I have two tags reading from the compact Logix PLC. According to plc program both tag will become high at a time ,but we have observed that one of the tag is updating with a delay which is causing an issue to execute the tag change script in client event.
We have changed the tag group of one tag with 1000ms another tag to 50ms (subscribed), but still the 50ms tag is not updating properly.
We have used 1000ms tag for tag change script event to trigger, and we are checking the status of 50ms tag inside the script ,but observe that the tag value is not updating some times.
What could be the reason ?
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OPC does not provide any delivery order guarantees for any subscribed values
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OPC Drivers cannot magically make subscriptions deliver at a given pace if a connection is overloaded. 50ms is overly optimistic in most applications. Have you looked at the driver's diagnostics page? You should screenshot it and show it here.
If you have a trigger tag, after which you wish to collect related values, you should not make tags for those related values. Instead, read them with system.opc.readValues(), which ensures the ordering you appear to need.