Control System - Open loop and Closed loop System

Introduction

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The technological advancement of modern society are majorly based on control system, Control system has a lot to play in things around us with the numerous application with higher efficency and sensitivity, automatic machine are based on control such as the rocket fire, robotics ,aeronautics locomotion ,material handling and a lot more. Control system can also be related to the human structural system, have you every wonder how you could differentiate a cup from a pencil even without looking at it, indeed the human system has been the greatest control system designed by God which can be classified under natural and artificial control system. So in this article, i will be enlightening you more on control systems.

Control System

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The control system essentially consists of various types of subsystem making up a complete system and also a plant which are combined to actually manages and regulates a device's behaviour using different type of control loops. the assembly of these subsystem are as a result of achieving a desired output with a perfect performance, given a specified reference. It collect the input and then operate on it, presenting a desire response called the output, a proper example of the control system is the elevator, imagine you were to be in an elevator going to the fifth floor, then you press on the fifth floor bottom on the first floor which you are in and the fifth floor is your actual place you ought to be, making that your output but acting as a desired response(input), the control system then process the operation and also take in consideration of the performance which are the steady state error and the transient response. In such case of the elevator, both the safety,patience and comfort of the passenger is to be considered, the transient response is a function of both the passenger comfort and patience, this means that the patience and comfort of the passenger depends on the transient response while the safety of the passenger is dependent upon the steady-state error. Control systems are adequately useful in perfecting safety, production and also efficiency in numerous area, having multiple use in the nuclear power plants and even more.

Advantages Of Control Systems

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It is very clear this days how technology has really improve the life of humans, seeing and making things that seems impossible to be possible, most advance technological equipments works under this control system, control systems has gone so advantageous that humans do not have to bother about carrying or moving large equipment because these things can now be done with precision. With the help of control systems in elevators, humans can move quickly to their various destination and this is done automatically, you might be thinking how satellites are being control in space, this is also done with the help of control system. On earth, one can also receive radio signals with antennas to the farthest point of the universe and also speed and position can be controlled with control systems. Majorly; control systems are built to account for four reasons and they are:

● Remote control.

●Amplification of power

●To compensate disturbance

●For convenience

Remote control

There are some places that humans are not advised to go to due to the dangerous nature of that location which are contaminated as a result some nuclear explosion, making the environment radioactive and in such a situation, robots are designed with the help of control system and these robots are assigned to such location to either pick up materials from there or to carry out some important survey of the environment.

Amplification Of Power

Most electrical and electronics devices require a large amount of power for a better achievement in the output but sometimes the input power is not enough to achieve that but with the help of control systems assembled together to attain the desired power for the output to function well and this process account for power amplification.

Compensation for disturbances

Most devices are not limited to disturbance, just like the antenna that has been positioned to receive signal from the satellite at a particular angle to the satellite, knowing fully well that it actually take that position to obtain the required information or signal from the satellite but the antenna can be affected by the forces in wind or noise internally which will definitely change the position of the antenna and result to improper information but with the help of the control systems designed in a way that when ever such disturbances occur, the system will itself take note of the amount of disturbances and then correct it which means that no matter what kind of disturbances, the antenna will still get the required information from the satellite.

Convenience

To get any form of output of your taste, all you have to alter is the input, just like the thermostat which works on temperature control and having position as the input and heat as the output, so to have a desire output, you need to change its position.

System Configurations

There are various types of configuration but in this article, i will be talking more on just two which can be considered as the internal architecture of the control system and these two system configuration are

● Open loop systems

● Closed loop systems

Open Loop Systems

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The open loop systems also referred to a non-feedback system, made up of various subsystem, starting from the input which is also referred to as reference and this input comes in through the input transducer, the input transducer convert any form of the input to that required by the controller and this controller drives the physical system called the plant/process and then you get your output which can also be referred to as controlled variable. Both the controller and process output are connected via summing junction to a signal which is seen as disturbances and this disturbance can not be accout or compensated for in the open loop system, no correction to disturbances can be made and this type of systems are being controlled by the input, the disturbances also affect the plants and causes instability in the system. It happened to me during my preparation for my second semester examination in my school in a course called CVE, three weeks to the exam, I had already prepared a roster for reading and to cover all part being thought by the lecturer just to obtain an A for the course but to my greatest surprise, the lecturer just came two weeks to the exam to Bring up a new topic to study and at that point, i became an open loop system because I couldn't compensate for the disturbance which was the new topic that the lecturer brought and this topic came out as a compulsory question in the exam, this resulted in me not getting an A in the course.

