OPC-UA Device Service

The Open Platform Communications - Unified Architecture (OPC-UA) Device Service provides a means of integrating OPC-UA devices with Edge Xpert. For further information about OPC-UA, refer to the OPC Foundation website.

The Edge Xpert OPC-UA Device Service is based on open62541, a well-known open-source implementation of the IEC-62541 OPC-UA standard.

Key Features

The OPC-UA Device Service supports the following key features:

Secure and insecure connections to a remote OPC-UA Server
Reading and writing OPC-UA nodes
Monitored Item Service for monitoring Data Change Items and Event Items
Browse Service capabilities
Discovery of OPC-UA endpoints

Subscriptions

OPC-UA subscriptions allow the monitoring of nodes in a remote server.

Each connection sets up a distinct Subscription Item, which can contain one or more Monitored Items. When a Monitored Item changes on the server, the server is responsible for notifying subscribed Device Services of the change. When the OPC-UA Device Service is notified of a change, it returns the new value for the Monitored Item in a POST command to Edge Xpert.

For further information on Monitored Items, see Add Monitored Items.

Supported Data Types

The following table lists the OPC-UA data types and their equivalent Edge Xpert data types.

OPC-UA Data Type	Edge Xpert Data Type
UA_Boolean	Bool
UA_Byte	Uint8
UA_DateTime	Int64
UA_Double	Float64
UA_Float	Float32
UA_Int8	Int8
UA_Int16	Int16
UA_Int32	Int32
UA_Int64	Int64
UA_String	String
UA_UInt16	Uint16
UA_UInt32	Uint32
UA_UInt64	Uint64

OPC-UA Device Profile

The device profile defines what resources are available on a particular device. The following profile attributes are available:

Change in Edge Xpert v2.3

The attribute monitored and publishInterval have been removed

Attribute	Description	Valid Values	Mandatory
`nodeAttribute`	The node attribute that the resource is referencing	String - See the Node Attribute section for valid values	Yes, unless `browseStartNodeId` is defined
`nodeId`	The identifier of the node in the OPC-UA server	See NodeId	Yes, unless `browseStartNodeId` is defined
`dataTypeId`	The node identifier of the OPC-UA data type of the value attribute	See NodeId	No, only required if `nodeAttribute` equals `"value"`
`browseStartNodeId`	Information on the root node. Must contain the identifier, identifierType and namespace index. Note this information can also be passed to the device onboarding call via the OPC-UA RootNode protocol property	See NodeId	No
`browsePath`	The name of a child node qualified with a namespace URI, relative to either the `browseStartNodeId` attribute	String	No, only required if `browseStartNodeId` is set
`browsePathNamespaceIndex`	The namespace index of the node in the OPC-UA server	A valid UInt16 value	No, only required if `browseStartNodeId` is set

An example device resource can be seen below. This defines a node that is identified through the use of a dataTypeId and nodeId.

 - description: A Simulated Counter
   name: Counter1
   isHidden: false
   properties:
     valueType: Uint32
     readWrite: R
     units: String
     defaultValue: "0"
    attributes:
      dataTypeId:
        identifier: 4
        identifierType: NUMERIC
        namespaceIndex: 0
      nodeAttribute: value
      nodeId:
        identifier: Int16
        identifierType: STRING
        namespaceIndex: 5

For information on adding devices with the browsePath attribute instead of nodeID, see OPC-UA Browse Service.

OPC-UA Protocol Properties

The available OPC-UA protocol properties are described in the following table:

Parameter	Type	Description	Default Value
Address	String	Mandatory The URI of the OPC-UA server in the following format: `<myServerAddress>:<serverPort><endpointPath>` e.g `127.0.0.1:4840/Endpoint`	N/A
SecurityPolicy	String	Optional The security policy to be used for connecting to the OPC-UA server. Valid values are as follows: None Basic256 Basic128Rsa15 Basic256Sha256 Aes128Sha256RsaOaep	None
Username	String	Optional The username to be used during connection to an endpoint	N/A
Password	Base64-encoded String	Optional The password associated with the username used during connection to an endpoint	N/A
ApplicationUri	String	Optional The URI associated with any certificate used to connect to the remote OPC-UA server	Empty
SecurityMode	String	Optional The message security mode used with secure connections to the OPC-UA server Valid values are as follows: None Sign SignEncrypt	None
Certificate	String	Optional The name of the DER file containing the certificate to use when establishing a secure connection	N/A
PrivateKey	String	Optional The name of the DER file containing the private key to use when establishing a secure connection	N/A
RequestedSessionTimeout	UInt32	Optional The suggested timeout, in milliseconds (ms), for inactive sessions created between the device service and an OPC-UA server endpoint	1200000
SessionKeepAliveInterval	Float64	Optional The interval (ms) at which the client sends requests to keep the session alive	1000
RootNode	String	Optional The starting point for the Browse Service	The servers root folder node
ConnectionReadingPostDelay	UInt64	Optional Delay (ms) to receiving monitored item readings after the device is added	0
ReadBatchSize	UInt16	Optional Default batch size for grouping read requests. This value will be used if the servers capabilities can not be accessed	10
WriteBatchSize	UInt16	Optional Default batch size for grouping write requests. This value will be used if the servers capabilities can not be accessed	10
NodesPerBrowse	UInt16	Optional Default number of nodes that are requested in a browse request. This value will be used if the servers capabilities can not be accessed	5

Using the OPC-UA Device Service

For information on using the OPC-UA device service, see OPC-UA General Example and OPC-UA Security Example.