Ignition & PLC communication lags

Hello, my company bought new assembly line. MES on this line consist of SIT(simaticIT) <-> Ignition <-> PLC. I’ve been facing communication lags for two weeks. IGN <-> PLC communication takes sometimes even 20 seconds
Could You tell me potential root cause?

Hi Piotr, welcome to the forums!

I moved your post to Ignition category, as Ignition Exchange is specifically about this webpage: Ignition Exchange | Inductive Automation

The diagnostics page (Status → Devices → Details) will tell you a lot of details if you’re running the latest version of Ignition 8.1.6 or 8.1.7. (In prior versions, those diagnostics were also available, but just for Allen Bradley devices.) Often slow updates are because large numbers of tags are subscribed at a 1 second rate, and the PLC is too slow to keep up with the number of tags/requests.

Or for Allen Bradley fw versions above 21.something (15?) if you’re reading lots of AOI tags directly

Right. If we’re talking about modern Allen Bradley PLCs specifically, it’s worth noting that if the AOIs have any tags set to “Avoid External Access” you’ll significantly speed up the communication if you change all of the tags in the AOI (even ones you aren’t reading) to Avoid External Access = None.

If it’s not set like that, Ignition can’t read the whole AOI at once, and has to re-issue requests to read the individual tags, which takes a lot longer.

Sorry @Kevin.McClusky , but I was under the impression that there are always 2 members, EnableIn and EnableOut, that cannot have this property changed and so AOI reads will always be far less efficient than reading the same tag from fw < 21. Is this not the case?

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I have siemens s7-1200 device, so it seems it is not the case.

Is this diagnostic page working with siemens or not?
Is siemens capable to work with Ignition properly?

thanks a lot for your help.

Ignition version is 8.0.14

Have you looked into this?


One common mistake is to construct Ignition OPC tags for everything in your PLC, whether by tag import-export, or by dragging and dropping a browseable PLC’s entire OPC item tree.

Don’t do this! It will crush communications for all but the most trivial PLC setups. Only create Ignition tags for OPC items that you actually need, and pick a reasonable tag group rate.

I sure would hope this wouldn’t be very common at all - I certainly haven’t heard of people doing this before :worried: This applies for any SCADA platform. You also don’t want to just use the same structure that the PLC has, as you won’t have a fun time trying to create a good project structure.

Sadly, it is. For those with no experience with PLC protocols and the limited bandwidth of embedded devices in general, the concept of a communications penalty for what appears to be a trivial amount of data just doesn’t cross their minds.