OPC Server for AC 800M how do I prove that all OPC items are updated at least every second?
We have requirement regarding all values in the 800xA system coming from the AC800M must be updated at least every second.
I have searched for answers in the window “OPC Server for AC 800M” -> Help -> Manuals and also in the same window help->contents.
I think I understand how “items” are put in to different “uprate rate groups” in the OPC Server
The slowest task used in AC800M controllers are 1000ms.
In the window “Update rate” update interval for the groups in the OPC Server is default -> 500, 2000, 5000, 10000, 30000 all ms. In the same window we can see that 500 and 2000 ms are in use. Opening another window “OPC statistics – Data access” we see a group with update rate 3000ms number of items is not constant but so far 24 items are the maximum we have seen.
I am aware of the Items can be located in 2 groups.
Is it possible to find the names of the Items that is only updated every 2000ms or 3000ms depending which window I look in?
Is there a better way to prove that all OPC items are updated at least every second using AppLogviewer or other diagnostic tools?
Voted best answer
OPC is per design event driven, only items that have a new value or quality code will be updated by the OPC server.
An average system has probably hundreds of items that do not change for a day or more. These items will not change in the OPC server for a good reason.
The AC 800M OPC server will over MMS cyclically poll the controller for an update of every OPC item it has an active subscription on. The MMS poll rate depend on the OPC update rate. The OPC server selects the closest faster MMS rate than what the OPC client has chosen. 500ms is the fastest rate in factory default.
There exists no mechanism to verify if each active OPC item (there could be inactive items in terms of OPC) is updated or not. However, the Update Rate dialog (enabled when selecting a controller on the DA tab) will display the Requested vs Actual Update rate.
An overloaded or poorly task tuned controller may not be able to respond in a timely fashion on all MMS polls. This may show as an Actual Rate larger than the Requested Rate.
There is no good answer to say if *all* items were updated or not.
To know for sure, you probably need to deploy trend logs and verify that the data is delivered on every cycle. However, it will be a huge difficulty to know if a missed update depend on a steady (frozen) value or a missed MMS cycle.
Tune your controllers and keep them well out of overload, likely they will then provide all data requested by the OPC server.