Liquid level gauge

Claim 1

PRESSURE GAUGE APPARATUS FOR MEASURING THE DIFFERENCE BETWEEN INPUT PRESSURES WHOSE INDIVIDUAL MAGNITUDES EXCEED THE PRESSURE DIFFERENCE, SAID APPARATUS COMPRISING A SENSOR INCLUDING AN ELECTRICAL DIFFERENTIAL PRESSURE TRANSDUCER HAVING A SINGLE RESILIENT DIFFERENTIAL PRESSIVE DEVICE AND A PLURALITY OF PRESSURE INPUT CONNECTIONS IN COMMUNICATION WITH SAID RESILIENT DEVICE; MEANS FOR APPLYING ONE OF SAID PRESSURES TO ONE OF SAID INPUT CONNECTIONS; AND MEANS PROVIDING A CLOSED, LIQUID-FILL PRESSURE-TRANSMITTING SYSTEM BETWEEN A SOURCE OF ANOTHER OF SAID PRESSURES REMOTE FROM SAID SENSOR AND SAID RESILIENT DEVICE, SAID CLOSED PRESSURE-TRANSMITTING MEANS INCLUDING A PRESSURE-SENSING HEAD HAVING A CASING WITH FIRST AND SECOND OPENINGS THEREIN, A CHAMBER FOR LIQUID-FILL, AND A SLACK DIAPHRAGM SECURED TO SAID CASING AND EXTENDING ACROSS AND ENCLOSING SAID FIRST OPENING AND CHAMBER, AND AN ELONGATED CONDUIT FOR PRESSURE-TRANSMITTING LIQUIDFILL CONNECTED BETWEEN SAID SECOND HEAD OPENING AND ANOTHER OF SAID TRANSDUCER INPUT CONNECTIONS SO THAT LIQUIDFILL IN THE VOLUME BETWEEN SAID SLACK DIAPHRAGM AND THE RESILIENT PRESSURE-RESPONSIVE DEVICE OF SAID TRANSDUCER ACCURATELY TRANSMITS THE PRESSURE APPLIED TO SAID SLACK DIAPHRAGM TO SAID RESILIENT DEVICE IN A DIRECTION TO OPPOSE SAID ONE PRESSURE, SAID ELECTRICAL TRANSDUCER INCLUDING A CIRCUIT FOR PRODUCING ELECTRICAL SIGNALS THAT VARY IN ACCORDANCE WITH SAID PRESSURE DIFFERENCES, SAID CIRCUIT INCLUDING MEANS RESPONSIVE TO VARIATIONS IN AMBIENT TEMPERATURE FOR PRODUCING A VARIABLE IMPEDANCE TO SID SIGNALS TO COMPENSATE FOR VARIATIONS OF THE DENSITY OF LIQUID-FILL IN SAID CONDUIT WITH SAID TEMPERATURE.