Bias-controlled a. c.-operable voltage threshold circuit, and systems employing same

Claim 1

AN ELECTRICAL CIRCUIT FOR DETECTING THE PRESENCE OR ABSENCE OF A FLAME, COMPRISING: A PAIR OF FLAME ELECTRODES POSITIONED ADJACENT A SOURCE OF A FLAME OF RECTIFYING CHARACTERISTICS SO AS TO PROVIDE ELECTRICAL CONTACT TO SPACED REGIONS OF SAID FLAME WHEN SAID FLAME IS PRESENT; A SOURCE OF AN ALTERNATING VOLTAGE OF PREDETERMINED MAXIMUM PEAK-TO-PEAK AMPLITUDE; CAPACITIVE MEANS CONNECTED IN COMMON SERIES CIRCUIT WITH SAID SOURCE AND SAID FLAME ELECTRODES; AND VOLTAGE-BREAKDOWN MEANS HAVING A PAIR OF DISCHARGEELECTRODE MEANS CONNECTING SAID VOLTAGE-BREAKDOWN MEANS IN PARALLEL WITH SAID FLAME ELECTRODES, SAID VOLTAGE-BREAKDOWN MEANS BEING CHARACTERIZED BY A FIRING VOLTAGE WHICH, WHEN APPLIED BETWEEN SAID DISCHARGE-ELECTRODE MEANS WHILE SAID VOLTAGE-BREAKDOWN MEANS IS IN ITS LOW-CONDUCTION STATE WILL CHANGE SAID VOLTAGE-BREAKDOWN MEANS TO ITS HIGH-CONDUCTION STATE, AND ALSO CHARACTERIZED BY AN EXTINCTION VOLTAGE WHICH WHEN APPLIED BETWEEN SAID DISCHARGE-ELECTRODE MEANS WHILE SAID VOLTAGE-BREAKDOWN MEANS IS IN ITS HIGH-CONDUCTION STATE WILL CHANGE SAID VOLTAGEBREAKDOWN MEANS TO ITS LOW-CONDUCTION STATE; SAID COMMON SERIES CIRCUIT BEING RESPONSIVE TO SAID ALTERNATING VOLTAGE WHEN AND FLAME IS PRESENT TO CHARGE SAID CAPACITIVE MEANS WITH A DIRECT-VOLTAGES COMPONENT OF A GIVEN SIGN IN RESPONSE TO ONE POLARITY OF SAID ALTERNATING VOLTAGE AND TO ADD TO SAID DIRECTVOLTAGE COMPONENT A VARYING COMPONENT OF THE SAME SIGN DURING THE OCCURRENCE OF THE OPPOSITE POLARITY OF SAID ALTERNATING VOLTAGE, WHEREBY THE TOTAL VOLTAGE APPLIED BETWEEN SAID DISCHARGED-ELECTRODE MEANS DURING SAID OCCURRENCE OF SAID OPPOSITE POLARITY RISES TO A VALUE GREATER THAN THAT OF EITHER POLARITY OF SAID ALTERNATING VOLTAGE ALONE AND GREATER THAN SAID FIRING VOLTAGE OF SAID GAS-DISCHARGE MEANS, SAID COMMON SERIES CIRCUIT BEING RESPONSIVE TO SAID ALTERNATING VOLTAGE IN THE ABSENCE OF SAID FLAME TO GENERATE A VOLTAGE FOR APPLICATION BETWEEN SAID DISCHARGE-ELECTRODE MEANS WHICH IS NO GREATER THAN THE PEAK VALUE OF EITHER POLARITY OF SAID ALTERNATING VOLTAGE; SAID FIRING VOLTAGE BEING GREATER THAN THE ZERO-TO-PEAK VALUE OF EITHER POLARITY OF SAID ALTERNATING VOLTAGE BUT LESS THAN THE PEAK-TO-PEAK VALUE THEREOF, WHEREBY SAID VOLTAGE-BREAKDOWN MEANS IS CHANGED TO ITS HIGH-CONDUCTION STATE ONLY WHEN SAID FLAME IS PRESENT; SAID COMMON SERIES CIRCUIT HAVING SUFFICIENTLY LOW INDUCTANCE REACTANCE TO PERMIT SAID CAPACITIVE MEANS TO DISCHARGE THROUGH SAID VOLTAGE-BREAKDOWN MEANS, WHEN SAID VOLTAGE-BREAKDOWN MEANS IS IN SAID HIGHCONDUCTION STATE, UNITIL SAID VOLTAGE APPLIED TO SAID DISCHARGE-ELECTRODE MEANS FALLS BELOW SAID EXTINCTION VOLTAGE AND SAID CAPACITIVE MEANS RECHARGES, WHEREBY SAID VOLTAGE-BREAKDOWN MEANS ALTERNATES BETWEEN SAID HIGH-CONDUCTION STATE AND SAID LOWCONDUCTION STATE WHEN SAID FLAME IS PRESENT BUT IS IN ITS LOW-CONDUCTION STATE WHENEVER SAID FLAME IS ABSENT.