Hi all,
I have an OPC-UA Server from Siemens correctly configured in Ignition. I know this OPC Server can read/write at 100ms or less. I’ve set up a PLC program where I increase a tag by 1 every 100ms, but when I display that tag inside the designer or a client, I see it update every 200/300 ms even if I have a Scan Class at 100ms.
Can anyone help me out?
Cheers,
You’ll need to also adjust the project’s client poll rate. That’s the pace the client uses to ask the gateway for any tags that have changed. Note that maximum signal latency from PLC to client will be the sum of client poll rate and the relevant scan class.
I modified the setting you are talking about ( ScanClass at 50ms and Project-Properties-Project-General-Client Poll Rate at 100ms ) but I see no change 
Does the server have diagnostic nodes in its address space? If it does, you can find the session and subscription diagnostic summaries and verify the revised rates are what you expect.
It gets more strange, because if I go in " OPC Quick Client ", browse a TAG and keep spamming the ‘r’ ( read ), I can see it’s value changing at 100ms. Why inside Ignition I have not the same results?
Hitting read triggers a direct OPC read. It’s possible the OPC server isn’t respecting the scan rate specified in Ignition; you could try switching your scan class (within Ignition) to ‘Read’ OPC mode, though this has dramatic effects on the efficiency of the communication; especially at a fast scan rate.