Apparatus and method for shutting down fuel fired appliance

An apparatus for controlling the operation of a fuel-fired appliance burner having a gas valve solenoid circuit for enabling the flow of gas to the burner, comprising:

• a sensor capable of detecting the presence of flammable vapor;
• a first switch in series with the gas valve solenoid circuit for interrupting a thermocouple voltage to the gas valve solenoid to disable the flow of gas;
• a fuse that normally conducts a current to the first switch to maintain the first switch in a conductive state for applying a thermocouple voltage to the gas valve solenoid;
• a second switch that responds to detection by the sensor of the presence of a predetermined level of flammable vapor concentration, by supplying a current through the fuse sufficient to interrupt the current for maintaining the first switch means in a conductive state, such that the first switch interrupts the thermocouple voltage applied to the gas valve solenoid to shut off gas to the burner.

A control circuit for shutting off a fuel-fired appliance burner having a thermocouple voltage that enables a gas valve solenoid to supply fuel to the appliance burner, the control circuit comprising:

• a power source for powering the control circuit,
• a first switch that is connected in series with the gas valve solenoid of the appliance in a manner such that the thermocouple current to the gas valve solenoid is interrupted when the first switch opens to cause the flow of gas to the burner to be shut off;
• a sensor capable of detecting the presence of flammable vapor, the sensor responsively changing in resistance as the concentration of flammable vapor changes;
• a fuse that normally conducts current from the power source to the first switch to maintain a conductive state of the first switch for supplying thermocouple current to the gas valve solenoid;
• a second switch, which, responsive to detection by the sensor of the presence of a predetermined level of flammable vapor concentration, supplies a higher current through the fuse which opens to interrupt the current for maintaining the first switch in a conductive state, such that the first switch interrupts the thermocouple voltage applied to the gas valve solenoid to shut off the gas to the burner;
• and
• a voltage divider circuit including a resistor and the sensor, wherein the detection of a predetermined level of flammable vapors by the sensor causes the voltage potential between the resistor and the sensor to activate the second switch for switching a current from the power source through the fuse sufficient to open the fuse to interrupt current for maintaining the first switch in a conductive state, such that the flow of gas to the burner is shut-off.

A control circuit in connection with a thermocouple voltage source that powers a solenoid in a gas valve circuit of an appliance, for shutting off the flow of gas to discontinue operation of the appliance burner, the control circuit comprising:

• a power source for powering the control circuit,
• a first switch that is connected in series with the gas valve solenoid of the appliance in a manner such that the thermocouple current to the gas valve solenoid is interrupted when the first switch opens to cause the flow of gas to the burner to be shut off;
• a first sensor capable of detecting the presence of a predetermined level of flammable vapors, the first sensor responsively increasing in resistance as the concentration of flammable vapors increases;
• a second sensor capable of detecting the presence of a second vapor, where the second sensor responsively decreases in resistance as the concentration of second vapor increases;
• a fuse that normally conducts current from the power source to the first switch to maintain a conductive state of the first switch for supplying thermocouple current to the gas valve solenoid;
• a second switch, which in response to the first and second sensors detection of the presence of a predetermined level of a first or second vapor concentration, switches a current through the fuse which opens the fuse and interrupts the current for maintaining the first switch in a conductive state, such that the first switch interrupts the thermocouple voltage applied to the gas valve solenoid to shut off the gas to the burner;
• and
• a voltage divider circuit incorporating the first sensor and the second sensor, so that the detection of a predetermined level of flammable vapors by the first sensor or the detection of a predetermined level of a second vapor by the second sensor yields a voltage potential between the first sensor and the second sensor that activates the second switch device for switching a current from the power source through the fuse that will open the fuse to interrupt current to the first switching means to cause the flow of gas to the burner to be shut-off.