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Thread: PID thermocouples

  1. #21
    Super Moderator

    HATCH's Avatar
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    Sep 2008
    Lexington, SC
    Quote Originally Posted by AzElkhunter View Post
    That makes sense.
    I thought you might have to tell it what temp rating the actual TC is like 0 - 900 or 0 - 1200. Etc...

    Sent from my SM-G920V using Tapatalk
    This chart should give you a rough idea

    Click image for larger version. 

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    This is the same chart for ALL K type thermocouples regardless of who makes them or the length of the probe.

    Whats different between a 400C rated probe and a 600C rated probe could be the outer metal of the probe. The general construction of the TC.

    Doing the ice water test to verify 32 degrees F is fine but the problem is that isn't near the standard operating range that you would be using it at.
    So imagine tuning a car to run perfectly at idle compared to a 4K RPM.

    If the thermocouple is designed exactly to the spec then you are perfectly fine calibrating your PID at 32. But I doubt that a $5 Thermocouple will be built exactly to the K spec.
    it will be close though..

    We are casting boolits. It doesn't matter if we are off a few degrees.

    What you want with a PID is repeat-ability.
    Basicaly knowing that at a certain temp (lets say 700 F) that every time the PID reads 700 its gonna be the exact same temp as it was before.
    The reason I say that temp doesn't really matter because if you aren't casting good boolits at what it says it 700 then you turn it up or down.
    It doesn't matter if the PID is off a couple degrees or 50

  2. #22
    Boolit Master
    lwknight's Avatar
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    Nov 2009
    Fort Worth, Texas where the west begins
    The actual length of the probe is only to make it fit the application and means nothing except how deep it will go. The thermocouple is in the tip.
    Sent from my PC with a keyboard and camera on it with internet too.
    Melting Stuff is FUN!
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    L W Knight

  3. #23
    Boolit Master
    bangerjim's Avatar
    Join Date
    Apr 2013
    out of here, wandering somewhere in the SW.
    Better forget trying to fix it! And the "weld" used is not just solder. The two bi-metal wires are fused together by a special process that has NO OTHER metals between them. Remember, wherever there is a metal to dis-similar metal junction, that forms a t/c! Soldering the wires would form at least 3 junctions, each reading off temp from the others. And the long sheath is normally filled with a dielectric to keep the wires in place.

    Just better to buy a new one. And all these cheap-o t/c I hear about guys using ARE made to go in protective thermowells and not contact the process directly. The thin sheath over the junction is just not made to withstand the exposure/oxidization on the bare end.

    I use to be an engineer with a company that made industrial grade high quality t/c's (not these ChiCom things) and it is a very complex process...if done right!

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