In this study a comparison between PID controller in conventional control and PID control in Simulink was investigated. A control strategy was developed for purification of gold by aquaregia method. The aquaregia was composed of 1:3 HNO3 and HCL, therefor a ratio controller was designed to constantly adjust this ratio. The block diagram was drown and the transfer functions were cited from the literature. The stability of the control loops of the system ware calculated and used in the simulation of the loops. From the results of the simulation the controller that gives minimum interaction was selected. The loop paring was determined by the Relative gain array which gives the coupling with minimum interaction
