Paul,

     I have been secretly working on my fuel gauge/probe problem.  I couldn't
     get your suggested circuits to work (probably my limited electronics
     ability), so I broke down and purchased two capacitance-to-voltage
     converters, the same ones used by the Dynon folks and sold by ACS.  I've
     installed one and hooked it to a voltage channel on my efis box, and it
     works as I would have expected.  The sad part is that the new circuit
     has the same problem as the old circuit in that it drifts in flight.
     But it returns to normal when back on the ground.  That's telling me
     that something is going wrong with the signal.  My guess is static
     buildup across the wings is affecting the capacitance readings of the
     probes.   How can I check this theory?  Any suggestions on how to
     fix it?

     Additional info:
     1)  CTV is mounted inside the cabin (old circuit was in wing root)
     2)  Pigtail from probe to CTV is shielded (old was unshielded)
     3)  CTV uses voltage a channel (EI circuit used frequency channel)

     My thought at this time is to disconnect the CTV output from the EFIS
     and connect it to a volt-ohm meter and go fly to see if the voltage
     reading increases or decreases unexpectedly (drawing off the other
     tank).  This should tell me if the problem is with the EFIS or the probe
     circuit.  I doubt it is the EFIS as other instrumentation feeding into
     the EFIS is rock solid.

     Mark S.
     (rain today)

     Interesting theory. Plastic wings as opposed to metal wings.
     Do you have any static discharge wicks on your wings?

     One way to check for temperature affects is keep the same fuel
     (about half full) in the wing and check it in the morning when it
     is cold soaked overnight and again in late afternoon after the sun has
     its way with the fuel tank.

     Paul Lamar ...No rotor no motor.


So, just doing a touch and go restores the values to normal?  Or do you
have to cycle power to the system?  Does cycling the power in flight
have any effect?

If it's static in the tank - caused by sloshing fuel then wicks on the
outside won't help.

There are many plastic airplanes that are successfully running
capacitive fuel probes.  I'd think we can get this licked.

Can you doodle out a basic schematic of how the probes are wired
(including any grounds)?  Is one side of the probe grounded or are they
both floating?

Might post the question to the aeroelectric connection (on the matronics
board).



Regards,

Matt-

Mark,
Do you have a grounding strap into the fuel tank to discharge static electricity when fueling?
Bill Schertz



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