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Table of contents
1.
Introduction
2.
What is Control System?
3.
History of Control System
4.
Example of Control System
5.
Features of the Control System
6.
Importance of Control System
7.
Types of Control Systems
8.
Discrete-time Control System
9.
Continuous Time Control System
10.
Open-loop Control System
10.1.
Example of the open-loop control system
10.2.
Block diagram of an Open-loop Control system
10.3.
Advantages Of Open-loop Control System
10.4.
Disadvantages of Open-loop Control System
11.
Closed Loop Control System
11.1.
Example of a Closed-loop control system
11.2.
Block Diagram of Control System
11.2.1.
Feedback in the Closed Loop control system
11.3.
Advantages and Disadvantages of Closed-loop System
11.3.1.
Advantages 
11.3.2.
Disadvantages
12.
Differentiate between Open and Closed-loop Control Systems
12.1.
Comparison Basis
12.2.
Open-Loop System
12.3.
Closed Loop System
13.
SISO and MIMO Control System
14.
Applications of Control System
15.
Advantages of Control System
16.
Limitations of Control System
17.
Frequently Asked Questions
17.1.
What are the 3 elements required in the control system?
17.2.
How does a control system work?
17.3.
What is a closed-loop control system?
17.4.
What is feedback in a closed-loop control system?
18.
Conclusion
Last Updated: Mar 27, 2024
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What is a control system?

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Introduction

What is a control system?

Do you know what control systems are? Have you ever wondered exactly where we use it in our day-to-day lives and the control system's history? If not, then don’t worry. We will explain exactly what it is used for and its usage in our lives. Control systems are a central part of industry and automation, which provide the desired response by controlling the output. Control systems are essential for improving efficiency, safety, and quality. It is used widely in industries and has many applications.

In this article, we will discuss about the complete introduction to control system, its applications, importance, different types, advantages, and disadvantages. We will also discuss about open and closed-loop control systems and the feedback concept used in the closed-loop control system.

What is Control System?

A control system manages, directs, or regulates the behavior devices. It is designed in such a way that it monitors and controls the output of a process or system to give the desired result. Control systems are computerized. They are a central part of industry and automation, which provide the desired response by controlling the output. This system is a set of mechanical or electronic devices that regulates other devices or systems through control loops.

They involve sensors, actuators, controllers, and communication systems. Actuators are involved in controlling the output of the system. On the other hand, sensors measure various parameters related to the process, while Controllers process sensor data and determine the proper control signals to send to the actuators.

Therefore, control systems maintain the efficient and effective operation of various processes and systems. They also have multiple applications, for example, transportation, energy production, and communication systems. They are classified into two categories that are: open-loop and closed-loop systems. The Open-loop control system is the system where the output is not fed back to the input for comparison and correction. The control system, where the output of the system is fed back to the input through a feedback loop, is called a closed-loop control system. 

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History of Control System

  • Control systems have been believed to be used since ancient civilizations. Back in ancient times, humans first began using devices and mechanisms to regulate the behavior of physical systems. For example, water clocks were used in ancient times, mostly in Egypt and China, for measuring time and controlling water flow in an irrigation system.
  • In the late 18th and early 19th centuries, during the Industrial Revolution, there was a need for better and more efficient control over machines and manufacturing processes, which led to the development of automatic control systems. One earliest example was the centrifugal governor. It was invented by James Watt in 1788. This was used to regulate the speed of steam engines.
  • At the beginning of the 20th century, known as the golden age of control engineering, there were significant advancements in control theory due to the development of electrical engineering and the invention of feedback control systems. Norbert Wiener, in the 1920s, developed the first mathematical models of control systems, and Harlod Black, in 1927, introduced the concept of closed-loop control systems.
  • Control systems were widely used in military applications in World War II. Control systems were used for guns and anti-craft systems. When the world war ended, the field of control systems was revolutionized by the development of computers and digital technology. This enabled more complex and sophisticated control algorithms and systems.

In today's scenario, control systems are used widely in fields from aerospace and communication systems to manufacturing transportation.

