Continuously self-checking scanner alarm system

Claim 1

IN A SCANNER ALARM SYSTEM WHICH COMPRISES A SCANNER SWITCH HAVING A ROTARY CONTACTOR AND A PLURALITY OF CONTACTS, A PLURALITY OF ELECTRICAL SIGNAL SOURCES FOR SUPPLYING SIGNAL OF A FIRST POLARITY TO SEPARATE CONTACTS OF THE SWITCH, MEANS FOR SUPPLYING A SYNCHRONIZING PULSE OF OPPOSITE POLARITY TO THAT OF THE ELECTRICAL SIGNALS TO ONE OF THE CONTACTS, MEANS FEEDING THE OUTPUT FROM THE SCANNER SWITCH CONTACTOR TO A THYRATRON TUBE WHICH IS BIASED TO CONDUCT WHENEVER ONE OF THE ELECTRICAL SIGNALS EXCEEDS A PREDETERMINED VALUE, AND MEANS IN THE THYRATRON TUBE CIRCUIT OPERABLE TO PROVIDE AN INDICATION WHEN THE TUBE CONDUCTS FOR LONGER THAN A PREDETERMINED TIME; THE IMPROVEMENT WHICH COMPRISES A SELF-CHECKING CIRCUIT FOR USE IN COMBINATION WITH THE SAID SCANNER ALARM SYSTEM WHICH COMPRISES MEANS IN COMBINATION WITH THE SCANNING SWITCH CONTACTOR FOR PRODUCING A TEST PULSE AT SELECTED TIMES IN THE CYCLE OF ROTATION OF SAID SCANNER SWITCH, SAID TEST PULSE BEING OPERABLE TO CAUSE THE THYRATRON TUBE TO CONDUCT, AND MEANS FOR INTERRUPTING THE CONDUCTION OF THE THYRATRON TUBE SAID PREDETERMINED TIME AFTER THE TEST PULSE CAUSES SAME TO CONDUCT, SAID PREDETERMINED TIME BEING LESS THAN THE TIME REQUIRED FOR THE ROTARY CONTACTOR TO MOVE FROM ONE CONTACT TO THE NEXT, AND FURTHER MEANS IN THE THYRATRON TUBE CIRCUIT FOR GIVING AN "APPARATUS SAFE" INDICATION AS LONG AS THE THYRATRON TUBE FIRES EACH TIME A TEST PULSE IS APPLIED THERETO.