Control system of fluidized catalytic cracking unit (FCCU) is a good example to study multivariable control, interaction, decoupling system. In this work, basic energy balance around FCC unit is applied. Transfer functions were carried out using state space method. Regenerated catalyst flow rate and air flow rate were chosen to be manipulated variables whereas reactor temperature and regenerator temperature were chosen to be controlled variables. Determining the tight of interaction based on relative gain array (RGA). The Tuning of control parameters for PID feedback was calculated by...