Z axis calibration idea

[mike_biddell]

In theory, if you have three channels in a plastic tube (a centre channel sandwiched between 2 outer channels) and you put two narrow flat plates in the outer channels. Then you let water rise up the centre channel as the water in the tank rises. You have a very sensitive variable capacitor in which the capacitance varies with the fluid level. A capacitance bridge could measure the variation very accurately. This method would work for any depth of tank. The water acts as a dielectric between the plates. Oh, the outer tubes are sealed.