Methods and systems for using flame rectification to detect the presence of a burner flame

Abstract

Systems and methods for detecting the presence of a burner flame using flame rectification are shown and described. A conductive flame sensor is positioned to conduct electricity to a burner flame when the burner is lit. The flame provides a conductive path to the burner conductive body and when operatively connected to an alternating current source, half-wave rectifies the current flowing to the sensor. A flame sensing circuit provides an output signal that is conditioned for use as an input to a flame indicator and/or a controller that is configured to shut off gas flow to the burner when no flame is present after an attempt at igniting the burner.

What is claimed is: 
     
         1 . A burner flame detection system comprising:
 a conductive flame sensor comprising a conductive terminal and positioned proximal to a burner having a conductive body, the burner having an ignited state, and an unignited state, such that when the burner is in the ignited state, the burner and the conductive flame sensor are in electrical communication with one another; and   a flame sensing circuit comprising a flame detection signal output node, wherein the flame sensing circuit is configured to supply an alternating current having a frequency of from about 24 kHz to about 300 KHz to the conductive flame sensor conductive terminal, and when the burner is in the ignited state and the alternating current is supplied to the conductive terminal, the flame sensing circuit generates a rectified current from the conductive flame sensor conductive terminal to the burner.   
     
     
         2 . The burner flame detection system of  claim 1 , further comprising a switch that is operable to operatively connect a source of the alternating current to the flame detection signal output node when the burner is in the ignited state. 
     
     
         3 . The burner flame detection system of  claim 1 , wherein the flame sensing circuit comprises an input node, a conductive flame sensor driver circuit, and a signal conditioning circuit having a signal conditioning circuit output node. 
     
     
         4 . The burner flame detection system of  claim 3 , wherein the conductive flame sensor driver circuit comprises a flame sensor driver circuit input node, a flame sensor driver circuit flame sensor output node, a flame sensor driver circuit flame detection output node, a capacitor, and a bipolar junction transistor (BJT) having a collector an emitter and a base, and the flame sensor driver circuit input node is connected to the BJT emitter and the capacitor. 
     
     
         5 . The burner flame detection system of  claim 1 , wherein the alternating current has a square wave waveform. 
     
     
         6 . The burner flame detection system of  claim 1 , wherein the conductive flame sensor is a hot surface igniter. 
     
     
         7 . The burner flame detection system of  claim 6 , wherein the hot surface igniter comprises first and second insulating tiles and a heating conductive pattern located between the first and second insulating tiles, and the heating conductive pattern is connected to the conductive terminal. 
     
     
         8 . The burner flame detection system of  claim 7 , wherein the hot surface igniter comprises a flame sensing conductive pattern. 
     
     
         9 . The burner flame detection system of  claim 1 , wherein the conductive flame sensor is a flame rod. 
     
     
         10 . A burner flame detection system, comprising:
 a hot surface igniter comprising a conductive pattern connected to a conductive terminal and positioned proximal to a burner having a conductive body, the burner having an ignited state and an unignited state, such that when the burner is in the ignited state, the conductive terminal and the burner conductive body are in electrical communication with one another.   
     
     
         11 . The burner flame detection system of  claim 10 , further comprising a flame sensing circuit configured to supply a flame sensing alternating current to the hot surface igniter conductive terminal, wherein when the burner is in the ignited state and the flame sensing alternating current is supplied to the hot surface igniter conductive terminal, the flame sensing circuit generates a rectified current from the hot surface igniter conductive terminal to the burner. 
     
     
         12 . The burner flame detection system of  claim 10 , further comprising a flame detection signal output node and a switch that is operable to operatively connect a flame sensing alternate current source to the flame detection signal output node when the burner is in the ignited state. 
     
     
         13 . The burner flame detection system of  claim 11 , wherein the flame sensing circuit comprises a flame sensor driver circuit having an input node, and a signal conditioning circuit having a signal conditioning circuit output node. 
     
     
         14 . The burner flame detection system of  claim 13 , further comprising a flame sensing alternating current source having a frequency of from about 24 kHz to about 300 KHz connected to the flame sensor driver circuit input node. 
     
     
         15 . The burner flame detection system of  claim 14 , wherein the flame sensing alternating current has a square wave waveform. 
     
     
         16 . A method of determining if a burner is ignited using a conductive flame sensor comprising a conductive terminal and positioned proximate the burner, the method comprising:
 providing a flame sensing alternate current source operatively connected to the conductive terminal, the alternating current having a frequency of from about 24 kHz to about 300 kHz; and   generating a rectified current from the conductive flame sensor to the burner when the flame sensing alternating current source supplies the alternating current to the conductive flame sensor conductive terminal, and the burner is in an ignited state.   
     
     
         17 . The method of  claim 16 , wherein the conductive flame sensor is a flame rod. 
     
     
         18 . The method of  claim 16 , wherein the conductive flame sensor is a hot surface igniter having a conductive pattern connected to the conductive terminal. 
     
     
         19 . The method of  claim 18 , further comprising the step of selectively connecting the conductive terminal to a source of ignition alternating current. 
     
     
         20 . The method of  claim 18 , wherein the conductive pattern is a first conductive pattern, the hot surface igniter comprises a second conductive pattern, and the second conductive pattern is electrically isolated from the first conductive pattern and connected to a source of ignition alternating current. 
     
     
         21 . A method of determining if a burner having a conductive body is ignited, the method comprising:
 providing a hot surface igniter positioned proximate the burner and having a conductive pattern connected to a conductive terminal;   providing a flame sensing alternate current source operatively connected to the conductive terminal; and   generating a rectified current from the hot surface igniter conductive pattern to the burner when the flame sensing alternating current source supplies flame sensing alternating current to the hot surface igniter conductive terminal, and the burner is ignited.   
     
     
         22 . The method of  claim 21 , wherein the conductive terminal is a first conductive terminal, and the conductive pattern is connected to a second conductive terminal, the method further comprising the step of selectively connecting the first conductive terminal to a source of ignition alternating current and the second conductive terminal to ground. 
     
     
         23 . The method of  claim 22 , further comprising selectively disconnecting the first conductive terminal from the source of ignition alternating current and selectively disconnecting the second conductive terminal from ground. 
     
     
         24 . The method of  claim 21 , wherein the conductive pattern is a first conductive pattern, the hot surface igniter comprises a second conductive pattern, and the second conductive pattern is electrically isolated from the first conductive pattern and connected to a source of ignition alternating current.