PLC-Based Pressure Override Control for End-Barrel Pressure Regulation in PET Extrusion Systems
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Maintaining stable melt pressure is essential for ensuring product quality, process stability, and operational safety in polyethylene terephthalate (PET) extrusion systems. However, achieving effective pressure regulation through practical industrial Programmable Logic Controller (PLC)-based implementations remains a significant challenge. In this study, a pressure override control strategy for end-barrel pressure control of a PET extrusion system is developed based on a PLC. The innovation of the proposed approach is the use of a simplified first order process model in combination with a proportional-integral (PI) pressure override controller, which is implemented on a Siemens S7-1200 PLC, using the Totally Integrated Automation (TIA) Portal V15 environment. The control system was simulated in S7-PLCSIM in open loop and closed loop operating conditions and the transient-response characteristics along with Integral of Absolute Error (IAE), Integral of Squared Error (ISE) and Integral of Time-weighted Absolute Error (ITAE) were used to assess the performance of the control system. The results showed that the proposed controller was able to successfully preserve the end-barrel pressure close to the desired operating limit of 60 bar. The maximum pressure dropped from 95.9 bar to 64.6 bar and the pressure overshoot dropped from 59.9% to 7.7% compared to open-loop operation. Moreover, the settling time was shortened from 31.3 s to 11.3 s at 50% melt pump speed, while the IAE, ISE, and ITAE values were always decreased under all the investigated operating conditions, which showed that the pressure regulation and disturbance rejection were improved. Finally, the proposed PLC-based pressure override controller provides a practical, reliable, and computationally efficient solution for enhancing process stability, operational safety, and production reliability in industrial PET extrusion systems.
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