9211 module and IR Thermocouples

[PChemist]

Hi Everyone,

Once again I need a little guidance from the community.  I am working on a new apparatus and am using a cRIO-9074 chassis with a 9211 TC module. I am attempting to connect a mini IR thermocouple (link below, part number OS36SM-K-140F) for one of my measurements. The part of my apparatus I am trying to measure I cannot make physical contact with.  Supposedly this IR TC reads out as a K type thermocouple, it works great on my Fluke 52II TC reader. When I attach it to the 9211 I get a much higher reading that is accurate, something around 60C when the regular TC I am comparing it to reads 24-25C.  I have tried playing with the on board scale factors but can't get an accurate reading.  The IR TC should be able to read between 20-90C accurately.  I noticed on the data sheet that it has a high impedance that may interfere with some readers. Would this affect the 9211? Any help or guidance here would be very much appreciated.

http://www.omega.com/ppt/pptsc.asp?ref=OS36SM&ttID=OS36SM&Nav=

Regards,

PChemist

[johnsold]

The impedance is probably the issue.  Look at pages 11 and 20 of the NI9211 Operating Instructions and Specifications.

From the specs on page 20: 

"Gain error from

source impedance..............................Add 0.05 ppm per ohm when

source impedance >50 ohms"

Lynn

[PChemist]

I thought that was the issue, just wanted to confirm it.  Thank you for the response.

Regards,

PChemist

[PChemist]

I have measured the impedance of my IR TC, it is 20.4kOhm. According to the 9211 manual this will result in an error of 1.02mV in the measured signal.  Unfortunately I can't figure out how to input this into the channel scaling offered by the 9211. I have searched the help files and can't find and hints. Does anyone have any?

Regards,

PChemist

[PChemist · Accepted solution]

Hi Everyone,

I have manage to work out a solution for the problem I described above. It seems that a C-Module on a cRIO has a problem adding a scale since the DAQ Assistant doesn't work. My solution is in the picture below. I compared it to a calibrated IR thermometer and it is better than the std dev of a typical K type thermocouple.

Regards,

PChemist