The document presents a comprehensive overview of programmable logic controllers (PLCs) and the author's professional background, including his education and experience in electrical engineering with a focus on industrial process controls. It discusses the history, functions, components, and operational principles of PLCs, highlighting their advantages such as high reliability, flexibility, and modularity. Additionally, it outlines essential maintenance practices and common problem sources in PLC applications.

1. Basics of
Programmable
Logic Controllers
(PLCs)
Focused, To-The-Point and Practical!

2. Personal
Introduction
Engr. Arslan Ahmed Amin is a professional Electrical and
Instrumentation Engineer serving Pakistan’s pioneer Oil and Gas
Organization, Pakistan Petroleum Limited. He obtained his Bachelor's
degree in Electrical Engineering from the prestigious University of
Engineering and Technology, Lahore in 2010 and started his
professional career with Pakistan Petroleum Limited. He has served
this organization for 06 years and achieved lots of accomplishments in
the development of the systems of newly installed 210 MMSCFD gas
compression facility. He actively contributed his services in
commissioning, testing, maintenance and upgradation of the E&I
systems. He completed his Master’s in Business Administration
(M.B.A.) in 2014 from Virtual University of Pakistan, Lahore through
distance learning and afterwards obtained Masters (M.Sc.) in
Electrical Engineering from University of Engineering and Technology,
Lahore in 2015.

3.  P.H.D. Electrical Engineering (University of Engineering
and Technology, Lahore) In progress.
 M.Sc. Electrical Engineering (University of Engineering
and Technology, Lahore)
 M.B.A. Online (Virtual University of Pakistan, Lahore)
 B.Sc. Electrical Engineering with Honors (University of
Engineering and Technology, Lahore)
Education

4.  06 years’ experience in industrial process controls and
electrical power systems domain with Pakistan
Petroleum Limited (PPL) in CMMS (SAP) environment.
 Experience in commissioning, testing and maintenance
roles of latest systems regarding Power Generation,
Field Instrumentation, Distributed Control System,
Safety Instrumented System, Gas Turbines, PLCs,
Analyzers, SCADA, Well Head Control Panels and Utility
packages.
Experience

5.  ‘DCS Troubleshooting Practices’ by Haward Technology Middle
East from 16th to 20th May 2016.
 ‘Protective Relays Applications in Power System’ by Haward
Technology Middle East from 04th to 08th April 2016.
 ‘Circuits and Electronics’ from Massachusetts Institute of
Technology (MIT) USA.
 ‘Project Management’ from Virtual University of Pakistan
(VU).
 ‘Production and Operations Management’ from Virtual
University of Pakistan (VU).
 ‘Conflict Management’ from Virtual University of Pakistan
(VU).
 ‘Crisis Management’ from Virtual University of Pakistan (VU).
Professional
Courses

6.  QMS 9001, ISO 14001 EMS and OHSAS 18001, ERP System, Cost
of Quality, Productivity Improvement Techniques, Process
Safety Management, Hazard Identification and Risk
Assessment, HAZOP, SIL systems, Occupational health and
Safety, Permit to work system, Safety Modules
(Complete), Communication Skills, Team Work Skills, Decision
Making Skills (Organized by PPL)
 SAP System (R3P version) Maintenance Work Orders Processing,
Contracts Management, Spares and Material.
 ‘Instrumentation and Controls Fundamentals’ from OMS
Institute of Management and Technology, Lahore.
 Installation, calibration and maintenance of Fire and Gas
detectors by Det-tronics.
 Generation, Transmission and Distribution at WAPDA
Engineering Academy Faisalabad.
Professional Trainings

7.  Among Top 10 students in the session of 240 students in B.Sc.
Electrical Engineering.
 Received Dean’s Honor Role award in consecutive five semesters
for excellent academic performance in B.Sc. Electrical
Engineering.
 Overall Topped in F.Sc. in Board of Intermediate and Secondary
Education, Faisalabad 2006.
 Winner of Quaid-e-Azam Scholarship.
 Gold medal winner in District Science Quiz Competition Faisalabad.
 Represented as ‘Talent of Pakistan Youth’ in China in 2007 by
Ministry of Youth, Pakistan.
Academic
Achievements

8. P L C C O U R S E
 Introduction
 PLC history
 PLC functions
 PLC selection
 Logic Gates in PLC
 Combination of Gates
 Simple Logic Examples
 Exercise

9. What is a PLC?
 A PLC is a device that was invented to replace the
necessary sequential relay circuits for machine control.
 The PLC works by looking at its inputs and depending
upon their state, turning on/off its outputs.
 The user enters a program, usually via software, that
gives the desired results.

10. What is a PLC?
 For example, let's assume that when a switch
turns on we want to turn a solenoid on for 5
seconds and then turn it off regardless of how
long the switch is on for. We can do this with a
simple external timer. But what if the process
included 10 switches and solenoids? We would
need 10 external timers. What if the process also
needed to count how many times the switches
individually turned on? We need a lot of external
counters.

