Control Systems Tutorial

A Control System is an interconnected system of various components designed to control and regulate the behavior of a large system or process to produce a desired output. Therefore, the primary objective of a control system is to adjust the input of a process so that we can get a desired output.

This comprehensive tutorial on control systems is designed to provide overview of essential concepts of control systems. This tutorial is written in a beginner friendly writing style to build a solid foundation in control system engineering.

Introduction to Control Systems

A control system is a key component of modern industrial processes. It is used for making decisions in real-time to ensure seamless operation of large machinery and sophisticated processes. Control systems play a very important role in keeping the operations and processes safe, smooth, and efficient, as per the standards and regulations.

Today, control systems are integral parts of variety of industries such as goods manufacturing facilities, energy industries, chemical industries, food industries, textile industries, traffic control, mining, and more. In all these industries and processes, control systems are entirely responsible for optimizing the performance, improving the product quality, maintaining the safety and compliances.

Why Control Systems are Important in Industries?

In industrial facilities, efficiency, precision, and safety are the topmost concerns. A control system provides a control on all these parameters and it decides how the processes and systems function to ensure maximum efficiency, precision, and safety with the high-quality output.

Control systems are the essential components of an industrial setup that make the operations smooth, prevent errors, and increase the efficiency.

Types of Control Systems

Control systems are broadly classified into the following two types −

• Open Loop Control System
• Closed Loop Control System

An open-loop control system is one which has no feedback path between output and input. Hence, the output of the open-loop control system at a point of time depends only on the inputs applied to it at that point of time.

On the other hand, a closed-loop control system is one which has a continuous feedback path from output to input. Hence, this control system is dynamic and adaptive, and it gives more accurate outputs. Since, a feedback path is there, hence, the output of the closed loop control system depends on the inputs applied as well as past outputs.

Hardware and Software Components of a Control System

A control system is basically a combination of various hardware and software components. The common hardware and software components of a typical control system are as follows −

• Programmable Logic Controllers (PLCs) − PLCs are the most fundamental components of a control system. They are programmable microcontrollers and are used for automating the processes.
• PID Controllers − Proportional-Integral-Derivative controllers are devices used for fine control of processes. These devices are used in control systems to minimize errors in outputs and keep the systems operating smoothly.
• APC Systems − APC (Advanced Process Control) systems are devices that use predictive algorithms to optimize the system performance in real-time.
• Supervisory Control and Data Acquisition (SCADA) − This component of control systems provides an interface between human and machine. It allows operators to control processes from a remote location and provides data and insights for performance optimization.

Control System Terminology

The following are some very common and important terms related to control systems −

#1) Feedback

Feedback is an important component of a closed loop control system that connects output to the input for stability and performance optimization.

#2) Mathematical Models

Mathematical models are the abstract descriptions of a control system developed using mathematical concepts and language. They are important for designing and analyzing control systems.

#3) Block Diagrams and Signal Flow Graphs

Blocks diagrams are schematics that graphically visualize the interconnections of different components of control systems. Signal flow graphs are graphical representations of algebraic equations of control systems.

#4) Time Response Analysis

Time response analysis is used for analyzing and understanding the behavior of control system with respect to time.

#5) Stability Analysis

Stability analysis is another fundamental concept in control system engineering. This tool is used for determining systems stability under different operating conditions.

#6) Root Locus and Frequency Response Analysis

Root locus is a graphical tool for determining how the roots of a closed loop control system change with variations in certain system parameters like gain in feedback loop. The frequency response analysis is a tool used for analyzing the performance of control systems in the frequency domain.

#7) Compensators and Controllers

Compensators are vital components of a control system that are used for improving the response of the system to the inputs. While, controllers are those devices that regulate the behavior of the control system depending on the applied inputs and feedback signal.

#8) State Space Model and Analysis

State space model and analysis is one of the advanced techniques used for designing and analyzing control systems. State space model is a mathematical representation of a control system and it consists of inputs, outputs, state variables, and differential equations.

Who Should Learn Control Systems?

This Control System Tutorial is primarily meant for students as well as professionals working in the field of electrical, electronics, control engineering, automation, and industrial engineering.

This tutorial explains all the fundamental concepts of control systems in a beginner friendly style, making it suitable for absolute beginners. However, it can be used as a reference for practicing control engineers as well.

What are the Prerequisites to Learn Control Systems?

This tutorial is designed for absolute beginners to explain the fundamental concepts of the control system engineering. However, to completely benefit from this tutorial, one should have a command over basic subjects like mathematics, basic electrical and electronics engineering, linear algebra, mechanics, signals and systems, and Laplace transforms.

FAQs on Control Systems

In this section, we have collected a set of Frequently Asked Questions on Control Systems followed by their answers −

1. What is a control system?

A control system can be defined as an interconnected group of components or devices that can control and regulate the behavior of other systems or processes according to commands.

A typical control system consists of a variety of sensors, controllers, and other automation devices. The main function of a control system is to monitor the outputs and make the necessary changes in the input to produce the desired outputs.

2. Where are control systems used?

Control systems are integral parts of modern industries. They are widely used in following applications −

• In manufacturing industries for process control and automation.
• In automotives for cruise control, self-driving, auto-breaking, etc.
• In home automation like air conditioners, refrigerators, room heaters, security systems, etc.
• In medical devices like ventilators, etc.
• In power industries for energy generation and distribution automation, etc.

3. What are the four basic elements of control system?

A typical control system has the following four basic elements: Input signals, Process or system to be controlled, Controller to process the input signals and regulate the process, and Output corresponding to the applied inputs.

4. How do control systems work?

The step-by-step working of a typical control system is explained below −

Step 1 − Applying input signals.

Step 2 − Measurement of current state of the process or output of the system.

Step 3 − Comparison of measured state or output with the reference value.

Step 4 − Calculation of error or difference between the reference value and actual output value.

Step 5 − Controller adjusts the process or system output as per the error.

Step 6 − Feedback the new output to repeat the above process again.

5. What is the most common control system?

Closed-loop control system is the most common type of control system used across various industries. This control system is popular because of its ability to auto-correct the errors.

6. How important are control systems?

Control systems are very important in industrial facilities because of the following key reasons −

• They help in error reduction and minimizing the human intervention.
• They improve the quality of output and keep it consistent.
• They reduce wastage of energy and conserve it.
• They improve the safety by introducing automation, etc.

7. What is a simple control system?

A very simple example of a control system is a refrigerator. It has a thermostat to measure the temperature inside the fridge and provides feedback to the control algorithm.

The consumer sets a desired temperature on the thermostat as the input value. If the temperature inside the refrigerator goes beyond the set value, the control mechanism turns off the cooling process.

8. What is the formula for Mason's loop gain?

Mesons loop gain formula is used for calculating the gain of a control system to determine its transfer function. It is given by,

$$\mathrm{T=\frac{\sum_{i=1}^N P_{i}\Delta_{i}}{\Delta}}$$

Where,

• T is the transfer function,
• P_i is the forward path gain of i^th forward path
• Δ_i = 1 [Sum of all loop gains which are not touching the ith forward path]

Δ = Graph determinant and is given by the following formula −

Δ = 1 [sum of all individual loop gains] + [sum of gain products of all possible two non-touching loops] [sum of gain products of all possible three non-touching loops] +

9. What is control system engineering?

Control system engineering is a multidisciplinary engineering branch that deal with the study of design, analysis, and applications of control systems in various industries like mechanical, electrical, electronics, communication, etc.