**4. Case Study**

The monitored parameters of the experimental set-up which are presented in Table 2 are the following: temperature, pressure, and rotation.


**Table 2.** Parameters of the experimental set-up.

The experimental stand is composed of: the CPU (Central Processing Unit) with automation panel assembly (Figure 11), the local CPU connections box (Figure 12), and the automation panel box (Figure 13). Figure 14 shows the positioning of the temperature sensors on the primary exchanger.

**Figure 11.** CPU and automation panel.

**Figure 12.** Local CPU connections.

**Figure 13.** Automation panel.

**Figure 14.** Positioning of temperature sensors on the primary exchanger.

The main objective of this study was to ensure the operation and functioning of the Stirling engine in safe conditions with the achievement of the designed performances.

The sensors mounted on the engine generate the following types of signal:


The control signals generated from the control interface are of the following type:


The signals from the motor are acquired in the connection box mounted on the Stirling engine and are transmitted to the control panel via multilayer cables. The control of the installation is implemented on a programable automaton—Modicon premium type.

The Stirling engine instrumentation system provides the following functions:

• temperature measurement.

Twelve temperatures are measured through 11 thermocouple type-K sensors and one PT100-type sensor [37–39]. Minimum- or maximum-type alarms are generated in the PLC in order to keep the process within normal limits.

• Pressure measurement.

Two relative pressures are measured in the mixing tank and the compression chamber through pressure transducers with an output signal of 4–20 mA; minimum- or maximum-type alarms are generated in the PLC in order to keep the process within normal limits.

• Engine rotation measurement.

Engine rotation is measured by a frequency sensor connected to a signal interface that generates an output signal of 4–20 mA corresponding to the engine rotation.

• Pump/fan control.

The control of the pump and of the fan is done as needed, either manually or automatically. Thus, in the distributed control system (DCS), command keys are virtually implemented for choosing manual or automatic man/auto mode, as well as for the manual on/off control. In manual mode, the pump and the fan are switched on/off directly by the operator by choosing the on or off position. In automatic mode, the pump and the fan start and stop according to the logic implemented in the DCS.

• Control of automatic valves.

Valve control is done as needed, either manually or automatically. Thus, in the DCS, command keys are implemented virtually for choosing the manual/automatic (man/auto) mode, as well as for the manual control open/close. In manual mode, the valves are opened/closed directly by the operator by choosing the open or close position. In automatic mode, the valves open and close according to the logic implemented in the DCS.