Also see, Difference Between Verilog and Vhdl

Example of Control System

Control systems is widely used in our daily lives. Some examples of everyday life applications of control systems are as follows:

  • Thermostats: are the control systems used to regulate the temperature of a room or building. It senses temperature and turns the heating or cooling system on or off to maintain the desired temperature.
  • Automatic Washing Machines: Washing machines use control systems for regulating the water level, cycle time, and temperature.
  • Cruise Control: A control system maintains constant speed in automobiles.
  • Home Security Systems: Control systems are used in monitoring and controlling various aspects of home security—for example, motion detectors, cameras, and door locks.
  • Elevators: Control systems are used in elevators to regulate speed, acceleration, and braking.
  • Power grid control systems: Power grid control systems use control systems to regulate electrical power generation, transmission, and distribution. This ensures a reliable and stable supply.
  • Automatic coffee maker: They use control systems for regulating water temperature, coffee strength, and brewing time. All these properties help in achieving desired flavor and aroma.
  • Anti-lock Braking System (ABS): ABS is a control system that prevents the wheels from locking during braking. This control system senses wheel speed and adjusts the brake pressure accordingly. This prevents skidding and improves stability.

Features of the Control System

Some standard features of control systems are as follows.

  • Input and Output: Every control system has input and output signals. The input signal is designed to control or regulate. On the other hand, the output signal is the system’s response to the input signal.
  • Feedback: It is an essential part of control systems, which involves measuring the output signal and using it to adjust the systems’ input to maintain the desired output.
  • A control algorithm is a set of instructions for determining how the system processes the input signal to produce the desired output. This algorithm can be designed using empirical testing, mathematical modeling, and machine learning techniques.
  • Sensors and actuators: These are the devices used for measuring the input signal and, in turn, for producing the output signal. They convert the physical or electrical quantities into signals the system can process. Actuators convert the system’s output signal into physical or electrical actions.
  • Control modes: Control systems can perform in various control modes, for example, open-loop control,closed-loop control, and feedforward control. They determine how the system processes input signals to produce the desired result.
  • Stability and performance: Stability means the system’s ability to maintain the desired result without any instability or oscillations, while performance means achieving the desired output efficiently and accurately.
  • Dynamic response: Whenever there are changes in the input signals, the system responds to those changes, so the dynamic response is how the system responds to those changes. If the control system is fast enough, the response can quickly adjust to changes in input signals. On the other hand, the control system, which has a slow dynamic response, takes a little longer to adjust.

Importance of Control System

Control systems are necessary for several reasons, some of which are as follows:

  • Automation: Automation is enabled by the control system in many commercial, industrial, and residential processes. They are efficient in reducing human intervention.
  • Improved performance: Control systems are very helpful in improving process performance. To achieve the desired result, it regulates and optimizes the input signals.
  • Predictive maintenance: The predictive maintenance technique helps determine the service-equipment condition for estimating when maintenance will be performed. Control systems are helpful in such processes by monitoring equipment performance and predicting when maintenance is required.
  • Safety: Control systems are instrumental in improving many processes. They help in regulating and optimize input signals for achieving desired outputs.
  • Consistency: They can ensure consistency in processes. The control system maintains a set of desired parameters/outputs over time.
  • Scalability: Control systems can be designed for scaling to larger or more complex systems. They also ensure that efficiency is not decreased and results in productive output.
  • Consistency: The control systems ensure consistency is maintained in the processes. They maintain the set of outputs or parameters over time.

Types of Control Systems

There are many types of operating systems. Some of the common types of control systems are mentioned below:

Open-loop control systems: These systems do not use feedback for adjusting outputs. Open-loop control systems rely on pre-determined input signals for producing the desired output.

Closed-loop control systems: Closed-loop systems continuously measure and compare the system's output to the desired outputs. The input signal is then adjusted accordingly. These systems, also known as feedback control systems, use feedback to adjust their outputs.

Linear control systems: Linear control systems show linear behavior. This means that the output is directly proportional to the input.

Non-linear Contol systems: Linear control systems show non-linear behavior. This means that the output is not directly proportional to the input.

