OPC-UA

OPC-UA (Open Platform Communications Unified Architecture) is a standardized communication protocol for the secure and reliable exchange of data between industrial devices and systems. It enables access to both real-time process data and structured information in the form of a hierarchical information model.

In the VISIONWEB platform, OPC-UA is integrated using two separate components:

a client that establishes a connection to an OPC-UA server and allows you to read and write data to specific nodes;
and a subscription that, via the connected client, periodically accesses defined data points (nodes) and triggers an event whenever that data changes.

A subscription can only be used if a corresponding client has been created beforehand. Both are linked together via the "Connection Name" parameter.

Connection parameters

Parameter	Type	Unit	Description	Example
Connection Name	String		This refers to the configured client component through which the connection is established. A subscription cannot be created without a client.	evoviu-cam1
OPC-UA Endpoint	String		Specifies the connection address (URL) of the OPC-UA server to which the client should connect.	opc.tcp://opc.myfactory:4840 opc.tcp://192.168.0.123:4840
Timeout	Int32	[ms]	This setting defines the maximum amount of time to wait for a server response or for the completion of a specific action.	5000
Security Enabled	Boolean		This attribute can be used to verify the trustworthiness of the endpoint.
Auto Create Certificate	Boolean		This setting determines whether a certificate should be created automatically or not.
Variable Name	String		Specifies the NodeId of the desired OPC-UA variable that needs to be accessed.	ns=2;i=1234 ns=5;s=myUAnode
Cycle Time	Int32	[ms]	This specifies the polling interval in milliseconds, which determines how often the subscription updates the values of the specified nodes from the OPC-UA server. The event will only be triggered again if the data changes.	250

Workflow Setup

Differences between OPC-UA Client and OPC-UA Subscription

The OPC-UA client establishes a connection to an OPC-UA server and allows access to its data points (nodes). An OPC-UA subscription, on the other hand, enables automatic reception of values from these nodes when they change, without the need for active polling. However, the frequency of this automatic polling is set using a predefined cycle time.

The VISIONWEB platform allows you to configure any number of clients and subscriptions. Multiple subscriptions can be managed through a single client connection, by linking them to the respective client using a unique connection name.

A subscription can only be created after a client has been established. The client component is responsible for establishing the connection to the OPC UA server.

For example, a change in a measured value (such as a production parameter) can be detected via a subscription and used to trigger a workflow, while the same client can use additional subscriptions to monitor other values from the same server. At the same time, it is possible to use a separate client to retrieve data from another OPC UA server, such as status or diagnostic data.

Creating the OPC-UA Client - step by step

In Workflows, under Components, click the ➕.

Search for "OPC-UA Client" and select the entry to add the component.
A new component named "OPC-UA Client" will appear. You can change this name at any time.
Please enter the connection parameters.

The minimum requirements are the client name (for later linking with a subscription) and the URL. All other fields are optional and can be used depending on the authentication method.

Select the Event Graph tab and open the context menu by right-clicking.
Search for the "Write Value" node under OPC-UA and add it to your workflow to send data.

Next, select the "Get OPC-UA Client" component and connect it to the "Write Value" node. Enter the desired "Variable Name" – which is the node identifier of the OPC-UA connection, e.g., ns=2;i=1234.

Select the variable or data structure you want to send, and then paste it into the Value wildcard field.

If desired, you can display the result of the transfer as a Boolean value to check whether the transfer was successful. The message containing any relevant information can also be stored in a variable, or, as shown in this example, displayed in the Output tab using the "Print" node.

Congratulations! You can now send your data to the desired OPC-UA server.

Conversely, if you want to read data during a flow, you can use the "Read Value" node of the OPC-UA connection.

Congratulations! You can now read data from your desired OPC-UA server node.

Creating the OPC-UA Subscription - step by step

Before performing this step, an OPC UA client (see above) must be created, and a connection name (in our example, "opc-evoviu-1") must be defined for linking to the client component. This name can be chosen freely.

In Workflows, under Components, click the ➕.

Search for "OPC-UA Subscription" and select the entry to add the component.
A new component will appear with the name "OPC-UA Subscription". You can change this name at any time.
Please enter the connection parameters.

In this example, the system checks every 150 ms whether the value of the node ns=2;i=1234 has changed. As soon as a change is detected, the flow is triggered. Please note that the execution of this flow only begins after the previous flow has completed. This may result in a slight delay.

Select the Event Graph tab and open the context menu by right-clicking.
Under Events, search for the "Data Changed (OPC-UA Subscription)" node and select it to trigger a flow when the node is updated on the server.

Retrieve the dataset directly into the desired variable using the wildcard parameter.

Please note: The server determines the data type that comes from each node.

If you have multiple data types or nodes on the OPC UA server that need to be monitored for updates, you can create multiple subscriptions. These subscriptions can each trigger a separate flow independently (see example 1) or work sequentially in parallel (see example 2), depending on the desired behavior.

Setting up components for multiple subscriptions

Congratulations! You can now retrieve data from your desired OPC-UA server using a subscription.