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INTRODUCTION TO AUTOMATION SYSTEM
UNIT 1
STUDENTS LEARNING OUTCOME
At the end of the lesson, students will be able
to define industrial automation system.
to explain fixed/hardwired automation.
to explain programmable automation.
to compare fixed/hardwired automation to
programmable automation from the points of
flexibility, economy, space needed and ease of
maintenance.
Industrial automation systems
Automation systems used in industrial such as robotic arm, electro-pneumatic system and others to increase product
quality, productivity, reduce production cost and reduce intervention of human in
the process of production.
manual
automation
Fixed /hardwired automation
● In fixed/hardwired automation, the control logic functions are determined by the way devices are electrically interconnected.
●Hardwired logic can be implemented using relays and relay ladder schematics
●Hardwired control logic also can be implemented by using logic gate.
Logic gate implementation have the advantages over relay logic in term of space utilisation, less wiring requirement and more economical.
Implementation using gate
Programmable automation
In Programmable automation, the control function of the system is determined by software implemented through embedded system, computer or PLC ( programmable Logic Control )
Replace by software
Comparison between hardwired and programmable automation system
Hardwired automation
• Too many wiring work in the Panel
• Difficult to modify and make changes
• Difficulty in troubleshooting
• Due to difficulty in troubleshooting and drawing update,
machine down time is longer
• High power consumption as many relays are used
Comparison between hardwired and programmable automation system
Programmable automation• Wiring of the system usually reduces by 80% compared to hardwired control
system• Power consumption is greatly reduced.• Self diagnostic function enable easy and fast troubleshooting of the system• Flexible. Control sequence can be changed by reprogramming.• Faster response time• More robust and reliable because less moving part• Modular design- easy to repair and expand.• Less expensive• Hardcopy of documentation can be easily printed out and maintained.
UNDERSTAND RELAYS, CONTACTORS,
ELECTROMECHANICAL TIMER AND ELECTROMECHANICAL
COUNTER
Section 1.2
STUDENTS LEARNING OUTCOME
At the end of the lesson, students will be able
To draw symbol and structure, to explain the operation
and application of relay.
To draw symbol and structure, to explain the operation
and application of contactor.
To draw symbol and structure, to explain the operation
and application of timer.
To draw symbol and structure, to explain the operation
and application of counter.
Although PLC has replaced much of the relay control logic, electromagnetic relays are still used as auxiliary devices to switch I/O field devices
RELAY
Relay ladder diagram symbol Electrical symbol for relay
• An electrical relay is a magnetic switch. It uses electromagnetism to switch contacts.
• A relay will usually have only one coil but may have any number of different contacts.
• The contact can be single pole single throw (SPST), single pole double throw (SPDT) double pole single throw (DPST) , double poles double throw (DPDT) or more than 2 poles double throw.
Operation
• With no current flow through the coil (de-energized), the armature is held away from the core of the coil by spring tension.
• When the coil is energized, it produces an electromagnetic field. Action of this field, in turn, causes the physical movement of the armature.
• Movement of the armature causes the contact points of the relay to open or close.
• The coil and contacts are insulated from each other: therefore, under normal conditions. no electric circuit will exist between them
START
STOP
X1
X2
X1 X2
Y
Y
Y
Application example
Start /stop control of motor
CONTACTOR
Power Contacts
Electromagnetic coil
power Contacts
power Contacts
NC auxiliary Contacts
NO auxiliary Contacts
• Contactor works like a relay except that it can handle a much higher current at its contacts.
• It is usually operated by AC voltage applied across it magnetic coil.
• Other than the power circuit contacts for connecting the controlled device such as motor to the 3 phase lines, it also has auxiliary contacts ( consist of NC and NO type )for building control circuit.
Controlling a high current pump by PLC through a contactor
Since PLC output only capable of handling low current, a contactor is needed to interface the pump to PLC
The output of PLC is connected in series with the coil to form a low current switching circuit.
The contacts of the contactor are connected in series with the pump motor to form a high-current switching circuit.
Application
3 phase motor forward reverse control
Power circuit Control circuit
Forward: A1 , B2, C3Reverse : A2, B1, C3
Application
OL overload protection
relay
OL heater coil
OL contact
ApplicationOL heater coil
OL contact
heater coils are connected in series with the motor winding
If the motor draws excessive current from the main, temperature on the heater raises and triggers the OL relay
The contact of the OL relay then cuts off the supply to the contactor coils in the control circuit.
the contactors de-energize and disconnects the motor from the main supply
Application
When forward button is pushed
Contactor M1 is energized
When forward button is release
Contactor M1 is latched through its’ own contact M1.
Power contacts of M1 close, connect A,B,C to 1,2,3 respectively This contact opens to present motor
from changing to reverse mode when reverse button is pressed. This precaution is called interlock
Motor can be stopped by pressing this stop button
When reverse button is pushed and released
Contactor M2 is latched through its’ own contact M2.
Application
Power contacts of M2 close, connect A,B,C to 2,1,3 respectively
This contact opens to present motor from changing to forward mode when forward button is pressed. This precaution is called interlock
Timer connection Coil symbol
on relay
off relay
Timer
Contact symbol
Introduction
• A timer can provide a delay in time operation.
• Usually the duration of delay can be adjusted by changing the dial setting.
• The most commonly used timer are the on delay timer and off delay timer
• An on delay timer’s contact would not operate until a preset delay time has elapsed after it is energized,
• An off delay timer’s contacts will immediately operate and stay in this active state once it is energized
• But its’ contacts will only deactivate after a preset time has elapsed once it is de-energized.
Motor driven cam timer
In most industrial and factory applications, electromechanical timers are driven by a synchronous motor that turns the cam through the switch contacts.
Application example
Star-delta motor starter
• Induction motor when started from stall , draw high current from supply. cause disturbance to main supply
• Once move at rated speed, current reduces to normal; very much smaller than the starting current.
• To avoid this situation,
– apply lower voltage during start
– Apply normal voltage after motor run steadily – after a few second
• One method of doing it is by using star connection at start and switch to delta connection for the motor winding after a few seconds
Application example
Application exampleControl and power circuit for star-delta starter
Application examplestar-delta starter operation
pressed M1 closes
M1 opens
M3 energizes
M3 closes for latching
Energize on delay timer
M1Energizes
M3 closes for latching
Application examplestar-delta starter operation
release
M1 opensM3 closes to supply power to motor
M1 closes for star connection
Application exampleStar connection
M1 opens
Application exampleDelta connection
M1 closes
After a few second this timer contact opens
this timer contact closes
M1 deenergizes
M1 opensM2 energizes
Application exampleDelta connection
M2 contact closes to connect motor winding into delta connection
Application exampleStop motor running Press this button will
stop motor running
Application example
Press this button will stop motor running
Stop motor running
Electromechanical counter
Digit wheels
electromagnet
Electromechanical counter, uses an external power source to magnetize and demagnetize the electromagnet and thus drive the digit wheel through an internal mechanism.
Counter applicationCounting object on conveyor belt .
counter
sensor
Sensor sends electrical pulse to counter every time it detects an object.
QUIZ 1 : 1.0 Introduction to Automation System (10 MARKS)
S1a What is hard wired automation in control system ?b. What is the main component used in this system ?c. What does NO contact mean in Relay?d. Name TWO types of Relay contact.e. The operation of Relay and Contactor are similar, what is the difference in usage between them?
