PXI-5105 seems to be skipping samples

[mfdupuis]

Hi all,

Now I know that my PXI-5105 isn't actually skipping samples, but for some reason the signals on my chart are flaky when I set the sampling rate too high. Is this somehow due to my loop? If anyone knows how to solve this I would be really appreciative.

Also, even if the signal is incomplete on the chart, does this mean that when I'm saving the signal is incomplete as well? If you look at my VI, you will see that I use both a NI-Scope Multi Fetch and Multi Read WDT. The reason for this is that I couldn't figure out how to split my signals from different channels using only the Multi Read.

Thanks,

Marc

[mfdupuis]

I actually just noticed that my VI doesn't save the whole signal from the time I press Save Waveform to the time I press it again...

[TimmTheEnchanter]

Hi mfdupuis,

Are you reading from multiple channels or just one channel?  If you are reading from multiple channels, the 1D array of Waveforms that is returned by the Read function will contain an array that looks something like this:

[array element 1 - waveform from first channel]

[array element 2 - waveform from second channel]

[array element 3 - waveform from third channel]

[etc. on to the last channel]

[void data]

[void data]

[void data]

[etc.]

You can break apart this array of 1D waveforms by using the "index array" function in LabVIEW.  In other words, calling the Read function in addition to the Fetch function should not be necessary.

If you are only reading from one channel, you should be returning a 1D array of Waveforms that looks like this:

[array element 1 - waveform from first channel]

[void data]

[void data]

[void data]

[etc.]

You might want to try starting from an example--for instance, niScope EX Configured Acquisition.

Please let me know if this helps,

Andrew

[mfdupuis]

Hey Andrew,

I'm trying to record from multiple channels. Let's start with three for example. I can display my three different waveforms on the chart in three different colors. The problem is when I try to record these three signals. I don't know how to split them using indexing or whatnot... Ideally what I would have is a program that allows me to click "Save Waveform" and output three different files with the three different waveforms.

I don't have access to LabVIEW right now, but I'll have a look at that example as soon as I do!

Marc

[James_M.]

Hi Marc,

Along with Andrew's suggestions, the 'Index Waveform Array VI' might be useful for you:

https://www.ni.com/docs/en-US/bundle/labview-api-ref/page/vi-lib/waveform/wdtops-llb/index-waveform-...

Also, this might clarify a few things with regards to arrays in Labview:

https://www.ni.com/docs/en-US/bundle/labview/page/grouping-data-with-arrays.html

Hope that helps,

James M. | Applications Engineer | National Instruments