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Canabalising old thermocouples

J

justinmg

Active Member
Our aircraft has EGT thermocouples which are compressed onto the outside of the exhaust pipes. They cables are a thin brown wire (possibly standard vans issue?) I have decided to replace these with drilled and clamped EGT probes.
The ones I have purchased are not long enough, by about 18in for cyl2. cyl3 might just reach. If I am binning the old thermocouples, can I use some of the old wire as extensions ( assuming that when I strip them, they are red and yellow.)
If so, can they be soldered and heat sleaved, or just twisted and heatsleved. Also does each need exteding by the same amount?

Thanks
 
Check this out

You can extend thermocouple wires by making a secure mechanical connection (twisting tight and solder) but you have to use the same type of thermocouple wire (yours sound like type K) and always match the wire types e.g. Ni-Cr to Ni-Cr and Ni-Al to Ni-Al to avoid making 'new' thermocouples... (I assume they will solder... hmm type K, been awhile..)

Standard thermocouple wire colors and descriptions may be found here:
http://www.omega.com/toc_asp/frameset.html?book=Temperature&file=tc_colorcodes

Minor differences in length won't matter.

Have fun.
 
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Lucky has it right, I just want to emphasize that you MUST twist the wires together. They need to be in intimate contact with no solder in between or you'll form miniature thermocouples in series with the real ones.
 
What Guy said..

Guy Prevost said:
Lucky has it right, I just want to emphasize that you MUST twist the wires together. They need to be in intimate contact with no solder in between or you'll form miniature thermocouples in series with the real ones.
Click to expand...

Yeah, I didn't really point that out so well.. the connection must be mechanical. In this case, the solder is just glue. If you twist the wires tight enough (and you MUST), you don't need solder but under conditions of vibration, thermal cycling etc. the solder helps keep things together.

'Real' thermocouple guys spot-weld the wires together.. I still twist..

BTW.. I guess I should add that in all properly soldered electrical connections, the solder is just glue. The connection must be mechanically secure before soldering... ... Ha! Sometimes, I make myself laugh... Seriously, you should do it that way.. I was just thinking of all of the stuff I've glued together with solder... bad me :rolleyes:
 
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Ordinary crimped fast-on terminals may be used to join thermocouple wire to extension wire provided that both sides of the terminal splices are at the same temperature and of the same resistance. I have a pretty expensive thermocouple calibrator sitting on my desk right now that I've used to test this exact thing.

Ordinary thermocouple wire is fine to use for extension wire provided it is the same type of wire used in the thermocouple. Extension wire is just cheaper wire. EGT probes are K-type, which is red and yellow. J-type are red and white. I'd love to smack whoever came up with the color scheme, because red is the negative side of the thermocouple.
 
Hadn't thought of that..

rocketbob said:
Ordinary crimped fast-on terminals may be used to join thermocouple wire to extension wire provided that both sides of the terminal splices are at the same temperature and of the same resistance.

Ordinary thermocouple wire is fine to use for extension wire provided it is the same type of wire used in the thermocouple. Extension wire is just cheaper wire. EGT probes are K-type, which is red and yellow. J-type are red and white. I'd love to smack whoever came up with the color scheme, because red is the negative side of the thermocouple.
Click to expand...

For the accuracy in question, that would work as well as long as the temps of the connectors were roughly the same.

I agree on the smacking.. who and when do we start?
 
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