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
Hi Mark,
Matt may be on the right track with the handheld idea. If its possible
align the antenna of the handheld as parallel to the installed cap. tube
as you can then key the handheld while someone else watches the gage.
Get as close as you can to get the greatest and quickest effect. If you
get no response try aligning perpendicular to the tube and key the
handheld again. It's possible that you were lucky (?) enough to get your
installed tube and installed antenna exactly in parallel
geometric planes and the radiated energy is the culprit. Dave M
The alignment probably isn't all that critical. Within a fairly large
range of angles of antenna polarization/orientation, energy transfer
will not fall off dramatically. Being off axis even 45deg would only
cause a relatively small difference. That's why it's okay that many
aircraft comm dipoles are tipped or even bent. It's also why two
aircraft can talk to each other even if both are maneuvering - even
aerobatics.
In the case of the fuel sensor circuit, just the overall field strength
caused by the transmitting comm is the likely culprit.
Mark, is your comm radio working well? Can people hear your
transmissions clearly (and at a distance)? If not, the fuel sensors may
be fine and some portion of the comm feed or antenna may not be up to
snuff...
Matt-
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