Digital control system: These control systems use microprocessors or computers to control the system.

Optimal control system: Optimal control systems optimize performance criteria, like minimizing cost or maximizing efficiency.

Discrete-time control system: Discrete-time control system operates in discrete time. That means the inputs are processed, and the output is produced at a specific, discrete time interval.

Continuous time control system: A continuous-time control system operates on continuous time signals. That means the inputs are processed, and the output is produced continuously over time. 

Discrete-time Control System

Discrete-time control system operates in discrete time. That means the inputs are processed, and the output is produced at a specific, discrete time interval. A discrete time control system Operates on sample data instead of continuous signals. They are implemented using microprocessors or digital computers. This control system can process digital signals and perform mathematical operations on them.

Discrete-time control systems prove to be advantageous over continuous-time control systems. The advantages include using digital signals processing algorithms for control, filtering, and other applications. But they also have some disadvantages, such as aliasing and sampling errors.

Continuous Time Control System

A continuous time control system operates on continuous time signals. That means the inputs are processed, and the output is produced continuously over time. They are commonly used in various engineering applications, such as industrial control, communication, and power systems. Continuous time control systems operate on analog signals instead of sampled data. The input signals are produced using mathematical algorithms such as transfer functions, differential equations, or Laplace transforms for producing desired output signals.

One advantage of a continuous-time control system over a discrete-time control system is that a continuous-time control system processes signals with high accuracy and precision. Also, the signals are operated in real-time. But, they also have a few disadvantages, including noise, difficulty implementing complex control algorithms, and interference in the analog signals.

Open-loop Control System

The Open-loop control system is the system where the output is not fed back to the input for comparison and correction. Therefore the control action is not influenced by the output of the system. The system operates based only on the input command. They do not require sensors or feedback mechanisms. These control systems are being used in applications where there is no compulsion for precise or critical output. Open-loop control systems are simple and prove to be inexpensive in implementation.

They are widely used in washing machines with a timer. The duration of the washing machine is controlled by a timer. The machine operates according to the preset time, i.e., without any feedback from sensors or the users. In addition to their use in washing machines, they are widely used in many industrial applications, like conveyor systems or assembly lines. Also, note that an external disturbance cannot affect the output. But in many use cases, closed-loop control systems are opted for due to their flexibility, efficiency, and greater accuracy.

Example of the open-loop control system

  • There are many examples of open-loop control systems. A typical example of an open-loop control system is a toaster. We know that toasters are used to toast bread slices. Most toasters have timers controlling the duration of the toasting cycle. The user sets the desired toasting time according to their needs. The toaster operates at a preset time without any feedback from sensors or users.
  • The toaster hets the bread cycles during the toasting cycle. Based on the selected time by the user, the heating elements are energized for a fixed duration. Therefore the slices are toasted according to the desired level.
  • The sensors do not need feedback to adjust control action as the toaster operates according to the fixed heating duration. The toaster simply follows the preset time and heating duration. 

Block diagram of an Open-loop Control system

block diagram of an open loop control system

Advantages Of Open-loop Control System

There are several examples of Open-loop control systems, some of them are mentioned below:

  • Open-loop control systems are easy to design.
  • They have an easy implementation.
  • The open-loop control system can be used for controlling high-speed systems that require a quick response.
  • They are comparatively low in cost and easy to maintain.
  • Not much processing is required in an Open-loop control system.
  • Open-loop control systems are used where there is a little compulsion for high accuracy and precision.

Disadvantages of Open-loop Control System

Some of the disadvantages of open-loop control systems are mentioned below:

  • The performance of the open-loop control system can be affected by external factors such as noises, environmental variations, or disturbances.
  • They are not adjustable to changes in the system. These changes include degradation, wear, and tear, or aging.
  • As they cannot adapt to environmental changes, they cannot be used in complex control applications.
  • Open-loop control systems cannot correct errors, nor can they compensate for the changes in the system.
  • They cannot provide feedback on the actual output or performance.
  •  The open-loop control system is unsuitable for high accuracy, stability, and precision applications, such as medical science or aerospace.

