Could the pressure increase inside the tank going up with speed
           via the venting cause a capacitance variation thus a
   different DC
           reading.

           It could be verified on the ground by increasing lightly the
           pressure in the
           tank.
           Or in flight taking a reading in slow flight and another one at
       cruising
           speed.

           Just guessing have no logical explanation for such a phenomena.

           JP



       JP,
       I paid close attention to the fuel level readings on my last
   flight and
       I have to say that they appeared to be pretty steady in level
   flight.  I
       may have caused some of the change in readings via uncoordinated
   turns.
       Not that the ball was all the way left or right, but just a little,
       possibly enough to cause the fuel inside the capacitive probes
   to move
       up the tube a bit, which would cause the fuel readings to vary a
   bit.

       The big surprise was when the right gauge, the one with the
   Dynon CTV
       converter installed, went to zero as soon as I keyed the mic.  Up to
       that point, it had been the more reliable of the two.  I'll have to
       check again, but the left gauge, the one with the stock EI circuitry
       (square wave a/c) appeared to drop by a few gallons while the
   mic was
       keyed.  An undesirable feature, but not as drastic as the right
   side.

       I plan on doing the following:
       1)  re-route the antenna cable away from the efis and other wiring
       2)  mount the CTV in a grounded metal box
       3)  run a separate ground from the capacitive probe to the a/c
       ground bus
       4)  Purchase an EI fuel gauge and hook them up and forget about
   reading
       fuel levels on the EFIS.  ;-)

       Mark S.


   It's somewhat likely the noise is radiated as opposed to conducted to
   the sensor circuit.

   Do you have access to a handheld transceiver (with a "rubber ducky"
   antenna)?  While transmitting with it (on a locally inactive frequency),
   you may be able to identify a portion of the circuit that is vulnerable
   to the RF radiation.  If you don't find any part of the circuit
   responding to the handheld then grounding properly likely will improve
   things.

   There are instruments sold by Van's which are vulnerable to RF.  The
   only solutions found have been to shield the instrument (in your case,
   probably the CTV box) with metal - heavy foil may work, but a metal box
   might be better.  Or ignore it.  When the mic is un-keyed, do the
   readings return to normal immediately?


   Regards,

   Matt-

Matt,
I hadn't considered using a hand-held radio to trouble-shoot this
problem.  I'll give that a try.  Once the mic is unkeyed, the readings
will return to normal, but not immediately since they have a built in
damping factor.

For now, my most reliable method of tracking remaining fuel is with the
Real World Solutions EM-2 engine monitor.  This unit calculates the fuel
used based on the duty-cycle of the injectors.  I enter the number of
gallons added when I refuel, and it counts down (or up if you wish) from
there.  Even though it doesn't track fuel levels in each individual
tank, it is still a pretty nice backup system.

I also have a 7-gallon low fuel warning light for each tank, driven by a
GEMS sensor.  Again, nice to have a backup system when the primary is a
bit quirky.

Mark


The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2007 All world wide rights reserved.