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  • thermocouple repair

    Can you just cut the bead off a thermocouple (with a little of each wire), and solder it further up? will it affect measurement?

    I have about 3 that are broken and seems a waste to throw them away.

    Thanks, Damian.

  • #2
    Re: thermocouple repair

    Originally posted by 686D61656D623D0C0 link=1232273529/0#0 date=1232273529
    Can you just cut the bead off a thermocouple (with a little of each wire), and solder it further up? will it affect measurement?
    Yep, t/c junctions can be repaired. Ordinary solder wont do it though, youll need to grab some "Cadmium Free" Silver Brazing Rod (1.5mm OD) to do a proper job of it. I think you can also buy lead-free "soft" Silver Solder too that is comprised mainly of Tin and about 2-5% Silver. This should be OK to use as well but it would need a higher temperature soldering iron and maybe some special flux to ensure a good electrical bond. Check out what BOC Gases have available, they should be able to help you out....

    You need to try and make the junction quite small and with NO tails hanging off the end. Use a pair of pliers to twist the cores together in a nice, neat and tight joint; apply some flux only on the twisted wires and then solder/braze the joint. Cut a little off the end so as to achieve a small, effective junction mass and then youre ready to go. Heres a link to some general info on thermocouples... http://www.picotech.com/applications/thermocouple.html

    All the best

    Mal.

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    • #3
      Re: thermocouple repair

      thanks for that Mal. Ive got some plumbing solder, which has a melting point around 260c from memory. From my previous reading about solder/brazing, I think this fits into your "soft"silver solder category. Ill heat insulate it, so should hopefully be ok. Im not sure if my benzomatic mapp torch would braze.

      So from what I read in your link, it is not the bead at the end that is the important bit, but composition of 2 different types of wires? I take it I need to ensure I dont join the wires in the opposite way they came off?

      Thanks again for your help.

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      • #4
        Re: thermocouple repair

        Originally posted by 4045494D454A15240 link=1232273529/2#2 date=1232307135
        but composition of 2 different types of wires?
        Yes... It is the interaction between the dis similar metals that generates a voltage...  That is why calibration is an issue as if the flying leads get deformed / twisted together / broken insulation / or the point on the join/bead is poor....  You readings will not be correct or can be reading at a point other than where you think.

        The difference between the many types is in fact the actual make up of the flying leads and the stability; then effect accuracy.  i.e. platinum is very accurate but expensive.

        J and K types are cheep / have large inaccuracies and are not liner. Specs for these are easily found and once over  120C they really are just an Indicator and not a accurate measuring device.

        Note: Then you add in the inaccuracy of the cheep DVM and you then in effect combine the potential errors. Not uncommon for a accuracy or +/- 5C @ 95% confidence even when measuring 50C....

        For some it is easy to comprehend the dif between Accuracy / Precision/ Reproducibility and thus you have an Uncertainty factor... However many when working in measurement forget or become confused. For me it is critical in Mechanical and Medical testing and the biggest issue is that Auditors (Sorry TG) often do not understand and cause us lots of pain and excessive expenses for no gain...


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        • #5
          Re: thermocouple repair

          Originally posted by 113E3735221D313E3137353D353E24500 link=1232273529/3#3 date=1232318389
          Sorry TG
          No offence taken.
          I understand.
          Im pragmatic though and try to get to know why auditees do things, then I can weigh up my response.
          "Return for effort" looms large on my radar.

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