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Thread: Shortening thermocouple wire

  1. #1
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    Default Shortening thermocouple wire

    I am replacing my westach quad gauge with a MGL EMS-2 engine monitor that allows 4 cylinder monitoring which the westach does not provide. Instead of looping up excess thermocouple wire (CHT and EGT) like I have done in the past, I would like to cut off the excess for custom lengths. Any problem with doing this? Bruce N199CL

  2. #2
    Senior Member Dave S's Avatar
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    Default Re: Shortening thermocouple wire

    Bruce,

    I'd recommend against cutting the lead because in the process a person may end up creating a "cold junction" which may alter the resistance value of the assembly, or introduce another bimetallic junction, of the manufactured part. In other words - it might not read predictably with the design value.

    I'd stay with a loop for the excess and cleverly call it a "Service Loop"

    There are a lot thermocouple references out there and it is similar to voodoo. Cut to the chase would be to contact Westach.

    DS
    Dave S
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  3. #3
    Administrator DesertFox4's Avatar
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    Default Re: Shortening thermocouple wire

    This may be of some help. MGL carries a splice kit for cht wires.

    http://www.mglavionics.com/CHT_Parallel_Splice.pdf


    DesertFox4
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    Building 7 Super Sport
    912 ULS Tri-gear

  4. #4
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    Default Re: Shortening thermocouple wire

    Thanks for the responses Dave and Steve. Before I placed my order with MGL (the unit is on backorder so haven't received it yet) I took measurements from each cylinder(CHT) and exhaust stack(EGT) to where the RDAC (the smart box everything connects to on the firewall). Then called MGL and they told me their thermocouples come with 3 foot tails. Some of my runs are less than 3 feet some a bit longer (Steve I did order the splice kit for the longer runs). When the EMS-2 arrives I will check everything out and give the MGL tech support a call to see what they say. There was a discussion on the RV forum , and the consensus was it is OK to cut to length but I will see what MGL says. Looking forward to installing this neat little feature rich engine monitor (the post OSH spending continues!) Thanks guys Bruce N199CL

  5. #5
    Senior Member jmodguy's Avatar
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    Default Re: Shortening thermocouple wire

    The measurements we use on our engines are not that critical. If they were, manufacturers would be requiring cold junctions and/or chrome and alumel contacts in the connectors. You can shorten the leads without any major effect.
    I work on an experimental 747-200 that has a LOT of this wire installed on a couple hundred thermocouples. We do not leave excess wire on any harness. Our measurements are much more critical so we use both chromel and alumel contacts and cold junctions.
    Jeff
    KF 5
    340KF

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    Default Re: Shortening thermocouple wire

    Thanks Jeff good to know that this can be done , as Dave mentioned above from what i've read , this is like voodoo science and its tough to get a definitive answer. Hopefully my MGL stuff arrives this week and I will talk to their tech support after seeing what the thermocouples look like. Can't wait to see your monster Kitfox fly. Looking pretty cool and have enjoyed following your build . Bruce N199CL

  7. #7
    Senior Member jmodguy's Avatar
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    Default Re: Shortening thermocouple wire

    Thanks Bruce! Final push is under way...
    For what itís worth, I was reviewing my documentation to ensure I understand how all of this is supposed to work and re-read my GRT EIS manual and it also mentioned it was ok to trim the wire lengths.
    Jeff
    KF 5
    340KF

  8. #8

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    Default Re: Shortening thermocouple wire

    As long as you use the same type thermocouple wire and connectors (ex K), you can shorten or extend. Just do not use regular cooper wires or pins. Thermocouples create a voltage proportional to a difference between hot and cold end, so the unit thermocouple plugs into needs to compensate for Cj

  9. #9
    Rodney's Avatar
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    Default Re: Shortening thermocouple wire

    Once you get your new gage installed and have some time on it - would appreciate a review of what you think of it. I too would like to set up CHT/EGT for all four cylinders.

    Are the CHT probes the kind that fit on the plugs?

    Thanks
    Rodney

  10. #10
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    Default Re: Shortening thermocouple wire

    Hi Rodney, MGL just notified me today, that the back ordered Blaze EMS-2 is on the way , so I will keep you posted on installation and function. At OSH this summer I was able to play with the instrument some and liked how much info it was able to display. Primarily , I purchased it to replace my Westach quad gauge(CHT,EGT oil pres and temp) that can only monitor one cylinder for EGT and CHT. The MGL unit will monitor all 4 cylinders as well as oil press and temp. The thermocouple probes come in any configuration , either plug ring or bayonette, your choice. Also compared to all the others I looked at , this one was the most economical at a 1000 buckaroos. Bruce N199CL

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