Question

A servo control loop responds for

• A. Load changing
• B. Set point changing
• C. Both load and set point changing
• D. Neither load nor set point changing

Hint:

A servo control loop is designed for set point tracking, while a regulatory control loop handles disturbances like load changes.

Answer 1

The Correct Option is B

Step 1: Define a servo control loop. 
A servo control loop (or servo mechanism) is a control system designed to track a desired reference input, often a set point. In control theory:
Servo problem: The system adjusts the controlled variable to follow a change in the set point (e.g., changing the desired temperature in a reactor).
Regulatory problem: The system maintains the controlled variable at the set point despite external disturbances (e.g., load changes like a change in feed flow rate). A servo control loop specifically refers to the system’s response to a set point change, ensuring the output tracks the new desired value. 
Step 2: Analyze the response context. 
Load changing: A change in external conditions (e.g., a disturbance like a change in inlet flow rate or temperature). This is handled by a regulatory control loop, not a servo loop.
Set point changing: A change in the desired value of the controlled variable (e.g., adjusting the set point temperature from 100°C to 120°C). This is the primary function of a servo control loop.
A control system can be designed to handle both set point changes (servo) and load changes (regulatory), but the term “servo control loop” specifically refers to set point tracking.
Step 3: Evaluate the options. 
(1) Load changing: Incorrect, as load changes are associated with a regulatory problem, not a servo control loop. Incorrect.
(2) Set point changing: Correct, as a servo control loop is designed to respond to set point changes, tracking the new desired value. Correct.
(3) Both load and set point changing: Incorrect, as a servo control loop specifically addresses set point changes, not load changes (which are regulatory). Incorrect.
(4) Neither load nor set point changing: Incorrect, as a servo control loop does respond to set point changes. Incorrect.
Step 4: Select the correct answer. 
A servo control loop responds to set point changing, matching option (2).