Rif.: Measure temperature using thermo-couple and NI 9201

[Krish101]

I have NI 9201 module and i need to measure and acquire temperature using thermo-couple. I dont know how to get the CJC value to get the reading. 

[pep91]

Hello Krish101,

if you are acquiring the temperature using the low level DAQmx functions, you can specify the type of thermocouple directly inside your vi.

So firstly you have to create the virtual channel specifying that you want to read temperature with a thermocouple, then you specify the type and then you start the acquisition of the channel in which you have connected the thermocouple. 

I hope that my answer helped you.

Kind regards

[GerdW]

Hi Krish,

the NI9201 is a simple analog input module with 12 bit resolution and a ±10V input range: not quite the one you want to use for TC measurements…

And it provides no internal CJC: you need to measure the temperature using some other means. On a cRIO you might use the internal cRIO temperature sensor. Or you use another analog input channel and a 2nd sensor next to your 9201 module…

[Sam_Sharp]

The 9201 module won't be very suitable for thermocouple measurements - it has a fixed +-10V range and 12 bits so that's a maximum resolution of 20 / 2^12 = 0.004V = 4000uV. Thermocouples vary by uV / degC (e.g 56uV/degC for a J-type) so one bit of change in your analogue input will span about (4000/56) 70 degrees! You also need to take the accuracy/temperature drift into account so realistically it will be even worse than that.

In short: You can't use that module for thermocouple measurements. Get an NI9211 (4-ch), 9212 (8-ch), 9213 (16-ch) or 9219 (multipurpose AI) module instead - these modules usually have a +-80mV range and a 24-bit resolution which is much more suitable for thermocouple measurements. You can also get USB thermocouple devices or ICs.