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Accuracy of a thermometer

  1. Jul 16, 2009 #1
    I wonder whether the accuracy of that thermometer with a type K sensor is as follow:

    encironment: 90'C
    Sensor type: resistance sensor
    so the accuracy = +/- 90*0.005+0.5 = +/-0.95'C

    Thanks for your help.

    Attached Files:

  2. jcsd
  3. Jul 17, 2009 #2
    It's a K-type thermocouple:

    Usually accuracies are measured as a function of the full scale (FS). In the first instance this would be a full scale of 1350°C (from -50 to 1300). so +- 0.2% of that would be 2.7°C then plus the 0.5°C would be +- 3.2°C. Or it is +- 2.7°C + 0.5, which would be +3.2/-2.2°C So if it reads 90°C it the temperature could actually lie anywhere between 86.8°C and 93.2°C... or between 87.8°C and 93.2°C
  4. Jul 17, 2009 #3
    Since the catelog said the calabration (* it has not said measured accuracy) is performed at 18-28 Celsius, may I say the accuracies is not FS any more? just the error is (0.14°C+0.5°C = 0.64°C)

    Btw, it is thermocopule type sensor

    Thank you very much for your help.
  5. Jul 17, 2009 #4
    No, I don't think so. From what I know, typical k-type thermocouples have between +-1.5°C and +-2.5°C accuracy in the lower temperatures (-50°C to 350°C) and around 0.4 to 0.75% of the temperature for higher temperatures (above 350°C). So, 0.64°C seems a little low for a typical K-type.

    if you want something more accurate, i would suggest a Pt100 temperature sensor, although it depends on your situation and what range you want to measure and what accuracy you really require.
  6. Jul 18, 2009 #5
    Thanks for your advise.

    Since the Type K thermometer will have +- 1.5 to 2.5'C at -50-350'C, it is poorer than a mecury glass tube thermometer!!

    The application of the sensor is conduct a flow measurement for compressor by getting pressure difference between a nozzle(measure the mass flow rate and transform back to volume flow). The temperature is around 100'C.

    I wonder Pt100's principle and is it much more expensive?

    Thanks for your reply.

    p.s. the attached is the spec. of the thermometer

    Attached Files:

  7. Jul 27, 2009 #6
    sorry that it took a while to get back to you, i was on holiday.

    here is a interesting link for considerations whether to use a thermocouple or a pt100 (a typical type of resistance temperature detector or RTD): http://en.wikipedia.org/wiki/Resistance_thermometer#When_to_use_RTDs_or_thermocouples

    Bear in mind that you can log the measurements from a thermocouple or RTD electronically if you want to measure and analyse data over a longer period experiment. Whereas, with a standard thermometer you have to either write down the observed values or set up a video camera to read the results.

    Thermocouples react quicker than RTD's (from fractions of a second instead of 2-10seconds), but are less accurate (+-2% instead of 0.2%). Thermocouples also have larger temperature ranges.
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