Artefact in Analog signal

[LudovicR]

Dear All,

We have an analogue-controlled XY scanner equipped with a PCI 6711 and a BNC-2110. During a raster scan, artefacts appear in the Y scan (the ramp is broken) at certain X positions (around 0V). I put the signals on the oscilloscope. Changing the cables has no effect; the problem appears to originate from AO1.

Could you advise me on how to identify the source of the problem?

Best regards,

Ludovic R.

[santo_13]

Source of the problem is clearly your code that generates the ramp signal and definitely doesn't look like DAQ (if you assumed so)

[altenbach]

• We would need to see the code that generates these ramps.
• You seem to have 20us/point. Is this hardware or software timed?
• I assume this is running in windows, not a RT OS.
• Why is the signal generally so noisy? Are things properly terminated?

[LudovicR]

Thank you very much for your advice.

 It is Windows 10 and Labview 2011.

I have attached the vi. It is an old code (< 15 years old) and has not caused any problems until now.

As a result, I had not made any changes to it. But it is clearly very basic, which accentuates the problem.

 The connection to the oscilloscope is direct: PCI6711-> BNC 2010-> BNC cable -> oscilloscope.

 What is strange is that the artifacts in AO1 (4 ramps over 256)  are correlated to the voltage in AO0, regardless of the scanner configuration.

 At this time/point, this is controlled by the software.

Best regards

[LudovicR]

Vi and sub vi

[Henrik_Volkers]

You have the code

it was running flawless in the past

.

.

What has changed? Only the output ? Something else? 

(the PCI card rely on the PCI bus .. DMA etc .. other software/tasks running? )  

I would swap ouput channels in software (and change the cabling accordingly) to see if the problem stay with the hardware channel or the software channel.

[altenbach]

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@LudovicR wrote:

I have attached the vi. It is an old code (< 15 years old) and has not caused any problems until now.

As a result, I had not made any changes to it. But it is clearly very basic, which accentuates the problem.

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I agree that the code is probably OK, but I had a quick glance at some of your VIs and if you ever get a chance, some could be dramatically simplified.

For example the raster could be done more easily as follows. (I am not 100% sure if LabVIEW 11 had the concatenating tunnel, but here's how you could write it today. much less clutter and fewer places for bugs to hide.

I am pretty sure that your ellipse (which is a circle because you ignore the y) is buggy, because it only converges to a circle for very high point counts. As you can see, the actual radius fluctuates because one of the shift registers starts with a non-empty array, so the first point is an "almost" duplicate of the second point. (Note that if you don't want to close the circle, you can change N and set "exclude end=true" for the ramp.)

A circle is most easily done using a complex datatype. The tiny code on top does the same (and better!) as your entire subVI.

(Most of your other code could be corrected similarly.)

[LudovicR]

Thank you very much, Altenbach, for looking at the code and for your advice. I will make the changes and check to update the rest of code.

I will see what impact they have.

Regarding past events on the machine, I had a broken hard drive this spring.

Replacing it with the backup worked fine, but there may have been a bug during the update process, although that seems unlikely.

Best regards