The document provides an overview of PLC programming within mechatronics, covering essential concepts such as architecture, ladder logic programming, input/output devices, and timer and counter functions. It outlines the objectives and outcomes for understanding key components, system modeling, and control principles in industrial applications. Additionally, it discusses SCADA systems and their role in monitoring and controlling industrial processes.

1. Unit IV
Mechatronics (302050)
Lecture Notes / PPT
UNIT IV

2. Syllabus
PLC Programming
 Introduction, Architecture,
 Ladder Logic programming for different types of logic gates,
 Latching,
 Timers, Counter,
 Practical Examples of Ladder Programming,
 Introduction to SCADA system

3. Objectives
1. Understand key elements of Mechatronics system,
representation into block diagram
2. Understand concept of transfer function, reduction and analysis
3. Understand principles of sensors, its characteristics, interfacing
with DAQ microcontroller
4. Understand the concept of PLC system and its ladder
programming, and significance of PLC systems in industrial
application
5. Understand the system modeling and analysis in time domain
and frequency domain.
6. Understand control actions such as Proportional, derivative and
integral and study its significance in industrial applications.

4. Outcomes
1. Identification of key elements of mechatronics system and its
representation in terms of block diagram
2. Understanding the concept of signal processing and use of
interfacing systems such as ADC, DAC, digital I/O
3. Interfacing of Sensors, Actuators using appropriate DAQ
micro-controller
4. Time and Frequency domain analysis of system model (for
control application)
5. PID control implementation on real time systems
6. Development of PLC ladder programming and implementation
of real life system

5. Reference Books
 Johnson, Process Control Instrumentation Technology, 7th Ed,
Prentice Hall of India, 2005.
 Bolton, Programmable Logic Controllers, 4th Ed, Elsevier
Newnes, 2006.

6. Introduction
 A Programmable Logic Controller (PLC) or Programmable
Controller is a digital computer used for automation of
electromechanical processes in modern factory automation.
 Eg. - Control of machinery on factory assembly lines, as well
as heating, ventilation, air-conditioning, plastic injection
moulding machines, commercial washing machines...

7.  PLCs are members of the computer
family, using integrated circuits
instead of electromechanical devices
to implement control functions.
 They are capable of storing
instructions, such as sequencing,
timing, counting, arithmetic, data
manipulation, and communication,
to control industrial machines and
processes. Figure illustrates a
conceptual diagram of a PLC
application.
Introduction

8. Why PLC?
 Hard wired panels / relay logic are very time consuming to implement
due to wiring and debugging related issues.
 In need of another controller which:
 Is faster and operates in real time
 Withstands vibrations, temperatures, humidity, noise
 Has inbuilt interfacing for inputs and outputs
 Is flexible and adaptable (easy to program/re-program), easy to
troubleshoot and maintain
 Consumes less space, requires less wiring, comparatively cheaper

9. Selection Criterion for PLC
 Application Requirement
 Input / Output Requirement
 Memory Requirement
 CPU Requirement
 Software Requirement & Operator Interface
 Communication Requirement
 Environmental Requirements

10. I/O Devices
Input Devices provide inputs to the control system.
In case of discrete-state process control, the inputs
are two state specifications such as:
 Limit switches – open or closed,
 Comparators – high or low,
 Push buttons – depressed or not depressed

11. Output Devices accept outputs from the control system. In
discrete-state process control, the outputs accept only two state
commands such as:
• Lights: On / OFF,
• Motors : Rotating or not rotating,
• Solenoids : Engaged or not engaged
I/O Devices

12. Input Devices Output Devices
I/O Devices

13. Use of Relay Controllers and Ladder
Diagram
Use of momentary push-button switches
and a relay to implement a latch

14. Relay Sequencers
 Before the PLC, control, sequencing, and safety interlock logic for manufacturing
automobiles was mainly composed of relays, cam timers and dedicated closed-loop
controllers.
 One way to provide a discrete state controller is to use physical relays to put
together a circuit that satisfies the requirements of the ladder diagram.
 When a program has been wired into the relays that make up the relay logic panel, it
has been programmed to meet the ladder diagram.
 If the event sequence is to be changed, it is necessary to rewire all or part of the
panel. It may even be necessary to add more relays to the system, or to use more
relays than the previous program.

15. The move from relay logic controllers to computer-based
controllers was an obvious one because :
1. The input and output variables of discrete state control
systems are binary in nature, just as with a computer.
2. Many of the control relays of the ladder diagram can be
replaced by software, which means less hardware control.
3. It is easy to make changes in a programmed sequence of
events when it is only a change in software.
4. Special functions, such as time-delay actions and counters,
are easy to produce in software.

16. Architecture of a PLC
A Programmable controller can be studied by considering the
basic elements shown in Figure : the processor, I/O modules and
the software.

