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AeroElectric-List Digest: 20 Msgs - 02/17/06

 
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glcasey(at)adelphia.net
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PostPosted: Sat Feb 18, 2006 5:20 am    Post subject: AeroElectric-List Digest: 20 Msgs - 02/17/06 Reply with quote

I think you are over-reacting to the cold junction thing. True, for
instrumentation-grade measurements (temperature accuracy to a
fraction of a degree) it is a good thing to have no metal changes in
the circuit all the way back to the cold junction. However, that
would mean that all the connector terminals would also have to be
made from like materials. As long as both wires make the transition
to another metal at the same temperature the measurement error will
be small, like a few degrees. Is the extra accuracy worth the
effort? The commercial systems of which I am familiar use copper
wire for interconnects. If that's not true I still have time to
replace all the copper in my system...
Gary Casey

Quote:
Hi Bob and all,

After examining carefully the TC probe sold with the UMA CHT, the
situation
appears even worse than I expected. The probe has only 2 ft TC
lead wires,
and then copper extension wires. So with my in-line engine,
cylinder 2 the
hottest, the "cold" junction will be INSIDE the engine compartment,
where
temperature can rise somewhat higher than the 75F the instrument is
calibrated for!

So, I bought TC connectors and extension wires from Omega to move
the cold
junction close to the instrument.
Jean-Pierre Castiello, who designed the A320 brakes temp
monitoring, is to
craft for me an external compensation box based on the same AD594.
Input is
the J extension, output will directly drive the CHT air core movement.

I will let you know the result...

Thanks to all of you for the so precious informations I could
gather from
the list!

Gilles



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