Low power control system and associated methods for a water heater with flammable vapor sensor

Abstract

A transistor used as a normally open switch is connected in the millivolt electrical circuit of a fuel-fired natural draft water heater in series with a thermopile device impinged upon by a standing pilot flame, and the solenoid coil portion of the pilot fuel valve. A variable resistance type flammable vapor sensor is connected in a control circuit which is powered by a DC battery and is coupled only to the transistor portion of the millivolt circuit. In the absence of flammable vapor detection by the sensor the control circuit outputs an electrical signal to the transistor that holds it in a closed position to thereby maintain the standing pilot flame. In response to sensor detection of flammable vapor, the control circuit output signal terminates to cause the transistor to return to its normally open switch position, thereby shutting off the pilot flame.

1 . Fuel-fired heating apparatus comprising: 
 a burner adapted to receive fuel and combustion air and create a flame therefrom;    a normally closed fuel valve coupled to said burner for supplying fuel thereto when opened;    a thermoelectric circuit having connected in series therein (1) a thermoelectric device positioned to receive heat from said flame and responsively generate an electrical voltage, (2) a solenoid structure operative to receive electrical power from said thermoelectric device and responsively hold said normally closed fuel valve in an open position, and (3) a normally open switch device; and    a low power electrical control circuit, operable by an electrical power source and coupled to said thermoelectric circuit only via said normally open switch device, for protecting said heating apparatus against an undesirable operating condition, said low power electrical control circuit having connected therein a variable resistance sensor operative to detect said undesirable operating condition, 
 said control circuit, in the absence of detection by said sensor of said undesirable operating condition, outputting an electrical signal to said switch device to maintain it in a closed state, and terminating said electrical signal upon detection by said sensor of said undesirable operating condition to return said switch device to its normally open state.  
   
   
   
       2 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said fuel-fired heating apparatus is a water heater.    
   
   
       3 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said burner is a pilot burner.    
   
   
       4 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said thermoelectric device is a thermopile structure.    
   
   
       5 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said normally open switch device is a normally open solid state switch device.    
   
   
       6 . The fuel-fired heating apparatus of  claim 5  wherein: 
 said normally open solid state switch device is a field effect transistor.    
   
   
       7 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said electrical power source is a non-thermoelectric electrical power source.    
   
   
       8 . The fuel-fired heating apparatus of  claim 7  wherein: 
 said non-thermoelectric electrical power source is a DC battery.    
   
   
       9 . The fuel-fired heating apparatus of  claim 1  wherein: 
 neither of said thermoelectric circuit and said low power electrical control circuit is operative to receive an electrical current flow from the other of said thermoelectric circuit and said low power electrical control circuit.    
   
   
       10 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said variable resistance sensor is a flammable vapor sensor.    
   
   
       11 . The fuel-fired heating apparatus of  claim 1  wherein: 
 said low power electrical control circuit further includes a multi-resistor bridge section, and    said variable resistance sensor forms a resistive portion of said bridge section.    
   
   
       12 . The fuel-fired heating apparatus of  claim 11  wherein: 
 said low power electrical control circuit further includes an operational amplifier having an input portion operatively connected across said bridge section, and an output portion coupled to said normally open switch device.    
   
   
       13 . The fuel-fired heating apparatus of  claim 12  wherein: 
 said operational amplifier is an open collector output type operational amplifier.    
   
   
       14 . The fuel-fired heating apparatus of  claim 13  wherein: 
 said low power electrical control circuit further includes a first electrical lead interconnecting said output portion of said operational amplifier to said normally open switch device, a second electrical lead interconnected between said first electrical lead and said bridge section, and a pull-up resistor connected in said second electrical lead.    
   
   
       15 . A method of inhibiting extraneous flammable vapor ignition by a fuel-fired heating appliance having a burner adapted to receive fuel and combustion air and create a flame therefrom, a normally closed fuel valve coupled to said burner for supplying fuel thereto when opened, a thermoelectric circuit having connected in series therein a thermoelectric device positioned to receive heat from said flame and responsively generate an electrical voltage, and a solenoid structure operative to receive electrical power from said thermoelectric device and responsively hold said normally closed fuel valve in an open position, said method comprising the steps of: 
 installing a normally open switch device in said thermoelectric circuit in series with said thermoelectric device and said solenoid structure;    providing a low power electrical control circuit having an electrical power source and a variable resistance type gas sensor incorporated therein, said control circuit having an output portion operative to create and maintain an electrical output signal in the absence of said sensor being exposed to a predetermined concentration of a gas, and to terminate said electrical signal when said sensor is exposed to at least said predetermined concentration of the gas; and    coupling said output portion to said thermoelectric circuit, only via said normally open switch device so that the resistance of said sensor is not present in said thermoelectric circuit, in a manner such that said normally open switch is closed during the presence of said electrical signal, and is open in the absence of said electrical signal.    
   
   
       16 . The method of  claim 15  wherein: 
 said fuel-fired heating appliance and said thermoelectric circuit are existing apparatus, and    said method is performed as a retrofit method in which said low power electrical control circuit and normally open switch device are operatively coupled to the existing thermoelectric circuit.    
   
   
       17 . The method of  claim 15  wherein: 
 said installing step is performed using a solid state switch.    
   
   
       18 . The method of  claim 15  wherein: 
 said installing step is performed using a field effect transistor.    
   
   
       19 . The method of  claim 15  wherein: 
 said providing step includes the step of using a DC battery as said electrical power source.    
   
   
       20 . The method of  claim 15  wherein: 
 said providing step is performed using a flammable vapor sensor as said variable resistance type gas sensor.    
   
   
       21 . The method of  claim 15  wherein: 
 said providing step includes the step of incorporating said gas sensor as a resistive portion of a multi-resistor bridge section of said low power electrical control circuit.    
   
   
       22 . The method of  claim 21  wherein: 
 said providing step includes the step of connecting the output side of an operational amplifier across said bridge section, and    said coupling step is performed by electrically connecting the output side of said operational amplifier to said normally open switch device.    
   
   
       23 . The method of  claim 22  wherein: 
 said operational amplifier is an open collector output type operational amplifier,    said coupling step includes the step of connecting a first electrical lead between said output side of said operational amplifier and said normally open switch device, and    said providing step includes the steps of interconnecting a second electrical lead between said first electrical lead and said bridge section, and connecting a pull-up resistor in said second electrical lead.