OPC UA Writer Sink¶

The OPC UA Writer block enables you to write data to a variable on an OPC UA server, leveraging the asyncua library for seamless communication.

Supported Data Types¶

This block supports writing the following data types to OPC UA server variables: - Numbers (integers, floats) - Booleans - Strings

Note: The data type you send must match the expected type of the target OPC UA variable.

Node Lookup Mode¶

The block supports two methods for locating OPC UA nodes via the node_lookup_mode parameter:

• hierarchical (default): Uses standard OPC UA hierarchical path navigation. The block navigates through the address space using get_child(). Each component in the object_name path is automatically prefixed with the namespace index.
• Example: object_name="Roboflow/Crane_11" → path 0:Objects/2:Roboflow/2:Crane_11/2:Variable

• Best for: Traditional OPC UA servers with hierarchical address spaces

• direct: Uses direct NodeId string access. The block constructs a NodeId as ns={namespace};s={object_name}/{variable_name} and accesses it directly via get_node().

• Example: object_name="[Sample_Tags]/Ramp" → NodeId ns=2;s=[Sample_Tags]/Ramp/South_Person_Count
• Best for: Ignition SCADA systems and other servers using string-based NodeId identifiers

Cooldown¶

To prevent excessive traffic to the OPC UA server, the block includes a cooldown_seconds parameter, which defaults to 5 seconds. During the cooldown period: - Consecutive executions of the block will set the throttling_status output to True. - No data will be sent to the server.

You can customize the cooldown_seconds parameter based on your needs. Setting it to 0 disables the cooldown entirely.

Asynchronous Execution¶

The block provides a fire_and_forget property for asynchronous execution: - When fire_and_forget=True: The block sends data in the background, allowing the Workflow to proceed immediately. However, the error_status output will always be set to False, so we do not recommend this mode for debugging. - When fire_and_forget=False: The block waits for confirmation before proceeding, ensuring errors are captured in the error_status output.

Disabling the Block Dynamically¶

You can disable the OPC UA Writer block during execution by linking the disable_sink parameter to a Workflow input. By providing a specific input value, you can dynamically prevent the block from executing.

Connection Pooling¶

The block uses a connection pool to efficiently manage OPC UA connections. Instead of creating a new connection for each write operation, connections are reused across multiple writes to the same server. This significantly reduces latency and resource usage for high-frequency write scenarios.

• Connections are automatically pooled per server URL and username combination
• If a connection fails during a write operation, it is automatically invalidated and a new connection is established on the next write attempt

Retry Logic¶

The block includes configurable retry logic with exponential backoff for handling transient connection failures:

• max_retries: Number of connection attempts before giving up (default: 3)
• retry_backoff_seconds: Base delay between retries in seconds (default: 1.0). The delay doubles after each failed attempt (exponential backoff).

Note: Authentication errors (wrong username/password) are not retried as they will continue to fail.

Cooldown Limitations¶

Type identifier¶

Use the following identifier in step "type" field: roboflow_enterprise/opc_writer_sink@v1to add the block as as step in your workflow.

Properties¶

The Refs column marks possibility to parametrise the property with dynamic values available in workflow runtime. See Bindings for more info.

Available Connections¶

Input and Output Bindings¶

The available connections depend on its binding kinds. Check what binding kinds OPC UA Writer Sink in version v1 has.

{
    "name": "<your_step_name_here>",
    "type": "roboflow_enterprise/opc_writer_sink@v1",
    "url": "opc.tcp://localhost:4840/freeopcua/server/",
    "namespace": "http://examples.freeopcua.github.io",
    "user_name": "John",
    "password": "secret",
    "object_name": "Line1",
    "variable_name": "InspectionSuccess",
    "value": "running",
    "value_type": "Boolean",
    "timeout": 10,
    "fire_and_forget": true,
    "disable_sink": false,
    "cooldown_seconds": 10,
    "node_lookup_mode": "hierarchical",
    "max_retries": 1,
    "retry_backoff_seconds": 0.015
}