How-to: OPC UA Alarms and Conditions Interface with WinCC Unified

OPC UA client configuration

To set up a basic WinCC OA OPC UA client for connecting to a Unified OPC UA server to facilitate basic data exchange, you can follow the steps outlined in the OPC UA Client Configuration section of the online help guide. However, before you begin, it's crucial to set up valid certificates. For instructions on how to achieve this with self-signed certificates, please refer to the subsequent section titled Using self-signed certificates (Unified PC as OPC UA server).

OPC UA Alarms and Conditions (WinCC Unified)

This chapter deals with the function of the OPC UA Alarms & Conditions (A&C) implementation for the WinCC OA OPC UA client. This allows receiving and acknowledging alarms from a WinCC Unified OPC UA server.

The alarm is mapped to a data point element in the WinCC OA OPC UA client project via a corresponding peripheral address. To trigger an alarm on the WinCC OA client system, an Alert handling for multi instance alerts (_alert_hdl config) must be configured at this data point element. Multi instance alarms have the advantage that an alarm action like came, acknowledge, went can be triggered externally and are not calculated by the Event manager. In addition, for this alarm type additional information can be stored in so-called additional values (see Contents of additional values for OPC UA). Furthermore, a special alert class can be passed for each alarm, i.e. not the specified alert class will be used.

You can find important notes and restrictions on OPC UA AC in the chapters Supported alarm types and restrictions and Notes and Restrictions.

Requirements and limitations

In order that the OPC UA client can receive alarms and conditions, the following requirements must be fulfilled:

  • The config entry driverAckClassPrefix must be set in the [drivers] section of the config file. See Acknowledgement of alarms .
  • An OPC UA connection data point to the server (see Configuration of the Servers ) with a subscription of the type Alarms and Conditions was created (see Configuration of a subscription ).
  • Setting of an internal data point named "EventNotifier". The value assigned to this EventNotifier is crucial for the connection process and the overall functionality of the system. This value can be retrieved using third-party tools such as "UaExpert", a software for testing and simulating OPC UA devices and clients.
  • OPC UA severities were mapped to WinCC OA alarm classes. See Mapping of alarm data .
  • A peripheral address (_address) with the created subscription and the receive mode Alarm was created on the DPE which shall receive the alarms. According to that only alarm conditions will be returned when browsing for items. See Configuration of a peripheral address .
  • An alert handling for multi instance alarms (_alert_hdl) was created on the same DPE. The alarm in WinCC OA will not be triggered by the value of the DPE, but directly. I.e. the driver sets the attribute _alert_hdl.._event. See Alert handling for multi instance alarms .
  • To facilitate secure communication between systems in the OPC UA model, the use of valid certificates is imperative. These certificates should either be signed by a recognized Certificate Authority (CA) or, in the case of self-signed certificates, they must be manually added to the other system's trusted certificates store. For instance, when working with WinCC Unified, any self-signed certificates must be copied into the appropriate trusted folder, allowing WinCC Unified to establish trust. This crucial step ensures that systems can verify each other's identities and maintain encrypted communication, thereby reinforcing the overall security of the OPC UA-based systems.