Self-balancing impedance measuring bridge

Claim 1

AN ELECTRICAL BRIDGE TO GIVE AN OUTPUT IN ACCORDANCE WITH THE MAGNITUDE OF AN UNKNOWN IMPEDANCE COMPRISING A VOLTAGE SOURCE, A STANDARD IMPEDANCE, MEANS FOR APPLYING A VOLTAGE FROM SAID SOURCE TO SAID STANDARD IMPEDANCE TO PROVIDE A FIRST CURRENT CONSITUTING A REFERENCE, A VOLTAGE-CONTROLLABLE RESISTANCE, A FIXED RESISTOR CONNECTED IN SERIES WITH SAID VOLTAGE-CONTROLLABLE RESISTANCE TO FORM A POTENTIAL DIVIDER, MEANS FOR APPLYING A VOLTAGE FROM SAID SOURCE ACROSS SAID POTENTIAL DIVIDER, MEANS FOR APPLYING THE VOLTAGE BETWEEN ONE END OF THE POTENTIAL DIVIDER AND THE JUNCTION OF THE VOLTAGE-CONTROLLABLE RESISTANCE AND FIXED RESISTOR TO THE UNKNOWN IMPEDANCE TO PROVIDE A SECOND CURRENT, COMPARISON MEANS FOR COMPARING SAID FIRST AND SECOND CURRENTS TO PRODUCE A CONTROL SIGNAL DEPENDENT ON THE DIFFERENCE TO THE TWO CURRENTS, CIRCUIT MEANS FOR APPLYING SAID CONTROL SIGNAL TO SAID VOLTAGE-CONTROLLABLE RESISTANCE TO CONTROL THE VOLTAGE FROM SAID POTENTIAL DIVIDER IN THE SENSE TO TEND TO BRING THE TWO CURRENTS TO EQUALITY AND OUTPUT MEANS RESPONSIVE TO THE VOLTAGE APPLIED TO THE UNKNOWN IMPEDANCE.