Redundant Ignition Control Circuit and Method

Abstract

A redundant ignition control system and method for gas burning appliances is provided. The system utilizes a main processor and a supervisory processor to provide the redundant, fail safe operation of both the pilot valve and the main gas valve of the appliance. Three switching elements under the control of the two processors, as well as the use of high pass filters to block DC from the gas control valves provide redundant, fail safe operation. The use of variable duty cycle or frequency pulse width modulated signals enables use in low power applications and ensures system safety. Inclusion of a gas valve verification sequence, ignition sequence, burner monitoring sequence, and heat shutdown and standby sequences ensures safe, low power operation during normal control, and fail safe operation upon the failure of any component of the system.

1 . A ignition control system for use with intermittent pilot systems for gas burners having a pilot gas valve and a main gas control valve, comprising:
 a main processor;   a supervisory processor;   a gas valve supply switch controllably coupled to the supervisory processor, the gas valve supply switch having a power input and a gas valve supply output;   a pilot valve switch controllably coupled to the main processor, the pilot valve switch having a first gas valve supply input coupled to the gas valve supply output and a pilot valve power output;   a main gas valve switch controllably coupled to the main processor, the main gas valve switch having a second gas valve supply input coupled to the gas valve supply output and a main gas control valve power output; and   wherein the main processor is configured to generate a pulse width modulated mode control signal to control operation of the supervisory processor, the main processor further configured to sense the gas valve supply output to verify proper operation of the supervisory processor.   
     
     
         2 . The ignition control system of  claim 1 , wherein the main processor is configured to generate a pulse width modulated mode control signal of a first duty cycle to cause the supervisory processor to enter a gas valve verification mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal to cause the gas valve supply switch begin a switching sequence, and wherein the main processor is further configured to monitor the gas valve supply output to verify proper operation of the supervisory processor. 
     
     
         3 . The ignition control system of  claim 2 , further comprising a pilot gas valve high pass filter coupled to the pilot valve power output, and wherein the supervisory processor is configured to turn on the gas valve supply switch control signal to close the gas valve supply switch, and wherein the main processor is configured to generate a pilot valve switch control signal to close the pilot valve switch, the main processor further configured to monitor the pilot valve power output to ensure proper operation of the pilot valve switch. 
     
     
         4 . The ignition control system of  claim 3 , wherein the main processor is configured to generate a main gas valve switch control signal to close the main gas valve switch, the main processor further configured to monitor the main gas control valve power output to ensure proper operation of the main gas control valve switch. 
     
     
         5 . The ignition control system of  claim 4 , further comprising a main gas control valve high pass filter coupled to the main gas control valve power output. 
     
     
         6 . The ignition control system of  claim 2 , further comprising a flame sense circuit, and wherein at least one of the main processor and the supervisory processor is configured to monitor the flame sense circuit during the gas valve verification mode of operation. 
     
     
         7 . The ignition control system of  claim 6 , wherein both of the main processor and the supervisory processor are configured to monitor the flame sense circuit during the gas valve verification mode of operation. 
     
     
         8 . The ignition control system of  claim 1 , wherein the main processor is configured to generate a pulse width modulated mode control signal of a second duty cycle to cause the supervisory processor to enter an ignition sequence mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a high duty cycle to cause the gas valve supply switch begin a high power switching sequence, and wherein the main processor is further configured to generate a pilot valve switch control signal to close the pilot valve switch. 
     
     
         9 . The ignition control system of  claim 8 , further comprising a flame sense circuit, and wherein the main processor is configured to monitor the flame sense circuit during the ignition sequence mode of operation and, upon verification of the presence of flame, to generate a main gas valve switch control signal to close the main gas valve switch. 
     
     
         10 . The ignition control system of  claim 8 , further comprising a flame sense circuit, and wherein at least one of the main processor and the supervisory processor is configured to monitor the flame sense circuit during a trial for ignition period, and wherein at least one of the main processor and the supervisory processor disables at least the gas valve supply switch control signal when no flame is sensed during the trial for ignition period. 
     
     
         11 . The ignition control system of  claim 9 , wherein the main processor is configured to generate a pulse width modulated mode control signal of a third duty cycle to cause the supervisory processor to enter monitor burner mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a low duty cycle to cause the gas valve supply switch begin a low power switching sequence. 
     
     
         12 . The ignition control system of  claim 11 , wherein the main processor is configured to disable the mode control signal once a call for heat is removed, and wherein the supervisory processor is configured to disable the gas valve supply switch control signal to close the gas valve supply switch. 
     
     
         13 . A ignition control system for use with direct spark systems for gas burners having a main gas control valve, comprising:
 a main processor;   a supervisory processor;   a gas valve supply switch controllably coupled to the supervisory processor, the gas valve supply switch having a power input and a gas valve supply output;   a main gas valve switch controllably coupled to the main processor, the main gas valve switch having a gas valve supply input coupled to the gas valve supply output and a main gas control valve power output; and   wherein the main processor is configured to generate a pulse width modulated mode control signal to control operation of the supervisory processor, the main processor further configured to sense the gas valve supply output to verify proper operation of the supervisory processor.   
     
     
         14 . The ignition control system of  claim 13 , wherein the main processor is configured to generate a pulse width modulated mode control signal of a first duty cycle to cause the supervisory processor to enter a gas valve verification mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal to cause the gas valve supply switch begin a switching sequence, and wherein the main processor is further configured to monitor the gas valve supply output to verify proper operation of the supervisory processor. 
     
     
         15 . The ignition control system of  claim 14 , further comprising a high pass filter coupled to the gas valve supply output, and wherein the supervisory processor is configured to turn on the gas valve supply switch control signal to close the gas valve supply switch, and wherein the main processor is configured to generate a main gas valve switch control signal to close the main gas valve switch, the main processor further configured to monitor the main gas control valve power output to ensure proper operation of the main gas control valve switch. 
     
     
         16 . The ignition control system of  claim 14 , further comprising a flame sense circuit, and wherein both of the main processor and the supervisory processor are configured to monitor the flame sense circuit during the gas valve verification mode of operation. 
     
     
         17 . The ignition control system of  claim 13 , wherein the main processor is configured to generate a pulse width modulated mode control signal of a second duty cycle to cause the supervisory processor to enter an ignition sequence mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a high duty cycle to cause the gas valve supply switch begin a high power switching sequence, and wherein the main processor is further configured to generate a main gas valve switch control signal to close the main gas valve switch. 
     
     
         18 . The ignition control system of  claim 17 , further comprising a flame sense circuit, and wherein at least one of the main processor and the supervisory processor is configured to monitor the flame sense circuit during a trial for ignition period, and wherein at least one of the main processor and the supervisory processor disables at least the gas valve supply switch control signal when no flame is sensed during the trial for ignition period. 
     
     
         19 . The ignition control system of  claim 17 , wherein the main processor is configured to generate a pulse width modulated mode control signal of a third duty cycle to cause the supervisory processor to enter monitor burner mode of operation wherein the supervisory processor generates a pulse width modulated gas valve supply switch control signal of a low duty cycle to cause the gas valve supply switch begin a low power switching sequence. 
     
     
         20 . The ignition control system of  claim 19 , wherein the main processor is configured to disable the mode control signal once a call for heat is removed, and wherein the supervisory processor is configured to disable the gas valve supply switch control signal to close the gas valve supply switch.