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Contents

Control Systems

Introduction

Open Loop Systems Closed Loop Systems Control System Components Transfer Function Block Diagram Basics Block Diagram Reduction Signal Flow Graph Construction Mason Gain Formula

Time Domain Analysis

Test Input Signals First Order System Response Second Order System Parameters Second Order Underdamped Response Second Order Overdamped Response Second Order Critically Damped Response Time Domain Specifications System Type Number Steady State Error Steady State Error Improvement Dominant Poles

Stability Analysis

BIBO Stability Routh-Hurwitz Criterion Routh Array Special Case Zero Element Routh Array Special Case Zero Row Root Locus Concept Root Locus Construction Rules Root Locus Breakaway Points Root Locus Angle of Departure Root Locus and Stability Complementary Root Locus

Frequency Response

Frequency Response Concept Bode Plot Construction Bode Plot of First Order System Bode Plot of Second Order System Gain Margin Phase Margin Gain and Phase Margin from Bode Polar Plot Nyquist Plot Construction Nyquist Stability Criterion Nichols Chart All Pass and Minimum Phase Systems

Compensators

Lead Compensator Design Lag Compensator Design Lead-Lag Compensator P Controller PI Controller PD Controller PID Controller Ziegler-Nichols Tuning

State Space

State Variables State Space Representation State Space from Transfer Function Transfer Function from State Space State Transition Matrix Controllability Observability State Feedback Control Observer Design Diagonalization

Digital Control

Sampled Data Systems Z-Domain Analysis Digital PID Controller Stability in Z-Domain Bilinear Transformation w-domain

Other Topics

Other Subjects

Analog Electronics Digital Electronics Signals & Systems Electromagnetic Theory Digital Communication Analog Communication Network Analysis Microprocessors VLSI Design Verilog HDL Power Electronics Embedded Systems DSP Electronic Devices

Section Progress90%

9 of 10 articles

Root Locus and Stability

Gain margin from root locus, critical gain.

Updated: 19 March 2026

7 min read

#Control Systems

Root Locus Stability Quiz

Test your ability to extract gain margin and critical gain directly from the root locus plot.

Question 1 of 3

Q1.The root locus of a system crosses the imaginary axis at s = +/- j2 when K = 16. What is the gain margin of the system?

Related Articles

Root Locus Concept

Locus of closed-loop poles as gain K varies.

12 min read

Root Locus Construction Rules

Number of branches, symmetry, asymptotes, angles.

10 min read

Root Locus Breakaway Points

Departure from real axis, dK/ds = 0 condition.

9 min read

BIBO Stability

Bounded input bounded output, pole location requirement.

12 min read

Stability in Z-Domain

Unit circle criterion, Jury stability test.

8 min read

Root Locus Angle of Departure

Complementary Root Locus