The OPC UA Connection Tag provides a connection to an external OPC UA Server. Fernhill SCADA uses this tag to work out how to connect to OPC UA Servers. The data in the external OPC UA Server can be read at a fixed interval, or on demand, or both.
The OPC UA Connection Tag supports the configuration properties of the Active Channel Tag plus these properties:
| Property | Type | Version | Description |
|---|---|---|---|
| ScanInterval | TIME | 3.69 | The interval between each read. An interval value of zero (T#0s) disables periodic query execution. See Interval and Offset for information on how timed activities are scheduled. |
| ScanOffset | TIME | 3.69 | The offset added to the ScanInterval to get the actual read time. See Interval and Offset for information on how timed activities are scheduled. |
| EndpointURL | WSTRING | 3.69 |
The Endpoint URL of the connection.
This property must be a valid Uniform Resource Locator. For example:
opc.tcp://192.168.1.8:20296/ |
| MaxItemsPerRead | UDINT | 3.98 | The maximum number of items to read in one read request. In large configurations, multiple read requests will be used to read the items required by data point tags. If the OPC UA Server has limited processing capacity, consider reducing the value of this property. |
| SecureChannelLifetime | TIME | 3.69 | The requested lifetime of the security token of the communication channel. The actual lifetime of security token is negotiated with the OPC UA Server and may be different from the requested lifetime. |
| SecurityPolicy | USINT | 3.69 |
The security policy to use. Use one of these values to set the security policy:
|
| AuthenticationMethod | USINT | 3.69 |
How the OPC UA Connection authenticates with the OPC UA Server.
Use one of these values to set the authentication method:
|
| UserName | WSTRING | 3.69 | The username to authenticate with the server. |
| Password | WSTRING | 3.69 | The password used to authenticate with the server. Note: The password value is encrypted and not stored as plain text. |
The OPC UA Connection Tag supports the data properties of the Active Channel Tag plus these properties:
| Property | Type | Description |
|---|---|---|
| ScanTimer | TimerStatus | The status of the scan timer. |
| SecurityTokenTimer | TimerStatus | The status of the security token refresh timer. |
The OPC UA Connection Tag supports the tag commands of the Active Channel Tag, plus these tag commands:
| Tag Command | Version | Description |
|---|---|---|
| Refresh | 3.69 | Requests an immediate read of the tags associated with this OPC UA Connection Tag. |
Note: Event triggered data reads (from the Refresh Tag Command) and periodic data reads (defined by the ScanInterval property) are independent. You can use the Refresh Tag Command, or the ScanInterval property, or both to determine when the tags are read.
The OPC UA Connection Tag builds on the features of these tag types:
To learn how activities are scheduled using Interval and Offset.
To learn about the I/O Analog Data Point Tag that can be associated with the OPC Classic Connection Tag.
To learn about the I/O Digital Data Point Tag that can be associated with the OPC Classic Connection Tag.
To learn about the I/O String Data Point Tag that can be associated with the OPC Classic Connection Tag.
To learn about the I/O Word Data Point Tag that can be associated with the OPC Classic Connection Tag.
I/O Double Word Data Point Tag
To learn about the I/O Double Word Data Point Tag that can be associated with the OPC Classic Connection Tag.
To learn about the I/O Long Word Data Point Tag that can be associated with the OPC Classic Connection Tag.
OPC Client DriverFor an overview of the OPC Client Driver.
For the meaning of terms used in Fernhill SCADA.