temperature control with NI cDAQ-9172

[holo1]

Hi steve,

After I downconverted the file and tried to run it, it even had more error messages popping out.   I tried to add a DAQmx Configure between DAQmx Start task to increase buffer size, and it did not work. So how could I fix the error 2000279?

Thanks a lot.

[Esteban_B]

Hi holo1,

I’m a little bit confused with your hardware configuration, you said in the first post that you are using a NI 9401 and a NI 9263, the 9401 is a Digital I/O Module and the NI 9263 is the analog ouput module. Then you mention that you are using a NI 9211and this is a Thermocouple Input Module.

This is what I did here:

I used the VI that I posted here, then simulated the chassis and modules that you are using and set up the tasks and started the program It run with no errors. I only got an error in highlight execution mode, but not in normal mode.

Regards,

[holo1]

Hi steve,

    I use NI 9211 and 9401 for my project, not 9263. Sorry about letting you be confused. Actually, I almost solved the problems I mentioned before after I get a referencefrom a close loop, On/Off versus hysterisis example.

However, the only problem now is that the temperature measured from AI TC cannot match the temperature measured from an individual thermometer. The temperature plotted on the waveform chart is much lower than that in thermometer during heating process. So I wonder to know how could I increase the sampling rate to retrieve data points faster?

Thanks for your help.

[Esteban_B]

Hi holo1,

There are two things that I would like you to take in consideration, one is the thermocouple type that you have, is it really a K thermocouple?

Then, I would like you to read the voltage output from the thermocouple using a DMM, to see how fast it changes and also to see if the voltage that you are reading actually matches the real temperature.

In the code that you posted, you don’t have a DAQmx Timing.vi and you don’t have a wait in the while loop, so your application is software timed and also should be running fast.

Regards,

[holo1]

Hi Steve,

I am quite sure the thermocouples we are using is K-type. According to your suggestions, I connected multimeter to TC+,TC- and measured the voltage from AI TC port. the voltage changing rate is about the same as the temperature reading from AI TC,however, they still changed slower than the temperature reading from the thermometer, and the temperature differences between AI TC and thermometer could be 20 degree C during the heating process.

Besides, according to the K-type thermocouples calibration table I found, the voltage measured from multimeter does not match the temperature read from thermometer. So how could I fix this problem?

Thanks a lot.

[Esteban_B]

Hi holo1,

If you want to control the acquisition of your temperature, you can follow the examples VI in Hardware Input and Output » DAQmx » Analog Measurements » Temperature. If you are following these examples (as I think you are) you should be fine.

What you describes is a difference between a thermocouple and a thermometer, I don’t believe that NI hardware of software has do to whit the speed of the thermocouple, that is more related to the intrinsic characteristics of each device, A thermocouple works with a temperature difference between two different materials, and the thermometer is based in mercury. Both will react and work different. I think that the question here is: why is the thermometer updating faster than a thermocouple, but I think I’m not able to answer this completely.

Regards,

[holo1]

Hi steve,

I think I didn't clearly explain what kinds of thermometer I am using to monitor the temperature during the heating process.

We are using Omega HH309 digital thermometer with K-type thermocouples,too. So I believe the temperature reading should be the same because the K-type thermocouples connected to our NI 9211 module are the same as the thermocouples of digital thermometer.

So I don't know why the reading would have 20 degree C in differences. According to the K-type thermocouples calibration table, the voltage measured from DMM cannot match the real temperature,either.

[Esteban_B]

Hi holo1,

Have you tried with a different thermocouple connected to the DAQ card?

Have you also tried with one of our example VI’s just to measure the temperature?

Regards

[holo1]

I have tried  the other thermocouples from different ports but the same module and all of them behaved the same.

I was tring to run the sample code "Acq Thermocouple samples", the temperature from AI TC still far lower than that from thermometer, and the voltage is even smaller than the temperature reading from AI TC.

[holo1]

After I setup the CJC parameters of my AI TC DAQmx Read,the problem is solved. Thanks for your help.