NI 9211 Thermocouple Inaccurate Reading

[prashn]

Hello, 

I'm trying to build a simple VI that stores temperature versus time measurements from an Omega Type K thermocouple in a CSV file (please see attached). I am using an NI 9211 coupled with a NI cDAQ-9172 chassis (due to my older equipment, I am still using LabVIEW 2017).

The VI I have thus far seems to behave appropriately, but when I use my thermocouple to measure the temperature of an ice water bath, I get consistent erroneous readings of 50 degrees Celsius. I've verified that the thermocouple works with a 4 channel datalogging thermometer, so the problem lies with my program or the DAQs. 

In addition, I know the "Convert to Thermocouple Reading.VI" is not compatible with the NI 9211; is there any conversion I need to apply within my program to get the correct temperature reading?

Appreciate any insight!

[StevenD]

Your sample rate is set to 1kHz, the 9211 supports rates up to 14 S/s. TC's usually read much slower than other analog signals (at least in my experience) I usually just read 1 sample every 250 ms in a software timed loop. Start with that, you may want to also consider converting the express VI to proper Daqmx code. 

[prashn]

Hello, 

Thanks for your quick response. I reduced the sample rate to 3 Hz, but I still observed the same 50 degree measurement of an ice water bath. The module is quite old, so maybe it needs to be manually calibrated.

[StevenD]

Hmm.. Maybe. The cDaq 9172 is listed as a legacy device. Can you open up MAX (Measurement and automation explorer)  and read correct temperature with the test panels there?

[prashn]

No, I still encounter the same issue. 

[StevenD]

Not a good sign. Maybe time to open a ticket with NI or get new hardware. There may be a way to recalibrate it and get it working, but I don't know how.

[prashn]

Thanks for your help!

[niNickC]

You tried different thermocouples?

I would suggest that the thermocouple itself is most likely duff.

[prashn]

Hi Nick, 

I have three thermocouples and two NI 9211s. All port combinations with all three of my thermocouples yield the same result. 

[niNickC]

Rubbish.

Probably the device then. 

Can you verify the thermocouples on some other device maybe a hand-held meter?