Temperature acquisition on NI USB-6259

[GabrielPereiraaa]

I started LabView last week and I'm having troubles creating a program to capture temperatures from a thermocouple. I made the program, but the temperatures values are fluctuating more than I expected (you can see through the thermometer). I tried to put a filter, but by doing so, the values are now estatic at 29°C. 

The situation here is that I'm collecting the temperature from a copper wire, and when I grab it, to increase the themperature, the value stays at 29°C. 

Can someone help me? 

[GerdW]

Hi Gabriel,

the USB6259 is a general purpose DAQ device, but not made specifically to measure thermocouples. Did you read the specs?

Unfortunately your VI is saved in LV2024: can you downconvert it to LV2021 or older? (File-Save for previous)

[NIquist]

Please also show us how you have your TCs wired into the DAQ.  You will need to use the differential settings and take up two channels for each TC.

Gerd is correct that you will not get decent results from any DAQ that's not specifically designed for temperature.  I have done it before in a pinch, but the resolution and stability was terrible.  A good temperature DAQ is usually 24-bit to accommodate the small voltage changes and has built-in cold compensation circuits.  But, they are NOT cheap:

Temperature - NI

If you just need a simple one channel solution, the little USB-TC01 is a great choice.  If you have the proper NI software installed, it will even plug and play.  So easy your manager could use it. 😁

[GabrielPereiraaa]

Here it is!

[GabrielPereiraaa]

..

[GerdW]

Hi Gabriel,

you would get more help when you would down convert your VI. I prefer LV2019...

(File -> Save for previous)

[GabrielPereiraaa]

Here's the 2019 version

[GerdW]

Hi Gabriel,

---

@GabrielPereiraaa wrote:

Here's the 2019 version

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Finally. 😄

• Can you change the VI to a simple voltage measurement task (instead of AI TC channel)?
  Suggestion: read voltage at samplerate of 100Hz…
• Why do you read a single sample as waveform?
• What do you expect from filtering a waveform that contains only a single sample?
  What output do you expect from this estimator function? Why do you display the "low cutoff frequency"???

Keep in mind: your DAQ card is not made to measure thermocouples…

[NIquist]

Here is a corrected version of your VI.  I used a USB-6002 with a Type-J thermocouple and was able to see the thermometer go up and down with just my fingers squeezing it.

BUT, it is not scaled properly for the thermocouple (I just guessed that 50000 was close.  You will need the conversion formula for YOUR TC (you never said what type) to get anything remotely accurate.  You will see that it will still not work well as our 16-bit DAQs are just not designed for this.  This shows you the basic idea though.  Things are MUCH easier when the hardware is built to read TCs.  Then, DAQmx temperature functions can be used. 😎

[GabrielPereiraaa]

Hi!

I changed my VI to a simple voltage measurement task, but like that, my program doesn't read any temperature sample :c. So I'm using Analog Input, Temperature Thermocople.

The output I expect is the mean of all temperature samples captured. I'm want to use this program for temperature capture from a rotacional machine.

Here's the program with some changes I made. Now I can capture some temperature samples, but the thermometer still doesn't change when I grab the wire.