11. PLC History
 In the late 1960's PLCs were first introduced.
 The primary reason for designing such a device was
eliminating the large cost involved in replacing the
complicated relay based machine control systems.

18. PLC History
 Bedford Associates (Bedford, MA) proposed something
called a Modular Digital Controller (MODICON) to a
major US car manufacturer.
 The MODICON 084 brought the world's first PLC into
commercial production.

19. Programmable Logic Controller
( P L C ) – T Y P E S
 Modular:
 Capacity and functionality can be
added as required and then
removed to be used elsewhere.
 Industrial:
 Suitability for the temperature,
humidity, vibration and voltage
variation and design for 24 hour
operation.

20. Benefits of PLC
 Safe operation of plant
 In emergency, automatically shutdown the plant in fail
safe condition
 In startup check the prerequisite & then permit to start
 Logging the event.

21. Benefits of PLC
 High reliability
 Flexible control
 Easily modified
 Easy troubleshooting
 Reduced space requirement
 Revisable
 Lower cost
 Modularity

22. PLC Selection
 Safety
 Reliability and maintainability
 Availability
 Flexibility
 Cost
 Speed of operation
 Security
 Space
 Events logging

23. Safety
For the term of safety, there are
numerous definitions that have been
worked out the different boards. All
definitions have in common that safety
means a sufficient protection form
danger. In the DIN 31 000 standard
document, part 2 safety is defined as a
situation in which the risk is not
higher than the risk limit. This also
means that absolute safety cannot be
achieved in technology.

24. Safety
Safety related controls are needed for trains, lifts, escalators,
burners etc. the safe controls must be designed in a way that
any component fault and other imaginable influences do not
cause dangerous states in the plant.

25. Safety
The safe state is the state to which a system can be put out of its
current operational state and which has a system specific lower
hazard potential than the operational state. The absolutely safe
state is always the state with the lowest amount of energy
involved.

26. Reliability
Reliability is the ability of a technical device to
fulfill its function during its operation time.
This is often no longer possible if one
component has a failure. So the MTBF (Mean
time Between Failure) is often taken as a
measurement of reliability. It can either be
calculated statistically via systems in operation
or via the failure rates of the components
applied.

27. Note
 The reliability does not say anything about the safety of
a system! Unreliable systems are safe if an individual
failure put the plant to the safe state each time.

37. PLC Components
 The PLC mainly consists of a
 CPU (Processor)
 Memory areas
 Input/output data devices
 Separate relays
 Counters
 Timers
 Data Storage locations
 Power Supply
 Programming unit

38. Processors
 Processor is the brain of PLC
 5 basic parts
 CPU control the operation of PLC.
 Memory instruction & data that tell the cpu
what to do.
 Communications processor: handles
communication from outside world.
 Battery :- keeps time & maintain the
programme.
 Power supply: supply to run the processor.

39. Power supply
 Two sources of power are used in PLC.
 Battery power
 Local power from plant
 Battery power used to maintain the user programme /
keep the time of day, clock running, maintain the status
of certain bits and register.

40. PLC Components
 Do these counters, timers, etc. really exist? No, they
don't "physically" exist but rather they are simulated
and can be considered software counters, timers, etc.
 These internal relays are also simulated.

41. PLC Components
INPUT RELAYS-(contacts)
 Connected to the outside world.
 They physically exist and receive signals from switches,
sensors, etc.
 Typically they are not relays but rather they are
transistors.
INTERNAL UTILITY RELAYS-(contacts)
 Do Not Receive Signals From the Outside World nor Do
They Physically Exist.
 They Are Simulated Relays and Are What Enables a PLC
to Eliminate External Relays.

42. PLC Components
COUNTERS
 Do not physically exist. They are simulated counters and
they can be programmed to count pulses.
 Counters can count up, down or both up and down.
 Since they are simulated they are limited in their counting
speed.
 Increments vary from 1ms through 1s.

43. PLC Components
TIMERS
 Do not physically exist.
 They come in many varieties and increments. The most
common type is an on-delay type.
 Others include off-delay and both retentive and non-
retentive types.
 Increments vary from 1ms through 1hr.

44. PLC Components
 OUTPUT RELAYS
 Connected to the outside world.
 They physically exist and send on/off signals to solenoids, lights, etc.

45. PLC Components
 DATA STORAGE
 Typically there are registers assigned to simply store data.
 They are usually used as temporary storage for math or
data manipulation.
 They can also typically be used to store data when power
is removed from the PLC.
 Upon power-up they will still have the same contents as
before power was removed.
 Very convenient and necessary

46. Logic gates in PLC
 Logic gates in a PLC are implemented in software as
compared to conventional hard-wired logic.
 Any size of the logic can be implemented using same
PLC. It will not increase the size of PLC as it was the
case with conventional systems.

