Apparatus for the remote measurement of capacitance

Claim 1

IN AN APPARATUS FOR TESTING CAPACTIANCE OF A DEVICE AT A REMOTE LOCATION, THE COMBINATION OF: A LENGTH OF CABLE HAVING FIRST, SECOND AND THIRD CONDUCTORS; A CHARGING VOLTAGE SOURCE CONNECTED ACROSS SAID FIRST AND THIRD CONDUCTORS AT ONE END OF SAID CABLE, SAID SOURCE GENERATING A CYCLICAL SQUARE WAVE VOLTAGE; A HIGH IMPEDANCE D.-C. VOLTAGE MEASURING DEVICE CONNECTED ACROSS SAID SECOND AND THIRD CONDUCTORS AT SAID ONE END; A CHARGE SENSING UNIT CONNECTED IN SERIES WITH THE DEVICE UNDER TEST ACROSS SAID FIRST AND THIRD CONDUCTORS AT THE OTHER END OF SAID CABLE, SAID CHARGE SENSING UNIT INCLUDING PARALLEL CIRCUITS WITH OPPOSITELY POLED RECTIFIERS THEREIN FOR CHARGING THE DEVICE THROUGH THE CIRCUIT AND DISCHARGING THROUGH THE OTHER CIRCUIT, WITH A RESISTOR CONNECTED IN SERIES WITH ONE OF SAID RECTIFIERS AT A JUNCTION POINT; AND A SMOOTHING FILTER CONNECTED BETWEEN SAID JUNCTION POINT AND SAID THIRD CONDUCTOR, WITH THE FILTER OUTPUT CONNECTED TO SAID SECOND CONDUCTOR AT SAID OTHER END OF SAID CABLE.