Gas detecting apparatus

Claim 1

APPARATUS FOR DETECTING THE PRESENCE OF SMALL QUANTITIES OF COMBUSTIBLE GAS IN AN ATMOSPHERE UNDER TEST INCLUDING, IN COMBINATION, CATALYTIC GAS DETECTING MEANS FOR PRODUCING AT AN OUTPUT CIRCUIT THEREOF AN ELECTRIC POTENTIAL DEPENDENT ON THE MOUNT OF COMBUSTIBLE GAS IN THE ATMOSPHERE, REFERENCE MEANS FOR PRODUCING AT AN OUTPUT CIRCUIT THEREOF AN ADJUSTABLE REFERENCE POTENTIAL, ELECTRIC SWITCHING MEANS COMPRISING AN INPUT STAGE WHICH INCLUDES A FIRST TRANSISTOR HAVING EMITTER, BASE AND COLLECTOR, A COLLECTOR LOAD RESISTOR CONNECTING THE COLLECTOR WITH A SOURCE OF COLLECTOR POTENTIAL, FIRST CIRCUIT MEANS CONNECTING THE EMITTER DIRECTLY WITH A SOURCE OF EMITTER POTENTIAL, AND SECOND CIRCUIT MEANS CONNECTING THE OUTPUT CIRCUITS OF THE GAS DETECTING MEANS AND THE RREFERENCE MEANS IN SERIES BETWEEN THE EMITTER AND BASE OF THE FIRST TRANSISTOR SO THAT THE DIFFERENCE OF THE TWO ELECTRIC POTENTIALS IS APPLIED BETWEEN THE EMITTER AND BASE, AN OUTPUT STAGE WHICH INCLUDES A SECOND TRANSISTOR HAVING EMITTER, BASE AND COLLECTOR, AN ELECTRICAL WARNING DEVICE CONNECTING THE COLLECTOR OF THE SECOND TRANSISTOR WITH THE SAID SOURCE OF COLLECTOR POENTIAL, THIRD CIRCUIT MEANS CONNECTING THE EMITTER OF THE SECOND TRANSISTOR DIRECTLY WITH THE SAID SOURCE OF EMITTER POTENTIAL, FOURTH CIRCUIT MEANS CONNECTING THE BASE OF THE SECOND TRANSISTOR TO THE COLLECTOR OF THE FIRST TRANSISTOR, AND A RESISTOR CONNECTING THE BASE OF THE FIRST TRANSISTOR WITH THE COLLECTOR OF THE SECOND TRANSISTOR, THE WARNING DEVICE BEING NORMALLY IN A NON-WARNING STATE AND BEING ENERGISED TO CHANGE TO A WARNING STATE ONLY WHEN THE POTENTIAL APPEARING AT THE OUTPUT CIRCUIT OF THE GAS DETECTING MEANS CORRESPONDS TO A PREDETERMINED HIGH AMOUNT OF COMBUSTIBLE GAS IN THE ATMOSPHERE AS DETERMINED BY THE VALUE OF THE ADJUSTABLE REFERENCE POTENTIAL, A SEMI-CONDUCTOR DIODE DEVICE CONNECTING THE OUTPUT CIRCUIT OF THE GAS DETECTING MEANS WITH THE COLLECTOR OF THE FIRST TRANSISTOR AND BEING POLED SO AS TO ENABLE THE FLOW OF CURRENT TO THE COLLECTOR OF THE FIRST TRANSISTOR ONLY WHEN THE POTENTIAL APPEARING AT THE OUTPUT CIRCUIT OF THE GAS DETECTING MEANS RISES ABOVE A PREDETERMINED HIGH VALUE, SUCH FLOW OF CURRENT TENDING TO PREVENT CONDUCTION OF THE SECOND TRANSISTOR AND HENCE TRANSFER OF THE WARNING DEVICE TO THE WARNING STATE, MEANS FOR PRODUCING A SECOND REFERNCE ELECTRIC POTENTIAL EQUAL TO THE POTENTIAL APPEARING AT THE SAID OUTPUT CIRCUIT OF THE GAS DETECTING MEANS WHEN NO COMBUSTIBLE GAS IS PRESENT IN THE ATMOSPHERE UNDER TEST, AND FAULT INDICATING MEANS CONNECTED TO RECEIVE THE SECOND REFERENCE POTENTIAL AND THE POTENTIAL APPEARING AT THE SAID OUTPUT CIRCUIT AND ARRANGED TO CHANGE FROM A NON-WARNING STATE TO A WARNING STATE WHEN THE OUTPUT POTENTIAL OF THE GAS DETECTING MEANS EXCEEDS THE SECOND REFERENCE POTENTIAL BY A PREDETERMINED HIGH VALUE WHEREBY TO INDICATE THE PRESENCE OF A FAULT IN THE GAS DETECTING MEANS.