Products > Test Equipment
Twist and solder k type thermocouple wires
<< < (2/2)
jpanhalt:
As Magic stated, the "Law of Intermediate Metals" (https://www.omega.co.uk/literature/transactions/volume1/infared1.html ) applies.  Oxides may affect conduction or far more likely cause an open circuit with K-type.  Neither should give a wrong reading with a decent circuit. 
Faringdon:
Thanks, the idea of the twisting, was to  ensure the wire ends are physically together, because as you kindly describe, soldering them is a little difficult.
It seemed to work OK though....and if there was oxidation, then its not likely to be able to insulate the wires from each other significantly, since the wires are twisted tightly together anyway.
jpanhalt:
Good luck.  I tried tightly twisted K-type, and while it did work on occasion, if I touched it or wiggled it, I got an OC (open circuit) error with the TC amplifier (MAX 31856) I was using.  That amplifier is a bit problematic in that it gives over-voltage and OC errors probably when others don't.  Welding the TC's completely eliminated the OC error.  Adding solder that doesn't actually wet the wires is no better than adding epoxy. 

Your comment about needing to twist before soldering made me suspect at least one of the wires is not wetting/tinning.  I would tin both wires, then twist together and reheat with a little flux/solder.

Be careful about noise.
jonpaul:
Hi: These chromel–alumel  metal alloys will NOT make reliable low R contact over time/temperature/vibration with either twisting OR soldering!

 YOU CANNOT SOLDER THEM !

Twisting will seem to work a while and eventually go intermittent or give false readings.

Suggest that you BUY READY MADE TC  or get a proper TC welder, Not that hard to DIY the welder.

Jon

PS:

We used and made 100s of Type K TC  in 1980s..1990s for QC/debugging of T1 and othet telecom rack terminal and network equipment.

Used Omega #32..36 Kynar type K, Omega connectors.

 welding 100s of pcs at a friend's lab. Took perhaps 1..2 hrs.
Faringdon:

--- Code: ---No regulatory will accept a PCB fuse as it is not reliable and will not break fire safe.
--- End code ---
Thanks, and in the face of it, you are of course correct.

However, we do not need them to work "over time"..but just for the immediate test that we are about to do......we will attach them to the FET....in 10 mins the FET will get up to steady state temperature.....and the soldered/twisted thermocouple wires will last ok for 10 mins...then,, during the following 2 hours of the soak test, any sudden changes in the FET temperature  would of course, indicate that the thermocouple had come to grief.......so we would at least know if it happened.
Navigation
Message Index
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod