Limit on data transferred from scope using VISA XOP

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Wed, 02/10/2010 - 06:53 am

This is most likely a question for Tektronix rather than Igor, but in the case that anyone has run into a similar problem, I thought I would pose the question here as well.

I am currently using Igor's VISA XOP to take some waveform data from a Tektronix oscilloscope and do subsequent processing with it. I am using the VISAReadBinaryWave command, and am attempting to read in a fairly large (100k point) acquisition into Igor. I have ensured that the settings are correct on the oscilloscope (i.e. the resolution is 100k points, and I have sent the "DATa:STOP 100000" command using viWrite). When I run my program with a test square wave as the input, the waveform does appear to be transferred correctly for the first 25000 points, but after this the waveform appears distorted. I have tried scaling down to using 25000 points (setting the resolution and size of the wave in Igor accordingly), and when I do this, the entire waveform is correctly transferred.

Is this some inherent limitation in the scope itself or (doubtfully) in Igor? Information is getting transferred past the 25000 but it appears to just be noise, so if there is any sort of inherent limitation I expect it to be from the scope rather than the software, but again, I was wondering if anyone has run into this before.

Thanks a lot.
From looking at the VISA XOP source code, it appears that VISAReadBinaryWave reads all of the bytes with a single call to the VISA library viRead function. Therefore, I don't think this is a problem in the VISA XOP or in Igor. I don't have a way to test it so I can't be 100% sure though.

February 10, 2010 at 12:30 pm - Permalink

Thanks Howard; I seem to have solved the problem. Seems like the encoding settings on the scope weren't set properly after all!

February 11, 2010 at 07:41 am - Permalink