Read Thermocouple with NI cFP-AI-110?

[duhtrev]

Is there anyway that I can read a thermocouple using the NI cFP-AI-110?

Thanks in advance.

[Pie56694]

Hi Duhtrev,

The short answer is yes, you can take a thermocouple (TC) reading with a cFP-AI-110.

The cFP-AI-110 has three specifications that work in favor of this measurement.  First, it has eight selectable voltage input ranges, including ±60mV.  Second, it has a build-in 50Hz Low Pass Filter (LPF).  Third, it has 16-bits of resolution.  However, since the cFP-AI-110 not a TC input module like the cFP-TC-120, a few specifications work against a TC measurement.  There is no built-in linearization (converts the non-linear TC voltage to a linear scale), no cold junction compensation, and each analog input is single-ended.

Each type of TC provides a standard, non-linear, differential voltage that correlates to the temperature at the TC hot junction.  The National Institute of Standards and Technology publishes TC standards here.  For example, let's say you had a J-type 0-300ºC TC.  The NIST site shows that you should measure 0mV at 0ºC, 0.762mV at 15ºC, and 1.537mV at 30ºC.  Let's assume 1.537mV is the range of data you expect.  You would set the input range of the cFP-AI-110 to ±60mV, and you should enable the 50Hz LPF.  At this setting, the cFP-AI-110 can detect voltage changes of about 1.83µV, so you can expect good voltage resolution, but you still have a cold-junction issue.  This issue has a thread here.

How to Determine the Thermocouple Type and the Correct Polarity of Signal Connections

I hope this points you in the right direction.

[Wayne.C]

The attached vi has shipped with LV in the past.  Maybe as part of the Traditional DAQ?  It is specifically designed to convert voltage to temperature.