Question

Response of a linear control system for a change in set point is called

• A. Frequency response
• B. Transient response
• C. Servo problem
• D. Regulatory problem

Hint:

In control systems, a servo problem refers to tracking a new set point, while a regulatory problem focuses on rejecting disturbances.

Answer 1

The Correct Option is C

Step 1: Understand control system responses. 
In control systems, the response of a system to different inputs or changes is categorized based on the type of disturbance or objective:
Set point change: When the desired value (set point) of the controlled variable (e.g., temperature, pressure) is changed, and the system must adjust to reach the new set point.
Frequency response: The system’s response to a sinusoidal input, typically analyzed in the frequency domain to understand stability and bandwidth.
Transient response: The time-domain behavior of the system as it moves from one steady state to another, often including overshoot, rise time, and settling time.
Servo problem: A control problem where the system must track a change in the set point (e.g., adjusting to a new desired value). This is also called a tracking problem.
Regulatory problem: A control problem where the system must maintain the controlled variable at the set point despite external disturbances (e.g., load changes). 
Step 2: Analyze the problem. 
The question specifies the response of a linear control system to a change in set point. This means the system is tasked with adjusting the controlled variable to match a new desired value. In control theory:
A servo problem (or tracking problem) specifically refers to the system’s response to a set point change, focusing on how well the system tracks the new set point.
While the response to a set point change involves a transient response (the dynamic behavior during the adjustment), the term “transient response” is more general and not specific to set point changes.
A regulatory problem deals with rejecting disturbances, not tracking a new set point.
Step 3: Evaluate the options. 
(1) Frequency response: Incorrect, as this refers to the system’s behavior under sinusoidal inputs, not a set point change. Incorrect.
(2) Transient response: Incorrect, as while a set point change induces a transient response, the term is too general and not specific to set point tracking. Incorrect.
(3) Servo problem: Correct, as the response to a change in set point is specifically termed a servo (or tracking) problem in control systems. Correct.
(4) Regulatory problem: Incorrect, as this refers to maintaining the set point against disturbances, not tracking a new set point. Incorrect. 
Step 4: Select the correct answer. 
The response of a linear control system to a change in set point is called a servo problem, matching option (3).