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 addressspace of the OPC UA server. Here you receive information about the OPC UA serverand 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 usesubscriptions.– To activate a subscription, enter the transmission interval "Publishing Interval" inthe 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 inorder 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 anumeric identifier access can be accelerated. For this reason, you should use theregistration 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 theOPC 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 registerednodes. 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 theOPC UA server.Due to the system, access to data in complex structures is not consistent.Setting the sampling intervals (sampling interval, publishing interval) tooshort may cause too much network load. Always choose intervals that arestill sufficient for your application.7.2.3 OPC UA data types and their conversionSiemens S7 data types are mapped in the namespace via SPEED7 PLC OPC UA datatypes. Siemens S7 data types do not always match the OPC UA built-in data types. TheCPU provides variables to the OPC UA server as an OPC UA built-in data type so thatOPC UA clients can access these variables with OPC UA built-in data types via theserver interface. A client can read the "DataType" attribute from such a variable andreconstruct the original data type.AccessVIPA System SLIO Deployment OPC UABasics OPC UA > OPC UA data types and their conversionHB300 | CPU | 013-CCF0R00 | en | 19-30 187