17. Components in PLC
Components
• Input Module
• Output Module
• CPU
• Memory
• Power Supply
• Programming Device
• Communication Channel

18. Input Module
 Figure shows the typical wiring to a
PLC input module.
 The input module examines the state of
the physical switches and other input
devices and puts their state into a form
suitable for the processor.
 It is able to accommodate a number of
inputs called channels.
 If the switch is closed, the input will be
24 V DC, and if open, 0 V DC. The
input module converts this into the 1 or
0 state needed by the processor.

19. Input Module
• Input Module: Convert real world voltage and currents to signals the PLC
can understand. Since there are different types of input devices, there is a wide
variety of input modules available, including both digital and analog modules.
• Discrete / Digital Module: Use 0 or 1 to depict state
• Analog Module: Use numbers to depict state e.g. 30 degree

20. Output Module
 Figure shows the typical wiring to the
PLC output module.
 The Output Module supplies ac power to
the external devices such as motors,
lights, solenoids, etc.
 Internally, the output module accepts a 0
or 1 from the processor, and uses it to
turn ON or OFF a device.
 An output module can have one or
several channels per unit. Each channel
is usually provided with an indicator
light to show whether the particular
channel is being driven ON/OFF.

21. Output Module

22. Processor
 The processor is a computer that executes a program to
perform the operations specified in a ladder diagram.
 It performs arithmetic and logic operations on input variable
data and determines the proper state of the output variables.

23. CPU & Memory
• CPU: The brain of PLC is the central processing unit (CPU).
• It executes the various logic and sequencing functions by operating on the
PLC inputs (sensor information) to determine the appropriate output signals
for the actuator.
• The processor is microprocessor very similar in its construction to those used
in personal computers and other data-processing equipment.
• Memory: Tied to the CPU is the PLC memory, which contains the program
of logic, sequencing, and other input/output operations.
• The memory for a programmable logic controller is specified in the same way
as for a computer, and may range from 1k to over 48 k of storage capacity.
• Memory types are ROM, RAM, EPROM

24. Power Supply
• Power Supply: A power supply of 115 volts is used to provide power to the
PLC and any other modules. Power supplies come in various forms:
• Power supply modules that fit into one of the slots in a chassis
• External power supplies that mount to the outside of a chassis
• Stand alone power supplies that connect to the PLC or I/O through a
power cable
• Embedded power supplies that come as part of the PLC block.

25. Programmable Device
• Programming Device: The PLC is programmed by means of a programming
device.
• The programming device is usually detachable from the PLC cabinet so that it
can be shared between different controllers.
• Different PLC manufactures provide different devices:
• Simple teach pendant-type devices, similar to those used in robotics
• PLC programming keyboards and CRT displays.

26. Communication Channel
Communication Channel: The CPU uses the:
• the data bus for sending data between the constituent elements,
• the address bus to send the addresses of locations for accessing stored
data
• the control bus for signals relating to internal control actions
• the system bus is used for communications between the input/output
ports and the input/output unit.

27. Communication Channel
• The buses are the paths used for communication within the PLC.
• The information is transmitted in binary form, i.e. as a group of bits with
a bit being a binary digit of 1 or 0, i.e. on/off states.
• The term word is used for the group of bits constituting some
information. Thus an 8-bit word might be the binary number 00100110.
• Each of the bits is communicated simultaneously along its own parallel
wire.

28. Communication Channel

29. Types of PLCs
• Single Box Type: The single box type (or, as sometimes termed, brick) is
commonly used for small programmable controllers and is supplied as an
integral compact package complete with power supply, processor, memory,
and input/output units. Typically such a PLC might have 6, 8, 12 or 24 inputs
and 4, 8 or 16 outputs and a memory which can store some 300 to 1000
instructions.
• Modular: The modular or the Rack type consists of separate modules for
power supply, processor, input module, output module, memory.

30. Types of PLCs
Brick Type PLC
Rack Type PLC

31. PLC Operation
The operation of the PLC can be considered in two modes:
1. The I/O scan mode
2. The Execution mode

32. I/O Scan Mode
 During the i/o scan mode, the processor updates all the outputs
and inputs the state of all inputs one channel at a time. The
time required for this depends on the speed of the processor.

33. Execution Mode
 During this mode, the processor evaluates each rung of the ladder
diagram sequentially, starting from the first rung and proceeding
to the last rung.
 As a rung is evaluated, the last known state of each switch and
relay contact in the rung is considered, and if any TRUE path to
the output device is detected, then that output is indicated to be
energized – that is, set to ON.
 At the end of the ladder diagram, the I/O mode is entered again,
and all outputs devices are provided with ON/OFF state
determined from execution of the ladder program. All inputs are
sampled, and the execution mode starts again.

34. PLC Addressing
 To identify the I/O devices,
the PLC uses the device
address or channel.
 It address designation
depends on the type of
programmable controller.
 Table shows a typical
address designation for
different I/O devices.

