Remote station signalling circuit having circuit maintenance

Claim 1

IN AN ELECTRICAL PROTECTION SYSTEM HAVING A PLURALITY OF SIGNALLING DEVICES CONNECTED IN SERIES IN A LOOP CIRCUIT AND BEING CAPABLE OF SUCCESSIVELY INCREASING AND DECREASING THE CURRENT FLOW IN SAID LOOP CIRCUIT IN ACCORDANCE WITH PREDETERMINED INDIVIDUAL SIGNALLING CODES, THE COMBINATION COMPRISING A SOURCE OF D.C. VOLTAGE, MEANS INCLUDING A FIRST IMPEDANCE ELEMENT INTERCOUPLING ONE SIDE OF SAID SOURCE AND ONE SIDE OF SAID LOOP, MEANS INCLUDING A SECOND IMPEDANCE ELEMENT INTERCOUPLING THE OTHER SIDE OF SAID SOURCE AND THE OTHER SIDE OF SAID LOOP WHEREBY CURRENT FLOWS FROM SAID SOURCE THROUGH SAID LOOP, A TRANSISTOR, MEANS TO SUPPLY THE VOLTAGE ACROSS SAID FIRST IMPEDANCE ELEMENT AS AN INPUT TO SAID TRANSISTOR TO ALTER THE OUTPUT CURRENT OF SAID TRANSISTOR IN ACCORDANCE WITH CHANGES IN LOOP CURRENT, A THIRD IMPEDANCE ELEMENT COUPLED IN THE OUTPUT CIRCUIT OF SAID TRANSISTOR WHEREBY THE VOLTAGE ACROSS SAID THIRD IMPEDANCE ELEMENT VARIES IN ACCORDANCE WITH CHANGES IN THE OUTPUT CURRENT OF SAID TRANSISTOR, A CAPACITIVE ELEMENT, MEANS INTERCOUPLING SAID SECOND AND THIRD IMPEDANCE ELEMENTS AND SAID CAPACITIVE ELEMENT WHEREBY SAID CAPACITIVE ELEMENT IS MAINTAINED CHARGED BY THE VOLTAGE ACROSS SAID SECOND AND THIRD IMPEDANCE ELEMENTS, AND SIGNAL REGISTRATION MEANS COUPLED TO SAID CAPACITIVE ELEMENT AND RESPONSIVE TO CURRENT FLOW THROUGH SAID CAPACITIVE ELEMENT TO REGISTER INCREASES AND DECREASES OF CURRENT FLOW IN SAID LOOP CIRCUIT.