What type of control action anticipates disturbance before it affects PV in advanced loop strategies?
A. Feedback
B. Cascade
C. Feedforward
D. Ratio
View Answer
Correct Answer: C. Feedforward
Explanation (Advanced Control Strategy)
In feedforward control, the system measures disturbances before they impact the process and takes corrective action in advance.
- Instead of waiting for PV to deviate, it acts based on a measured disturbance variable
- This makes the control action proactive, not reactive
How it works
- A disturbance (e.g., load change, inlet flow variation) is measured directly
- The controller calculates the required correction
- The output is adjusted before PV changes
Example:
If inlet flow suddenly increases, feedforward immediately adjusts the control valve before temperature or pressure deviates
Why Feedforward is Correct
- Anticipates disturbances
- Reduces deviation in PV
- Improves overall control performance
Why other options are wrong
- A. Feedback → Reacts after PV changes (reactive control)
- B. Cascade → Improves response speed, but still reacts after disturbance enters
- D. Ratio → Maintains proportional relationship, does not anticipate disturbance
Final Takeaway
Only feedforward control predicts and compensates disturbances before they affect the process.