A new algorithm for self tuning of proportionalintegral- derivative (PID) controllers is proposed. A combined least-squares estimation and Newton–Raphson search technique is used to determine the ultimate gain and period of an unknown system for the purpose of automatic tuning of PID controllers based on Ziegler and Nichols (ZN) or refined Ziegler and Nichols (RZN) formulas. The proposed algorithm can be applied to systems with known time delay, as well as those with unknown dead time. Simulation studies are used to demonstrate the performance of this algorithm. The performance of this PID self tuner is also compared with a popular commercial auto-tuner for simulated systems and a laboratory-scale real plant.