Alarm apparatus for industrial instrumentation systems

Claim 1

IN AUTOMATICALLY-OPERABLE ALARM APPARATUS FOR USE WITH AN INDUSTRIAL CONDITION MEASUREMENT AND/OR CONTROL SYSTEM WHICH INCLUDES SIGNAL-TRANSMISSION MEANS FOR TRANSMITTING A DIRECT CURRENT CORRESPONDING IN MAGNITUDE TO THE CONDITION BEING MEASURED AND/OR CONTROLLED; THE IMPROVEMENT IN SAID ALARM APPARATUS WHICH COMPRISES; A SERIES ELECTRICAL CIRCUIT INCLUDING A FIRST CIRCUIT ELEMENT CONNECTIBLE WITH SAID SIGNAL-TRANSMISSION MEANS TO DEVELOP A MEASUREMENT SIGNAL CORRESPONDING TO THE MAGNITUDE OF THE DIRECT CURRENT IN SAID SIGNAL-TRANSMISSION MEANS, D.-C. POWER SUPPLY MEANS FOR PRODUCING AN ALARM SET SIGNAL OPPOSITELY POLARIZED WITH RESPECT TO SAID MEASUREMENT SIGNAL, RECTIFIER MEANS ARRANGED TO PERMIT THE FLOW OF CURRENT THROUGH SAID SERIES CIRCUIT ONLY WHEN A PREDETERMINED ONE OF SAID SIGNALS IS GREATER THAN THE OTHER OF SAID SIGNALS, AND A SECOND CIRCUIT ELEMENT FOR DEVELOPING A BIAS VOLTAGE IN SAID SERIES CIRCUIT; ENERGIZING MEANS COUPLED TO SAID SECOND CIRCUIT ELEMENT AND INCLUDING MEANS TO PRODUCE THEREACROSS A PERIODIC PULSATING BIAS VOLTAGE POLARIZED TO TEND PERIODICALLY TO PREVENT CONDUCTION THROUGH SAID SERIES CIRCUIT; AN A.-C. AMPLIFIER COUPLED TO SAID SERIES CIRCUIT TO PRODUCE AN OUTPUT RESPONSIVE TO THE PULSATIONS OF CURRENT FLOW THROUGH SAID RECTIFIER MEANS; AND ALARM CONTROL MEANS OPERABLE BY THE OUTPUT OF SAID A.-C. AMPLIFIER.