*4.1. Acquisition, Control, and Monitoring of the Process Parameters*

The control system is a distributed type and consists of a Schneider Electric (PLC) programable automaton and a PLC control application done in Unity Pro software using the SCADA (HMI) human–machine control and monitoring interface.

The signals from the transducers and from the system equipment are taken over by the PLC where they are processed according to the program loaded in the internal memory of the programable automaton. The PLC transmits the data to the SCADA application through an OPC (Open Platform Communication) server (OLE (Object Linking and Embedding) for process control) via ethernet communication.

The architecture and structure of the program loaded in the PLC is realized in the programming language ladder diagram (LD) and function block diagram (FBD), according to the IEC standard 61131-3 (Figure 15) using the Unity Pro application.

**Figure 15.** Unity PRO Software—Stirling engine.
