Extending a Thermocouple

Brian Grimm

Greetings all.· I'm working on a project to control a small kiln.· Because of the temperature range, I'll be using a type K thermocouple.· The one I've purchased is 8 gauge, bare wires with ceramic beads for insulators.· I've seen thermocouple extension wire, but is it required?· Something I read (of course, I can't find it now) led me to believe that I can use stranded bell wire as long as it isn't exposed to the heat.

Anyone with experience out there?

Thanks,
Brian, N7QJB

Tracy Allen

Hi Brian,

A thermocouple is formed at every transition between dissimilar metals. So a connection from type K thermocouple wire to copper bell wire will form two junctions. However, it you keep both of those junctions at the same temperature (inside a little junction box?) the error will be minimum. The temperature of the kiln is so much higher than room temperature and a few (~10?) degrees of error are probably no sweat. Ideally, the type k extension wire would come all the way back to the meter or controller, forming a reference junction there that the meter can measure and compensate. Omega Scientific has lots of good reference materials and tutorials online.

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Tracy Allen
www.emesystems.com

Brian Grimm

Thanks Tracy. I've been looking through the materials at Omega, but couldn't find a good answer about the extension wire. However, I do remember seeing a diagram discussing the effects of multiple junctions. I'll have to go back and read that again.

Thanks again,
Brian, N7QJB