Unit 4 - PLC.pptx

UNIT 4 – Programmable Logic
Controller (PLC)

PLC video links
• https://www.youtube.com/watch?v=zEcAQZQ
8DGQ&list=PLGoZgwDrvRy92QyXIackQ0xv8pH
R5YQjZ
• Engineering graphics – M senthil kumar

Programmable Logic Controllers
(Definition according to NEMA standard ICS3-1978)
• A digitally operating microprocessor based
electronic apparatus
• which uses a programming memory for the
internal storage of user oriented instructions
• for implementing specific functions such as
logic, sequencing, timing, counting and
arithmetic
• In order to control various types of machines
or processes
• through digital or analog modules (I/O).
National Electrical Manufacturing Association (NEMA)

S.No Microcontroller PLC
1 Used for any type of
application
It is a special microcontroller
designed for
industrial application
2 Microcontroller
works with electronic
devices. Ex: Transistor
It will also work with
relays
PLC works with power devices.
Ex :relays,
3 It doesn’t work as a
stand alone controller
but it came as a part of
electronic circuit or
device
PLC is a stand alone controlling
device
that can be programmed for
any process.
4 I/O ports in MC is less I/O ports in PLC is more
5 Microcontroller is a chip PLC = number of chips

Historical Background
• The Hydramatic Division of the General
Motors Corporation specified the design
criteria for the first programmable controller in
1968
• Their primary goal
• To eliminate the high costs associated
with inflexible, relay-controlled systems.

Simple PLC
network digital inputs
digital outputs
analog inputs / outputs

example: turbine control (in the test lab)

Types of PLC
Box Type /Unitory/
Compact PLC
Modular or Rack Type PLC

PLC: Location in the control
architecture Enterprise Network
directly connected
I/O
Control Bus
(e.g. Ethernet)
Engineer
station
I/O
I/O
I/O
I/O
CPU
Sensor Bus (e.g. ASI)
Field Bus
gateway
Field Stations
Control Station
with Field Bus
direct I/O
I/O
Field Devices
FB
gateway
gateway
I/O
I/O
I/O
I/O
CPU
COM
I/O
I/O
I/O
COM
CPU
COM
COM
COM
I/O
Field Bus
CPU
COM
2
I/O
I/O
I/O
CPU
COM1
COM
2
I/O
CPU
Operator
station
large
PLCs
small PLC
PLC
PLC
COM1
COM1
Supervisor
Station
data concentrators,
not programmable,
but configurable

PLC Operation
PHASE 2
Program
Execution
PHASE 3
Diagnostics/
Comm
PHASE 4
Output
Scan
PHASE 1
Read Inputs
Scan

PLC Operation
PHASE 1 – Input Status scan
A PLC scan cycle begins with the CPU reading the
status of its inputs.
PHASE 2– Logic Solve/Program Execution
The application program is executed using the status of the
inputs
PHASE 3– Diagnostics
Once the program is executed, the CPU performs diagnostics
and communication tasks
PHASE 4 - Output Status Scan
An output status scan is then performed, whereby the stored
output values are sent to actuators and other field output
devices. The cycle ends by updating the outputs.

Inputs and Outputs Devices
• Push Buttons
• Proximity switches
• Photoelectric sensors
• Temperature sensors
• Pressure sensors
• Motors
• Solenoids
• Indicator lamps
• Resistive loads
• Contactors
Inputs Outputs
Push button Photo Sensor Pressure
Sensor
Motor

CONTROL DEVICES
1) Mechanical control - cam, governor, etc.,
2) Pneumatic control - compressed air, valves,
etc. (Electro-Pneumatics)
3) Electromechanical control - switches, relays, a
timer, counters, etc,
4) Electronics control - similar to
electromechanical control, except uses
electronic switches.

Example Process
Sensors,
Emergency
Shut off
Solenoids
PLC
(programmable
logic controller)
All Input
Devices
All Output
Devices
PLC

PLC
INPUTS
OUTPUTS
MOTOR
LAMP
CONTACTOR
PUSHBUTTONS

Example: Process Safety
Pressure Emergency Release
Solenoid
Counter
Pressure
Sensor
10 Second
Timer
Pressure
Release
Valve

Areas of Application
 Manufacturing / Machining
 Food / Beverage
 Metals
 Power
 Mining
 Petrochemical / Chemical

Applications of PLC
• Coin-Operated
Carwash
• Conveyor
Diverter Control
• Greenhouse
Irrigation
• Lumber Mill
Operation
• Oil recovery
systems

Leading Brands Of PLC
AMERICAN 1. Allen Bradley (Rockwell Software RSLogix500)
2. Gould Modicon (Modsoft)
3. Texas Instruments (Simatic)
4. General Electric (LogicMaster6
5. Westinghouse
6. Cutter Hammer
7. Square D (PowerLogic)
EUROPEAN 1. Siemens
2. Klockner & Mouller
3. Festo
4. Telemechanique (Modicon TSX Micro)
JAPANESE 1. Toshiba
2. Omron (Syswin)
3. Fanuc
4. Mitsubishi

• (a) Mitsubishi,
• (b) Siemens,
• (c) Allen-Bradley,
• (d) Telemecanique notations for the
addresses.

