The Step Closed Loop autotuning technique, which is used by the Step Closed Loop instance of the PID Online Autotuning VI, performs a closed-loop step test. This technique is very accurate and reaches steady state faster than the Step Open Loop technique.

In closed-loop tuning, the PID Online Autotuning VI applies the Step Open Loop response with the controller in a closed loop, and then back-calculates the dynamics of the system by removing the closed loop gain.

The Step Closed Loop autotuning technique measures the deadtime Td, time constant T, and process gain K values of a controller and multiplies them according to the formulas for the heuristic method in place. For example, most PID VIs use the Ziegler-Nichols method.