Can I Take Thermocouple Measurements With Regular Analog Input Modules?

Updated Oct 23, 2020

Reported In

Hardware

  • NI-9211
  • NI-9212
  • NI-9213
  • NI-9214
  • PXIe-4353

Driver

  • NI-DAQmx

Issue Details

I am trying to get some thermocouple measurements using my NI-9201, which is a regular analog input module. When I do this, I get erroneous /unexpected thermocouple measurements, how can I fix it?

Solution

In short words, using regular analog input (AI) modules is not recommended for taking thermocouple measurements. 

The resolution and voltage range for most of the AI modules are not suitable for thermocouple measurements. For example, the NI-9201 has fixed voltage range of +-10 V and a resolution of 12 bits. This means that the maximum resolution achivable is of 20/2^12 = 4.88 mV. Thermocouples vary in the order of uV/°C given by the Seebeck coefficient (i.e. 56uV/°C for a J-type).

Using temperature modules as the NI-9210, NI-9211, NI-9212, NI-9213 and NI-9214 will give much better thermocuple measurements. You can also find temperature modules in the PXIe form factor as the PXIe-4353 .
 

Additional Information

Other factors as accuracy and temperature drift must be considered in thermocouple measurements. These factors will deprecate even more your thermocouple measurements when using regular AI modules.