Closed Loop Control System

The control system where the output of the system is fed back to the input through a feedback loop is called a closed-loop control system. They are also known as feedback control systems. This control system is continuously involved in monitoring and adjusting its performance according to the difference between the actual output and desired output.

Error signal means the difference between the actual output and desired output. The closed loop signal compares the input signal with the output signal, and the error signal is used for adjusting the system’s operation.

The controller generates a corrective action when the error signal is fed to the controller. Then this corrective action is applied to the system’s input to bring the output closer to the desired setpoint or reference signal. One of the specialties of closed-loop control systems is that they can be designed to be flexible and adaptive if we incorporate them with advanced algorithms, actuators, and sensors.

Example of a Closed-loop control system

  • Closed-loop control systems, for example, in-home thermostats, are often used in our day-to-day lives. The thermostat sends a signal to the heater to turn it on or off. Temperature sensors are used for detecting the current air temperature. The heater is turned on when the temperature is below the set point.
  • Closed-loop control systems are used in water level controllers. Input water decides the level of water.
  • The speed of the motor can be controlled using the current sensor. The motor speed is detected by a sensor, and feedback is sent to the control system to change the speed.
  • Another example of a closed-loop control system includes electric iron that can be controlled automatically by heating the elements' temperature in the iron.

Block Diagram of Control System

block diagram of closed loop control system

Feedback in the Closed Loop control system

Feedback is the process of sensing the output or behavior and feeding it back to the control system's input. Feedback is needed to modify or adjust the control action.

Feedback in the control system occurs when withering the output is returned to the input side and utilized as a part of the system input. The feedback is used for adjusting the control action according to the difference between the setpoint and feedback signal. Feedback plays an essential role in ordering and improving the performance of the control systems. There usually are two types of feedback.

These are positive and negative feedback.
 

Positive feedback:

The reference input R(s) and feedback outputs are added in Positive feedback.

The transfer function of positive feedback is T=G/1-GH.

Where T = transfer function or overall gain of negative feedback control system

G= open loop gain, it is a function of frequency

H=gain of feedback path, it a function of frequency


Negative feedback:

In negative feedback, the error is reduced between the reference input, R(s), and the system output.

The transfer function of the negative feedback is T=G/1+GH.

Where T = transfer function or overall gain of negative feedback control system

G= open loop gain, it is a function of frequency

H=gain of feedback path, it a function of frequency.

Advantages and Disadvantages of Closed-loop System

The advantages and disadvantages of closed-loop system are as follows.

Advantages 

Disadvantages

  • A closed-loop control system allows regulation and monitoring of motor output
  • A closed-loop control system allows regulation and monitoring of motor output.
  • They help provide the required amount of control

 

  • They help provide the required amount of control

 

  • This type of control system proves to be more accurate even in non-linearities
  • This type of control system proves to be more accurate even in non-linearities

 

  • The closed-loop control system’s stability can be made small to make the system more stable.
  • The closed-loop control system’s stability can be made small to make the system more stable.

 

  • Closed-loop control systems are less affected by noise.sd
  • Closed-loop control systems are less affected by noise.

 

  • A closed-loop control system can handle uncertainties
  • A closed-loop control system is more difficult to troubleshoot.

Differentiate between Open and Closed-loop Control Systems

Comparison Basis

Open-Loop System

Closed Loop System

Definition Open-Loop System is a control system where control action is free from output

Closed Loop System is a control system where control action is dependent on output

 

Also Known As a Non-feedback system Feedback system
Construction Open-Loop System has simple construction Closed Loop System has complex construction.
Components Open-Loop System contains a controller, and the controlled process has components. Closed Loop System contains an amplifier, controller, controlled process, and feedback as its components.
Stability Stable Closed Loop Systems are less stable
Accuracy The accuracy of an Open-Loop System depends on calibration. Closed Loop Systems are accurate due to feedback.
Response Open-Loop Systems have a fast response Closed-Loop Systems have a slow response.
Calibration is complex in Open-Loop Control Systems. Calibration is easy in Closed Loop System
System Disturbance Open-Loop control Systems are affected by system disturbance. Closed Loop Systems are not affected by system disturbances.
Linearity In terms of linearity Open-Loop Control Systems are non-linear. In terms of linearity, Closed Loop Systems are linear.