Programming Device
• Also known as:
 Industrial Terminal ( Allen Bradley )
 Program Development Terminal ( General Electric )
 Programming Panel ( Gould Modicon )
 Programmer ( Square D )
 Program Loader ( Idec-Izumi )
 Programming Console ( Keyence / Omron )

Ladder Logic / Programming in PLC
Read real world inputs
Evaluate ladder
Write real world outputs

PLC Programming Techniques
• LD – ladder Diagram
• SFC - Sequential Flow chart
• FBD – Functional Block diagram
• ST – Structural Text
• IL – Instructional List

PROGRAMMING
• Ladder logic uses a
variety of programming
symbols
• Power always flows from
left to right
• Output devices are in the
ON state if power flows
through them
Normally Closed
Contact
Normally Open
Contact
Output Device
or Coil
Power rails

Ladder Logic
make contact
break contact
relay coil
Special Instruction
Power flows when the
input device is on
Power flows when the
input device is off
True/False

Ladder diagram used to write PLC
program

Normally Open Pushbutton
Normally Closed Pushbutton
Normally Open switch
Normally Closed switch
Normally Open contact
Normally closed contact

• Outputs “energize” when rung conditions
preceding them are “True”
• When Input 1 is True, Output 1 is energized.
IF THEN

• Compare a
circuits
diagram to a
ladder logic
diagram
Relay
Button Motor
24 V DC
Input
Button
Power Rails
Motor

• Boxes
• Boxes represent various instructions or
functions that are Executed when power
flows to the box.
• Some of these Functions are timers,
counters and math operations.

Ladder Logic
Rung 1
Rung 2
Rung 3
Rung 4
Power Rails
Ladder is evaluated (scanned)
starting from the top rung, left to
right, followed by the next rung,
and so on, until the bottom is
reached. Then starts again at the
top.

List of items required when
working with PLCs
1. Programming Terminal - laptop or desktop PC.
2. PLC Software. PLC manufacturers have their own
specific software and license key.
3. Communication cable for connection from Laptop
to PLC.
4. Backup copy of the ladder program (on diskette,
CDROM, hard disk, flash memory). If none, upload it
from the PLC.
5. Documentation- (PLC manual, Software manual,
drawings, ladder program printout, and Seq. of
Operations manual.)

Ladder Logic
Button
Motor
Motor
Motor
On lamp
(Green)
Off lamp
(RED)
Motor output
Lamp for power
applied
Lamp for power
not applied
Contacts

Mnemonics in PLC
The study and development of systems for
improving and assisting the memory. -
நினைவூட்டல்

Procedure to Write in Exams
1. Introduction about the logic gate with the
symbol.
2. Write and explain the TT with true/false as
theory part.
3. Draw and explain the electrical diagram
4. Ladder diagram
5. Explanation of Mnemonics in detail.
6. General Applications if any.

Headings must be
• Introduction
• Truth table
• Description for Electrical diagram
• Ladder diagram
• Timing I/O diagram (if possible)
• Program/Mnemonics explanation

AND OR NOT NAND NOR EXOR EXNOR
Logic
Diagrams
Truth table
IC number
IC
7408
IC 7432 IC 7404 IC 7400 IC 7402 IC 7486 IC 74266
Switch
diagram
(Electrical)
Ladder
diagram
(PLC)
Mnemonics

PLC Exclusive NOR (XNOR) LOGIC

Ladder Diagrams
Binary combinations are expressed by series and parallel relay contact:
+ 01 02
50
Coil 50 is active (current flows) when 01 is active and 02 is not.
01
02 50
Series
+ 01
40
02
Coil 40 is active (current flows) when 01 is active or 02 is not.
Parallel
Ladder Diagrams representation “logic" equivalent
01
02 40

Simplification of Ladder diagrams

Simplification of Ladder diagrams
• It is illegal due
to the reverse
power flow.
• In figure a, the
upper block is
shorter than
lower block.
• It legal by
switching
them.

Ladder Diagrams Example
01 02
50
01
02
03 50
03
relay coil
(bobine)
break contact
(contact repos)
make contact
(contact travail)
corresponding
ladder diagram
origin:
electrical
circuit
50 05
44
rung
"coil" 50 is used to move
other contact(s)

SEQUENCER
• Sequencers are used with machines or
processes involving repeating operating
cycles which can be segmented into steps.

