The Step Open Loop autotuning technique, which is used by the Step Open Loop instance of the PID Online Autotuning VI, performs an open-loop step test. This technique assumes that you can model any process as a first-order lag and a pure deadtime.

The Step Open 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.