topic moving data points on waveform display in LabVIEW

moving data points on waveform display

try_guy90 — Tue, 28 Jun 2016 20:38:52 GMT

Hello,

Any idea why the waveform display for my VI has moving data points? The display on the third tab does not display this issue. I've taken a video of what happens to better illustrate what I am talking about and attached my VI to find the problem.

I am currently sampling data from a DAQmx and storing it in a queue until the save data button is pressed. That all works fine, but the issue is the actual data display, which, although the points make sense, it shows them moving around in a small area around where they are initially plotted. It happens even when I clear the visible data and restart gathering data, as shown in the video.

Thanks for any help you may be able to supply.

Guy

Re: moving data points on waveform display

mikeporter — Tue, 28 Jun 2016 21:20:12 GMT

How much data are you plotting? If you are plotting significantly more datapoints than there are pixels on the graph's X axis you can get peaks that appear to move around due to the graphical interpolation that LabVIEW has to do.

Mike...

Re: moving data points on waveform display

try_guy90 — Tue, 28 Jun 2016 21:30:20 GMT

@mikeporter :

500 samples at a rate of 1000Hz. It's the same rate for the third graph, though, and that one does not appear to move.

Guy

Re: moving data points on waveform display

mikeporter — Tue, 28 Jun 2016 22:02:56 GMT

How much are you plotting at one time? How big is the graph (in pixels)? The effect is also dependent on the data being plotted. Very noisy data is the worst, smooth waveforms are the least susceptible.

Mike...