Which control loop operates in a narrow band close to the setpoint?

The control loop that operates in a narrow band close to the setpoint is the PI (Proportional-Integral) controller. This configuration effectively minimizes steady-state error by continuously adjusting the control output based on both the present error (the difference between the setpoint and the measured value) and the accumulated error over time.

The proportional component responds to the current error, providing an immediate corrective action, while the integral component accounts for past errors by integrating the error over time. This cumulative action helps drive the process variable back to the setpoint steadily and reduces the chance of fluctuations around the setpoint. Thus, the PI controller maintains tighter control within a narrow band around the desired setpoint, making it suitable for systems where accuracy and stability are crucial.

In contrast, other control strategies may not maintain such a precise control band. For instance, the PID controller includes a derivative component which aims to predict future behaviors based on the rate of change of the error, leading to potentially wider variations as it reacts to dynamic changes rather than maintaining a strict band. The PD controller, while also reactive, may not eliminate steady-state error as effectively as the PI controller. On/off control, while simple and effective in some scenarios, operates by toggling between fully on and fully