We are using the wire insulated with high temp cloth, Kevlar I believe. 
We have used them many times. The voltage / temperature values are
unchanged. 

This is a fundamental property of the materials. I would not expect to see
subtle drifting. 
If the weld is good and the connection at the plug is good, the wires
insulated one from the other up to the weld, the voltage measured at the
ends of the wire should be reliable and temperature dependent. 

I have seen failures of the insulation, cracks in the weld, and loose
connections inside the plug produce inaccurate measurements. 
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, October 02, 2007 2:04 PM
To: [log in to unmask]
Subject: [TN] Thermocouple Longevity?

Hi Everyone!
 
How many reflow profiles do ya'll put the same thermocouples through before
you think about replacing them?
 
I've typically used them until they quit working or the insulation
deteriorates so bad that I don't want to use them anymore. I was told that
was not a good practice. That your typical K thermocouple starts drifting
after only 4 or 5 thermal cycles. I said; "Really?" I didn't want to debate
a whole lot because it was a customer who said this, so I just agreed and
went on.
 
So, do any of you know this to be a fact, and do any of you trash a
thermocouple after only 4 or 5 profiles and replace them with new ones?
 
Kind regards,
 
Steve Gregory

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