1. INTRODUCTION

Control– it means to regulate, direct or command

System- it’s an arrangement of collection of things or units collected or related in such a manner to form an entire unit.

Control system- it’s an arrangement of physical components connected or related in such a manner to command, regulate or command itself or another system.

TYPES OF CONTROL SYSTEM

A) In terms of how and who made them

• Man made control system
• Hybrid control system
• Natural control system

Man made control system

These are items of control system which are made by man and rely on man on its operations.

E.g Switch controlling the flow of electricity by switching on and off. The switch controlling the flow of electricity by switching on and off.

Other examples include

• Vehicle
• Euraplane

Natural control system

These are control system that occur naturally.

E.g

1. solar system and stars

2. Many complex systems in the body– An elaborate control system required in the brain to control the body temperature at 37°C despite changes in physical activities and temperature changes.

The eye – The diameter of a pupil adjust to control the amount of light reaching the ratina.

An average human being is capable of performing awide range task including decision making.

This human being may be expected to perform some tasks. This task may be pointing an object or picking an object.

The action of picking or pointing is a biological system consisting mainly eyes,hands and brain.

The input is the present direction of the object w.r.t the reference.

This output is the actual picking of the object.

Hybrid control system

It consists of components that are man made and natural e.g a vehicle being driven by a driver who wants to maintain the position as the car in a particular direction w.r.t the direction of the road.

This painted guidelines on the site of the lane is the input while the output is where the car is heading to and the controls are eyes , brain, hands and legs.

B) In terms of what the system does

• Regulator
• Servo mechanism

Regulator

This is the control system that attempts to maintain the set condition e.g air condition

Servo mechanism

This is the control system that attempts to vary condition in a certain appropriate pattern.

C) In terms of how it perform it task

• Open loop system
• Closed loop system

Open loop control system

These are system where the control action is independent of the action valve or output. i.e

Manual system. The control action in this case is independent of the output of desired.

Input command and hence output has no command on it.

Example of open loop control system

a) Automatic washing machine
b) Coffee or Tea making machine
c) Volume on the stereo system
d) Electric hand drier
e) Bread toaster
f) Inkjet printers
g)Servo motor/Servo motor
h)Electric bulb
I)Clothes drier based on a timer
j)Light switch
k)TV remote control
L)Water faucet
n)Door lock system

Characteristics of open loop control system

1. There is no contrast between real and preferred values.
2. It has no control act on the value of output.
3. Every input setting decides a set operating location for the controller.
4. The changes within external conditions will affect to change the output directly.

Block diagram of an open loop control system

An input signal (I) is applied to the controller whose output (e), the signal actuate the process and tries to drive the control variable (c) to the desired value.

Advantages of open loop control system

• Very simple & easy to design these types of control systems.
• Low cost as compared with other systems
• Less maintenance
• The output is stable
• Very suitable to use
• Convenient operation

Disadvantages of open loop control system

• Any change in any component of a system cannot be taken care automatically.
• The bandwidth is less.
• Inaccurate
• The non-feedback system is not dependable when their output is influenced through some outside disturbances,
• The output differences cannot correct automatically.
• It needs timely recalibration.
• These control systems are more horizontal to errors.
• The changes within the preferred output can be the effect of disturbances.

Applications of open loop control system

• It is used in the controlling system of traffic light
• Immersion rod
• TV remote control,
• Automatic washing machines,
• Heaters in rooms
• Door opening & closing systems automatically.

Closed loop control system

Closed loop system is the one in which the control action also depends on the desired results output in addition to input command.

OR

Is a system that has a feedback loop (or) a control system that uses a feedback signal to generate the output.

Basic block diagram

The controlled signal is feedback and compared with reference input and an actuating signal proportional to the difference of input and output is send to correct the error.

Types of closed loop control system

Positive Feedback Signal
The closed-loop system including a positive feedback signal can be connected to the input of the system is known as a positive feedback system. This system is also named as regenerative feedback.

Negative Feedback Signal
The closed-loop system including a negative feedback signal can be connected to the input of the system is named as a negative feedback system. This kind of system is also named as degenerative feedback. These types of systems are very stable and also enhance strength.

Advantages of closed loop system

• Fast response
• Wide bandwidth
• Facilitate automation
• Reduced effect of disturbance
• Accurate
• Reliable

Disadvantages of closed loop system

• Relatively complex
• Expensive
• It’s potentially unstable under faulty condition
• The control system oscillates sometimes due to feedback signals.
• More efforts, as well as time, are required while designing the system.

Application of closed loop system

• Aircraft control system
• Missile control
• Automatic landing of aircraft
• Radar and gun control
• Machine tool control
• Remote position control
• Process control e.g chemical industries

THE END OF TOPIC ONE