Apparatus for testing capacitance type fluid level sensing equipment

Claim 1

APPARATUS FOR TESTING SYSTEMS OPERABLE TO DETERMINE THE LEVEL OF A STORED FLUID MEDIUM AND WHICH EMPLOY CAPACITANCE-TYPE FLUID-LEVEL SENSING ELEMENTS HAVING TWO CONCENTRIC TUBES, ONE TUBE HAVING A HIGH IMPEDANCE AND THE OTHER TUBE HAVING A LOW IMPEDANCE TO A GROUND CONNECTION, COMPRISING A SENSING ELEMENT CAPACITANCE TESTING SECTION, A SENSING ELEMENT IMPEDANCE TESTING SECTION, AND A FLUID-LEVEL INDICATOR TESTING SECTION, SAID CAPACITANCE TESTING SECTION COMPRISING SUPPLY TERMINALS FOR RECEIVING AN ELECTRICAL SUPPLY POTENTIAL, A PHASE-SENTITIVE TWO ARM BRIDGE CIRCUIT HAVING INPUT TERMINALS CONNECTED TO SAID SUPPLY TERMINALS, AND OUTPUT TERMINALS, FIRST SWITCHING MEANS CONNECTED TO SAID ONE ARM OF THE BRIDGE CIRCUIT, A PLURALITY OF FIRST CAPACITORS HAVING DIFFERENT PREDETERMINED VALUES CONNECTED TO SAID FIRST SWITCHING MEANS AND ARRANGED TO BE SELECTIVELY CONNECTED IN ONE ARM BY SAID FIRST SWITCHING MEANS, THE OTHER ARM OF SAID BRIDGE CIRCUIT BEING ADAPTED TO HAVE A SAID SENSING ELEMENT CONNECTED THEREIN AND SAID CAPACITOR SELECTED BEING DEPENDENT ON THE VALUE OF SAID SENSING ELEMENT CONNECTED IN SAID OTHER ARM, A FIRST VACUUM TUBE VALVE VOLTMETER CONNECTED TO SAID OUTPUT TERMINALS AND HAVING A CALIBRATED RANGE THE LIMITS OF WHICH CORRESPOND TO PREDETERMINED ACCEPTABLE LIMITS OF CAPACITANCE FOR A SAID SENSING ELEMENT, SAID LIMITS CORRESPONDING TO MINOR DEVIATIONS IN ONE SENSE AND THE OPPOSITE SENSE FROM THE BALANCED POSITION OF SAID BRIDGE CIRCUIT, SAID IMPEDANCE TESTING SECTION COMPRISING A SECOND VACUUM TUBE VALVE VOLTMETER CONNECTED TO SAID SUPPLY TERMINALS AND HAVING INPUT TERMINALS AND A RANGE CALIBRATED IN RESISTANCE, VOLTAGE STABILISER CIRCUIT MEANS CONNECTED TO SAID SUPPLY TERMINALS FOR DEVELOPING A SABILISED REFERENVE VOLTAGE AND SECOND SWITCHING MEANS FOR CONNECTING SAID HIGH IMPEDANCE TUBE AND SAID LOW IMPEDANCE TUBE OF SAID SENSING ELEMENT AND SAID GROUND CONNECTION IN A THREE ARM DELTA NETWORK COMPRISING THE LOW IMPEDANCE GROUND CONNECTIONS, THE HIGH IMPEDANCE-GROUND CONNECTIONS AND THE LOW IMPEDANCE-HIGH IMPEDANCE CONNECTIONS OF SAID SENSING ELEMENT, AND SELECTIVELY CONNECTING ONE ARM OF THE DELTA CONNECTION BETWEEN SAID VOLTAGE STABILIZER CIRCUIT MEANS AND SAID SECOND VACUUM TUBE VALVE VOLTMETER AND THE OTHER TWO ARMS OF THE DELTA CONNECTION ACROSS SAID INPUT TERMINALS OF THE SECOND VACUUM TUBE VOLTMETER, SAID INDICATOR TESTING SECTION COMPRISING A PLURALITY OF SECOND CAPACITORS HAVING DIFFERENT VALUES EACH CORRESPONDING TO THAT POSSESSED BY A SAID SENSING ELEMENT TO WHICH A SAID FLUID LEVEL INDICATOR IS ADAPTED TO RESPOND WHEN SAID SENSING ELEMENT RECORDS ZERO OR MINIMUM FLUID LEVEL. A PLURALITY OF THIRD CAPACITORS HAVING DIFFERENT VALUES EACH CORRESPONDING TO THAT POSSESSED BY SAID SENSING ELEMENT WHEN SAID SENSING ELEMENT RECORDS MAXIMUM FLUID LEVEL AND THIRD SWITCHING MEANS FOR CONNECTION TO SAID FLUID-LEVEL INDICATOR AND SWITCHABLE SELECTIVELY TO CONNECT A SAID SECOND AND A SAID THIRD CAPACITOR TO SAID FLUID-LEVEL INDICATOR FOR TESTING THE CALIBRATION THEREOF.