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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

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5 of 10 articles

Root Locus Concept

Locus of closed-loop poles as gain K varies.

Updated: 19 March 2026

12 min read

#Control Systems

Root Locus Concept Quiz

Test your understanding of what the root locus represents and the conditions that define it.

Question 1 of 3

Q1.The root locus of a closed-loop system is the locus of roots of the characteristic equation as K varies from 0 to +infinity. At K = 0, the closed-loop poles begin at:

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Root Locus and Stability

Gain margin from root locus, critical gain.

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Complementary Root Locus

Negative feedback, K from 0 to -infinity.

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Root Locus Angle of Departure

Angle condition at complex poles and zeros.

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Root Locus Breakaway Points

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

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BIBO Stability

Bounded input bounded output, pole location requirement.

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Routh Array Special Case Zero Row

Root Locus Construction Rules