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PLC Fundamentals
Module 1: Introduction to PLC
PREPARED BY
Academic Services Unit
August 2011
© Applied Technology High Schools, 2011
ATE1212 – PLC Fundamentals
Module 1: Introduction to PLC 2
Module 1: Introduction to PLC
Module Objectives Upon successful completion of this module, students will be able to:
1. Differentiate between manual and automatic control.
2. Define a ‘control system’ and draw its block diagram.
3. Differentiate between digital and analog control.
4. Mention the different types of controllers and give examples.
5. Differentiate between a microcontroller and a PLC.
6. Mention the main parts of a PLC.
7. Give examples of PLC applications and list the PLC manufacturers.
8. Select the most suitable controller for a given problem.
9. Identify the main parts of the Siemens LOGO! PLC Module.
10. Program the Siemens LOGO! PLC Module through its Basic Control Unit using simple commands.
Module Contents: Topic Page No.
1.1 Introduction 3
1.2 Types of Controllers 5
1.3 PLC Vs. Microcontroller 7
1.4 Basic PLC Operation 8
1.5 PLC Applications 9
1.6 PLC Manufacturers 9
1.7 Lab Activity 1 10
1.8 Lab Activity 2 13
1.9 Lab Activity 3 15
1.10 LOGO! Edutrainer Default Input and Output 19
1.11 Review Exercise 20
1.12 Assignment 27
ATE1212–PLC Fundamentals
Module 1: Introduction to PLC 3
1.1 Introduction
In everyday operations or industrial processes, we come across situations
where there is a need to control some device or a physical quantity such
as time, temperature, sound, light and so on, to get the required result or
output. For example, do you think an airplane would be useful to a pilot, if
he cannot make it go where he wants it to go? Or would an air-
conditioner be useful, if the temperature in a room cannot be
controlled? In both the examples, there is a need to control a process.
Electrical control can be defined as using electrical signals such as current
or voltage to enable or disable or direct a certain process. Electrical
control can be achieved in different ways, for instance; based on human
interaction we can say that the control is either manual or automatic.
Manual Control
Control is said to be done manually
when a user performs an action for
the system to function. For
example, the user might flip the
switch of a manual starter to start
and stop a motor (fig 1.1)
Fig 1.1: Example of Manual Control
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Module 1: Introduction to PLC 4
Automatic Contol
Control is said to be automatic
when the action is performed
automatically in response to a set
of conditions.
Fig 1.2: Example of Automatic Control
Machines can be controlled manually or automatically. Usually, there is a
combination of manual and automatic control. For example, a process
that is started manually may stop automatically when certain conditions
are met.
Fig 1.3: Manual & Automatic Control Example
A Control System is a system that can sense, switch and/or control an
operation. It operates on an input signal and controls the process in
order to provide an output signal. This is shown in the block diagram in
fig 1.4:
Fig 1.4: Elements of a Control System
Input Process Output
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Module 1: Introduction to PLC 5
Control
Discrete control Digital
Continuous control Analog
In terms of output value, a control system can be classified as either
Discrete control (Digital control) or Continuous control (Analog control).
Fig 1.5: Types of control based on the output value Discrete (digital) control: The value to be controlled can be either ON
or OFF. Example: Turning a light ON and OFF.
Continuous (analog) Control: The value to be controlled varies
smoothly. Example: Motor speed.
In this course we will study discrete control only.
1.2 Types of controllers Different types of controllers could be used based on the requirements of
the application. Some examples are included below:
1. Relays and Contactors
Simple electromechanical devices like relays and contactors are most
widely used for controlling a discrete manufacturing process.
Fig 1.6: Relay
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Module 1: Introduction to PLC 6
2. Programmable Logic Controllers (PLCs)
A Programmable Logic Controller (or PLC) is a
specialised digital controller that can control
machines and processes. it monitors inputs,
makes decisions, and controls outputs in order
to automate machines and processes. Fig 1.8
demonstrates its function.
Fig 1.7: PLC
Fig 1.8: PLC function
3. Microcontrollers (µCs)
Microcontroller is a special purpose computer
that can do one job, for example, the one that
is used in an automatic washing machine and in
a microwave.
Fig 1.9: Microcontroller
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Module 1: Introduction to PLC 7
1.3 PLC vs. Microcontroller
Usually PLCs are used in an industrial environment, where as the
microcontrollers are smaller and well suited for embedded situations.
PLCs are programmed with ready made blocks or programming elements,
whereas in Microcontrollers a programming language must be used to
write a programing code.
