Version: 3.0 (next)

OPC DA Nodes

OPC DA (Data Access) is the classic COM/DCOM-based protocol found in virtually every legacy SCADA and DCS installation. MaestroHub connects to OPC DA servers through a lightweight Windows agent and exposes read, write, and browse capabilities as pipeline nodes.

Configuration Quick Reference

Field	What you choose	Details
Parameters	`Connection`, `Function`, `Function Parameters`, `Timeout Override`	Select the OPC DA connection profile, function, configure function parameters with expression support, and optionally override timeout.
Settings	`Description`, `Timeout (seconds)`, `Retry on Timeout`, `Retry on Fail`, `On Error`	Node description, maximum execution time, retry behavior on timeout or failure, and error handling strategy. All execution settings default to pipeline-level values.

OPC DA Write Node

Write values to OPC DA server items. Supports writing multiple items in a single execution and dynamic values through expression syntax.

Supported Function Types:

Function Name	Purpose	Common Use Cases
OPC DA Write (`opcda.write`)	Send values to OPC DA server items	Update setpoints, write control commands, push recipe parameters

Node Configuration

Parameter	Type	Required	Description
Connection	Selection	Yes	OPC DA connection profile to use
Function	Selection	Yes	Write function from the selected connection
Function Parameters	Dynamic	Varies	Auto-populated from the function schema. See your OPC DA connection functions for full parameter details.
Timeout Override	Number (seconds)	No	Override the default function timeout

Function parameters for Write:

Parameter	Type	Required	Description
`data`	Array of objects	Yes	Array of path/value pairs to write (1–50 items)
`data[].path`	String	Yes	OPC DA item path to write to
`data[].value`	Any	Yes	Value to write

All function parameters support expression syntax ({{ expression }}) for dynamic values from the pipeline context.

Output Structure

{
  "result": {
    "results": [
      {
        "path": "Channel1.Device1.Setpoint",
        "success": true
      },
      {
        "path": "Channel1.Device1.Command",
        "success": false,
        "error": "Access denied"
      }
    ],
    "successCount": 1,
    "failureCount": 1
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 15, "timestamp": "2026-01-15T08:30:00Z" }
}

Field	Type	Description
`_metadata.success`	boolean	`true` when the function executed without errors
`_metadata.functionId`	string	ID of the executed function
`result.results`	array	Per-item write results
`result.results[].path`	string	OPC DA item path
`result.results[].success`	boolean	Whether this item was written successfully
`result.results[].error`	string	Error message (present only on failure)
`result.successCount`	number	Number of items written successfully
`result.failureCount`	number	Number of items that failed
`_metadata.durationMs`	number	Execution time in milliseconds
`_metadata.timestamp`	string	ISO 8601 / RFC 3339 UTC timestamp

Safety First

Always implement validation and safety checks before writing to industrial equipment. Consider adding condition nodes to verify values are within safe ranges.

OPC DA Read Node

Read tag values from an OPC DA server. Supports reading multiple items and optional direct device reads bypassing the server cache.

Supported Function Types:

Function Name	Purpose	Common Use Cases
OPC DA Read (`opcda.read`)	Fetch current item values from OPC DA server	Equipment telemetry, quality checks, process monitoring

Node Configuration

Parameter	Type	Required	Description
Connection	Selection	Yes	OPC DA connection profile to use
Function	Selection	Yes	Read function from the selected connection
Function Parameters	Dynamic	Varies	Auto-populated from the function schema. See your OPC DA connection functions for full parameter details.
Timeout Override	Number (seconds)	No	Override the default function timeout

Function parameters for Read:

Parameter	Type	Required	Default	Description
`tags`	Array of strings	Yes	—	OPC DA item paths to read (1–50 items)
`fromDevice`	Boolean	No	`false`	Read directly from the device instead of the server cache. Ensures the most current values but may be slower.

All function parameters support expression syntax ({{ expression }}) for dynamic values from the pipeline context.