Sequencing using PLC
(Cylinder Sequencing)

Internal Relays
• These 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.
• There are also some special relays that are
dedicated to performing only one task. Some are
always on while some are always off.
• Some are on only once during power-on and are
typically used for initializing data that was stored.

Latching
• Latching is the term for
a self-maintaining
circuit.
• Machine keep running
even after the start
button has stopped
being depressed.
• A latch is like a sticky
switch – when pushed
it will turn on, but stick
in place, it must be
pulled to release it and
turn it off.
Start button
Motor
Motor
Stop
button

Timers and its Types
• Two basic types of timers in
PLCs:
1. On-delay timers
2. Off-delay timers
Clock
Accumulator
contact
reset
output
Register
Contact
As an example, a certain step in the
manufacturing process is to begin 30
seconds after a signal is received from a
limit switch. The 30-second delay is the
on-delay timer's preset value.

Delay-off timer example
• When the input start,
the output energized
and the timer start.
• The output contacts
latch the input and
keep the output ON.
• After the preset time,
the timers come ON
and breaks the latch
circuit, so switching
the output OFF
For example, for an external cooling fan on a
motor. The fan is to run all the time the motor
is running and for five minutes after motor is
turned off. This is a five-minute off-delay timer.
The five-minute timing cycle begins when the
motor is turned off.

Example : Solenoid actuated door-lock
• Solenoid actuated when:
(i) ON signal from number-pad outside door
(ii) ON signal from door-open switch inside door
• Solenoid ON for 5 sec, then OFF.
While O:0/1 remains ON,
Timer COUNTS DOWN from PRESET
COUNT DOWN = 0  ( T4:1) set to ON

Example for Timers
 Done bit (DN),
 Enable bit (EN)
 Reset (RES) (RST)
 Accumalated value: The values are counting is displayed
from zero. Value becomes zero whenever the timer is reset

Cascaded Timers
A succession of devices or stages in a process, each of which triggers or initiates the next

Retentive Timer
• Retain the previous value.
• Retain the accumulated value even during
Power loss.
• Ex: Each time the motor is turned off, the
timer will remain motor’s elapsed running
time.

• When the push bottom PB1 is pressed, the timer starts working and the
reading starts accumulating.
• When we push the PB1 button then rung become false and the timer
stops working. Consider we are switching ON the push after a time, the
timer starts counting from the previous value before the timer is stopped.
• We have to add another switch PB2 to reset the values in the timer.
Retentive timer

Example: Industrial Mixer
• Filled with liquid
• Heated
• Mix for 10 minutes.

Sequential Function Chart
State 2
State 1
State 3 Rotate
Heat
Fill with
liquid
Level full switch
Timer
Temperature Switch

Switch / Simple electrical diagram

University Problem on PLC
14 b) Develop the ladder logic to fill the tank.
• (i) Fill the tank up to 80%. When the tank is
filled, turn ON the heater to raise the
temperature up to 70 deg.
• (ii) When this temperature is reached, turn
OFF the heater and open the outlet valve.
• (iii) When the level in the tank falls below
10%, close the outlet valve.

Sequential Function Chart
State 2
State 1
State 3 Open Outlet Valve
Heat
Fill with
liquid
Level 80% switch
Level 10% switch
Temperature Switch
State 4 Close Outlet Valve

Switch / Simple electrical diagram
Solenoid
Valve

80%
Level 10%
floater
Solenoid
for Outlet
Valve

Part C AU problem on Timers
• Design a PLC circuit that can be used to start a
motor and then after a delay of 100s start a
pump when the motor is switched off there
should a delay of 10s before the pump is
switched off. (Nov/Dec 2020 & 2021)

University Problem based on Timers
14 (a) Draw a ladder diagram for two motor
system having following conditions:
• (i) Starting push button starts motor 1
• (ii) After 10 seconds, motor – 2 is ON
• (iii) Stopping the switch stops motor 1 and 2
(Time base 1 sec). Nov/Dec 2021

Sample Answer
Stop Motor 1
Motor 2
Motor 1

Counters
• Count the number of occurrences of an event
• Examples:
– Pallet loading in factory
• After 10 parts arrive on conveyor, worker comes to load pallet
– Pneumatic press hammer
• Hit the part 20 times, then wait for part to be unloaded
– Rice cooker alarm
• Beep 5 times when rice is cooked

Counters
Register
Accumulator
contact
input
reset
output

Types of Counters
a. Counter up (CTU)
b.Counter down (CTD)
c.Counter reset (CTR)

Representation of Counters in
Boolean Programming

Example
• Consider the problem of control for a machine
which required to direct 6 items along one
path for packaging in a box and then 12 items
along another path for packaging in another
box.
• Draw the ladder diagram and Write down the
mnemonics for it.

