OPC UA® monitored item and subscription

An OPC UA® client can subscribe to a list of variables that are then monitored for changes by the GDS. The variables are checked for changes at a defined interval. When subscribing to a variable, the client can define a sample rate, which is then served by the server. You can choose from predefined sample rates. Sample rates are device-specific. 

The sample rates for the AXC F 2152 controller are defined as follows, for example:

• 100 ms
• 250 ms
• 500 ms
• 1000 ms
• 2000 ms
• 5000 ms

The server assigns the subscription to the group nearest to the desired value and returns this value to the client as  RevisedSamplingInterval. If an OPC UA® client requests a variable with the desired rate of 600 ms, for example, it will be assigned to the 500 ms group. The available sample rates of the PLCnext Control devices can be found in the device-specific OPC UA settings. 

Note: Subscriptions may affect the real time behavior of the application program. To avoid this refer to Accessing variables via OPC UA subscriptions.