Output Structure

{
  "result": {
    "values": [
      {
        "path": "Channel1.Device1.Temperature",
        "value": 78.5,
        "quality": "Good",
        "timestamp": "2026-01-15T08:30:00.123Z"
      },
      {
        "path": "Channel1.Device1.Pressure",
        "value": 145.2,
        "quality": "Good",
        "timestamp": "2026-01-15T08:30:00.150Z"
      }
    ]
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 42, "timestamp": "2026-01-15T08:30:00Z" }
}

Field	Type	Description
`_metadata.success`	boolean	`true` when the function executed without errors
`_metadata.functionId`	string	ID of the executed function
`result.values`	array	Array of item read results
`result.values[].path`	string	Full OPC DA item path
`result.values[].value`	any	Current item value — type depends on the OPC DA item data type
`result.values[].quality`	string	Quality indicator (`"Good"`, `"Bad"`, `"Uncertain"`, `"Bad_CommFailure"`, etc.)
`result.values[].timestamp`	string	ISO 8601 timestamp from the OPC DA server
`_metadata.operation`, `_metadata.tagCount`, `_metadata.fromDevice`	string, number, boolean	The call's own facts: `read`, how many tags came back, and whether the values were read straight from the device rather than the server cache
`_metadata.durationMs`	number	Execution time in milliseconds
`_metadata.timestamp`	string	ISO 8601 / RFC 3339 UTC timestamp

OPC DA Browse Node

Browse the OPC DA server tag hierarchy to discover available items. Useful for dynamic tag discovery, building tag catalogs, and verifying server structure within pipelines.

Supported Function Types:

Function Name	Purpose	Common Use Cases
OPC DA Browse (`opcda.browse`)	Traverse server tag hierarchy	Tag discovery, catalog building, server structure verification

Node Configuration

Parameter	Type	Required	Description
Connection	Selection	Yes	OPC DA connection profile to use
Function	Selection	Yes	Browse function from the selected connection
Function Parameters	Dynamic	Varies	Auto-populated from the function schema. See your OPC DA connection functions for full parameter details.
Timeout Override	Number (seconds)	No	Override the default function timeout

Function parameters for Browse:

Parameter	Type	Required	Default	Description
`path`	String	No	`""`	Item path to browse. Empty string browses from the root.
`limit`	Number	No	`5000`	Maximum number of nodes to return (100–50,000)

All function parameters support expression syntax ({{ expression }}) for dynamic values from the pipeline context.

Output Structure

{
  "result": {
    "path": "",
    "nodes": [
      {
        "name": "Channel1",
        "itemId": "Channel1",
        "type": "branch",
        "hasChildren": true
      },
      {
        "name": "Temperature",
        "itemId": "Channel1.Device1.Temperature",
        "type": "leaf",
        "accessRights": "readWrite",
        "hasChildren": false
      }
    ],
    "truncated": false
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 85, "timestamp": "2026-01-15T08:30:00Z" }
}

Field	Type	Description
`_metadata.success`	boolean	`true` when the function executed without errors
`_metadata.functionId`	string	ID of the executed function
`result.path`	string	The path that was browsed
`result.nodes`	array	Array of discovered nodes
`_metadata.truncated`	boolean	`true` if results were limited by the `limit` parameter — a fact about the call, so it rides with the execution facts
`_metadata.operation`, `_metadata.nodeCount`	string, number	The call's other facts: `browse`, and how many nodes came back
`result.nodes[].name`	string	Display name of the node
`result.nodes[].itemId`	string	Full OPC DA item identifier
`result.nodes[].type`	string	`"branch"` (folder) or `"leaf"` (tag)
`result.nodes[].accessRights`	string	`"read"`, `"write"`, or `"readWrite"` (leaf nodes only)
`result.nodes[].hasChildren`	boolean	Whether this node has child items
`_metadata.durationMs`	number	Execution time in milliseconds
`_metadata.timestamp`	string	ISO 8601 / RFC 3339 UTC timestamp

Settings Tab

All OPC DA node types share the same Settings tab:

Setting	Type	Default	Description
Description	Text	—	Optional description displayed on the node
Timeout (seconds)	Number	Pipeline default	Maximum time the node may run before timing out
Retry on Timeout	Toggle	Pipeline default	Automatically retry the node if it times out
Retry on Fail	Toggle	Pipeline default	Automatically retry the node if it fails
On Error	Selection	Pipeline default	Error strategy: Pipeline Default (the pipeline's Error Handling setting), Stop Pipeline or Continue Execution

When left at their defaults, these settings inherit from the pipeline-level execution configuration.

Configuration Quick Reference​

OPC DA Write Node​

Node Configuration​

Output Structure​

OPC DA Read Node​

Node Configuration​

Output Structure​

OPC DA Browse Node​

Node Configuration​

Output Structure​

Settings Tab​

Configuration Quick Reference

OPC DA Write Node

Node Configuration

Output Structure

OPC DA Read Node

Node Configuration

Output Structure

OPC DA Browse Node

Node Configuration

Output Structure

Settings Tab