Example
• Input 1 closes its contacts to
start the counting cycle,
resetting both counters.
• Counters 1 start to count pulses
in input2, it counts 6 items and
then closes its contact.
• This activates the output,
closes one path and start
another. when counter 2 has
counted 12 items it reset both
counters and opens counter 1
contacts.
1
Output 2
Counter 2
1

Example
• Pallet loading in factory
– After 4 parts arrive on conveyor
– STOP conveyor belt
– Turn ON the indicator light

Shift Register
• Imagine an ice-cream cone
machine. We have 4 steps.
• First
– we verify the cone is not broken.
– Next we put ice cream inside the
cone (turn on output 500)
– Next we add peanuts.(turn on output
501)
– And finally we add sprinkles.(turn on
output 502)
• If the cone is broken we
obviously don't want to add
ice cream and the other items.

Shift Register
• Therefore we have to track the
bad cone down our process line
so that we can tell all the
machine not to add each item.
• We use a sensor to look at the
bottom of the cone.(input 0000)
If its on then the cone is perfect
and if its off then the cone is
broken.
• An encoder tracks the cone
going down the conveyor (input
0001) A push button on the
machine will clear the
register.(input 0002)

Shift Register
• Here's what the 1000 series register (the
register we're shifting) looks like initially:

Shift register applications
• Tracking parts in an assembly line
• Controlling machine operations
• Inventory counter
• System diagnostics

Master Control
• Master controls can be thought of as
"emergency stop switches”.
• But this instruction isn’t a substitute for a
"hard wired" e-stop switch. There is no
substitute for such a switch!

Master and Jump control
• MC/MCS – Master
control Set
• MCR – Master Control
reset

Master Control
• Rungs 2 and 3 are only
executed when input 0000
is on(true).
• If input 0000 is not true the
plc pretends that the logic
between the MC and MCR
instructions does not exist.

Master Control
• When input 0000 is false,
inputs 0001 and 0002 are
forced off regardless if
they're physically on or off.
• MCR just tells the PLC
"that's the end of the
MC/MCR block.
Note: Timers should not be used inside the MC/MCR block because some manufacturers will
reset them to zero when the block is false whereas other manufacturers will have them retain
the current time state.

Master and Jump control Example
• An OUTB (OutBar or OutNot) instruction would not be
physically on. It is forced physically off.
• If the MC/MCR block were not there 0500 would be physically on
only when input 0001 was false(physically off). But since the
MC/MCR block is there, this happens only when input 0000 is true.
• When input 0000 is false it is impossible for 0500 above to be on.

Jump Control
• Conditional
jump function
enables
programs to be
designed so
that if a certain
condition exists
then a section
of the program
is jumped.

DATA Movement
LDA - LoaD Accumulator
STA - STore Accumulator
DIFU - differentiate up/down – NO/NC

Data Movement
• Copy File Instruction (COP) :
– Output instruction that copies a user-defined
group of 16-bit data file words

DATA conversion
• What is BCD
Understanding BCD: Write BCD of 89351
Answer : 1000 1001 0011 0101 0001

DATA conversion
• TOD (value,destination) -
convert from BCD to 2s
compliment
• FRD (value,destination) -
convert from 2s
compliment to BCD
• DEG (value,destination) -
convert from radians to
degrees
• RAD (value,destination) -
convert from degrees to
radians 2’s Compliment: The negative of a binary
number represented by switching all ones to
zeros and all zeros to ones and then adding
one to the result

BCD to Decimal conversion
(from 2’s compliment)

Application of 2’s compliment

Data Comparison
Equal instruction:
• Test when two values are equal.
• Instruction is true when source A is equal to source B.
Not Equal Instruction (NEQ) :

Data Comparison
• The Less Than Instruction (LES)
• Less Than or Equal (LEQ)

Data Comparison
• Greater Than Instruction (GRT)
• Greater Than or Equal (GEQ)

Addition operation
LDA - LoaD Accumulator
STA - STore Accumulator
DIFU - differentiate up/down – NO/NC

Math operations in PLC
• Square roots
• Scaling
• Sine
• Cosine
• Tangent
• Natural logarithm (ln / loge)
• Base 10 logarithm (log10)
• X^Y (X to the power of Y)

Selection of PLC
General Criteria
»Number of logical inputs and outputs.
»Memory
»Number of special I/O modules
»Scan Time
»Communications
»Software

Pros and Cons of handheld
programming terminal

Pros and Cons of software
programming (PC) with PLC

Programmable Automation Controller

Coin Operated Car parking barrier

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