Question:
What is meant by “open-loop control”?
Options:
A) With feedback
B) Auto mode
C) Fixed output
D) No feedback
View Answer
Correct Answer: D) No feedback
Detailed Explanation
Open-loop control is a system without feedback.
In this type of control:
- The controller does not measure the process variable (PV).
- There is no comparison between SP and PV.
- Output is applied without knowing whether the desired result is achieved.
Since there is no feedback, the system cannot automatically correct disturbances.
Why Other Options Are Incorrect
A) With feedback → That defines closed-loop control.
B) Auto mode → Auto mode usually implies feedback operation.
C) Fixed output → While open-loop often uses fixed output, the defining feature is the absence of feedback.
Practical Example
- Heater ON for 10 minutes (no temperature measurement) → Open-loop
- Heater adjusts based on temperature sensor → Closed-loop
Quick Comparison
| Feature | Open Loop | Closed Loop |
|---|---|---|
| Feedback | No |
Yes |
| Self-correction | No |
Yes |
| Accuracy | Low | High |