*4.2. Human-Machine Interface HMI*

The human-machine interface (HMI) for controlling and monitoring the parameters of the Stirling engine system is realized on the Citect Scada platform from Schneider Electric (Figure 16).

The HMI provides an interface between the system and its human user. This graphical interface converts the data received from the control system into human-intuitive representations of the process systems. The operator visualizes the scheme of the system, and can control the on/off of the dynamic equipment (cooling-water recirculation pump, fan, and solar radiation shutter motor), as well as adjusting the fan speed depending on the cooling-water temperature of the engine.

Two operating modes were realized: manual (MAN) and automatic (AUTO). In MAN mode, each equipment can be operated individually for single tests. When the AUTO mode is active (during normal engine operation), the protection program starts (protection related to minimum and maximum pressures, minimum and maximum temperatures, cooling pump on, cooling fan on, and state of

pressure switches for cooling water pressure and helium pressure). The AUTO mode is made in Unity Pro and loaded into the PLC memory, each process parameter being automatically controlled by the PLC.

**Figure 16.** HMI control and monitoring interface. Process control screen.

The graphic symbols for the equipment are created so that the condition of the equipment is indicated at any time by colors representing normal operation, start/stop, as well as the discrepancy between the command and the state of the equipment.

The collected data are saved in Excel files using the trend and process analyst functions in the Citect Scada application.

The significance of the colors on the graphical interface is presented in Table 3.


**Table 3.** Graphic interface color-assignment interpretation.
