Basic PLC Training .pdf

PLC taring for beginner

1. PLC BASICS COURSE
By Himanshu Mishra
Schneider Electric India
New Delhi

2. Good Morning

3. Questions to start with…...
1)Which Industry embraced PLC Globa
lly & how was it different in
India?
2) Who w
a
s the fi
rst user
of PLC? When & why?
3)Who was the first vendor? 4)What w
a
s the alternate technol
ogi
es in other parts of the world?
5)What is the common langua
ge of PLC programming &
why ?
6) What’s traditional PLC applications?
Why was the suffix
“L” dropped from PLC ?
7) Which brands prod
uct starts with PLC? What
will you compete against?
8)What makes a PL
C Micro or Nano?
9) What are the possible Inst
ruction features of
Nano & Micro? C
a
lcul
ator exam
pl
e.
10)What’s the market si
ze of Nano+ Micro in
India? Micro goes upto ?
11)What are the cons
ti
t
u
ent
s of PLC’s?
12) List down the Inputs
& Outputs you are aware of?
13)How many types of ou
tput cards are there?
14)What’
s
a vol
a
til
e
m
e
mory? What’s EEPROM, PCMCIA?
15)Whats a bit in PLC par
lance?Relationship of
a bit, byte & word?
16)How does a PLC operate? 17) What is RS 232 C? 18)What is data table? 19) What is a EOI ? Does it sa
ve I/O’s? How many
types are there?
20)How do I si
ze & sel
e
ct a PLC?

4. PLC Workshop
™
Upon completion:
™
The student will be familiar with
the basic structure, operation, and
optional interfaces of a PLC
™
Have an understanding of the Centra
l Processing Unit, the structure
of User Memories, Program Prot
ection options, the CPU and I/O
System Scans will als
o
be explained.
™
The student will be able to :
¾
Describe the Input/Output interface;
¾
Describe the functional operation;
¾
Describe the PLC components.

5. Block Diagram of a Control System
PB1 LS1
INPUTS
M1
M2R
LOGIC
OUTPUTS
M1
SOL

6. What is a Logic?
™
The first step involv
ed in automating any industrial process or
machine is to determine the
sequence of operation
or
events
which are specific to its operatio
n. This
sequence is then arranged
into a set of logic functions.
™
Logic functions are of two types:
¾
Combinatory
: Where r
e
sults depends only on
the pres
ent state of the
inputs.
¾
Seque
n
tial
: Where r
e
sults depends on th
e present and past state of the
inputs
™
Then this Logic scheme is turned in
to a physical system using the
bas
ic building bloc
ks of the particular technology selected,i.e.
Mechanical, Fluidic, Pneu
matic, Electromec
ha
n
i
cal,
Electronics
.

7. Which Logic System and why?
™
There are three basic system options that are open to a design engineer.
¾
Relay Logic
¾
It h
a
s for many years b
e
en th
e w
o
rk
horse o
f
most elect
rical installations.
¾
Advantages:
It was simple for sm
all systems, hence co
st advantages
due to wide range of
available coil voltages.
¾
Disadvantages:
As the number of rela
ys increases, it
req
u
ires larg
er
physical area, coupled with costly en
clo
s
ures, th
e lab
our charges, th
e
schematic and connection
diagrams, escalates
the final cost.
¾
Wired Logic
¾
Progra
m
mable Logic
¾
Improved installation time
¾
eliminate the need for exte
nsive wiring of timers,
relays and other components
¾
Improved flexibility
¾
enable control system ch
anges simply
by reprogramming
¾
Much more compact than
relay control panels
, yet enables comple
x, high-level
cont
rol
¾
Improved reliability
™
Selection of the most suitable system is largely dependent on the application, availability and acceptability.

8. 1.Programmable Controllers
The most significant development in the
industrial control field in previous half-century
…..
The Control of the
Future

9. What is a Programmable Controller?

10. What is a PLC?
Programming
Device
Input/Output
System
Output Devices
Input
Devices
User
Program
Data
Storage
Output
Table
Input Table

11. 4 Basic PLC Parts
Processor Processor I/O Interface I/O Interface Power Supply Power Supply Programming Device Programming Device
+ Electronic Operator Interface

12. 4 Basic PLC Parts
Processor
Central Processing U
n
it
Memory
Input/Output Rack
Adapter
Module
Module
Module
Module
Module
Module
Module
Module
Output Devices
Soleno
ids
Motor Starters
Alarms
Ind
icators D/A
Logic BCD
Input Devices Limit Switches Pres. Switches Prox.
Sw
it
ches
Temp. S
w
itches
Push Buttons
A/D
Logic BCD
Program Panel
Power Supply

