multimeter thermocouple problem

Discussion in 'General Electronics Chat' started by cowboy303, Feb 12, 2012.

  1. cowboy303

    Thread Starter New Member

    Jan 30, 2012
    I got this Multimeter (Extech EX530) when I measured the temperature with the thermocouple that it came with I got 72 degrease inside the house which is the right answer. But when I take it outside (20 degrease) it goes down to 25 then goes up to about 55 and stays there for 5 minutes at which time I came back in side. I can test it for longer if it helps.

    Thank you for your time.
  2. holnis


    Nov 25, 2011
    The voltage generated by the thermocouple is proportional to the temperature, so the errors have generally the largest impact when thermocouple is measuring temperature at the edge of it's supported range.

    Refer to the thermocouple documentation to understand its accuracy impact to the overall measurement.
  3. russ_hensel

    Well-Known Member

    Jan 11, 2009
    Actually I think the problem is that the thermo couple has 2 junctions, a hot and a cold, and the reading is of voltage, not temperature and depends upon the temperature of both junctions. In other words there is a reference junction which you also took out into the cold.
  4. cowboy303

    Thread Starter New Member

    Jan 30, 2012
    The thermocouple is rated from -50 to 250 degrease.

    Thats what I was thinking but the manual said nothing about it.
    you have your reference junction and your test junction your reference point has to be at the right temp to read accurately because it just reading the voltage difference between the two junctions and if there the same then it will read about 72+/- degrease
    bottom line I can't go outside with the meter and read the temperature:(

    Thank you and please tell me if I'm wrong
  5. Wendy


    Mar 24, 2008
    Did you pay attention to your wire. The two most used wire types is Type K and Type J. This describes the alloys used by the two wire types. They can't be mixed up, or you will get anomalous readings.

    I bring it up because you didn't mention it. It is critical.
  6. MrChips


    Oct 2, 2009
    There are two separate matters. The thermocouple itself is rated from -50 to 250 degrees.
    The thermocouple is basically two pieces of wires bonded together and there is not much to go wrong.

    The principle of the thermocouple is based on the two junctions, a hot and cold junction. For the thermocouple to give correct voltages one of the junctions must be at a known reference temperature, usually a 0C ice bath.

    The second issue is the digital multimeter. The multimeter provides the thermoelectric reference junction instead of the ice bath. If this circuit is out of whack you will get incorrect readings.

    So in conclusion, there is nothing wrong with the thermocouple. The fault is in the meter.

    (Bill makes a good point. Make sure you have the correct type of thermocouple for the particular meter or meter setting.)
  7. cowboy303

    Thread Starter New Member

    Jan 30, 2012
    it says K CROMEL+ ALUMEL- I take that to mean K type.
    And that plugs into a little white Extech thing that takes the k type and makes it so I can plug it in to my meter via banana plugs all it says on it is Extech instruments I can post pics if it helps.
    but when I pinch that little white adapter to warm it up it brings the temp reading down.

    Thanks and the thermocouple is rated to -58 to 482F not -50 to 250 like I said it was.