Fig 1.10 Programming PLC
Fig 1.11 Programming a µC
The price of the µC could vary from 5 Dirhams to 50 Dirhams. Some of
the cheapest PLC's could cost AED 400 for the basic frame (with digital
inputs and outputs).
PLC Advantages
• They are highly reliable, fast and flexible.
• They can handle severe conditions such as dust, humidity etc.
• They can communicate with other controllers.
• They are easy to program and troubleshoot.
• They include display units.
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Module 1: Introduction to PLC 8
1.4 Basic PLC Operation In the example shown in fig 1.12, pushbuttons are connected to the PLC’s
inputs and a motor is connected to the PLC’s output. Here the
pushbuttons are used to start and stop the motor.
Fig 1.12: Motor control using a PLC
PLC Basic Parts A PLC consists of the following basic parts:
• Inputs • Central Processing Unit (CPU) • Outputs
Examples of PLC input devices are sensors,switches,pushbuttons etc Examples of PLC output devices are valves, motors, solenoids etc
Inputs CPU Outputs
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Module 1: Introduction to PLC 9
1.5 PLC Applications
A PLC can be used in a wide range of applications, some of which are shown below:
Production and assembly lines
Automatic Doors
Traffic Lights
1.6 PLC Manufacturers The PLC that will be introduced in this course is the LOGO! PLC from
Siemens.The table below shows a list of other PLC Manufacturers.
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Module 1: Introduction to PLC 10
1.7 Lab Activity 1 Objective: To familiarise with the Siemens LOGO! PLC Module. Procedure: The following are the 12 main components of the LOGO!
Basic PLC module:
• One LOGO! Basic which operates on 24V dc supply and has: 8 digital inputs 2 analog inputs 4 digital outputs
• Display unit • Control Unit for LOGO! Programming • PC Interface • Two expansion modules that have:
4 digital inputs 4 digital outputs
• Status display LEDs that indicate RUN/STOP status • Submin D Socket • 24VDC safety socket • 0V safety socket • Control elements • Emergency-stop bridge • SysLink Interface
1. Identify the LOGO! Basic PLC module components on the
EduTrainer that are marked in the figure and write them in the table provided:
ATE1212–PLC Fundamentals
Module 1: Introduction to PLC 11
Number Component/Part
1
2
3
4
5
6
7
8
9
10
11
12
Table 1.1
Review the parts and mark them in the picture below:
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Module 1: Introduction to PLC 12
2. Identify the three parts on the LOGO! Basic control unit and name them:
1. __________________________________________________
2. __________________________________________________
3. __________________________________________________
What is the function of this unit? _____________________________________________________ ________________________________________________
3. Measure the output voltage of the power supply unit with the help of a multimeter as shown in figure below:
Record the dc output voltage. ____________________________________________________
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1.8 Lab Activity 2 Objective: To familiarise with the LOGO! Basic Control unit using simple commands. Procedure:
1. Set the day, time and date Follow the steps below to set the day, time and date. Switch on the power supply. Press the ESC key on the LOGO! Basic module Select Set Select Clock Press the and to change the day and press OK to
confirm. Move to date by using the side arrows. Follow the same procedure to set the date and year and press
OK to confirm. Press ESC to return to the main screen.
2. Enter your first program on LOGO! using the on-board keys. The digital inputs are denoted by the letter I such as I1, I2 and so
on, and the digital outputs are denoted as Q1, Q2 and so on. Program the PLC to turn on Q1 when I3 is ON.
Press ESC to come to the main screen and follow the steps below: Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
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Observation:
1. Press ESC to return to the main screen and press start to run the program.
Press the white pushbutton (I3) and observe the result. Can you
identify the Q1 output? What do you observe? __________________________________________________ __________________________________________________
2. Stop and clear the program. Repeat the steps by changing the input to I1. What do you observe?
________________________________________________________ ________________________________________________________
3. Based on your experiment, identify which control element is connected to the following PLC inputs and outputs:
PLC input Control Element
I3
I1
PLC Output Control Element
Q1
Table 1.2
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1.9 Lab Activity 3 Objective: To perform simple control tasks by entering commands
through the BASIC Control Unit.
Procedure:
A. Write a program to turn on the Green Indicator light when the selector switch is turned on. Refer to table 1.3 to identify the inputs and outputs.
Control Elements PLC Input/Output
Selector Switch I4
Green Indicator Light Q1
Is it possible to leave the green light in the ON state? What is the difference you observe between the pushbutton and the selector switch?
