CAPACITIVE GAUGING METHOD AND APPARATUS

摘要

Method and apparatus for deriving a correction factor used in calculating corrected liquid (e.g., fuel) quantity of a tank having a probe capacitance which varies in accordance with the quantity of liquid contained within the tank. The correction factor reduces sensing diode voltage drop errors and stray capacitance errors (affecting the capacitance of the probe) through use of a switchable high/low amplitude Lo-Z oscillator. All oscillator outputs are "low" amplitude relative to the output amplitudes of conventional devices. Signal processing is effected by inputting raw data (both reference and probe-sensed signals) to an analog-to-digital sampling circuit, which raw data are used for deriving the correction factor. The correction factor is then applied to the raw data to determine a corrected liquid quantity indication. Recalibration of the correction factor periodically permits automatic adaption to changing error magnitudes (i.e., changes in the deleterious effects of diode-voltage drop and/or stray capacitance). Additionally, the relative "health" of the component elements of the tank unit is monitored by tracking changes occurring during recalibration of the correction factor. Establishment of a correction factor outside a predetermined range might indicate faulty probe components or other such difficulties. Numerous practical advantages and economies are obtained by the method and apparatus presently disclosed because of the enabled use of an oscillator with a relatively low voltage output (e.g., under 10 volts peak).