OPC UA communication
9.1 What you need to know about OPC UA
Communication
144 Function Manual, 12/2017, A5E03735815-AF
In the following example a subscription has been created: The client receives a message
with the new values (publishing interval 50 ms) every 50 milliseconds here.
Preventing server overload
You can set the OPC UA server of the S7-1500 CPU by means of the "Minimum publishing
interval" in such a way that it does not serve extremely short send intervals requested by the
client; see Settings of the OPC UA server (Page 164).
Example: A client wants to be operated at a publishing interval of 50 ms as detailed above.
Such a short publishing interval would, however, result in a high network and server load.
You should therefore set 1000 ms as the "Minimum publishing interval" for the server.
Clients whose subscription requires shorter publishing intervals are "braked" to 1000 ms and
the server is protected from overload.
When the Subscription has been created, you inform the server which tags are to be
monitored with it. In the following example, the "Voltage" tag was added to the subscription.
The "Voltage" tag contains the value of a voltage that is detected by an S7-1500 CPU (via an
analog input module AI 4xU/I 2-wire).
The Sampling Intervall contains a negative value (-1). This specifies that the OPC UA server
checks for changes to the values with the smallest possible interval.
In this example, the length of the queue is set to "1": Only one value is read from the CPU at
an interval of 50 milliseconds and subsequently sent to the OPC UA client when the value
has changed.
The "Deadband" parameter in this example is "0.1": Changes in value have to amount to 0.1
Volt; only then does the sender send the new value to the client. The server does not send
smaller changes in value. You can use this parameter, for example, to disable signal noise:
Slight changes in a process variable which do not have a real meaning.
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