thermocouople readings are jumpy

[MrDoc]

I understand what your saying but ...

The T/C's and the SCXI have not been touched, moved, anything done to them.

I can switch between the rev 5.1 PC and the rev 8.5 PC with the PC interface harnesses to the SCXI.

So on the rev 5.1 PC there is a much stabler, less "jumpy" update of the temp readings than the rev 8.5 PC.

The rev 5.1 DOES NOT have the different levels for each SCXI board, that the rev 8.5 does.

The rev 5.1 doesn't have the 0.5°C variance; it does have some just not that extreme.

Is it just part of rev 8.5 that I have the temp swings?

I am more concerned with the defferent levels I see from each 1102 board.

[Broken_Arrow]

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MrDoc wrote:

I can switch between the rev 5.1 PC and the rev 8.5 PC with the PC interface harnesses to the SCXI.

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Yes, but that "PC interface harness" you speak of may connect to a DAQ in your PC. SCXI systems don't have their own DAQ, so unless you have a combination chassis with a PXI DAQ in it or your are tethered to a PCMCIA DAQ into laptops, then you are using two DAQs, and it could explain the difference.

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MrDoc wrote:

[...]

The rev 5.1 DOES NOT have the different levels for each SCXI board, that the rev 8.5 does.

[...]

I am more concerned with the different levels I see from each 1102 board.

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This sounds like, at this point, with newer, faster, multi-threaded software and a new DAQ interface (DAQmx), you are simply seeing more of reality than you used to. It makes perfect sense that each 1102 board will read slightly different (see my last response). If you don't like these differences, you need to calibrate each T/C to a known good one. Without calibration, it's asking too much for 100 thermocouples to synchronize perfectly. For one thing - electrical errors, and for another thing,  there very well could be 0.5 degree differences. How do you know that the temperature at all 100 of those places is spot on?

Maybe it's time to realize that you now have a better setup - and you're seeing data that you don't like. It happens all the time.

Message Edited by Broken Arrow on 04-20-2010 11:11 AM

[MrDoc]

So you think the Bds in the PC themselves are causing the different readings?

The rev 5.1 we just did a calibration on and the T/C's had maybe 2-3 tenth variation from the known temp.

And the rev 5.1 had ALL 100 T/C in a very tight spread.  I have a JPG of that.

What is confusing is with the DAQ assit I can do the calibration and get the T/C to be almost the same.  Yet when I use the DAQmx with the channel set up,timing, start / read,  I get the different levels.  And these levels are not small.

One reads at a +7°C from the rest, one reads +3°C from the rest, one is almost correct(maybe +0.7), and one is just about 1 to 1.5 degrees off on the higher side.

I was afraid of the fact that the new DAQmx would just be a bit more "accurate" and have a  more uneven output.

I have a pic of the chart display so you can see the different levels. (chart.jpg)

There's no calibration for this type of setup?

[Broken_Arrow]

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MrDoc wrote:

So you think the Bds in the PC themselves are causing the different readings?

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Well it is possible. Using two different DAQ's is not comparing Apples to Apples. All channels of the SCXI multiplex down to that one A/D converter. Chances are the DAQ is fine, but what if one is noisy due to a bad cable or shielding? 

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MrDoc wrote:

What is confusing is with the DAQ assit I can do the calibration and get the T/C to be almost the same.

[...] 

There's no calibration for this type of setup?

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The DAQ assistant is an Express VI, and is writing code for you. If you want to use the individual DAQmx VI's, you will need to apply the calibration yourself. Either in MAX, or programmatically with a Property Node like I have shown.

Note that because your DAQ assistant is inside the loop, it is opening references and configuring the SCXI and applying the calibration every time you run through the loop - that's why it is slow, but also why it seems so stable. With the DAQmx VI's, as you know, you configure it outside the loop.

Try this: right click on your DAQ assistant and use Generate Code (something like that) and the DAQ assistant will become DAQmx code. You should be able to pick apart the configuration part and the Read Data part. Put the Red Data part in the loop. This should give you calibration and fast response.

Message Edited by Broken Arrow on 04-20-2010 02:17 PM

[MrDoc]

OK, two things -

I don't see any way to calibrate the thermos in MAX. There is a calibration for the SCXI, but not for the 1102 or the 1303 or anything else.

Next, I did a generate code from the DAQ assistant, and got two icons. I wired them in and ran the vi.  Funny thing is that the vi will run for a few minutes and then the PC will reboot and when I log in a get a message that a serious error has occurred.

This happens every time.

I did a complete Windows reload and reloaded the Labview program, but it still happens.

Any ideas on this?