Accuracy of a thermometer

1. Jul 16, 2009

Su Solberg

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

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2. Jul 17, 2009

redargon

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

3. Jul 17, 2009

Su Solberg

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.

4. Jul 17, 2009

redargon

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.

5. Jul 18, 2009

Su Solberg

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?

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

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6. Jul 27, 2009

redargon

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.