Colyn writes
<<<
While we're on that, I had a situation
with a grt eis 6000 (similar to the eau that Chelton sells or used to).
One day my MAP started indicating zero
concurrently with erratic indications on several of the egt's. On
investigating I found that squeezing or moving the wire harness from
the probes to the eis caused different erratic indications. Tearing
apart the wire harness revealed several spade connectors that weren't
connecting anymore. It's also possible that some were shorting to
ground via the shielding on adjacent probes.
The unexpected (for me) finding was
that fixing the egt connections is what made the MAP work again. I
would guess there is a way to build a more robust interface to the
probes such that badness on one input doesn't cause badness on
another. Is there any way I can provide better isolation outside the
box?
>>>
It was likely the terminal to shielding short that was the problem. I
have never seen inside a EIS 6000 but I have seen the guts of an EAU
(designed and built by GRT). Extrapolating those observations, I would
say that it is very likely that there is a long list of things that can
be done to harden the system against faults and failures. Most of
these would be internal to the electronics box.
Your question was about what can be done on the outside. The most
obvious one is get rid of the damn spade terminals! Get yourself some
silver solder, flux and a jeweler's torch at the local welding store, cut the spades out of the
system and splice the thermocouple wire using silver solder and heat
shrink. The time you spend doing the splicing right will pay off in
spades (npi) by reducing the faston terminal maintenance. Remember, for
every spade connection replaced by a splice you are eliminating three
failure points, wire to spade, spade male to female and spade back to
wire. Remember also that with thermocouples you are dealing in
millivolt signal levels.
I do not know what wiring is supplied GRT but the VMS came with a pile
of Radio Shack spaghetti that quickly found its way into the bin in
favor of some aircraft grade MIL-27500/18 tefzel cable.
Bottom line. The reliability of any aircraft electronics is highly
dependent on the quality of the materials used for the installation and
the skill of the technician doing the work.
Regards
Brent Regan
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