What is the reason for string subscriptions will take more time ?
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Below is some good advice when handling strings.
• The handling and copying of strings creates considerable CPU load. Variables
of type string require a great deal of memory, and the execution time is long during copying and concatenation.
• Always use square brackets, [ ] around strings, to limit string variables or string
• Copy strings every scan only when required. Remember that a connection to a
function block actually involves copying variables from one to the other, see
the System 800xA, Control, AC 800M, Configuration (3BSE035980*).
• Concatenation of strings should only be performed when absolutely necessary.
• Use the attribute by_ref for in and out function block parameters whenever possible. Unquote
In general strings don't load the OPC server/Controller more than any other datatype, but yes they can load it.
It has to be distinquished between the update rate between the OPC Server and the controller (MMS) and the Update Rate (SubscriptionRate) between the Client (800xA) and the OPC server.
AC 800M, OPC Server, System Version 5.1
The OPC Server should always have its update rate set twice as fast as the OPC client(s) update rate.
Yes, there is a way to change the Default String Subscription Delay (10sec).
Open -> OPC Server Configuration Panel,
Select Data Access Tab, then select the controller(Smiling Face) from where String is Updated to OPC.
Go to Settings Menu --> Update Rate.
String --- 10000 (ms) Default Value --> Try to reduce default Value Step by Step.
The above steps can be followed only after stopping the OPC DA Connector Service in the Service Structure.
Other wise OPC will get Over Load.