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K Type thermocouple installation

Discussion in 'General Electronics Discussion' started by Blue, Apr 20, 2014.

  1. Blue

    Blue

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    0
    Apr 20, 2014
    Hi
    I'd appreciate some advice re installing a K Type thermocouple, with a small stub end, into a brass block. The brass block will be used to heat and blue steel screws and clock hands. A PID temp controller will be used.
    Obviously I will need to drill and tap a hole to receive the retainer bolt/screw on the thermocouple. I am thinking at the end of that hole there needs to be a recess to snugly take the end of the thermocouple node, is this enough? do I have to use some sort of heat conductive gel or paste? If so, any suggestions what it is I should use?
    The temp will go up to 310deg Centigrade.
    Thanks in advance.[​IMG]

    [​IMG]
     
  2. duke37

    duke37

    5,224
    718
    Jan 9, 2011
    The drilled and tapped hole will make a good thermal connection if screwed up tight. Do not use any gunge, this may not stand the temperature and if it sets will make dismantling impossible.
     
  3. Blue

    Blue

    19
    0
    Apr 20, 2014
    Many thanks duke, appreciated
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,186
    2,692
    Jan 21, 2010
    I'd agree with almost everything Duke said.

    I'm not sure that you need to screw it up *tight*. Screw it in firmly, then check to see that it is still firm at the operating temperature. If not, repeat the tightening. Depending on relative expansion, it may get tighter or looser at a higher temperature, but looser would be my guess.
     
  5. Blue

    Blue

    19
    0
    Apr 20, 2014
    Thank you Steve. I've got a picture of below of the actual thermocouple I shall be using, differs a little to the one above in fact. You see that the end of the node has a smaller diameter than the threaded retainer, which makes me think I should counter sink this into its own hole past the retainers thread length to get contact with the block, and also to avoid it being damaged when the retaining screw is made firm. Am I making sense?
    [​IMG]
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,186
    2,692
    Jan 21, 2010
    Yeah, make sure that the threads mate and that nothing else interferes with that. If that requires a deeper hole because of that bit on the end, or some clearance at the top to allow for the shoulder, then that's what you need.

    The 2 points of contact should be the thread and the flat part of the head of the device.

    This does not apply if the specifications of the device require something different (perhaps the tip is spring loaded, for example, or perhaps the device is not firmly attached to the threaded part.)

    If the threaded part is only loosely attached to the actual thermocouple, then you may have to use the threaded part to push the tip of the device into or against the thing to be measured.
     
  7. Blue

    Blue

    19
    0
    Apr 20, 2014
    "...or perhaps the device is not firmly attached to the threaded part...If the threaded part is only loosely attached to the actual thermocouple, then you may have to use the threaded part to push the tip of the device into or against the thing to be measured"
    This is indeed/will need to be the case/method
     
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