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.
Solved! Go to Solution.
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"
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?
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.