This question was asked inGPSC Deputy Executive Engineer (Electrical) Class-2 Master Paper 2026Question 120 of 195 published · Gujarat Public Service CommissionOpen paper
Q120ModerateSteady-State Error

Consider the following statements regarding Steady-State Error:
1. Type of system determines steady-state error for standard inputs.
2. Increasing system gain reduces steady-state error.
3. Integral control eliminates steady-state error for step input.
4. Steady-state error is independent of system type.
Which of the above statements is/are correct?

Answer & step-by-step solution
Correct answer: C. 1, 2 and 3 only
Quick explanation

It determines which standard polynomial inputs can be tracked with zero or finite steady-state error. Integral action increases low-frequency gain and improves steady-state accuracy, but it can also affect transient stability margins. Key relation: Kp=lim G(s), Kv=lim sG(s), Ka=lim s²G(s) as s→0 for unity feedback.

Exam focus: Type-0/1/2 classification comes from poles at the origin. Common trap: Do not infer stability from system type alone.

Kp=lim G(s), Kv=lim sG(s), Ka=lim s²G(s) as s→0 for unity feedback.

Statement-wise Verification

  • Statement 1 - Correct.
    Type of system determines steady-state error for standard inputs.
    It determines which standard polynomial inputs can be tracked with zero or finite steady-state error.
  • Statement 2 - Correct.
    Increasing system gain reduces steady-state error.
    Integral action increases low-frequency gain and improves steady-state accuracy
  • Statement 3 - Correct.
    Integral control eliminates steady-state error for step input.
    Integral action increases low-frequency gain and improves steady-state accuracy
  • Statement 4 - Incorrect.
    Steady-state error is independent of system type.
    The correct principle is: It determines which standard polynomial inputs can be tracked with zero or finite steady-state error.

Core Concept

In unity-feedback control, system type is the number of pure integrators in the open-loop transfer function. It determines which standard polynomial inputs can be tracked with zero or finite steady-state error. Integral action increases low-frequency gain and improves steady-state accuracy, but it can also affect transient stability margins.

Formula / Key Relationship

Kp=lim G(s), Kv=lim sG(s), Ka=lim s²G(s) as s→0 for unity feedback.

Why the Other Options Are Wrong

Option A is incorrect because it omits correct statement(s) 1. Option B is incorrect because it omits correct statement(s) 2. Option D is incorrect because it includes incorrect statement(s) 4.

Exam Shortcut / Approach

Type-0/1/2 classification comes from poles at the origin.

Common Mistake

Do not infer stability from system type alone.

Quick Revision

System Type Gain and Integral Action is linked with Steady-State Error, Steady-State Analysis and Control Systems. Type-0/1/2 classification comes from poles at the origin.

Exam tipType-0/1/2 classification comes from poles at the origin.
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