OPC UA communication
9.1 What you need to know about OPC UA
Communication
142 Function Manual, 11/2019, A5E03735815-AH
Monitoring of PLC tags
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.
The sampling interval ("Sampling Interval") contains a negative value (-1). This determines
that the default setting of the OPC UA server is used for the sampling interval. The default
setting is defined by the transmission interval ("Publishing Interval") of the subscription. If
you want to set the smallest possible sampling interval, select the value "0".
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.
9.1.7 Mapping of data types
SIMATIC and OPC UA data types
SIMATIC data types do not always correspond with OPC UA data types.
S7-1500 CPUs provide SIMATIC tags (with SIMATIC data types) to their own OPC UA
server as OPC UA data types. OPC UA clients can then access these tags with OPC UA
data types via the server interface.
A client can read the attribute "DataType" from such a tag and reconstruct the original data
type in SIMATIC.
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