Proportional, PI, and PID Control (Algorithms)

By using all three control algorithms together, process operators can:

❑ Achieve rapid response to major disturbances with derivative control;
❑ Hold the process near setpoint without major fluctuations with proportional control;
❑ Eliminate offset with integral control.


Not every process requires a full PID control strategy. If a small offset has no impact on the process, then proportional control alone may be sufficient.
PI control is used where no offset can be tolerated, where noise (temporary error readings that do not reflect the true process variable condition) may be present, and where excessive dead time (time after a disturbance before control action takes place) is not a problem. In processes where no offset can be tolerated, no noise is present, and where dead time is an issue, customers can use full PID control. The Table on Picture 1 shows common types of control loops and which types of control algorithms are typically used.

Picture 1: Control Loops and Control Algorithms Table