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Diagnosing Problem with Capacative Fuel Gauge

ExtraKatana

Well Known Member
I am not the builder but understand Vans capacitive plates were used. The builder sent the tanks out to be built so he's not positive but thinks they are Vans. I am getting erroneous readings, mostly showing less than 5 Gal on a full tank conjunction with an EI FL-2CA Gauge. I have used auto fuel before but there is none in the tank now. Problem still exists.

https://www.aircraftspruce.com/catalog/inpages/ei-digitalgraphic5c.php

I replaced the IMC that connects at the BNC connector at the tank(I believe this is the voltage converter.) Cleaned all of the connections including at the circular connector. Re-Calibrated the sensor by adding 3 gallons at a time. Besides selling me the IMC, EI doesn't really have any more advice for me. They don't have any other "loaner" modules that I could plug and play to see if the problem exists in the head.

Would anyone be willing to guide me through how to diagnose this capacitive fuel gauge problem?
 
Some multimeters have a capacitance scale. If you had one of those you could see if the capacitance is changing as you would expect. It should effectively double when you go from empty to full with 100LL.

If you are getting a consistently low reading I would suspect you might have a broken internal connection. A low reading represents a low capacitance so with the plates attached it should be higher as the fuel is added. Again you could check this basic function with a proper multimeter.
 
I guess checking with a multimeter is next on the list. Will need to learn how to read capacitance. The EI fuel gauge requires you calibrate every few gallons. I did and the values kept getting proportionally higher. So, wasn't I reading the capacitance by performing the calibration? Looked great until 10 min. into the flight. Now it reads constantly low. Something tells me I have a loose ground or something. Anyone with history with the EI-FL2CA would be appreciated.
 
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