35. Programmed Diagram Interpretation
 In a programmed diagram, the ON / OFF state of the output of
the rung is determined by testing the elements of the rung for a
TRUE / FALSE condition.
 If a complete TRUE element path to the output exists in the
rung, then the output will be made TRUE / ON.

36. Programmed Diagram Interpretation
 The symbol for a NO contact indicates that the device should
be interpreted as FALSE if the contact is tested and found to be
open, and TRUE if it is found to be closed. It is to be
“Examined ON”, and if ON, it is TRUE.
 The symbol for a NC contact indicates that if it is tested and
found to be closed, then it is FALSE, and if tested and found
open, it is ON. It is to be “Examined OFF”, and if OFF, it is
TRUE.

37. Use a NC push-button switch to turn ON a
red light

38. Programming of PLCs
• Ladder Logic: Used for machine control
• Function Block Diagram: Used for process control
• Called "ladder" diagrams because they resemble a ladder, with two
vertical rails (supply power) and as many "rungs" (horizontal lines) as
there are control circuits to represent.

39. Ladder Diagram: Scanning

40. Ladder Diagram: Rung

41. Elements of Ladder Diagram

42. Elements of Ladder Diagram

43. Ladder Diagram: AND Logic
The lamp energizes only if contact A and contact B are
simultaneously actuated.

44. Ladder Diagram: OR Logic
The lamp energizes if either of contact A or contact B are actuated.

45. Ladder Diagram: NOT Logic
The lamp energizes if the contact is not actuated, and de-energizes
when the contact is actuated.

46. Ladder Logic Diagrams for AND Gate

47. Ladder Logic Diagrams for OR Gate

48. Ladder Logic Diagrams for NOT Gate

49. Implement a latch to turn ON and OFF a motor using 2
NO push-button switches.

50. (NC)

51.  In a certain bank, each of
the three bank officers has
a unique key to the vault.
The bank rules require that
2 of the 3 officers be
present when the vault is
opened. Develop a PLC
ladder program that will
unlatch the door and turn
ON a light when 2 of the 3
keys are inserted.

52.  A small house has 3
windows and 2 doors.
Each window and door
has a switch attached such
that the contacts close
when a door or window
opens. Develop a PLC
ladder that will turn ON a
light if one or more
windows are open, or if
both doors are open.

53. PLC Timer Function
 The Programmed timer function plays an important role in PLC
applications to provide for needed delays in some manufacturing sequence
and to specify the period of time that some operation is to last.
 While activated by a true path, the timer begins to accumulate time in form
of “ticks”.
 Each “tick” is worth a certain amount of time.
 The timer is preloaded with a certain number of these ticks.
 When the accumulated time ticks equals the preload value, the timer itself
becomes TRUE.
 The timer only counts while it has a TRUE input. If the input becomes
FALSE and then TRUE again, the timer will reset to ZERO and start to
count again.

54. PLC Timer Function

55. PLC Counter Function
 A counter is a programmed function that counts (increments)
every time the input changes from FALSE to TRUE.
 If in one scan, the input is False, and in the next scan, the input
is True, the counter increments. No further counts will occur
until the input goes False again and then True.
 The counter has an address and a preset number of counts.
When the preset number of counts have been accumulated, the
counter becomes TRUE and can activate some other part of the
ladder program.

56. PLC Counter Function

57. Design and write ladder logic for a
simple traffic light controller for
following
sequence of operation as below,
Step 1 : Turn Green on for 35 seconds
Step 2 : Turn Yellow 1 on for 5
seconds.
Step 3 : Red 2 on for 40 seconds.
Step 4 : Sequence repeats thereafter.

58.  Automatic Extension and Retraction of a
Hydraulic Cylinder

59. SCADA
 SCADA (supervisory control and data acquisition) is a type of
industrial control system that monitors and controls industrial
processes that exist in the physical world.
 Industrial processes include those of manufacturing,
production, power generation, fabrication, and refining, and
may run in continuous, batch, repetitive or discrete modes.

60. Components of a SCADA system
 A SCADA system usually consists of the following sub-
systems:
 A human-machine interface or HMI which presents process
data to a human operator, and through this, the human operator
monitors and controls the process.
 A supervisory (computer) system, acquiring data on the
process, and sending commands (control) to the process.

61. Components of a SCADA system
 Remote terminal units (RTUs) connecting to sensors in the
process, converting sensor signals to digital data and sending
digital data to the supervisory system.
 Programmable logic controller (PLCs) used as field devices
because they are economical, versatile, flexible.
 Communication infrastructure connecting the supervisory
system to the RTUs.

62. • RTU: Remote Terminal Unit
• MTU: Master Terminal Unit
• DAS: Data Acquisition System
• HMI: Human Machine Interface