Capacitance fuel tank gauge

Claim 1

An electrical measuring circuit for capacitance fuel gauge measuring systems independent of input power variations comprising, in combination: an amplitude and frequency stable signal source means associated with a capacitance-type liquid tank probe means for immersion into non-gaseous fluids, said frequency stable signal source means being arranged to excite the capacitance tank probe, said liquid tank probe means further including rectifying means connected to said liquid tank probe means to convert the output of said liquid tank probe means to DC; first balancing means to balance out frequency and amplitude variations on empty system indication; D.C. amplifier means connected between said rectifying means and a DC display means, said DC amplifying means being connected as an integrator means, the output of said amplifier means being displayed on said display means; and second balancing means associated with said tank probe for setting maximum reading on said display means, wherein said first balancing means is a bridge circuit which includes said tank probe and said rectifying means, and further includes a potentiometer, the tap of which is connected to form a series circuit with additional rectifying means and a capacitor said series circuit connected in parallel with the tank capacitance which are connected across the opposite points on said bridge circuit, the balancing voltage being derived from said potentiometer being connected across the output of the amplitude and frequency stable excitation source, and further including a voltage dividing means and wherein said DC amplifier means connected between said rectifying means and said display means has its operating point referenced to the negative side of said display means which is also referenced to the mid point of said voltage dividing means which is connected to the power supply, said referencing renderiNg the output of said amplifying means displayed on said display means insensitive to supply voltage variations.