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What's better? re: thermocouple switching...

 
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steve(at)tomasara.com
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PostPosted: Fri Nov 07, 2008 9:04 am    Post subject: What's better? re: thermocouple switching... Reply with quote

Bob and the group,

I've read and understood the book and list info on switching
thermocouples (i.e. importance of iso-thermally balanced couples etc.)
and haven't found the answer as to which is better between the following
choices related to type "K" to copper transition connections going
into/out-of the "switch box" (which is via a single "DB" style connector).

A) terminate "K" wires with "K" type pins (Expensive, but I already have
them. They are stamped, not machined, pins. ), terminate copper wires
with standard machined gold pins -> resulting balanced couples between
"K" wire types and gold at pin/socket interface. (how important is
contact pressure to a repeatable "couple" connection?)
B) terminate "K" wires with standard gold pins, terminate copper with
mating pins -> resulting balanced couples between "K" wire types and
gold at a machined pin crimp connection (my favorite at my current level
of ignorance... but I don't know the mechanical stability of "K" type
wire in this type of crimp - at least the "K" type wire IS stranded
here, and I also don't know the voltage/temp relationship between "K"
wire types and gold)
C) terminate "K" wires with copper pig-tails via single crimp over both
wires (i.e. put both wires into one side of a butt splice and crimp)
terminate copper pigtails with machined gold pins, terminate switch
copper with mating gold pins. -> resulting matched couples are gas-tight
crimps between "K" wires and copper. (seemingly best for bi-metal
interface but worse for ensuring iso-thermal connections and logistics)
D) some other option I haven't thought of?

Anyone know the voltage/temp relationship between the two "K" wire types
and gold?

I except that each of the above is likely to work "good enough" but hey,
if I have to choose anyway, I might as well pick a method I can argue is
the best of the options.

Thanks in advance,

Steve Stearns
Boulder/Longmont, Colorado
CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)
Restoring (since 1/07): N45FC O235 Longeze Cothern/Friling CF1 (~1000 Hrs)
Flying (since 9/86): N43732 A65 Taylorcraft BC12D


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mrspudandcompany(at)veriz
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PostPosted: Fri Nov 07, 2008 9:42 am    Post subject: What's better? re: thermocouple switching... Reply with quote

Steve & Bob,

I have been led to believe that the connector pin material does not matter
if the temperature of both sided (male and female) are the same. I am not
sure of this, and maybe Bob has an answer.

Roger

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