Create a new OPC UA connection

When you configure an OPC UA Client worksheet, you must select the connection that the client will use. This task describes how to create that connection.

Before you begin this task, you should know the communication and security settings for the OPC server to which you want to connect. If you do not, contact the server administrator.

To create a new connection to an OPC UA server:

1. Do one of the following:

   • On the Insert tab of the ribbon, in the Communication group, click OPC Client, and then select OPC UA Connection from the drop-down list; or

   • In the Comm tab of the Project Explorer, expand the OPC UA folder, right-click the Connections folder, and then click Insert on the shortcut menu.

   The Server Configuration dialog box is displayed.

   

2. In the Connection Name box, type a name for the connection.

   This name will be displayed in the OPC UA > Connections folder in the Project Explorer, and it is the name you will look for when you configure the OPC UA Client worksheet.

3. In the End point box, do one of the following:

   • If you know the URL of the OPC server to which you want to connect, type it in the box.

   • If you do not know the URL, click the More button (…) to open the Discovery dialog box, use it to find a discovery server that publishes a list of OPC servers on your network, and then select the server to which you want to connect.

   

   • If you want to be able to change the URL during project run time, type an appropriate string expression (for example, {MyEndpointUrl}). When the OPC UA Client Runtime task is started, it will get the value of the string expression and then connect to that URL. This happens only when the task is started, which typically happens when the project itself is run. If the value of the string expression changes after the task is started, the task must be restarted in order to get the new value and then connect to the new URL. To restart the task while the project is running, use either the Runtime Tasks dialog box or the EndTask and StartTask functions.

   Note: At this time, the OPC UA Client feature in this software supports only binary communication with OCP.TCP end points (for example, opc.tcp://<host name or IP address>:8000/<server name>). SOAP-based communication with HTTP and HTTPS end points is not supported.

4. In the User Name and Password boxes, type your credentials for the OPC server.

   You can leave these boxes empty if you want to connect anonymously and the server is configured to accept anonymous connections.

5. If your OPC server is configured to require secure communication (also called a "SecureChannel" in the OPC UA specification), you must take extra steps to configure the security settings and program certificates. The steps differ somewhat depending on whether you are using self-signed certificates or certificates signed by a certificate authority (CA):

   • Configure an OPC UA connection to use self-signed certificates

   • Configure an OPC UA connection to use CA-signed certificates

6. Click Test Connection.

   If the program can successfully connect to the OPC server using these settings, a confirmation message is displayed.

7. Click OK to save your changes and close the Server Configuration dialog box.

   The connection is saved in the OPC UA > Connections folder in the Project Explorer.

In certain situations, if the connection does not behave as expected during project run time — and especially if you see OPC communication errors in the runtime log — you might need to adjust the connection's advanced settings: in the Server Configuration dialog box, click Advanced, and then in the Advanced dialog box, review and configure the settings.

Session

Various session timeouts for the connection itself:

Session Timeout

The session timeout (in milliseconds) for the connection. If a session times out from inactivity, a new session must be started to resume communication.

SecureChannel Lifetime

The time (in milliseconds) after which the SecureChannel between the client and server is automatically renewed.

For more information about the SecureChannel Services, see the OPC UA specification.

Watchdog Time

The time (in milliseconds) between watchdog checks.

Watchdog Timeout

The timeout (in milliseconds) for a specific watchdog check.

Server Calls

Advanced settings that control individual calls to the OPC server:

Call Timeout

The timeout (in milliseconds) for individual server calls. If there is a failure writing to the OPC UA server, the connection will recover after reaching this timeout value. The default value is 10000 (10 seconds).

Call Timeout

The timeout (in milliseconds) for individual server calls.

Verify time synchronization

When this option is selected, the time stamp on each value received from the server is compared against the system time on the client, and if the difference between the times is equal to the specified number of hours (that is, the number of time zones between the server and client), the server and client are deemed to be synchronized and the value is accepted. Otherwise, if the difference is not equal to the specified number of hours, the value is rejected and communication is interrupted.

The default number of hours is 25, which is a special setting that means the hours portion of the time stamp should be disregarded and only the minutes and seconds portions should be compared. This enables the client to receive values from the server without knowing the server's time zone.

When this option is cleared, the time stamp on each value received from the server is ignored and the client's system time is used instead to save the value in the project database.

Browse

Advanced settings that control how you browse server items/nodes on the OPC server as you configure an OPC UA Client worksheet:

Max nodes per call

When browsing for an item/node on the server, the maximum number of nodes to be returned per server call.

Check node type

When browsing for an item/node on the server, check the node's data type. In some situations, the OPC server might not be able to get data types from field devices, and that might cause browsing to become slow and unusable. If that happens, clear the Check node type option.

This option can also interfere with tag expansion, so if tag expansion is used in any of the OPC UA Client worksheets that depend this connection, clear the Check node type option.