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TC wire and dsub

 
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jan_de_jong(at)casema.nl
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PostPosted: Thu Aug 15, 2019 5:38 am    Post subject: TC wire and dsub Reply with quote

Theoretically, extending thermocouple wires using a dsub connector
(with, say, gold over bronze contacts) should be ok provided any
temperature gradient across the connector is ignored. The thermocouple
voltages across the connector cancel out to 0.

In practice there could be a problem with corrosion of a thermocouple
wire where it meets gold.

Is there experience?

Thanks,
Jan de Jong


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nuckolls.bob(at)aeroelect
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PostPosted: Thu Aug 15, 2019 6:28 pm    Post subject: TC wire and dsub Reply with quote

At 08:36 AM 8/15/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl>

Theoretically, extending thermocouple wires using a dsub connector (with, say, gold over bronze contacts) should be ok provided any temperature gradient across the connector is ignored. The thermocouple voltages across the connector cancel out to 0.

In practice there could be a problem with corrosion of a thermocouple wire where it meets gold.

Gold is electrolytically inert. I think
most thermocouple alloys are similarly
resistant to oxidation. I've run
TC wires though d-subs for decades with
good success . . . with one caveat:

My tasks were temporary instrumentation
installations so I've not personally
observed/demonstrated longevity in
field service. But given the low
reactivity of the alloys involved,
I'm pretty confident that they'll
last a long time.



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Fri Aug 16, 2019 6:15 am    Post subject: TC wire and dsub Reply with quote

At 08:36 AM 8/15/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl>

Theoretically, extending thermocouple wires using a dsub connector (with, say, gold over bronze contacts) should be ok provided any temperature gradient across the connector is ignored. The thermocouple voltages across the connector cancel out to 0.

In practice there could be a problem with corrosion of a thermocouple wire where it meets gold.

Gold is electrolytically inert. I think
most thermocouple alloys are similarly
resistant to oxidation. I've run
TC wires though d-subs for decades with
good success . . . with one caveat:

My tasks were temporary instrumentation
installations so I've not personally
observed/demonstrated longevity in
field service. But given the low
reactivity of the alloys involved,
I'm pretty confident that they'll
last a long time.



Bob . . .


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racerjerry



Joined: 15 Dec 2009
Posts: 189
Location: Deer Park, NY

PostPosted: Sun Aug 18, 2019 3:55 am    Post subject: Re: TC wire and dsub Reply with quote

I might be more concerned when using Type J (Iron / Constantan) thermocouples. You sure would want to make every effort to keep any moisture out and away from the iron.

Jerry King


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jan_de_jong(at)casema.nl
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PostPosted: Sun Aug 18, 2019 6:09 am    Post subject: TC wire and dsub Reply with quote

Thanks,
Jan de Jong

On 16-8-2019 04:25, Robert L. Nuckolls, III wrote:

Quote:
At 08:36 AM 8/15/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl> (jan_de_jong(at)casema.nl)

Theoretically, extending thermocouple wires using a dsub connector (with, say, gold over bronze contacts) should be ok provided any temperature gradient across the connector is ignored. The thermocouple voltages across the connector cancel out to 0.

In practice there could be a problem with corrosion of a thermocouple wire where it meets gold.

 Gold is electrolytically inert. I think
 most thermocouple alloys are similarly
 resistant to oxidation.  I've run
 TC wires though d-subs for decades with
 good success . . . with one caveat:
 
 My tasks were temporary instrumentation
 installations so I've not personally
 observed/demonstrated longevity in
 field service. But given the low
 reactivity of the alloys involved,
 I'm pretty confident that they'll
 last a long time.



  Bob . . .


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