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K Type Thermocouple Accuracy

  1. May 8, 2012 #1
    Hello all,

    I'm looking to buy an accurate K Type thermocouple and I have a couple questions concerning accuracy before I make my decision.
    -If it is a K Type thermocouple, does it matter how the probe is configured? e.g. length etc.?
    -Is there any discrepency in accuracy between different priced probes? (assuming they are all K type)
    -If I already have a K Type probe will that have no problem matching the new thermocouple?

    FYI here is the thermocouple I am looking at buying:
    The accuracy is ±(0,05% v.Mw. + 0,3°C)
    and the temperature resolution is 0,1°C

    Thank you in advance,
    fictionx
     
  2. jcsd
  3. May 14, 2012 #2
    For my expericence, the accuracy of thermocouple measure system (including sensor, record) are always >0.5℃ even after calibration.

    And the main error for temperature measure is not the sensor self, but the way how stick it to target and which size of thermocouple you used (for small source, the thermocouple has notable "heatsink effect", which decrease the source temperature)
     
  4. May 30, 2012 #3

    Averagesupernova

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    Gold Member

    I have worked with K type thermocouple instruments. As far as I know the temp accuracy of the thermocouple wire should be as consistent as the thermocouple wire is pure. A length of K type wire with one end having the wires shorted will generate a voltage at the open end of the wire based on the difference in temp from one end to the other. It is NOT an absolute thing. It is a diffential from one end to the other. Sooooo, to get a meaningful measurement of the temp at the shorted end of the wire we need to know the temp at the open end of the wire (reference). This can be a significant inaccuracy in the system. If you have a thermistor with poor repeatability/accuracy to determine the reference temp then the whole thing is no more accurate than that crappy reference. Of course the small voltage that the thermocouple generates needs to be amplified. The linearity and accuracy of the amplifier can introduce more error in the measurement. In other words, I don't believe the thermocouple probe itself is the largest source of error. Maybe how it is attached to what it is trying to measure could be, but that is a different issue. Did this help?
     
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