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n
MonitoredItem Service Set
–
Services for the client to create and manage monitored items.
–
Monitored items are used to log in for data and event notifications.
n
Subscription Service Set
–
Services for the client to create and manage subscriptions.
–
Subscriptions control the way of the data and event notification.
n
To access an
OPC UA
server, the
endpoint
must be known.
n
You can navigate via the
endpoint
using the navigation function through the address
space of the
OPC UA
server. Here you receive information about the
OPC UA
server
and the CPU and have access to the objects created in the
OPC UA
configuration,
such as tags, data blocks, etc.
n
Lower network load through
‘subscriptions’
–
If variables are to be transmitted only if their value has changed, you have to use
subscriptions
.
–
To activate a
subscription
, enter the transmission interval "Publishing Interval" in
the
OPC UA
client.
–
When the
subscription
is created, tell the server which variables to monitor.
Among other things, you can specify the amount by which a value must change in
order a transfer takes place.
–
Since only a change in value of a transmission takes place, the use of
subscrip-
tions
leads to a reduced network load.
n
Fast access through
‘registration’
–
Normally the addressing takes place by means of identifier strings. By using a
numeric identifier access can be accelerated. For this reason, you should use the
registration
for regular access to certain variables.
–
During
registration
, the
OPC UA
client assigns the variable to the
OPC UA
server.
The
OPC UA
server then generates a numeric identifier and sends it back to the
OPC UA
client.
–
The numerical identifier is valid for the duration of the session.
–
In the properties of the CPU, you can set the maximum number of registered
nodes. This must be taken into account by the
OPC UA
clients.
–
Since the registration takes time, you should put them in the start-up phase of the
OPC UA
server.
Due to the system, access to data in complex structures is not consistent.
Setting the sampling intervals (sampling interval, publishing interval) too
short may cause too much network load. Always choose intervals that are
still sufficient for your application.
7.2.3 OPC UA data types and their conversion
Siemens S7 data types are mapped in the namespace via SPEED7 PLC OPC UA data
types. Siemens S7 data types do not always match the
OPC UA
built-in data types. The
CPU provides variables to the
OPC UA
server as an
OPC UA
built-in data type so that
OPC UA
clients can access these variables with
OPC UA
built-in data types via the
server interface. A client can read the "DataType" attribute from such a variable and
reconstruct the original data type.
Access
VIPA System SLIO
Deployment OPC UA
Basics OPC UA > OPC UA data types and their conversion
HB300 | CPU | 013-CCF0R00 | en | 19-30
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