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Hello Larry,
The RF in the composite airframes can really wreak havoc. I assume from your email that the fuel gauges are a Skysport or similar and not ours (we don't make an electromechanical gauge set) ? If so, I don't think these have a completely metallic shielded enclosure either, as ours do. The RF bombarding the circuit elements (as well as the conducted RF from the wires) will upset the readings as you have seen. Have you tried ferrite beads as the RFI chokes on the wires and wrapping the fuel probe circuitry with shielding foil ?
With respect to the VMS indicators, they should be quite immune to the RF field strengths seen even in the composite airframes. Good sense does dictate that you route transmitter coax cables away from ANY of your aircraft's' other wiring harnesses to prevent RFI problems. We have heard of many cases of operation upset on various products, whether TSO tested or not, (although the TSO testing does guarantee that the equipment will withstand certain high levels of RFI, if TSO tested to MAJOR category, such as the VM1000 is).
While we cannot supply tech support for other manufacturers, we hope our input here will help. Let us know how it works !
Best Regards,
Dave
-----Original Message-----
From: Larry Graves [SMTP:larry@aircraftersllc.com]
Sent: Thursday, September 21, 2000 6:09 PM
To: lancair.list@olsusa.com; support@visionmicrosystems.com; avionics@lancair.com; marvkaye@olsusa.com
Subject: Re: Vision Micro problems
We've been chasing a similar problem with the electromechanical fuel gauges
in a newly completed Glasair-II S RG. Whenever the PTT switch activates the
transmitter(s), both fuel gauges (main & header) jump nearly to the peg.
There are capacitance type sender units in each tank, and as part of our
investigation, I keyed my handheld AC-22 in the cockpit and got exactly the
same reaction.
Clearly the fuel gauge wiring is acting as an antenna in this builder's
installation, and we initially have wound some of each gauge's wiring around
a magnetic choke. This has dramatically reduced the effect, but not
eliminated it. We are going to try adding a small capacitor across each of
the probe/sender unit leads next. Shielded wiring is a third option.
Haven't noticed yet if the effect extends to any of the indicators on the
VMI LCD. Will have to watch for this.
Best Regards,
Larry Graves
AirCrafters Builder Assistance Center
140 Aviation Way, Watsonville, CA 95076
Tel 831-722-9141 Fax 831-722-9142
www.AirCraftersLLC.com
----- Original Message -----
From: <JOSCALES@aol.com>
To: <lancair.list@olsusa.com>; <support@visionmicrosystems.com>;
<avionics@lancair.com>; <marvkaye@olsusa.com>
Sent: Thursday, September 21, 2000 11:52 AM
Subject: Vision Micro problems
> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
> << Lancair Builders' Mail List >>
> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
> >>
> I am sending this note to the Lancair Mail List as well as Lancair
Avionics
> and Vision Microsystems. I am hopeful that I will get a solution or at
least
> some direction from someone. Seems that, within their areas of
> responsibility, everyone has taken an understandable position, but I still
> have a situation.
>
> I have experienced problems with my fuel gauges since first flying my
Super
> ES. I have Electronics International probes and initially had EI fuel
gauges
> and OAT gauge.
>
> Both gauges were affected when the PTT was used. After having the
> instruments inspected and cleared by the manufacturer, I re-installed them
> with no noticable improvement. My avionics shop and the A & P who had
done
> the panel installation tried many, many things (shielding, filters,
diodes,
> wiring checks, wiring re-routing, etc.) with no improvement in the
situation.
>
> After talking with Lancair about the problem, it was decided to change
both
> instruments to VMI units. We did this and saw the same problems with the
new
> units. VMI took the position that the problem was with the probes and
that
> if VM probes were installed the problem may go away. This obviously was
not
> sufficient motivation to cause me to remove the wings of a finished and
> flying airplane.
>
> Basically, I was told by those connected with this situation that there
was
> nothing that could be done and I would have to live with it. I
disconnected
> the warning buzzer for the EC 100 annunciator panel and "lived with it".
> Turned out that living with it involved explaining to my passengers each
time
> the EC 100 showed WARNING: LOW FUEL that it was just a glitch and there
was
> no real problem. So far, to my surprise, no one has questioned my
> explanation.
>
> With all this as background, here is the kicker. As I have become
> comfortable in the plane, I have been able to be more observant of
details.
> Recently, I noticed that when the PTT was used the oil temperature number
as
> well as the outside air temperature number went down. Took me a few tests
to
> realize what was really happening and, yes, when I talked on the radio the
> numbers on those two instruments, along with the aforementioned fuel gauge
> numbers, changed. When the PTT was released, the numbers would return to
> normal after about a minute. Interesting part of this latest information
is
> that these two instruments use all VMI wiring, sending units and probes.
>
> I assumed that I would have to once again "live with it". On a whim, I
> mentioned the problem to my next door hanger neighbor who has a Glastar
with
> the VM 1000 display and VM outside air temp gauge. We checked his plane
and,
> sure enough, when his PTT was used the oil temp and outside air temp
numbers
> changed. Verrrrrry interrrrrresting.
>
> Please excuse the rambling and excess detail but I need some input on
this.
> I no longer believe the problem is built into the plane. I think the VM
1000
> may have some problems. Anyone else having this problem? Anyone solved it
> yet? Any suggestions? Perhaps there is a need for some sort of an inhibit
> circuit (like the one used with the Stormscope) that would "freeze" the
> displayed numbers until the PTT is released. Any and all input will be
> appreciated. I freely admit lack of knowledge about avionics. If I have
> said something really dumb don't hold it against me.
>
> Thanks for any help.
>
> Jim Scales
> N98AF
> (115 hours on it and flying great)
>
>
>
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
> LML Builders' Bookstore: http://www.buildersbooks.com/lancair
>
> Please send your photos and drawings to marvkaye@olsusa.com.
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>
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