Abstract: A new online controller tuning method in closed-loop mode improves over the Ziegler-Nichols continuous cycling method. The method is a closed-loop setpoint step experiment PI/PID controller tuning method, which uses a P-controller with a gain Kc0, runs a setpoint experiment, and obtains a plurality of PI/PID-controller settings directly from three data from the setpoint experiment, wherein the three data are overshoot (?yp??y?)/?y?), time to reach overshoot or first peak tp, and relative steady state output change b=?y?/?ys, wherein ?ys is a setpoint change, ?y? is a steady-state output change after setpoint step test, and ?yp is a peak output change at time tp.