How Connections Work
Each function defined in the Scheduler uses a connection. A connection is a set of parameters that allows communication with a third-party system. A connection can be used by multiple functions.
There are 3 types of connections in the Scheduler:
- Connection to the internal OPC-UA server
- OPC-UA client connections
- OPC-DA client connections
The internal OPC-UA server is an OPC-UA server that is always executed by the Scaderis Scheduler Processor service.
The connection to the internal OPC-UA server is the only connection that exists by default and cannot be deleted or modified. This is the connection that allows connecting to the internal OPC-UA server of the Scheduler Processor service.
When the internal OPC-UA server is used, third-party systems connect to the OPC-UA server to detect value changes. Multiple third-party systems can be connected simultaneously to the OPC-UA server. All supervisory systems can use the internal OPC-UA server: either they have a native OPC-UA client driver, or it is possible to use gateways that allow connection to an OPC-UA server (for example, SoftwareToolbox TopServer/Kepware KepServer).
When a function uses an OPC-UA or OPC-DA client connection, the Scheduler Processor service updates the current value of the function in the third-party system. In this case, only one third-party system can be controlled by a function.
An OPC-UA or OPC-DA client connection can be used to connect directly to a PLC: either the PLC itself runs an OPC-UA server (for example, a Siemens S7-1500 PLC), or a gateway is used to convert the OPC-UA protocol to the PLC protocol (for example, SoftwareToolbox TopServer/Kepware KepServer).
In both cases, complex scenarios can be programmed in third-party systems when they detect a change in the function's value.
Using the internal OPC-UA server is the recommended method for communicating with third-party systems.