This tutorial walks you through tuning a PID control loop using the Ziegler-Nichols Reaction Curve, or Open-Loop tuning method. This method as presented in this tutorial has a few requirements:

The process response time should be around twice the loop dead time.
The process should self-stabilize for a given step change in the controlled variable (the output).
Your PID loop controller must be able to graph the PID loop.
You should have access to either a printer or screen capture software so graph measurements can be taken at the end of the process.
You'll also need a metric ruler to take precise decimal measurements and enter them into the tutorial.

The assumed measurement for time is seconds. You can enter a unit of measure (for example, degrees or PSI) for your process variable (y-axis) and for your ruler (mm, cm) in the fields below. These units of measure will be displayed wherever measurements are required to clarify whether you are measuring the process variable, the time, or the linear distance on your graph printout.

PID: Reaction Curve Tuning