Charting real time data from S7 PLC on RPi too slowly

Industrial
,
1

Hi everyone,

I am trying to create a dashboard that has two charts on it, both graphing real time data coming in from an S7 PLC. I want the data capture to be as fast as possible (50ms) since I need the chart to display small changes in the data. The data can be captured at that rate and displayed just as text on the dashboard no problem, very close to real time.

As soon as I link the graph nodes to the dashboard, the ui runs much slower and the data being displayed on the graph is very delayed. I am running the editor and the ui on a raspberry pi 3.

When I increase the data capture to being every 500ms, the data displays on the chart nearly real-time, but I need to chart it faster to be useful.

Is there anything I can do? Thanks,

Maddie

2
  1. Dont run the browser on the PI (that and the overall GUI running on a PI is resource heavy)
  2. Use alternative graph component - one designed for fast updates (search the forum)
    i. Please note: your screen has a finite resolution - at 50ms, a 1080 pixel graph can only truely display 1080 pixels === 54 seconds of data!
  3. Do you really need 50ms data? What do you expect to see? What if the data glitch you are looking for happens at the 5ms mark an is only present for 40ms - you would STILL miss it.
    i. In cases like these, I would add a simple bit of ladder that captures the "glitch" as it occurs. This way, you dont have to "watch for a problem" and it will capture any anomality no matter how short the duration.
3

Have you tried running the UI on a PC with many gigabytes of memory and a good processor?

4

Yes, then it plots fine in real time...

Do you think that the processing power and the memory of the pi is just not enough?

5

Thanks Steve
This is for a display for a trade show, so needs to be a good quality graph, not jumping every 0.5 seconds. About a minute of data sounds perfect to display. I will try and find a different graphing node to use!

6

Yes, for running the browser. The browser needs a lot more processor than node-red will for this task.

7

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