What is NodeId

NodeId is the unique identifier for nodes (variables/objects/methods, etc.) in the OPC UA information model. NG Gateway's OPC UA Point/Action uses nodeId string to represent the node to read/write.

Common NodeId Forms

Common spellings (Based on opcua crate parsing):

• String Identifier: ns=2;s=Channel1.Device1.Tag1
• Numeric Identifier: ns=2;i=12345
• GUID Identifier: ns=2;g=550e8400-e29b-41d4-a716-446655440000
• ByteString Identifier: ns=2;b=...

Where:

• ns: namespace index
• s/i/g/b: identifier type

How to Get Correct NodeId (Suggested Workflow)

1) Confirm Endpoint & Security Policy First

In Server management interface or UA client tool (UAExpert, Prosys Client), confirm:

• endpoint URL (Usually opc.tcp://host:4840)
• Supported SecurityPolicy / SecurityMode
• Whether username/password/certificate is needed

2) Browse Tree with UA Client Tool

Recommend:

• UAExpert (Cross-platform)
• Prosys OPC UA Browser (Cross-platform)

Find the target variable (Variable Node) in the Browse tree and view its NodeId.

3) Prefer "Stable Identifier"

Best Practice:

• Try to use stable path form of s= (e.g., Tag Path of KEPServerEX), avoid i= drifting after restart/configuration change (Depends on Server implementation).

4) Verify DataType & Collection Mode

Confirm in UA Client for the variable:

• UA DataType (Boolean/Int32/Double/String/DateTime/ByteString etc.)
• Whether Subscription is allowed (MonitoredItem)
• Whether Writing is allowed (AccessLevel)

These information directly determine:

• How to choose Point's data_type
• Whether Channel's readMode chooses Subscribe or Read

Common Errors

• Wrong ns: Same name node under different namespace will be different NodeId.
• Treating Method Node as Variable Node: Method needs call, not read value; current driver mainly covers variable read/write.
• Array Node: Current version does not support Array Variant; suggest splitting into multiple scalar nodes or providing scalar mapping on Server side.