Response to a Setpoint Change in PID Controlled Time-Delay Feedback Systems

The response to a setpoint change in PID controlled feedback systems plays an important role for the tuning methods. This response may be easily evaluated in linear systems without delay by solving the related ordinary differential equations. These equations are also obtained for system with delay, if the delay exponential term is approximated to a polynomial by one of the Pade expressions. If this simplification is avoided, one must deal with differential difference equations. In this paper their explicit solution, obtained with the method of steps, is presented. Moreover a second order equation is investigated as example and the complete set of the coefficients formulas is given.