Implementation of Proportional Integral Controller Parameter Tuning for Spherical Tank System using Root Locus Technique

Abstract

In process industries the control of liquid level for a spherical tank system is a difficult task. It is mainly used to store the large volumes of highly pressurized liquids, semi liquid and solid mixtures. Due to variation in cross sectional area with respect to height, the spherical tank system is highly nonlinear. The entire operating region of spherical tank system is categorized in to three approximate linear regions. The open loop responses for these regions are obtained and their transfer function models are derived. The acquired model is examined and validated with the actual data. To control the liquid level in spherical tank system, a Proportional Integral (PI) controller has been designed by using the conventional Ziegler-Nichols tuning (Z-N) method and Root Locus Technique (RLT). The servo response of the spherical tank system for PI controller parameter tuning by Z-N method and RLT are compared. Based on the comparison, it is found that RLT is superior in terms of rise time, peak time, settling time and steady state error.