Intrinsically safe switching systems

Claim 1

A SYSTEM FOR CONTROLLING FROM AN INTRINSICALLY SAFE CONTROL STATION LOCATED IN AN AREA WHERE A HAZARDOUS ATMOSPHERIC MIXTURE MAY BE PRESENT AN ELECTRORESPONSIVE DEVICE LOCATED IN A NONHAZARDOUS AREA COMPRISING: GENERAL PURPOSE SWITCHING MEANS AT THE HAZARDOUS AREA; A CONTROL CIRCUIT AT THE NONHAZARDOUS AREA FOR CONTROLLING ENERGIZATION OF THE ELECTRORESPONSIVE DEVICE; A SEALED ELECTRIC CONDUIT COMPRISING CONDUCTORS CONNECTING SAID CONTROL STATION TO SAID CONTROL CIRCUIT AND PREVENTING PASSAGE THERETHROUGH OF THE HAZARDOUS ATMOSPHERIC MIXTURE FROM THE HAZARDOUS AREA TO THE NONHAZARDOUS AREA; AND SAID CONTROL CIRCUIT COMPRISING SENSITIVE ELECTRORESPONSIVE MEANS; A SOURCE OF DIRECT CURRENT FOR SUPPLYING UNIDIRECTIONAL ENERGY TO SAID SENSITIVE ELECTRORESPONSIVE MEANS; MEANS CONNECTING SAID SWITCHING MEANS THROUGH SAID ELECTRIC CONDUIT IN CIRCUIT WITH SAID SENSITIVE ELECTRORESPONSIVE MEANS AND SAID SOURCE OF DIRECT CURRENT FOR CONTROLLING THE ENERGIZATION OF SAID SENSITIVE ELECTRORESPONSIVE MEANS AND REDUCING ANY CAPACITIVE EFFECT IN THE CONDUCTORS BETWEEN SAID SWITCHING MEANS AND SAID CONTROL CIRCUIT; AND MEANS CONNECTING IN CIRCUIT SAID SENSITIVE ELECTRORESPONSIVE MEANS, SAID SWITCHING MEANS AND SAID SOURCE OF DIRECT CURRENT FOR TRANSMITTING TO SAID SWITCHING MEANS AT THE HAZARDOUS AREA AN AMOUNT OF UNIDIRECTIONAL ELECTRICAL ENERGY INSUFFICIENT TO CAUSE IGNITION OF THE HAZARDOUS ATMOSPHERE WHEN SAID SWITCHING MEANS IS OPERATED BUT SUFFICIENT TO CAUSE OPERATION OF SAID SENSITIVE ELECTRORESPONSIVE MEANS WHEN SAID SWITCHING MEANS IS OPERATED.

Claim 2

A SYSTEM FOR CONTROLLING FROM AN INTRINSICALLY SAFE CONTROL STATION LOCATED IN AN AREA WHERE A HAZARDOUS ATMOSPHERIC MIXTURE MAY BE PRESENT AN ELECTRORESPONSIVE DEVICE LOCATED IN A NONHAZARDOUS AREA COMPRISING: GENERAL PURPOSE SWITCHING MEANS AT THE HAZARDOUS AREA; A CONTROL CIRCUIT AT THE NONHAZARDOUS AREA FOR CONTROLLING ENERGIZATION OF THE ELECTRORESPONSIVE DEVICE; A SEALED ELECTRIC CONDUIT COMPRISING CONDUCTORS CONNECTING SAID CONTROL STATION TO SAID CONTROL CIRCUIT AND PREVENTING PASSAGE THERETHROUGH OF THE HAZARDOUS ATMOSPHERIC MIXTURE FROM THE HAZARDOUS AREA TO THE NONHAZARDOUS AREA; AND SAID CONTROL CIRCUIT COMPRISING SENSITIVE ELECTRORESPONSIVE MEANS; A SOURCE OF DIRECT CURRENT FOR SUPPLYING UNIDIRECTIONAL ENERGY TO SAID SENSITIVE ELECTRORESPONSIVE MEANS; MEANS CONNECTING SAID SWITCHING MEANS THROUGH SAID ELECTRIC CONDUIT IN CIRCUIT WITH SAID SENSITIVE ELECTRORESPONSIVE MEANS AND SAID SOURCE OF DIRECT CURRENT FOR CONTROLLING THE ENERGIZATION OF SAID SENSITIVE ELECTRORESPONSIVE MEANS AND REDUCING ANY CAPACITIVE EFFECT IN THE CONDUCTORS BETWEEN SAID SWITCHING MEANS AND SAID CONTROL CIRCUIT; AND MEANS CONNECTING IN CIRCUIT SAID SENSITIVE ELECTRORESPONSIVE MEANS, SAID SWITCHING MEANS AND SAID SOURCE OF DIRECT CURRENT FOR TRANSMITTING TO SAID SWITCHING MEANS AT THE HAZARDOUS AREA AN AMOUNT OF UNIDIRECTIONAL ELECTRICAL ENERGY INSUFFICIENT TO CAUSE IGNITION OF THE HAZARDOUS ATMOSPHERE WHEN SAID SWITCHING MEANS IS OPERATED BUT SUFFICIENT TO CAUSE OPERATION OF SAID SENSITIVE ELECTRORESPONSIVE MEANS WHEN SAID SWITCHING MEANS IS OPERATED.