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Thread: Home made thermocouple

  1. #1
    Join Date
    Jan 2002
    Posts
    333

    Post Home made thermocouple

    I was loking at the thermocouple on my neycraft oven. It looks like two different wires twisted together to creat a voltage when heated.

    Would it be possible to make my own? Perhaps for a hand held pyrometer. I have a analog guage for that porpose but no thermocouple.

    Seems I need to know what the different wires are and where to obtain them.

    Just another crazy idea,

    Bob

  2. #2
    Join Date
    Jul 2002
    Posts
    280

    Post

    Bob -

    Try http://www.omega.com/

    Omega Engineering has long been a good source for thermocouple info with a lot of free data tables.

    ------------------

  3. #3
    Join Date
    Nov 2001
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    1,241

    Post

    depends on what wires you have around.

    Copper / constantan is one type, the constantan is an alloy which you can look up.

    really any two different materials will make a thermocouple, but most are pretty useless.

    Your gage will likely be for one of the standard types, if it is for direct hookup. Look carefully for a "type" letter somewhere on the dial near the pivot cutout, or on back of gage.

    Best to just buy the right type. Omega, given above, is a good source.



    [This message has been edited by Oso (edited 10-09-2002).]

  4. #4
    Join Date
    Jan 2002
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    333

    Post

    Went to the omega site, great link- Thanks.
    Bob

  5. #5

    Post

    Bob:
    You can buy thermocouple wire from Granger or McMaster Carr. All you have to do is twist the ends (without insulation) and fuse it together with a spot welder or welding torch.
    Make it as long as you want for your use. The wire is available by the foot. You can get several types. Look up the temperature range you want in the Omega catalog and figure out what ones are compatible with your instrument. You may also need to order a thermocouple connector for your instrument to plug it in unless it has screw terminals. You may want to consider a metal sheathed unit from omega but the response time will be longer than a bare thermocouple.

    ------------------
    Dick
    Dick

  6. #6
    Join Date
    Feb 2002
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    2,362

    Post

    One of the shops that worked for me used to make all their own thermocouples. we used them for testing jet engines in test stands. Dick has described the process very well. if yu need real accuracy you need a "cold sink'. this is basicaly a thremocouple (it may be a ral thermocouple placed at a known temperature or a voltage generated that cooresponds to some temp.

    you can extend the leads with copper or other metals so lng as the junctions are at the same temp. not desirable but a lot less expense than long runs of iron/constantan.

    a thermocouple welded to spark plugs is a good test device. the lean running cylinder runs hot. it suprised me how much unequal fuel distribution there was in good engines way back when. I suspect things are more equal today (PC rules even in engines?)

  7. #7
    Join Date
    Jan 2002
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    333

    Post

    I want to make a K type that would go up to 2115F. I was unable to find the type of wires used. Any help?

  8. #8
    Join Date
    Oct 2002
    Posts
    2

    Post

    Type K thermocouple is made from Chromel and Alumel wire. Purity of the wire will influence the accuracy of the thermocouple made from it. We used to make type J (iron & Constantan wire) thermocouples where I used to work. We stripped about 1/4" of the fibreglass insulation off the 20 gauge wires and twisted them together a couple of turns and then fused them with a oxy/acetylene mini torch. We purchased wire from Thermo Electric (Toronto Ontario or Saddlebrook NJ)
    but Omega is also a good supplier.

    Ross

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