Closed Loop System

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Major set backwardness in the open loop system, was the inability to compensate and account for disturbances which can alter the transmission. In the closed loop systems which is also referred to as feedback control systems have a design that is not far different from the open loop system, in that the closed loop system has an additional output transducer which is connected from the output of the control system to a summing junction which is placed between the input transducer and the controller. The input and output signal are added up algebraically by the first summing junction, this summation returns from the output to the summing junction through the feedback and in this case, the output signal is then substrated from the input signal and this happens, it's referred to as Actuating signal but in a case where both output transducer and also the input transducer have same unity gain then the actuating signal's value will be the actual difference of the input and that of the output and when this occur, the actuating signal will be referred to as Error. With the design of this system, disturbances can be compensated for through the feedback measurement of the output and compare it with the input at the summing function but if there is any difference in the two signal response, the system then drives the process through the actuating signal, in other to compensate and make correction else the system see no reason in driving the process.

Advantages Of Closed Loop System Over The Open Loop System

● The operation of a closed loop system is more accurate and robust when compared with the open loop system and this is as a result of the complex construction.

● Due to the Feedback mechanism,the closed loop systems are able to eliminate any form of errors between the output and input of the system.

● The closed loop systems improve performance and provide less sensitive to unwanted signal called noise.

● The closed loop system can compensate for disturbances which occur at the summing junction.Both steady state error and transient response can be controlled.

Advantages Of Open Loop System Over The Closed Loop System

● The Open loop systems are more simple in construction than the closed loop systems.

● More economical, which means that they are cheaper compared to the closed loop system.

● More stable than the closed loop systems.

In this modern days, most control systems are being controlled by the use of computer and this enhance the control and compensation of many loop by using same computer, changes are mostly done in the software rather than the hardware.

Objectives in system control

The two major objectives to consider when carrying out a control system are the Analysis And Design, in the analysis objective, the performance of the system can be determined just like in the case of system performance specifications, one has to check if the steady state error and transient response meets the desired specifications of the system. While in the case of Design objective, the performances of the system can be altered. For example if taking consideration of both the transient response and the steady state error and found out that they don't meet the system specifications, you can chosen to make changes in the parameters just to ensure its meet the desired system specifications.

A typical Control system.

The major elements of control systems are the

●Plant/Process

●Actuator

●Sensor

I will explain those elements in relation to the control system of a car, the plant is the physical system of which one can alter while the actuator is just like the engine of the car which generate the forces that will enable you achieve what you want and it is desired to be of right size and have a minimum wave effect to hysteresis and also backlash of the system and also the sensor act as the speedometer, tachometer of the car (it is always desired that the sensor is reliable and accurate).

Stability

The response of any control system is as a result of both the forced response and natural response which is referred to as the total response of the system and with the idea of these responses, you can explain the stability. The discussion of both the steady state error and transient was as a result of instability of the system. The gain and loss of heat is being described by the natural response and this is dependent on the system, not the system input while the forced response depends on the system input rather than the system on his own.

Total response = Forced response + Natural response

A better control system is only obtain when the natural force is equal to zero and doesn't occur in the system, knowing fully well that if the natural response is too much thus this will result to instability of the system and could lead to self destruction of the system, same as when the transient response is too high and when it dies out, leaving just the steady-state error which then becomes the difference between the input of the system and the output of the system.

Steady-state error = Input - Output.

Step To Consider In Designing a Control System

Step 1 Determine the system requirements and the equipment needed.

Step 2 Determine a physical system.

Step 3 Draw the functional block diagram for the system.

Step 4 Obtain the mathematical model for the system schematically.

Step 5 Make a reduction of the block diagram.

Step 6 Analyze if the system meets the requirements and specifications.

Summary

In this article, we have seen the usefulness of a control system and knowing fully well that mostly everything we find around us are based on control systems, the human system is a good example of a control system although complex but accurate. We went further to see two major type of system configuration of a control system which are the open loop system and the closed loop system, seeing also the advantages over each other. Stated clearly well the objectives of the control system and finally the steps to take when designing a control system.

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Reference.

● Wikipedia

●Control_System_Engineering_Norman_S._Nise

●Lecture Note.

● www.electronics-tutorials.ws

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thanks to dave for the gif