______________________________________________________
______________________________________________________
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Module 1: Introduction to PLC 16
B. Write a program to move the table forward when the white pushbutton is pressed.
Control Elements PLC Input/Output
Table (forward) Q5
Table (backward) Q6
White pushbutton I3
What changes should you make in the program to move the table backward when the white pushbutton is pressed?
______________________________________________________
______________________________________________________
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Module 1: Introduction to PLC 17
C. Write a program to start the conveyor belt motor when the green
pushbutton is pressed.
Control Elements PLC Input/Output
Conveyor belt motor Q8
Green pushbutton I1
Branching arm Q7
What changes should you make in the program to move the branching arm when the green pushbutton is pressed?
______________________________________________________
______________________________________________________
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Module 1: Introduction to PLC 18
D. Write a program to turn on the White indicator light when the
inductive sensor senses a metal piece.
Control Elements PLC Input/Output
White Indicator light Q2
Inductive sensor I12
What changes should you make in the program to move the branching arm when this sensor senses a metal piece?
______________________________________________________
______________________________________________________
White Indicator Light
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Module 1: Introduction to PLC 19
1.10 LOGO Edutrainer Default Input and Output (Note: students are not required to memorise this configuration as it might be changed or modified)
Control Elements PLC Input/Output
Green pushbutton (N.O) I1
Red pushbutton (N.C) I2
White pushbutton (N.O) I3
Selector Switch I4
Emergency Jumper I5
Fiber optic barrier I9
Fiber optic barrier I10
Fiber optic sensor I11
Inductive sensor I12
Green Indicator Light Q1
White Indicator light Q2
Table (forward) Q5
Table (backward) Q6
Branching arm Q7
Conveyor belt motor Q8
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Module 1: Introduction to PLC 20
1.11 Review Exercise 1. What are the elements of a control system? Include the elements to
complete the block diagram given below:
2. Study the following situations and decide which controller is the
best for each task. Justify your answers:
a) The school management decided to control the main gate automatically, and this includes open and close the gate barrier and count the number of cars that enter the school. (hint : the environment must be taken into consideration )
__________________________________________________ __________________________________________________
__________________________________________________
b) A water tank is required to be filled manually using a small
pump and two pushbuttons, one to start filling the tank and one to stop. (hint : cost should be considered)
__________________________________________________ __________________________________________________
__________________________________________________
c) You are required to design a portable device that measures
human blood pressure.
__________________________________________________ __________________________________________________
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Module 1: Introduction to PLC 21
3. What does PLC stand for? ______________________________________________________ ______________________________________________________
4. Based on what you have studied in this module, what do you think is the difference between a PLC and a microcontroller? Complete the T-chart below to show the difference:
PLC
Microcontroller
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Module 1: Introduction to PLC 22
5. Mark the parts that are indicated in the table below:
Number Component/Part
1
3
4
8
11
12
6. List three advantages of using a PLC:
______________________________________________________ ______________________________________________________ ______________________________________________________
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Module 1: Introduction to PLC 23
7. What is the difference between Discrete control and Continuous
control? Give one example for each type of control.
______________________________________________________ ______________________________________________________ ______________________________________________________
8. With reference to the table of the default configuration (Page 20) try the following programs and then write down your comments:
Program
Comments
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Module 1: Introduction to PLC 24
9. The green light of the LOGO! Edutrainer is required to turn ON when the green pushbutton is pressed, while the white light is required to turn ON when the white pushbutton is pressed: a. Draw the LOGO PLC program for this problem.
b. How can you implement this task using a relay. Draw the control diagram for this circuit.
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Module 1: Introduction to PLC 25
10. Discuss the following industrial applications and decide which
controller is the best to be used for each one.
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1.12 Assignment Complete any one of the tasks using one of the suitable Microsoft Office tools. Task-1: Use the internet to identify one commercial application and two industrial applications of a PLC other than the ones listed in the module, and prepare a powerpoint presentation or a poster that lists those PLC applications. The powerpoint slides (or the poster) must include the following contents:
Assignment Title: PLC Applications
Title of application-1, picture and brief description.
Title of application-2, picture and brief description.
Title of application-3, picture and brief description. Task-2: Prepare a powerpoint presentation or a chart that includes the following:
• A picture of the LOGO! Basic Control unit with all its parts marked neatly.
• A list of all the LOGO! Edutrainer control elements that you have used in your lab activities in this module. Include the following details:
Control Element Input or Output? PLC Input/Output
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