P, PI, PD or PID — which controller should you use?

Not every loop needs all three terms. Choosing the simplest structure that meets the requirement makes tuning easier and the loop more robust.

P — proportional only

Fast and simple, but leaves a steady-state offset on a self-regulating process. Fine where a small residual error is acceptable, such as some level loops.

PI — the workhorse

Adds integral action to remove offset while staying immune to measurement noise. This is the right default for flow, pressure and most process control loops.

PD — fast and damped

Good for motion and servo systems that need speed and damping and can tolerate a static error. Rarely used on process loops because it leaves an offset.

PID — the full three-term

Use it for demanding loops with significant lag or dead time, such as temperature control. The derivative term must be filtered and taken on the measurement to avoid amplifying noise and to prevent derivative kick.

Try each structure in the PID calculator on the same plant and compare overshoot, offset and noise sensitivity.