Tuning Rules for PI and PID

Determining Which Controller to Use

A key challenge in setting up a control system is determining what type of controller to use. The PID controller is generally accepted as the standard for process control, but the PI controller is sometimes a suitable alternative. A PI controller is the equivalent of a PID controller with its D (derivative) term set to zero.

It is important to understand how controllers interact with each different type of process. For details, see Table 1.

Table 1 – How PI and PID Controllers Interact with Different Kinds of Processes

Controller	Pl Controller	PID Controller
Effective for These Processes	Fast processes, such as flow, pressure, and some temperature loops.	Slower processes, such as level and insulated temperature.
Tuning Parameters	P = Proportional I= IntegralPl controller is the equivalent of a PID controller with its D (derivative) term set to zero.	P = Proportional I= Integral D = DerivativeThe derivative term is particularly important for integrating processes, such as level, position, & well-insulated temperature.In general, using a derivative term can significantly increase the speed of the response of a non-integrating process and suppresses overshoot.
Response Speed	Response is slower, thus enabling a smooth and accurate PV change.	Response is faster, thus enabling setpoint to be reached more quickly.
Overshoot	Overshoot will likely occur.	Reduced or no overshoot.