Capacitive gauge for aircraft fuel tank - compensates for dielectric constant using fuel density meter with programmable amplifier

摘要

The contents of a fuel tank in an aircraft are measured by a gauge in which capacitive electrodes are placed in the fuel. Compensation for dielectric constant is provided by a density meter to provide precise measurements. A 400 Hz signal is applied via a transformer (10) to a bridge circuit containing the capacitive electrodes (11) in one arm and located in a fuel tank (12). A capacitor (13) in air balances the electrode caoacity. Another arm contains a capacitor (14) and rebalancing potentiometer (15) with a correction capacitor (16) located in the fuel in parallel with this capacitor. The potentiometer is adjusted for balance by a servo motor (18) driven from the bridge via an amplifier (17) and which also drives a gauge pointer. Correction for fuel density is provided by potentiometer voltage adjustment from a programmable amplifier circuit (25).