Fluid quantity indicator

Claim 1

In an apparatus responsive to the quantity of a fluid within a container therefor of predetermined volume, said apparatus comprising a capacitive sensing means disposed within said container volume so as to be immersible within said fluid and any air within said container volume, said capacitive sensing means having an associated variable dielectric constant, said dielectric constant being proportional to the proportionate amount of fluid within said container volume, said sensing means capacitance varying in accordance with the variation in said proportionate amount of fluid; a reference capacitive means disposed within said container so as to normally be immersible within said fluid and responsive to variations in the dielectric constant of said fluid due to environmental conditions; the improvement comprising AC reference means operatively connected to said sensing means for providing a signal having a predetermined phase and frequency thereto; first microprocessor control means for providing a control signal output indicative of said fluid quantity; first digital-to-analog conversion means having a magnitude input operatively connected in parallel to said first microprocessor control means control signal output for providing an output in response to said input, said first digital-to-analog conversion means output being operatively connected to said reference capacitive means, said output comprising a signal having a predetermined phase opposite to said AC reference means signal phase and a predetermined frequency identical therewith; said first microprocessor control means being programmable to enable a universal apparatus full scale set compensation for containers for said fluid substantially independent of said container configuration for compensating for variations in full scale capacitance of a given container and to directionally count in response to directional counting command signals provided thereto; first differential amplifier summing means having an input operatively connected to said capacitive sensing means and said capacitive reference means outputs for summing the output signals provided therefrom; first means operatively connected to said first summing means output for providing a directional counting command signal in response to said first summing means output, said counting command signal being operatively connected to said first microprocessor control means input, said first microprocessor control means counting in response to said directional counting command input signal for providing a display control signal output dependent thereon, said first microprocessor control means output further being operatively connected in parallel to a digital display means for controllably providing a digital of said fluid quantity on said digital display means in response to said display control signal output; said AC reference means capacitive sensing means, capacitive reference means, first summing means, first directional counting signal providing means, first microprocessor control means and first digital-to-analog conversion means comprising a first independent digital servo control loop which is nulled when said first microprocessor control means output is equivalent to said fluid quantity, whereby a container configuration independent real time digital display of fluid quantity within a given container is provided.