EC (Type Of Controls) Ch 6

Question 1

How is a transducer used in a closed-loop control system?

Answer 1

A transducer converts a physical quantity into an electrical signal that can be measured. In a closed-loop system, this signal is sent back to the controller as feedback to compare against the setpoint, enabling real-time corrections.

Examples of physical quantities include temperature, pressure, or position.

Question 2

Explain proportional control.

Answer 2

Proportional control (P control) adjusts the output in proportion to the error.
* More error = stronger correction
* It provides fast response but can leave a steady-state error (offset).

Steady-state error refers to the difference between the desired setpoint and the actual output after the system has settled.

Question 3

Effect of increasing the gain of an amplifier in a closed-loop system?

Answer 3

Increasing gain:
* Reduces steady-state error
* Speeds up system response
* May cause instability if too high

Instability can manifest as oscillation or overshoot in the system response.

Question 4

How to compensate for leakage across the valve spool?

Answer 4

Introduce a small bias or offset current to maintain the desired position or use integral action in the controller to eliminate steady-state errors caused by leakage.

Integral action helps to adjust for persistent errors over time.

Question 5

Explain the term error × time.

Answer 5

This refers to integral action in a controller:
* The longer the error persists, the greater the correction
* It’s the basis of I (integral) control in PID systems.

This concept is critical for eliminating steady-state errors in control systems.

Question 6

What is meant by three-term control?

Answer 6

Three-term control = PID control:
1. P – Proportional: Immediate response to error
2. I – Integral: Corrects accumulated past errors
3. D – Derivative: Predicts future error based on the rate of change

PID control combines the strengths of each term for fast, accurate, and stable control.