ABSTRAKKendali PID analog, yang realisasinya menggunakan komponen elektronika, memiliki keterbatasan yaitu nilai toleransi yang terbatas. Saat ini spesifikasi kontroler dituntut untuk dapat berkomunikasi dengan sistem yang lebih besar seperti SCADA dan DCS sehingga lebih cocok menggunakan pengendali digital. Penelitian ini menganalisis metode konversi PID analog ke digital agar dihasilkan difference equation yang dapat direalisasikan ke dalam pemrograman komputer. Metode yang dipakai adalah diskritisasi langsung dan Backward Difference. Perbandingan kedua metode dilakukan dengan menganalisis respons berdasarkan initial paramater yang dihasilkan oleh metode Ziegler Nichols. Hasil pengujian menunjukkan kendali PID diskrit menggunakan Backward Difference menghasilkan respons sistem yang lebih baik dibandingkan metode diskritisasi langsung dengan nilai Kp, Ti, dan Td adalah 50, 80 dan 0,001 menghasilkan respons dengan nilai rise time, settling time dan overshoot berturut-turut sebesar 33,66s, 90,39s dan 0,9%.Kata kunci: PID diskrit, diskritisasi langsung, Backward Difference, Ziegler Nichols ABSTRACTThe analog PID control, where its parameters are realised using the electronic component, has disadvantages due to the limitation of its tolerance value. Currently, the specifications of controller are required to be able to communicate with larger systems such as SCADA and DCS, therefore digital controller is more appropriate to use. This study analyzes the analog to digital PID conversion method to generate a difference equation that can be realized in computer programming. The direct discretization and Backward Difference method are used. Comparison of both methods is by analyzing response based on initial parameters obtained of Ziegler Nichols method. The results show that discrete PID control using the Backward Difference indicates a better response than using the direct discretization method with Kp, Ti, and Td values are 50, 80, and 0,001, respectively. Those parameters generate response with rise time, settling time, and overshoot values of 33,66s, 90,39s, and 0,9%, respectively.Keywords: discrete PID, direct discretization, Backward Difference, ZieglerNichols
In Distributed Control System (DCS), multitasking management has been important issues continuously researched and developed. In this paper, DCS was applied in global temperature control system by coordinating three Local Control Units (LCUs). To design LCU's controller parameters, both analytical and experimental method were employed. In analytical method, the plants were firstly identified to get their transfer functions which were then used to derive control parameters based on desired response qualities. The experimental method (Ziegler-Nichols) was also applied due to practicable reason in real industrial plant (less mathematical analysis). To manage set-points distributed to all LCUs, master controller was subsequently designed based on zone of both error and set-point of global temperature controller. Confirmation experiments showed that when using control parameters from analytical method, the global temperature response could successfully follow the distributed set-points with 0% overshoot, 193.92 second rise time, and 266.88 second settling time. While using control parameters from experimental method, it could also follow the distributed set-points with presence of overshoot (16.9%), but has less rise time and settling time (111.36 and 138.72 second). In this research, the overshoot could be successfully decreased from 16.9 to 9.39 % by changing master control rule. This proposed method can be potentially applied in real industrial plant due to its simplicity in master control algorithm and presence of PID controller which has been generally included in today industrial equipments.
Mold cavity pressure in injection molding machine plays an important role in determining the quality of molded products. However, the dynamic of cavity pressure is time varying in relation to the hydraulic servo-valve opening. A cavity pressure control scheme was proposed by applying Model Reference Adaptive Control (MRAC) to deal with the time varying nature of cavity pressure. The adjustment of controller gains was carried out by MIT Rule. A lead compensator was also employed to improve the transient response. The simulation demonstrated the effectiveness of MRAC-based system during filling and packing phases even in the presence of parameter variations, zero mismatches, and measurement noise. The actual cavity pressure response is able to follow the output of prescribed reference model with varied set point profile. In the future, the proposed control scheme is potential to be implemented in the real system.
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