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.


    Mark:

    FWIW: To help narrow down your options:  I believe my Lancair ES has the
    same EI fuel probes as yours, but mine are connected to a standard
    EI fuel
    gage.  I have no problems with wandering indications in flight.

    Composite wings do generate static charges in flight--especially in
    light
    rain.  I flew through a very light rain shower enroute to Oshkosh in
    2003.
    The electric trim position indicators went absolutely wild, flashing all
    kinds of lights, and then went blank.  The trim motors still worked,
    and the
    EI fuel gage indications remained steady.

    Tom Parkes



Tom,
Are your gauges affected by the nav/com?

Mark



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