system can be used if we use a controller-based system and modify the
program.
A controller of a control system is a system that can direct, command
and regulate itself or another system. The control system starts with input
Module 1
signals that activate the process to control output devices. The block
diagram of a control system is shown in fig 1.2:
1. Control system has input process and output
Input
Process
Output
2. Manual and
automatic
Figure
1.2:system:
Elements of a control system
In terms Manual
of output
value,
control
system
can be
means we do theaaction
like press
the switch,
openclassified
the door. as either
Discrete control
(Digital
control) by
or machine
Continuous
control
(Analog
control).
Automatic
means performed
like corridor
lights
turned on
when
person enters.
Barrier opens in parking when car comes.
3. Continuous (analog) and discrete (digital) control:
Continuous means varying level like changing temperature, speed of car,
volume of music
Digital means ON and OFF, HIGH or LOW, PRESENT or ABSENT (only
Figure
1.3: Types of control based on the output value
two
levels)
Discrete (digital) control: The value to be controlled can be either ON
4. Advantages of PLC:
or OFF. Example: Turning a light ON and OFF.
• They are highly reliable, fast and flexible.
Continuous
(analog)
Control:
value
to be etc.
controlled varies
• They can
handle severe
conditionsThe
such as
dust, humidity
smoothly.
Example:
Motor speed,
light
intensity, etc.
• They
can communicate
with other
controllers.
1.3 PLC Basic Parts
In this•course
weeasy
willtostudy
discrete
control only.
They are
program
and troubleshoot.
A PLC •consists
of the
following
basic
parts:and outputs.
They have
built-in
interfacing
for inputs
Input module
Central Processing Unit (CPU)
5. PLC block
diagram
Output
module
4
Module 1: Introduction to PLC
Examples of PLC input devices are sensors,switches,pushbuttons etc
Examples of PLC output devices are actuators, motors, solenoids etc
Fig 1.6 demonstrates the PLC inputs and outputs.
6. Some Applications
•
Sorting application
•
Labeling application
•
Traffic lights
1.5 LOGO!
• Hardware
Automatic
door
LOGO! Basic Module
7. Manufacturer name is Siemens
LOGO!12/24 RC is the LOGO! Controller that will be used in our
8. LOGO! Hardware
applications.
Common inputs
Figure 1.8: LOGO! Basic Module
All Switches
Common outputs
Motor
1. Inputs: The
LOGO! Basic Module has 8 inputs
and they are
All pushbuttons
Solenoid
designated as I1, I2, I3, …. I8. Inputs I1 to I6 are digital inputs, and
All sensors
Light
the inputs I7 and I8 can function as digital or analog.
2. Outputs: The LOGO! has 4 digital outputs Q1, Q2,Buzzer
Q3, Q4.
3. Display Unit (LCD)
Fan
4. Control Panel
5. Module Slot: to connect the programming cablePump
from the PLC to
Valve
computer
9. Digital inputs: all switches and pushbuttons are digital
10. Analog inputs: Ultrasonic sensor (measure distance), Load (force) sensor and
Temperature sensor
Module 1: Introduction to PLC
11. All outputs in PLC are always DIGITAL
11
12. Capacitive Sensors to detect metals and non metals and even liquids
13. Inductive sensor to detect metals
14. Optical sensor mainly for sorting and counting
15. Drawing refer to worksheets answer key in D2L
Normally open PB
Normally closed PB
When not pressed no current flow
When not pressed no current flow
When pressed current flows
When pressed current flows
Module 2 and 3:
Refer answer keys of worksheets in D2L
Module 3 FBD
Inputs
Module 4 LAD
Normally open contact and normally
closed contact
Outputs
Relay coil
AND gate
Series connection
OR gate
Parallel connection
NOT gate
Use normally closed contact
When to use AND gate:
-A question like two inputs are pressed together
-two conditions must satisfy to start an output go for AND gate
When to use OR gate:
A question like any two inputs are pressed
-one among the two conditions need to satisfy to start an output go for OR
gate
NOT gate:
Whenever normally closed pushbutton is used in question
Memory or RS LATCH:
When two inputs are controlling one output in such a way one input starts
output and other one stops output go for memory
TIMER:
On delay:
When the output is turned on after a delay
OFF delay:
When the output is turned off after a delay
Counter:
Whenever to count