Our daily activities are getting automated every day. Control System plays an important role in making our life automated and modernized. A microwave, refrigerator, an air conditioner, a geezer, an automatic iron, are some examples of a control system. Many engineering fields use control system principle in many applications.
System
It is an interconnection of different physical components which add together as an entire unit to achieve the certain objectives.
Control System
It is an interconnection of physical components to provide the desired function involving some kind of controlling action in it. The typical control system, we may have a controller, process, feedback, etc. In other words, a control system is a mechanism that is capable of altering a future state of a system.
Controller
It is the element of the system which controls the plant or the process.
Types of Control System
1. Open loop Control System
2. Closed-loop Control System
1. Open loop Control System
A system in which output is dependent on input but the controlling action is independent of the output is called an open loop control system.
2. Closed-loop Control System
A system in which controlling action or the input is somehow dependent on the output is called a closed loop control system. Such system utilizes feedback to compare with the actual output to the desired output response.
Advantages of Open Loop Control System
1. It is easy from a maintenance point of view.
2. The problem of stability is not concerned with such system.
Advantages of Closed Loop Control System
1. The accuracy of Closed-loop Control System is always very high.
2. Such system senses environmental changes.
3. Such system reduces the effect of nonlinearity and distortion.
Disadvantages of Open Loop Control System
1. Such system is inaccurate and unreliable.
2. Such system can not sense environmental changes.
3. Recalculation of the controller is necessary from time to time in order to maintain quality and accuracy.
Disadvantages of Closed-loop Control System
1. Such system is complicated and time consuming from a design point of view.
2. They are costly systems.
3. In such system, feedback tries to correct the error from time to time. The tendency to over-correct may cause oscillations without binding in the system.
Disturbance
It is a signal that tends to affect the value of the output of a system. Disturbance created inside the system is called as internal disturbance while an external disturbance is generated outside the system.
Hence disturbances are of two types as
Feedback Control
It is the operation that in the presence of disturbance tends to reduce the difference between the output fed and the reference input. Feedback uses the output of control system as some portion of the input. Feedback is of two types as
1. Positive Feedback
2. Negative Feedback
Positive Feedback reinforces or encourages a behaviour while the negative feedback correct or control the behaviour.
Note: Feedback used in the practical control system is negative feedback. Positive feedback is not used in control system.
Effect of disturbances on Control System
1. External Disturbance Effect
The effect of this type of disturbance on open loop system is 100% of external disturbance i.e. any disturbance entering a system gets completely superimposed on the output.
In closed loop control system, the effect of disturbance is only 1% of external disturbance i.e. the disturbance entering the system causes a very small change.
2. Internal Disturbance Effect
These type of disturbances arises due to change in open loop and feedback transfer function.
The effect of this type of disturbance on open loop system is 100% of internal disturbance i.e. any disturbance due to change in open loop and feedback transfer function gets completely superimposed on the output.
In closed loop control system, the effect of disturbance is only 1% of external disturbance i.e. the disturbance due to change in open loop and feedback transfer function, the system causes a very small change in output.
