The different methodologies of controller tuning, known as Ziegler-Nichols method have been illustrated in the earlier sections.
It is to be remembered that the recommended settings are empirical in nature, and obtained from extensive experimentation with number of different processes; there is no theoretical basis behind these selections.
As a result, a better combination of the P, I, D values may always be found, that will give less oscillation and better settling time.
But with no a-priori knowledge of the system, it is always advisable to perform the experimentation and select the controller settings, obtained from Ziegler-Nichols method.
But there is always scope for improving the performance of the controller by fine-tuning. So, ZieglerNichols method provides initial settings that will give satisfactory, result, but it is always advisable to fine-tune the controller further for the particular process and better performance is expected to be achieved.
Nowadays digital computers are replacing the conventional analog controllers. P-I-D control actions are generated through digital computations. Digital outputs of the controllers are converted to analog signals before they are fed to the actuators. In many cases, commercial software are available for Auto tuning the process.
Here the controller generates several commands those are fed to the plant. After observing the output responses, the controller parameters are selected, similar to the cases discussed above.