Double bridge circuit for measuring resistance of energized alternating current apparatus

Claim 1

AN ELECTRICAL CIRCUIT FOR MEASURING THE RESISTANCE OF AN ELECTRICAL APPARATUS ENERGIZED FROM AN ALTERNATING CURRENT SOURCE COMPRISING A TRANSFORMER HAVING A PRIMARY WINDING CONNECTED ACROSS SAID SOURCE AND A FIRST AND SECOND SECONDARY WINDING RESPECTIVELY CONNECTED WITH A FIRST AND A SECOND PAIR OF TERMINALS CONNECTED TO SAID APPARATUS, A BRIDGE COMPRISING A FIRST AND SECOND MAIN RATIO ARM, A FIRST AND A SECOND AUXILIARY RATIO ARM, SAID MAIN RATIO ARMS HAVING A COMMON JUNCTION AND SAID AUXILIARY ARMS HAVING A COMMON JUNCTIONS, A GALVANOMETER JOINING SAID COMMON JUNCTIONS, MEANS COMPRISING A CURRENT CONNECTED ACROSS THE APPARATUS AND INCLUDING SAID FIRST SECONDARY WINDING AND A DIRECT CURRENT SOURCE SERIALLY CONNECTED WITH AN INDICATING AND ADJUSTABLE RESISTOR, A POTENTIAL CIRCUIT CONNECTED ACROSS THE APPARATUS AND INCLUDING SAID SECONDARY WINDING, AN ADJUSTABLE RESISTANCE ELEMENT AND SAID MAIN AND AUXILIARY RATIO ARMS AND SAID INDICATING AND ADJUSTABLE RESISTOR, SAID ADJUSTABLE RESISTANCE ELEMENT BEING VARIABLE TO CHANGE THE RESISTANCE BALANCE OF SAID MAIN AND AUXILIARY RATIO ARMS TO ACHIEVE ZERO CURRENT FLOW THROUGH THE BRIDGE, AND SAID ADJUSTABLE RESISTOR BEING ADJUSTABLE TO SHOW THE RESISTANCE OF THE APPARATUS WHEN CURRENT FLOW THROUGH THE GALVANOMETER IS ZERO.