CHAPTER 1 : INTRODUCTION TO CONTROL SYSTEM

 WHAT IS CONTROL SYSTEM ?

Nowadays a lot of control systems lead to Automation Control System. Where have we gone, we are surrounded by such systems in the home, on the street, in vehicles and buildings. In industry, the automation control system is very necessary because it can improve the quality and increase productivity. Therefore, this automation control systems greatly affect the future way of life.



1.  ELECTRICAL CONTROL

          Electric control system is a control system which uses electric current whether direct current (DC) or current shuttle as supply source. Electrical control system is current law and Kirchoff voltage law. Kirchoff current law (the law of nodes) states that the algebraic sum of all currents entering and leaving a node is zero. Kirchoff's Law (Law loop) state in any instant the algebraic sum of the voltages around any loop in a circuit is zero. A mathematical model of the electrical circuit can be obtained using one or both of the Kirchoff laws. The studied electrical control system involves a resistor, capacitor, inductor and amp.

Figure1.1: Electrical control system Block diagram

2.  PNEUMATIC CONTROL

          Pneumatic system is deployed using pressurized air media. Continuous development of technology has seen a drastic development in low-pressure pneumatic control systems for industrial control systems. In between is included blast-resistant features, simplification and easy maintenance. Today, planning and development in the field of automation allows the system to operate to replace human labor. 

Use of Pneumatic Systems 

i. industrial processes 

ii. Position and speed control system 

iii. The braking system of vehicles, horns and stamping 

iv. Water spraying systems, elevators and automatic doors

Figure1.2: Pneumatic control system Block diagram

3.  HYDRAULIC CONTROL

           Compressed air is rarely used for continuous control of movement of the device that has mass range due to the load from the outside, except for the low-pressure pneumatic controller. In this case the hydraulic control system is usually preferred. In engineering, the term describes the hydraulic fluid systems that use oil.

Hydraulic control system is a system which uses fluid to generate force / energy to carry out work. Hydraulic system many in use in automobile industry like power system, system brake, crane, jack car,satellite and so on. Fluid that commonly used is oil.

The use of hydraulic circuits in machine tools, aircraft control systems and similar operations occur because of factors such as positivity, accuracy, flexibility, weight ratio of high horsepower fast start, stop and reverse the lancardan accurate and facilitate operations. The combination of electronic and hydraulic systems are widely used because it combines the advantages of both control and hydraulic power. 

Use of Hydraulic Systems 

i. Power steering and braking systems on vehicles 

ii. The mechanism driving the big ships 

iii. Machine control system

GENERAL TERMS USED IN CONTROL PROCESS

 In this section we will give focus on terms that commonly used inprocess control.

1.  System : An interconnection of elements and devices for a desired purpose

2.  Process : The device, plant, or system under control.

3.  Feedback control system : Feedback control system is a system where product always compared with entry set point and difference between value made foundation for control.

4.  Servo control : Servo control is a feedback control system where the product is position, velocity or acceleration.

5.  Dynamic variable : Dynamic variable is physical any parameter that variable the value spontaneously or through external influences.

6.  Error signal : Difference between entry signal and feedback signal/product.

7.  Process compound variable : process compound variable is process which contains more than one variable. 

8.  Controller : Device which control process certain system and acts against error signal to reduce error to product like is wanted.

 

 

Figure 2.1 : General Terms in Block diagram

Basic Process Control System 

It is a system which handles process control and monitoring for the facility. It will take inputs from sensor and process instruments and provide output based on control functions in accordance with approved design control strategy.

Typically, Basic Process Control System  performs the following functions:

§  Control the process within pre-set operating condition, optimize plant operation to produce a good quality product and attempt to keep all process variables within its safety limit. 

§  Provide operator interface for monitoring and control via operator console (Human Machine Interface) .

§  Provide alarm/event logging and trending facilities.

§  Generate production data report.

LEVEL CONTROL SYSTEM IN  WATER TANK 

Float liquid level switch are based on the principle of buoyancy and static magnetic fieldThe position of floating ball 

with magnets (float) in the measured medium is affected by buoyancy effect.The change of liquid level lead to the change of the magnetic float position.

The magnet in the float ball and sensors (magnetic reed switch) interact and product switch signal.

application:

Used in petroleum, chemical industry, electric power, textile printing, environmental protection, civil construction 

and so on all sorts of exposure or airtight container liquid level control and alarm.

Block Diagram of the modal above :

OPEN LOOP SYSTEM:

An Open loop System is athe control system without feedback . These systems do not have any any portion of output feedback to the input for comparison and measurement. The components of these system are: input, processing system and output.

Block Diagram Of Open Loop System

CLOSED LOOP SYSTEM:

These system are also known as the system with feedback.In this system a portion of output is feedback to the input side which is compared with the reference element and thus the error occurred at that time is filtered out and output is desire output. The components of these system are: input, reference element,controller, processing system and output.

Block Diagram Of Closed looop system 

ADVANTAGES OF OPEN LOOP SYSTEM AND CLOSED LOOP SYSTEM

OPEN LOOP SYSTEM	CLOSED LOOP SYSTEM
They Reduces the effect of non linearities	They reduces the effect of non linearities
They are economical in nature	They are less economical in nature
Have stability problem	These system are highly stable