What type of control features a controller that continually adjusts output in response to deviations from the set point?

• A. Proportional control
• B. Proportional plus reset control
• C. Integral control
• D. Derivative control

Answer: (B)

The type of control that features a controller that continually adjusts output in response to deviations from the set point is known as proportional plus reset control. This control strategy combines both proportional and integral actions, allowing the system not only to react to the current error (the difference between the set point and actual process variable) but also to correct past errors.

The proportional component reacts to the present error, making immediate adjustments based on that value, while the reset (also known as integral) component accumulates past errors over time. This ensures that any residual steady-state error is corrected, striving to drive the process variable back to the desired set point more effectively than using proportional control alone.

This combination leads to improved accuracy and stability in process control, as it addresses both immediate and historical deviations. In contrast, proportional control alone may leave a small steady-state error, while integral control focuses solely on adjusting past discrepancies, potentially leading to overshoot or oscillation if not properly tuned. Thus, the blend of these components in proportional plus reset control offers a more comprehensive solution for maintaining the desired process variable.