subscribe

Monitor nodes for data change notification

Since R2023b

Syntax

SubscrObj = subscribe(UaClient,NodeList,DataChangeFcn)

SubscrObj = subscribe(UaClient,NodeList,{DataChangeFcn,UserData})

SubscrObj = subscribe(___,PublishInterval=PubIntv)

Description

SubscrObj = subscribe(UaClient,NodeList,DataChangeFcn) creates a subscription request with the specified NodeList for the UaClient. When the server sends notification of a data value change on any of the nodes, the specified DataChangeFcn is triggered to execute in MATLAB^®.

SubscrObj = subscribe(UaClient,NodeList,{DataChangeFcn,UserData}) provides additional data for the DataChangeFcn function to use. Its type and format depends on the function.

SubscrObj = subscribe(___,PublishInterval=PubIntv) specifies a periodic rate of notification, PublishInterval, as PubIntv seconds. This controls the rate at which the server monitors the node values, sending a notification, indicating if any changes have occurred. The default is 1 second.

Examples

Subscribe to List of Nodes

Create an OPC UA client, and subscribe to a list of nodes.

UaClient = opcua('localhost',51210);
connect(UaClient);
NodeList = browseNamespace(UaClient);  % Manually select nodes.
SubscrObj = subscribe(UaClient,NodeList,@mycallback,PublishInterval=3);

Subscribe while providing custom arguments to the callback function.

SubscrObj = subscribe(clientObj,nodes,{@mycallback,UserData})

Input Arguments

UaClient — OPC UA client

opc.ua.Client object

OPC UA client specified as an opc.ua.Client object. You can create the client with the opcua function.

Example: UaClient = opcua(...)

Data Types: object

NodeList — List of nodes

opc.ua.Node object

List of nodes to be monitored, specified as an array of node objects. For information on node object functions and properties, type

help opc.ua.Node

Example: NodeList = browseNamespace(UaClient)

Data Types: object

DataChangeFcn — Function to execute at data change notification

function handle

Function to execute at data change notification from subscribed nodes, specified as a function handle. Typically, this function assesses the changed data sent from the server. The input arguments to the function are the subscription object, the notification object, and the optional UserData. The notification object, provided by the server, includes Node and Data properties that include the changed nodes and values.

Example: @mycallback

Example: {@mycallback,UserData}

Data Types: function_handle

PubIntv — Periodic notification rate

double

Periodic notification rate, specified in seconds as a double. The default is 1 second. This is the rate at which the server monitors variable value changes on the nodes. When a change is detected, notification is sent to the client indicating the change, triggering the callback.

Example: PublishInterval=0.1

Data Types: double

Output Arguments

SubscrObj — Subscription object

opc.ua.Subscription object

Subscription, returned as an opc.ua.Subscription object, with the following properties.

Property	Description
Server	OPC UA server name
Nodes	List of OPC UA nodes to monitor in subscription
ID	Numerical ID of this subscription
Enabled	Indicator of subscription on or off
PublishInterval	Notification rate in seconds
DataChangedFcn	Callback function to execute upon notification of data change

Version History

Introduced in R2023b