Question

What type of controller is used for the control of flow of liquid from a pump?

• A. P controller
• B. PD controller
• C. PID controller
• D. PI controller

Hint:

PI controllers are best suited for flow control applications because they eliminate steady-state error without the noise sensitivity of derivative control.

Answer 1

The Correct Option is D

For controlling the flow of liquid from a pump, a Proportional-Integral (PI) controller is most commonly used.
Let us understand why:
- A P (Proportional) controller adjusts the control output proportionally to the error signal. However, it cannot eliminate steady-state error completely.
- A PD (Proportional-Derivative) controller improves transient response but is poor at eliminating steady-state error and is sensitive to noise.
- A PID controller (Proportional-Integral-Derivative) adds derivative control to improve speed and stability, but is generally not required for flow control, as it can add unnecessary complexity.
- A PI controller, on the other hand, combines the benefits of proportional and integral actions: it offers good response speed (via the P part) and eliminates steady-state error (via the I part), which is crucial in maintaining constant flow under varying load conditions.
In flow control applications, disturbances and setpoint changes happen gradually and predictably. The derivative component is often avoided due to noise sensitivity and maintenance issues.
Hence, the PI controller is ideal for such scenarios and widely adopted in process industries for flow control.