Reverse data output from Agilent 3458A

[hammer3]

I'm taking 500 sub-samples of a 500mS ramp waveform from a function generator with the attached vi, and the data output is reversed in time. That is, the data as displayed on the waveform chart shows the TRAILING edge first - a time-mirror image of the actual waveform captured. I thought this had to do with LIFO/FIFO, so I forced FIFO, but it doesn't help. What must I do to get the proper time-sequence data from the DMM?

Can't seem to attach my vi , but it's identical to the Labview sample Agilent 3458 Acquire Multiple Measurement.vi, with the addition of a VISA Write MEM FIFO.

[hammer3]

AGAIN attachment didn't work. I'll try again.

[crossrulz]

How are you getting the data?  Is it just an array or a waveform (with data, dt, and T0)?  If you just have the array, use Reverse 1D Array and be done with it.  If you have a waveform, then use the In Place Element Structure to get the Y, reverse the array, and write back to the Y.

[RavensFan]

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@hammer3 wrote:

AGAIN attachment didn't work. I'll try again.

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See if this link applies to you.

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[hammer3]

I just turned off compatibility & let's see if I can attach the vi now... AND hope someone can address my original question.

[hammer3]

Wrong vi. This is the original.

[crossrulz]

Ok, the data just comes out as an array.  Well if you know that the data is backwards, just use Reverse 1D Array (as I already stated) to flip it back.

I remember working with that DMM before.  I never found a way to get the data to come out like a FIFO.  That's just the way the instrument works.  Reverse the array and be done with it.

[hammer3]

Clearly that will work as a  work-around or band-aid, but I was hoping to find someone knowledgeable to explain WHY it's happening. 

[Michelle_G]

Hi Hammer3,

I reviewed the code and was not able to find anything explicit that is reversing the data. Perhaps this happens because of how the instruments sends the data out. You can verify this by using the VISA test pannels in MAX to see how it receives information sent from the instruments. At the base of all of the subVIs used to read measurements is only a VISA read. Again, I don't see anything that would be flipping the data. Hopefully this helps, but at least you always have the option of just reversing the data if you see that it comes out in reverse order. I hope this helps.

Regards,

[JÞB]

It works that way becasue some FW engineer at HP wrote the dump routine that way.  LIFO/FIFO just sets which samples get overwritten when the buffer fills. 

The best explaination I ever came up with- and it has to do more with using the device than reality- is the operator usually stars with a input near 0 and triggers a digitization start.  when reading back its often likely that a value of 10 ADC counts can occur very near the trigger.  If you are using Term Chars to end your reads.  Yup you just read that "0x0A" and left all the interesting data in the unit.