RTD Temperature Measurement Accuracy

Updated May 1, 2018

Reported In

Hardware

  • PXIe-4357

Issue Details

Can we get a better temperature accuracy for RTD temperature measurements for 2-wire mode? I'm considering the PXIe-4357, but I'd like to get accuracy of 0.5 degrees Fahrenheit, which the device specifications does not align to for that wiring mode. Is this a limitation of 2-wire when compared to 4-wire mode? 

 

Solution

The PXIe-4357 is a great option within NI devices for RTD measurements, and the wiring actively checks what you’re seeing over the load when there are more wires used in the measurement. By nature of that setup for the wiring types, 4-wire is designed for better accuracy due to those additional checks, whereas the 2-wire mode will check the load over the resistance without the additional comparison points. 

If you really want to make the measurement work with 2-wire, you could try to make it happen in software using scaling to account for the loss of voltage over known resistances. That will change with varying environmental temperatures, however, so a constant environment is necessary, and it could become a system-level calibration of all components without warranted specs for accuracy. 

Additional Information

The question then is – is the environment constant? If yes, you may be able to make it work, albeit without guaranteed accuracy specs, as they are not tested to run in that manner. If no, it may be worthwhile for to re-evaluate the 2-wire setup and consider a 4-wire option, as the latter setup by nature will allow for better accuracy requirements and hit specs much closer to the desired range. 

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