There are no really simple words...Originally Posted by ngeronikolos
A capacitor is made up of 2 plates, separated by a dielectric material. When a capacitor holds 'capacitance', it has an electrostatic field on it, limited by a number of factors (plate area, plate material, dielectric material and constant, blah blah blah). You can look it all up in Wikipedia...
Anywho's....a capacitive liquid level sensor uses the fuel in the tank to change the dielectric constant of the dielectric material, thereby changing the total capacitance of the probes.
In aircraft, one of the ways to measure this is to measure the phase change between a reference sine wave and a sine wave that has been passed thru the capacitor. Higher cap's, bigger phase change. Another way is to 'measure' AC current flow thru a variable impedance (variable impedance here being the capacitor X(c) = 1 / (2 x PI x Freq x C ).
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