USB-TC Reading Different Temperatures in LabVIEW

[JamieM]

Hello,

I am using a USBC-TC to read room temperature. I have one vi that reads 18.6C and another vi that reads 25C. They both are using the same ULx vis and read the temperature the same way. I can stop one vi and run the other vi without making any other changes, yet the vis read different temperatures. Any advice on the discrepancy is appreciated! The two block diagrams for each vi are also attached. Thank you kindly in advance!

[Fausto]

Hello @JamieM.

I cannot see your entire vi block diagrams.  Please verify that your thermocouple is securely attached and check the surroundings for any heat/wind sources.

Next, please test the attached vi with your USB-TC and reply back.

 

 

Regards,

Fausto

ULx Acq Temperature Sample_modified for five channels and while loop.vi

[JamieM]

Hi Fausto,

 

Thank you for helping! I tested the .vi you sent and got reasonable temperature values. I also attached my .vi that is reading 18C. The code was started in an environment about 10F colder and ran when the environment heated up. Could the environmental temperature change the reading that significantly?

Thank you,

JamieM

PID_090222.vi

[Fausto]

Thanks for testing the vi.  If your measurements did not allow for a warm up period, then that may have been your issue.

https://www.mccdaq.com/pdfs/manuals/USB-TC.pdf

[JamieM]

Hi Fausto,

 

The vi that was reading 18C was running for four days (3 days with an environment of ~63F and one day with an environment of ~70F). I only ran the vi you sent for a few minutes, but I can run the vi for more than 30 minutes.

 

Thank you,

JamieM

[Fausto]

Details are necessary for troubleshooting an issue.

Would you say that for the 3 days in the ~63F environment, the readings were acceptable?

When the USB-TC module moved from the ~63F environment to the ~70F environment, did you connect the module to a different PC or not? 

What else was different going from one environment to another?

Why did you use a different vi?

Regards,

Fausto

[JamieM]

Hi Fausto,

 

At the beginning of the 3 days, the temperature readings were acceptable, but when the environment increased to ~70F the temperatures were no longer acceptable (it was still reading in the low 60Fs (which is about 18C).

The vi was running continuously when the environment was colder to when it was warmer (reading in the low 60Fs). I then stopped running the vi and did not change anything. I started it again and it continued to read in the low 60Fs. I tested the temperature readings on a vi I made that is similar to what you sent and was reading in the mid 80Fs (it should read in the low 70Fs). I then closed the PID vi to run the vi you sent and reopened the PID vi. The temperature to the PID after I closed it matched the temperatures with the vi you sent and the vi I made to test the temperature. I did not connect the module to a different PC. I also did not change the channels, thermocouple, any settings, or the block diagram. 

The lab I am in was doing maintenance to the heating system so the room temperature went from low 60Fs to low 70Fs.

Thank you again for the help,

JamieM

[JamieM]

Hello again,

The room temperature was 80F and I stopped the program, closed the window, reopened the window, and ran the program. I didn't change anything on the program and saw a jump in the temperature. However, I don't see this jump if I just hit "stop" and "run" without closing the window. Below is the data of the jump I saw. Hopefully this information helps.

Thanks,

Jamie

[Fausto]

Hello @JamieM.

I can open your file, but am unable to run it.  Please run a long-term test with my vi.  The CJC should be measuring the environment temperature near the module and account for any temperature fluctuations.

What is the serial number of your USB-TC as shown in InstaCal or on the backside label?

Regards,

Fausto

[JamieM]

Hi Fausto,

I just started a long-term test with your vi and will let you know what happens. 

The serial number of my USB-TC is 204AAFC.

Thank you for your help,

Jamie

[JamieM]

Hi Fausto,

I saw a spike in the temperature reading when I went from my vi to your vi after running my vi for a few hours. I then ran the program for about half a day and stopped and restarted the program. I didn't see a spike here. I waited for a few hours and stopped and opened my vi. I saw a small spike (~0.5C). 

Thank you,
Jamie

[JamieM]

Hi Fausto, 

Thank you for your help. I figured out my problem. My previous data wasn't getting purged so it was taking previous data and averaging that instead of the new data, which caused the jump. 

Thank you for your help,

Jamie

[JamieM]

I do get this noise readings when using yours and my new vi whereas this wasn't there on my previous vi....is this normal?

Thanks,

Jamie

[Fausto]

Hello @JamieM.

Are these noise readings new or did they exist prior to starting this post?

How many thermocouples do you have connected to the USB-TC modules?

How long are the thermocouples and are they securely fastened to the screw terminals?

Do you have any motors, pumps or EMF radiation near the thermocouples?

Are the thermocouples tips touching a conductive surface or do you have an electrically isolated barrier (i.e. Kapton or Mylar tape) between the thermocouple tips and the target surface?

If you remove the thermocouple and insert a short wire into the terminals (CxH and CxL), do you still see the noise readings?

Regards,

Fausto

[JamieM]

Hi Fausto,

Thank you. The reader sat on a shelf two feet away from a pump on the same shelf. After moving the reader, it solved my problem. I guess my previous code hid that problem.

Thank you,

Jamie