47. Logic gates in PLC
A
B
A
B
O
O
OA
A
B
O
(OR Gate)
(AND Gate)
(NOT Gate)
(XOR Gate)
= A . B
= A + B
= A
_
= A.B + A.B
_ _

48. Combination of Logic gates
A
A
B
B
C
C
O
Two out of three logic with digital Gates

49. Timer
 On-Delay timer:-This
type of timer simply
"delays turning on".
 Off-Delay timer:- This
timer simply "delays
turning off".
t
t
0
0

50. Timer
 Timed:-Pulse with defined
length after signal change
from L to H at the
input.Output carries H-
signal for preset time.
 Pulse:- Generate a pulse
of 1 second at the output
when input signal change
from L to H.
t

51. Flip Flop
 To understand this SR
flip flop we need its
truth table which is
below,
Q
Q
SET
CLR
S
RS R Q Q
1 0 1 0
0 0 1 0
0 1 0 1
0 0 0 1
1 1 X X

52. Relays
 PLC processes inputs, outputs, and the
actual program we are almost ready to
start writing a program.
 But first lets see how a relay actually
works. After all, the main purpose of a
plc is to replace "real-world" relays.
 We can think of a relay as an
electromagnetic switch. Apply a voltage
to the coil and a magnetic field is
generated.

53. Relays
 This magnetic field attracts the contacts of the relay in,
causing them to make a connection.
 These contacts can be considered to be a switch.
 They allow current to flow between 2 points thereby
closing the circuit.

54. Relays
 Consider example.
 Here we simply turn on a bell
 Whenever a switch is closed.
 We have 3 real-world parts.
 A switch
 A relay
 A bell
 Whenever the switch closes we apply a current to a bell
causing it to sound.
 Notice in the picture that we have 2 separate circuits.
 The bottom indicates the DC part. The top indicates the
AC part.

55. PLC Operation
 PLC works by continually scanning a program.
 We can think of this scan cycle as
consisting of 3 most important steps.

56. PLC Operation
 PLC operate very much just like a computer.
 PLC read input devices, execute its program using the status of
input devices, writes the appropriate values to the output
devices.

57. Principle of Operation
 Computer execute keyboard instruction while PLC follow the
program.
 PLC scan time varies from mS to Seconds.
 Step 1- CHECK INPUT STATUS
 PLC takes a look at each input to determine if it is on or off.
 Rerecords this data into its memory to be used during the next step.

58. Principle of Operation
 Step 2-EXECUTE PROGRAM
 PLC executes your program one instruction at a time.
 It already knows which inputs are on/off from the previous
step it will be able to decide whether the program output
should be turned on based on the state of the input.
 It will store the execution results for use later during the
next step.

59. Principle of Operation
 Step 3-UPDATE OUTPUT STATUS
 PLC updates the status of the outputs.
 It updates the outputs based on which inputs were on
during the first step and the results of executing your
program during the second step.

60. PLC and other type of
controller
 No. of input / output handling
 Micro PLC ( Relay Replacer )
 Small
 Medium
 Large

61. Response Time
 The total response time of the PLC is a fact we have
to consider when purchasing for a PLC. Just like our
brains, the PLC takes a certain amount of time to
react to changes.
 INPUT
 It takes certain amount of time for the processor
to notice the input signal.
 EXECUTION
 Certain amount of time to process the
information received from the input.
 OUTPUT
 Output receives a signal from the processor

62. Processor Scan
 Scan time
 PLC execute only one programme and it keeps on
doing it over and over again. The time out PLC takes
to execute this programme once is called the scan
time.
 Scan time can be reduced by stopping the solution
of a line of logic once it has determined it is False,
regard less of the rest of the line.
 House keeping
 Checking battery stakes.
 Verify memory integrity.
 Checking power supply.
 Vesting the watchdog timer.

63. Start up Procedure
 Operation Test
 Place processor in “Program mode” and turn
on main power switch.
 Load the pre-tested control program into the
programmable controller.
 Disable all outputs, select the run mode on
the processor, and verify that the run light
on the processor is activated.

64. Start up Procedure
 Check each rung of logic for proper
operation by simulating the inputs, proper
time and sequence in the program.
 Make any required changes to the control
program.
 Enable output modules & place processor
in “Run” mode.
 Test control system as per process
operating procedure.

65. Problem sources in PLC Applications.
 Field devices
 Wiring
 I/O modules
 Program
 Processor, racks, etc.
 Heat protection, loose connections
 Accumulation dirt, dust, failed ventilation.
Maintenance

66. PLC Preventive Maintenance
 Routine Maintenance Perform Weekly
 Change Filters.
 Check error log and scan time.
 Check diagnostic lights.
Maintenance

67. Visual Inspection Perform Quarterly
 Check for proper operation of ventilation system.
 Check for buildup of dust or dirt.
 Is any extraneous material in the cabinets.
 Look for loose connections.
 Are there signs of temporary modifications, jumps
etc.?
 Look for signs of heating, burning, or water
infiltration.
 Is all the documentation present and up to date?
Maintenance

68. Maintenance Perform Yearly
 Replace batteries.
 Backup Program
Maintenance

69. Programming device
 Copy the program to same secure media.
 Monitor the programme which it is running.
 Reload a programme from the storage media.
 Make changes to the programme.