Which Type of Sensor is More Accurate: Thermocouple or RTD?

[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

Thanks for your help.

 

[redargon]

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.

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

 

[Su Solberg]

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

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.

 

[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.

 

[Su Solberg]

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.

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

 

[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.