Create OPC-UA Thing Description

See Things documentation on how to manage Things in Altair IoT Studio.

A Thing for this device driver uses a schema as described on this page.

Once it exists in Studio it can be synced to the cluster (asset) as shown on the Sync Things page.

The following is an example of a Thing description to be instantiated by the OPC-UA driver:

{
    "@type": [
        "swx:opcua,endpoint=opc.tcp://localhost:26543,interval=1000"
    ],
    "id": "<leave blank when creating a thing>",
    "title": "My OPCUA Test Device",
    "properties": {
        "ns=1;s=Temperature": {
            "@type": "float64",
            "title": "Temperature",
            "type": "number",
            "readOnly": true
        },
        "opcuaInterval": {
            "title": "Reporting Interval",
            "type": "integer",
            "readOnly": false
        }
    }
}

The first item is essential for the OPC-UA driver to recognise this Thing description as a OPC-UA device. Details on how to construct this string can be found in the next section.

The second item is essential for the OPC-UA driver to recognise the node it needs to manage. Details on how to construct property keys and the rest of the property object can be found in a subsequent section.

Construct the "swx:opcua,endpoint=opc.tcp://..." "@type"

The following element in the "@type"` array is required to configure the OPC-UA endpoint. It is comma-separated string of parameters. The element has to start with swx:opcua.

"swx:opcua,endpoint=opc.tcp://localhost:26543,interval=1000"

The remaining items in the comma-separated list are key value pairs separated by equal signs. The following keys are allowed:

It is recommended to only set the basic options and leave the advanced ones to the default values. If the OPC-UA server does not allow self-signed certs to be used by clients then the advanced options can be used.

If either mode or policy are set to None then they will both be treated as set to None.

If both mode and policy are set to auto then the highest available security mode and level as recommended by the server will be used.

If only policy is set to auto then the highest available security level with the requested mode will be used.

If only mode is set to auto then the highest available security level with the requested policy will be used.

If no authentication method is configured, a UserIdentityToken for anonymous authentication will be set.

Construct a Property

The nodes to report are specified as keys in Properties section. Example below:

"ns=1;s=Temperature": {
    "@type": "float64",
    "title": "Temperature",
    "type": "number",
    "readOnly": true
},

The corresponding section of node discovery report is the following:

"Objects": {
    "MyDevices": {
        "Temperature": {
            "BrowseName": "Temperature",
            "DataType": "float64",
            "Description": "",
            "DisplayName": "Temperature",
            "NodeID": "ns=1;s=Temperature",
            "Value": 34.52512524858854,
            "Writable": false
        },

The complete NodeID should be used at the property key of the Thing description.

The @type is the DataType returned in the report.

The readOnly should be set to true if Writable is false (and vice versa).

The type can be determined from the DataType where available options are number, integer, string, etc (see the Web-of-Things Modelling section).

If it is desirable to change the subscription interval on-the-fly, then the opcuaInterval property as shown in the example of the introduction should be included in the Thing description.

Property Key Mapping

"ns=1;s=Temperature": {
    "@type": "float64",
    "title": "Temperature",
    "type": "number",
    "readOnly": true
},

It is possible to use a form of mapping from the user defined property key to the OPC-UA nodes by overriding the property's "@type". In this case the "@type" has to be defined as an array of strings where the DataType becomes one array item and the node ID another array item. The node ID has to be prefixed with "opcua-node:".

"myUserDefinedKey": {
    "@type": [
        "float64",
        "node-id:ns=1;s=Temperature"
    ],
    "title": "Temperature",
    "type": "number",
    "readOnly": true
},

Action/Event to Read Node Value

The OPC-UA Thing Description can have an Action and corresponding Event defined to read node values on request. When requesting the action, the result will be published as an event.

  "actions": { 
    "readNodeValue": { 
      "input": { 
        "type": "string" 
      }, 
      "title": "Read Node Value" 
    } 
  }, 

  "events": { 
    "readNodeValue": { 
      "data": { 
        "type": "string" 
      }, 
      "description": "", 
      "title": "Read Node Value Result" 
    } 
  },

OPC-UA Events

"ns=1;i=1465": { 
    "data": { 
        "type": "object" 
    }, 
    "description": "", 
    "title": "Tank" 
}, 

The underlying mechanism uses OPC-UA subscriptions, just like the mechanism used for property value publishing.

The "Construct the … @type" section describes a parameter to set the general subscription interval. This parameter is called "interval". This parameter applies to both the Data (property values) and the Events.

New parameters for use in the "@type" have been added to independently set the intervals for Data and Events: "intervalData" and "intervalEvent".

"swx:opcua,endpoint=opc.tcp://localhost:26543,intervalData=1000,intervalEvent=100"

Action/Event to Read Node History

The OPC-UA Thing description can have an Action and corresponding Event defined to read node values history on request. When requesting the Action, the result will be published as an Event.

"readNodeHistoryValues": { 
    "input": { 
        "properties": { 
            "endTime": { 
                "type": "string" 
            }, 
            "nodeId": { 
                "type": "string" 
            }, 
            "startTime": { 
                "type": "string" 
            } 
        }, 
        "type": "object" 
    }, 
    "title": "Read Node History Values" 
}, 

"readNodeHistoryValues": { 
    "data": { 
        "type": "array" 
    }, 
    "description": "", 
    "title": "Read Node History Values Result" 
}, 

Results come up in the event as an array.

[ 
  { 
    "at": "2024-02-20T14:00:01Z", 
    "properties": { 
      "ns=3;i=1005": 0.4158234 
    } 
  }, 
  { 
    "at": "2024-02-20T14:00:02Z", 
    "properties": { 
      "ns=3;i=1005": 0.8134732 
    } 
  } 
]