DC power source to power a microprocessor. 24 volt AC input signals are coupled to the input ports of the microprocessor through current limiting resistors and to AC ground through pull down resistors. AC ground is also connected to the IRQ port of the microprocessor. The output ports of the microprocessor are connected to a relay driver which in turn is connected to the relays. Several breakaway tabs in the board provide optional features such as eliminating a normally provided draft delay timing function. Test pads are provided on the board so that the board can be tested during manufacture. An optional feature is shown comprising an LED which can be used to indicate the status of the system. Another optional feature incorporates a zener diode and resistor coupled to each input port to increase input thresholds. This feature is provided for use with power stealing electronic thermostats.
The control calibrates itself on a continuing periodic basis to read the AC inputs synchronously at the peak of their wave and switches the relays asynchronously based on the real time clock of the microprocessor.
46 Citations
22 Claims
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1. Apparatus for controlling the energization of a main blower fan motor and an induced draft fan motor based on low voltage AC input signals comprising transformer means for providing a selected low voltage AC power supply from a line voltage AC power source having a selected frequency, means for providing a 5 volt DC power supply.
microprocessor means having input ports including an interrupt IRQ port and output ports and having a real time clock, the microprocessor means powered by the 5 volt DC power supply, low voltage input signal lines connected to the input ports and adapted to provide the low voltage AC input signals to the input ports, relays having contacts relatively movable into and out of engagement with one another is response to selected low voltage AC input signals to the input ports of the microprocessor means, the contacts adapted to energize high power lines coupled to the main blower fan motor and the induced draft fan motor, the low voltage AC power supply of the transformer means having an AC voltage common connected to the IRQ port, means to detect the falling edge of the AC voltage common wave at the IRQ port and, after a delay of a quarter of an AC wave length, to read the signals at the input ports, and, in response to the signals at the input ports, means to energize the relay contacts from an output signal at the microprocessor means based on the real time clock so that the output signal is asynchronous relative to the AC power line frequency.
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16. The method of controlling a system having a main blower fan motor with heat and cool speed windings and an induced draft fan motor responsive to input signals from a thermostat calling respectively for energization of the heat and cool speed windings and energization of the induced draft fan motor, the system having a microprocessor means for receiving the input signals and for generating output signals, the microprocessor means having an IRQ interrupt port and a real time clock, the system having transformer means for transforming line AC voltage to 24 volt AC power for the input signals including a transformer common, rectified 24 VAC power to energize relays and 5 volt DC power to power the microprocessor means, and respective separate relays for energizing the heat and cool speed windings and the induced draft fan motor in response to the output signals from the microprocessor means, the method comprising the steps of:
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coupling the transformer common to the IRQ interrupt port, executing a sub-routine on each falling edge of an AC voltage common wave on the transformer common, the sub-routine comprising the step of waiting one quarter of a wave of the AC voltage common wave and then reading the input signals to the microprocessor means so that the input signals are read at the peak of the AC wave of the input signals synchronously with the AC voltage, generating an output signal by the microprocessor means in response to respective input signals and the read time clock to coupled the 24 volt DC power to a selected relay asynchronously to the line AC voltage. - View Dependent Claims (17, 18, 19)
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20. Apparatus for controlling the energization of a load based on low voltage AC input signals comprising transformer means for providing a selected low voltage AC power supply from a line voltage AC power source having a selected frequency, means for providing a 5 volt DC power supply.
microprocessor means having input ports including an interrupt IRQ port and output ports and having a real time clock, the microprocessor means powered by the 5 volt DC power supply, low voltage input signal lines connected to the input ports and adapted to provide the low voltage AC input signals to the input ports, relay means having contacts relatively movable into and out of engagement with one another in response to selected low voltage AC input signals to the input ports of the microprocessor means, the contacts adapted to energize high power lines coupled to the load, the low voltage AC power supply of the transformer means having an AC voltage common connected to the IRQ port, means to detect the falling edge of the AC voltage common wave at the IRQ port and, after a delay of a quarter of an AC wave length, to read the signals at the input ports, the low voltage AC input signals being coupled to the input ports of the microprocessor means through current limiting resistors and selected input signals being connected to the AC voltage common through a pull down resistor, and, based on the input signals at the input ports, means to energize the relay contacts from an output signal of the microprocessor means.
Specification