High speed plotting in Axiom in Live Mode
When plotting a high speed data capture point in live mode, with a low total span of the plot (for example 10 seconds) , the live data plotted misses plotting some points in the plot.
It is not missing the data as when I stop live plotting and scroll backwards, the same data is plotted normally.
In the plot below, both of the sloped portions should look the same. I have put a box around the one on the right that missed a few sample points when drawing the plot. This was data at 100ms sample rate.
2 replies
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Hi john. patanian . We believe this caused by network latency when retrieving the data. When Axiom makes a call to get the last value in Live Mode, it virtually extends the timestamp of that value to whatever the current time of the historian is. For instance, if the value is virtually extended 0.25 seconds, there are 2 values within that time extension we didn't pick up. We can redraw the last pixel on the chart when we make another call to get the next value, but at that point, since the window is only 10 seconds, the chart has already shifted and the trend cannot be redrawn.
In short, there comes a point in which Axiom cannot draw the trend as fast as it is coming in. The data is there historically, which you demonstrated when scrolling backwards, but Axiom retrieves data differently when it's not in Live Mode. If you expanded your interval to something like 1 minute, you probably wouldn't see this behavior, but values would start getting average together as your window increases.
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I would agree this is not a bug. I am wondering if a future option would be to allow a setting to adjust how often an Axiom trend tries to go back to retrieve live data?
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