How to interface between PLC and SCADA?

A Programmable Logic Controller (PLC) is a microprocessor running special software. That software has communications elements, some of which are accessible to an internal database.

Supervisory Control and Data Acquisition software (SCADA) typically runs on a “standard” PC or Server. It, to, has communications elements, some of which are accessible to its own internal database.

When you wish to connect a PLC to SCADA, you first must establish the physical communication connection. Industrial Ethernet, for example. Industial Token Ring networks like ControlNet as another example. In either instance, the communications or network port of the PC will connect to wiring (usually) which connects to the PLC.

The next step is to assure that both systems can now communicate with each other, using what ever protocol you have selected for this purpose.

Finally, you will need to configure the SCADA database to gather the information across the network from the PLC database. This is typically done by having names or addresses in the PLC map to typically similar names within the SCADA.

Once that is all done, information may flow back and forth between PLC and SCADA, and various control aspects may be programmed into the SCADA to execute on the PLC, and similarly information collected by the PLC updates the SCADA, typically graphic elements.

Those are the basic steps. The details vary widely from manufacturer to manufacturer, and in many instances some or all of the software involved may be licensed and “closed source” for both revenue and security purposes. Consult your PLC and SCADA manufacturer for their specific details and recommendations.

Author - Ned Boff

1 Like

Interfacing between a PLC (Programmable Logic Controller) and SCADA (Supervisory Control and Data Acquisition) system typically involves establishing a communication link between the two systems.

This allows the SCADA system to monitor and control the PLC and the processes it is managing. The specific steps for interfacing between a PLC and SCADA may vary depending on the PLC and SCADA system used, but here is a general outline of the process:

1. Determine the communication protocol: The first step is to determine the communication protocol supported by both the PLC and the SCADA system. Common protocols include Modbus, OPC (OLE for Process Control), Profibus, Ethernet/IP, and others. Ensure that both systems support at least one common protocol for communication.

2. Set up communication hardware: Next, set up the necessary communication hardware components. This typically involves configuring communication modules or interfaces on both the PLC and SCADA system. Install and configure any required communication cards, modules, or converters to enable communication via the selected protocol.

3. Configure the PLC: In the PLC, configure the communication parameters and settings for the selected protocol. This includes specifying the communication protocol, addressing information (such as node or device addresses), and communication parameters like baud rate, parity, and data format. Refer to the PLC’s user manual or programming software to perform the necessary configuration.

4. Configure the SCADA system: Similarly, configure the SCADA system to establish communication with the PLC. This involves specifying the communication protocol, device addresses, and other relevant settings within the SCADA software. Consult the SCADA system’s documentation or configuration tools for guidance on configuring the communication parameters.

5. Establish the communication link: Once the PLC and SCADA system are appropriately configured, establish the communication link between them. This usually involves setting up a connection or channel within the SCADA software to establish communication with the PLC. Specify the PLC’s IP address, node address, or any other required information to establish the link.

6. Define tags or data points: In the SCADA system, define the tags or data points that will be exchanged with the PLC. These tags represent variables or data that the SCADA system will read from or write to the PLC. Examples include sensor readings, equipment statuses, setpoints, or control commands. Configure the tags or data points in the SCADA system based on the PLC’s memory map or addressing scheme.

7. Test and validate communication: Once the communication link is established, perform thorough testing and validation to ensure reliable data exchange between the PLC and the SCADA system. Monitor the data flow, verify correct tag values, and test control operations to ensure proper functionality.