Trying to get an accurate reading from thermocouple

[johnsold]

The large variations you are seeing with the NI 9201 appear to be due to interference, probably power line frequency interference. This may be due to a ground loop or some connection issues.

There is no guarantee that you will not have a similar problem with a thermocouple, particularly if the cause is a ground loop issue.  The insulated thermocouple should minimize the chances of a ground loop.

Lynn

[Eric-E]

I hesitate to point the finger at power line interference yet due to the large overall amplitude at which we are measuring and the fact that the module is well isolated. With your current VI, you could be creating the sine wave using a simulated channel instead of real physical channel.

I would try to duplicate your VI's sine wave results in MAX by performing the same test in MAX that I advised you to do before, but make the rate the same as in your VI (25.6Ksamp/sec). If we can see the same sine wave, then I'd be curious to see its actual amplitude (without the custom scaling in the VI). If we do not see the sine wave, then the VI is incorrect and may be using a simulated device by mistake.

If possible, post your MAX screenshot at 25.6Hz

Are you using battery power for your temp converter device? If you see the sine noise and you're using AC power to power the converter, switch to battery.

I hope this helps.

[iinWill]

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@Eric-E wrote:

I hesitate to point the finger at power line interference yet due to the large overall amplitude at which we are measuring and the fact that the module is well isolated. With your current VI, you could be creating the sine wave using a simulated channel instead of real physical channel.

I would try to duplicate your VI's sine wave results in MAX by performing the same test in MAX that I advised you to do before, but make the rate the same as in your VI (25.6Ksamp/sec). If we can see the same sine wave, then I'd be curious to see its actual amplitude (without the custom scaling in the VI). If we do not see the sine wave, then the VI is incorrect and may be using a simulated device by mistake.

If possible, post your MAX screenshot at 25.6Hz

Are you using battery power for your temp converter device? If you see the sine noise and you're using AC power to power the converter, switch to battery.

I hope this helps.

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I perform MAX test on different configuration. The first image is from the NI9201 DAQ connected to the Omega TAC80B-K while it is powered off. The second is with the DAQ connected to the Omega while its powered ON. The last image shows that DAQ not connected to the Omega. Hope this could help you figure out the issue. 

[iinWill]

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@iinWill wrote:

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@Eric-E wrote:

I hesitate to point the finger at power line interference yet due to the large overall amplitude at which we are measuring and the fact that the module is well isolated. With your current VI, you could be creating the sine wave using a simulated channel instead of real physical channel.

I would try to duplicate your VI's sine wave results in MAX by performing the same test in MAX that I advised you to do before, but make the rate the same as in your VI (25.6Ksamp/sec). If we can see the same sine wave, then I'd be curious to see its actual amplitude (without the custom scaling in the VI). If we do not see the sine wave, then the VI is incorrect and may be using a simulated device by mistake.

If possible, post your MAX screenshot at 25.6Hz

Are you using battery power for your temp converter device? If you see the sine noise and you're using AC power to power the converter, switch to battery.

I hope this helps.

---

I perform MAX test on different configuration. The first image is from the NI9201 DAQ connected to the Omega TAC80B-K while it is powered off. The second is with the DAQ connected to the Omega while its powered ON. The last image shows that DAQ not connected to the Omega. Hope this could help you figure out the issue. 

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I also used the VI and did different configuration. Hope this helps as well. 

[iinWill]

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@iinWill wrote:

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@iinWill wrote:

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@Eric-E wrote:

I hesitate to point the finger at power line interference yet due to the large overall amplitude at which we are measuring and the fact that the module is well isolated. With your current VI, you could be creating the sine wave using a simulated channel instead of real physical channel.

I would try to duplicate your VI's sine wave results in MAX by performing the same test in MAX that I advised you to do before, but make the rate the same as in your VI (25.6Ksamp/sec). If we can see the same sine wave, then I'd be curious to see its actual amplitude (without the custom scaling in the VI). If we do not see the sine wave, then the VI is incorrect and may be using a simulated device by mistake.

If possible, post your MAX screenshot at 25.6Hz

Are you using battery power for your temp converter device? If you see the sine noise and you're using AC power to power the converter, switch to battery.

I hope this helps.

---

I perform MAX test on different configuration. The first image is from the NI9201 DAQ connected to the Omega TAC80B-K while it is powered off. The second is with the DAQ connected to the Omega while its powered ON. The last image shows that DAQ not connected to the Omega. Hope this could help you figure out the issue. 

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I also used the VI and did different configuration. Hope this helps as well. 

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Here's the VI i used. 

[Eric-E]

OK I believe this was said once before in the posts, but I'll re-itterate. You don't need to account for the K thermocouple type, or the cold junction refference because you're not using the DAQ card to measure the thermocouple voltages. You are using the DAQ card to measure the output of the TAC80B-K. Therefore you should use a code like the one I attached (and pictured below). Try this out. It will be the best that the device(s) can combine to achieve in terms of accuracy.

[Eric-E · Accepted solution]

[iinWill]

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@Eric-E wrote:

I added a thermometer to the VI. How could I get the thermometer to read smoothly, because it's fluctuating rapidly. I try using a time delay in the loop, with 0.3 seconds, but it still doesn't run smoothly. Other then that, it's running fine, except for some poor temperature readings. Also your VI is incorrect, it's not +1000 it's x1000. 

[johnsold]

To remove the fluctuations you may want to do some averaging. If you take 100 samples per second and average over 100 samples you will get 1 update per second and it should be much smoother than what you now have.  If averaging does not smooth things, you may still have an interference problem.

Lynn

[iinWill]

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@johnsold wrote:

To remove the fluctuations you may want to do some averaging. If you take 100 samples per second and average over 100 samples you will get 1 update per second and it should be much smoother than what you now have.  If averaging does not smooth things, you may still have an interference problem.

Lynn

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Fluctuation is caused by interference, what I meant was how could I make the thermometer graph read smoother? I'm using a time delay and fooling around with it until I get a smooth reading. The fluctuation I can deal with, its normal as its reading many samples a second. It won't keep constant. I'm trying to adjust this to make it smoother.