# Design of PIDD(r) Controller for Robust Performance of Process Plants
## 4 Experimental Study
### Real-Time Pressure Process Plant  
The schematics of the real-time pressure process plant, which runs in real time, are shown in Figure 20. VL 202, the primary buffer tank, is designed to sustain up to 10 Bar of pressure from the centralised air compression system that provides it with air. The pressure inside the tank can be controlled using the hand valve, HV 202, while the process control valve, PCV 202, ensures that the pressure remains constant at the desired level. The pressure is measured using pressure transmitter PT 202, converted to digital voltage values ranging from 0 to 5 V. These signals are sent to the PCV 202 pressure-indicating controller, which sends the control signal to the host PC through I/O interface boards. An analogue pressure gauge that indicates pressure fluctuations inside the tank is provided for safety. If the valve PCV 202 malfunctions, a hand-operated valve at the bottom of the buffer tank releases compressed air from the VL 202 in an emergency. The hand valve can also be employed as an external disturbance injection channel during the experiment. Excess air is released through an exit on the top of the process tank, connected to another process control valve, PCV 203, to adjust the pressure inside the buffer tank. During the experiment, this valve is kept at 50% open to prevent excessive pressure buildup inside the VL 202. The host PC sends signals to the control valve actuator PCV 202 based on the set-point value. Figure 21 depicts the pressure process plant's P&ID diagram. The facility runs in \"Remote Desktop Connection\" mode for safety, with processes controlled from the central control centre. PCI cards connect the mainframe PC and field equipment, such as the control valve actuator, flow sensors, and pressure transmitter. These cards provide 2500 V DC isolation protection between PCI bus outputs. A 32-channel analogue input board dubbed PCI-1713U receives the process plant's analogue input. It features a 12-bit resolution and a sampling rate of 100,000 samples per second. A critical component of the PCI card, the PCI-1720U module, utilises a high-quality 12-bit, 4-channel analogue output port to transfer accurate control signals to the host PC. Furthermore, with 48 bits of parallel digital input/output, the PCI-1751 card enables remote management of the pressure process plant by transmitting digital signals from the PT 202 to the host PC. Figure 20: Schematic of real-time pressure process plant. Figure 23: Step response of controller structure for pressure process plant. Figure 24: Variable set-point tracking of controller structure for pressure process plant. Figure 25: Disturbance rejection of controller structure for pressure process plant. From the simulation results, PIDD2 and the proposed PIDD\({}^{\alpha}\) controllers have better overshoot values than PID and FOPID controllers. The proposed PIDD\({}^{\alpha}\) performs best with only 4.838% overshoot, while PID and FOPID controllers have 6.2148% and 5.5126%, respectively. The proposed PIDD\({}^{\alpha}\) also has the best rise time of 2.6272 s compared to PID, PIDD\({}^{2}\), and FOPID controllers, with rise times of 2.8287 s, 2.8486 s, and 2.8792 s, respectively. Moreover, the proposed PIDD\({}^{\alpha}\) outperforms its competitors in settling time with a value of 8.9543 s compared to PID, PIDD\({}^{2}\), and FOPID with values of 9.2664 s, 9.0571 s, and 8.96 s, respectively. In the set-point tracking, the initial set-point starts at one at zero seconds and changes to 2, 3, and 1.5 at 15 s, 30 s, and 45 s, respectively. These changes cover both positive and negative changes in the controller. All set-point changes reach their steady-state values, as shown in Table 6. Figure 24 illustrates that each controller structure can achieve each set-point change following the step response. For disturbance rejection, a disturbance with a magnitude of \(-0.6\) is introduced into the controller structure at 15 s to simulate real-world plant behaviour.