Issues with thermocouple data acquisition with NI 9212

[RohitMTU]

Hi,

Just to start with, i'm new to LabVIEW.

I wanted to sample data at 95 Hz which is the maximum the card allows me. I'm using a NI cDAQ-9178 chassis and as mentioned a NI 9212 card.

Whenever i'm setting up my DAQ assistant it's not giving me the device setting option to change my timing mode to high speed. As a result if i log the data even though i'm sampling at 95Hz the same value is repeating about 50 times each second, so essentially i'm sampling at only 1.8 Hz.

Would really appreciate of someone could help me with this. thanks!

Thanks!

[RandallCrandall'sCandleHandle]

Hi Rohit,

Could you post a screenshot of your DAQ Assistant configuration and your LabVIEW code? Generally you will not need to set your device to operate in a high speed mode to sample within its range.

Cheers,

Ryan

[RohitMTU]

Thanks for replying, i've attached the code, please take a look.

Rohit

[RandallCrandall'sCandleHandle]

Rohit,

It looks like your setup is good. Are you getting the exact same reading value 50 times in a row, or does it vary slightly? Also, is it always exactly 50 readings that are the same, or does it vary? It might be helpful to attach a screenshot.

Thermocouples generally read out fairly constant values, so I'd like to see what your data looks like.

Cheers,

Ryan

[KYC · Accepted solution]

Please try this.

[RohitMTU]

Hey Ryan,

I'm sorry i don't have the excel file at this moment and my laptop is not available to me. But i can tell you that it varies some readings are 55, 40, etc. Especially when in contact with the heating surface after you have started gathering the data, as soon as the heating surface is rmoved it the samples become more and more erratic, sometimes 20 are repeated sometimes 40 etc. but settles around the same 55 ish samples per second. I'm beginning to think the thermocouple is not able to keep up with the DAQ system and that is why this is happening.

P.S. i'll try to post the excel sheet ASAP

Thanks!

Rohit

[KYC]

The fix is in the vi that I posted earlier.

[RohitMTU]

That solved it thanks a lot!

Rohit