PID Regulatory Control Design for a Double Tank System Based on Time-Scale Separation.

An intuitive and simple yet efficient novel approach to the PID control system synthesis for load disturbance rejection in a cascaded tanks system is presented. It is assumed that the controller is fitted with a first order noise filter. The design method consists in choosing appropriate values of filter and controller parameters such that a time-scale separation takes place between control signal and output dynamics while keeping the noise amplification gain at a reasonable value. As a result, low measurement noise results in very high performance of load disturbance rejection. Moreover, the solution shows high degree of robustness against changes of the working point. Simple formulas providing analytical solutions for extrema of time responses are derived that allow to design control system with predefined characteristics.