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-


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