Reliability

 

Open-Loop control Systems are non-reliable. Closed Loop Systems are reliable.
Examples: TV remote, washing machine, immersion rod, etc. A temperature control system, toaster, pressure control, etc.

SISO and MIMO Control System

SISO refers to Single Input, Single Output, while MIMO refers to Multiple Input, Multiple Output. These are the two types o control systems used in control theory.

SISO is a simple single-variable control system that has one input and one output. They are typically less complex than the MIMO control system. With SISO, making an order of magnitude or trending predictions is easier. SISO is the simplest and most common system type. SISO has a more straightforward implementation. An example of SISO is the thermostat.

A MIMO system uses multiple sensors and actuators.MIMO is a more complex system than SISO. It is used in advanced applications like robotics and aerospace. They are also more challenging to design and implement and can take multiple interactions, which enables precise and efficient control.

Applications of Control System

There are many applications of the control system. A few of them are listed below:

  • Control systems are widely used in the industrial automaton.
  • Control systems are used to control the movement and behavior of robots. Therefore they are widely used in robotics.
  • They are also used in aerospace and for regulating the operation of aircraft, missiles, and spacecraft.
  • They help control parameters like direction, speed, and stability.
  • Control systems have wide usage in the field of biomedical as well. They are used for regulating the operations of medical devices and equipment.
  • Control systems are also used in communication systems for regulating transmission.

Advantages of Control System

There are several advantages of control systems few of them are listed below:

  • Control systems help regulate and optimize the operations of machines and processes.
  • Control systems help monitor and adjust machine performance and processes in real-time.
  • They can also be programmed to adapt to change conditions and requirements.
  • Control systems provide greater flexibility and responsiveness.
  • Control systems are also used in data collection and analysis on machine performance and process parameters.
  • Control systems provide valuable insights required for process improvement and optimization.

They can also be integrated with other systems like sensors, data analysis tools, or actuators, which provide comprehensive and efficient systems.

Limitations of Control System

We know that there are many advantages to the control system. But they also need to know that they also have some limitations. Some of them are listed below.

  • Control systems are complex.
  • They are challenging to design and maintain.
  • As they are designed to control only a specific process. They may have limited flexibility.
  • Control systems are expensive in implementation and maintenance.
  • As they require regular maintenance and troubleshooting for proper functioning, they can also be time-consuming and expensive.
  • If the control system fails, it can pose safety risks. Their failure can lead to accidents and other hazardous situations.

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Frequently Asked Questions

What are the 3 elements required in the control system?

he three components that a control system must have are an error detector, controller, and output element. 
The system's error detector measures the difference between the desired and actual outputs. The controller decides how to modify the output, and the output element modifies the output.

How does a control system work?

A control system operates by contrasting the desired and actual outputs. The error is defined as the discrepancy between these two values. After that, the controller utilises this error to decide how to modify the output to lower the error.

What is a closed-loop control system?

The control system where the output of the system I fed back to the input through a feedback loop is called a closed-loop control system. They are also known as feedback control systems. This control system is continuously involved in monitoring and adjusting its performance according to the difference between the actual output and desired output.

What is feedback in a closed-loop control system?

Feedback is sensing the output or behavior and feeding it to the control system's input. It is needed to modify or adjust the control action. Feedback in the control system occurs when withering the output is returned to the input side and utilized as a part of the system input. 

Conclusion

We hope this article helped you understand the complete introduction to control system. We have discussed the control system's applications, importance, different types, advantages, and disadvantages. We have also discussed open and closed-loop control systems and the feedback concept used in the closed-loop control system. We have discussed examples, block-diagram, and advantages and disadvantages of open and closed control systems. We have also discussed about SISO and MIMO control systems. In the end, we have discussed the applications and limitations of the control system.

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