Electrical fluid level gauge

Claim 1

AN ELECTRICAL FLUID LEVEL GAUGE FOR CONDUCTIVE FLUIDS COMPRISING MEANS PROVIDING TWO ALTERNATING VOLTAGES HAVING OPPOSED PHASES AND CONTROL MEANS FOR CONTROLLING THE AMPLITUDE OF ONE THEREOF, A MEASURING UNIT INCLUDED WITH ONE OF SAID VOLTAGES IN AN ARM OF AN ALTERNATING CURRENT BRIDGE AND HAVING SPACED ELECTRICALLY CONDUCTIVE ELETRODES ADAPTED TO BE SUPPORTED IN A FLUID CONTAINER TO PROVIDE A VALVE OF INTER-ELECTRODE ELECTRICAL CONDUCTANCE VARYING BOTH WITH THE LEVEL OF FLUID IN SAID CONTAINER AND THE VALVE OF CONDUCTIVITY OF SAID FLUID, A REFERENCE-COMPENSATING UNIT INCLUDED WITH THE OTHER OF SAID VOLTAGES IN A SECOND ARM OF SAID BRIDGE AND HAVING AT LEAST ONE ELECTRICALLY CONDUCTIVE ELECTRODES SPACED FROM SAID MEASURING UNIT ELECTRODES AND ADAPTED TO BE SUPPORTED IN SAID CONTAINER TO BE CONTINUOUSLY FULLY IMMERSED IN SAID FLUID AND PROVIDE A VALUE OF ELECTRODE ELECTRICAL CONDUCTANCE VARYING WITH THE CONDUCTIVITY OF SAID FLUID AND INDEPENDENT OF THE LEVEL THEREOF, A SOURCE OF ADJUSTABLE-AMPLITUDE ALTERNATING VOLTAGE OF SELECTABLE PHASE AND AN ELECTRICALLY RESISTIVE UNIT INCLUDED IN A THIRD ARM OF SAID BRIDGE TO EFFECT BALANCE THEREOF AT A PRESELECTED LEVEL OF FLUID IN SAID CONTAINER CORRESPONDING TO THE EMPTY LEVEL THEREOF, MEANS RESPONSIVE TO UNBALANCE OF SAID BRIDGE WITH CHANGE OF THE FLUID-LEVEL IN SAID CONTAINER FOR CONTROLLING SAID CONTROL MEANS TO MAINTAIN A SUBSTANTIALLY BALANCED STATE OF SAID BRIDGE, AND MEANS CONTROLLED BY SAID LAST NAMED MEANS FOR PROVIDING AN INDICATION OF THE PREVAILING FLUID-LEVEL SAID CONTAINER SUBSTANTIALLY INDEPENDENTLY OF THE PREVAILING VALUE OF FLUID ELECTRICAL CONDUCTIVITY.