The OPC Unified Architecture server (OPC UA server) allows the M241 Logic Controller to exchange data with OPC UA clients. Server and client communicate through sessions.
The monitored items of data (also referred to as symbols) to be shared by the OPC UA server are manually selected from a list of the IEC variables used in the application.
OPC UA uses a subscription model; clients subscribe to symbols. The OPC UA server reads the values of symbols from devices at a fixed sampling rate, places the data in a queue, then sends them to clients as notifications at a regular publishing interval. The sampling interval can be shorter than the publishing interval, in which case notifications may be queued until the publishing interval elapses.
Symbols that have not changed value since the previous sample are not re-published. Instead, the OPC UA server sends regular KeepAlive messages to indicate to the client that the connection is still active.
Access to the OPC UA server is controlled by user rights. Refer to Users and Groups in the EcoStruxure Machine Expert Programming Guide.
The following table describes the supported OPC UA services:
|
OPC UA Service |
Description |
|---|---|
|
Address Space Model |
Yes |
|
Session services |
Yes |
|
Attribute services |
Yes |
|
Monitored item services |
Yes |
|
Queued items |
Yes |
|
Subscription services |
Yes |
|
Publishing method |
Yes |