13. Optional Int
e
rfaces
Programming
Device
CRT
Monitor
Central Processor Unit
Power Supply
Proces
sor
Mem
o
ry
I/O
Comm
unications Port
Mod
e
m
Mod
e
m
Radio
Telephone Modems
Satellites
Input D
e
vices
Pushbutt
ons
Proxim
ity Switches
Lev
e
l Switch
e
s
Photoelectric Sensors Selector Switch
e
s
Lev
e
l Transm
itters
Pres
sure Transducers
Input D
e
vices
Pushbutt
ons
Proxim
ity Switches
Lev
e
l Switch
e
s
Photoelectric Sensors Selector Switch
e
s
Lev
e
l Transm
itters
Pres
sure Transducers
Output Devices Contactors Starters Solenoids Pilot L
i
ghts
Display
s
Output Devices Contactors Starters Solenoids Pilot L
i
ghts
Display
s
Peripheral Equi
pment
Other
P
LCs
Host Co
mputers
Color Graphics Etc.
Peripheral Equi
pment
Other
P
LCs
Host Co
mputers
Color Graphics Etc.
Other
P
LCs
Host Computers O
p
erator Interfaces Ethernet TCP/IP

14. PLC Definition
™
A
Programmable Logic Controller
(
PLC)
is an industrial computer
that accepts inputs from switches
and sensors, evaluates these in
accordance with a stored program, and generates outputs to control machines and processes.
™
A
Programmable Logic Controller
(
PLC)
is
is
a s
o
lid
state dev
ic
e
that uses soft wired logic contain
ed in the controller’s memory to
duplic
a
te the functions of relays
and hardwired solid state control
dev
ices. In operation, the memory
unit sequentially scans inputs(
sensors, limit switches, push buttons
, photocells) in cyclic fashion to
determine which outputs( contacts, mo
tor starters, solenoids, pilot
lights, converters, etc.)
should be turned on or off.
•A

Programmable Logic Controller
(P
LC)
is an electronic device
that control machines and proc
esses. It
uses a programmable
memory to store instructions and
execute specific functions that
inc
lude ON/OFF control, timing,
counting, sequencing, arithmetic,
and data handling
.

15. 2.Why Use a PLC ?????????????

16. Why Use a PLC?
™
Reliability
™
Flexibility
™
Advanced Functions
™
Communications
™
Speed
™
Diagnostics

17. PLC Advantages
™
Ease of programming
™
Ease of maintenance
™
Des
igned for indus
trial environment
™
Quick installation
™
Adaptable to change

18. Traditional PLC Concept
™
PLC performs relay equiv
a
lent functions
™
PLC performs ON/OFF control
™
Ladder diagram program representation
™
Des
igned for indus
trial environment
™
Des
igned for ease of use and maintenance
18

19. Traditional PLC Applications
™
Packaging
™
Bottling and canning
™
Material Handling
™
Power Generation
™
HVAC/building control systems
™
Security Systems
™
Automated Assembly
™
Water Treatment
™
Food and Beverage
™
Chemicals
™
Pulp and Paper
™
Pharmaceuticals
™
Metals
Virtually any application that requires electrical control can use a PLC

20. 3. History of PLC’s

21. Historically
™
Machines have been viewed
as operational entities
™
Processes have been viewed as functional entities
19781978
19671967
19711971
19581958
19751975
19691969
19631963
19701970
19791979
19771977
21

22. Evolution
•
PLC development began in 1968 in response to a
request from Hydramatic Division of General Motors. At that time GM frequently spent days or weeks replacing inflexible relay-based control systems whenever it changed car models or made any line modifications. To reduce the high cost of rewiring, GM’s control specs called for a solid state system that has the flexibility of a computer, yet could be programmed and maintained by plant engineers and technicians. It also withstand the dirty air, vibration, electrical noise, humidity and temperature extremes found in the industrial environment.
22

23. Evolution
™
Proliferation into other industries
¾
PLC performs relay-equivalent functions
¾
PLC’s applied in
¾
Manufacturing industries
¾
Food and bever
age industries
¾
Power industry
¾
Process industries
¾
Metals industry
¾
Pulp and paper
industries
23

24. Evolution
™
PLC usage proliferates into other indus
tries
24

25. Evolution
™
Introduction of the “intelli
gent” Programmable Controller
¾
PLC perfor
ms arithmetic
and data manipulation
functions
¾
Applications expand in all industries
25

26. Evolution
™
Introduction of “mini” Programmable
Controllers
¾
Intended for small scale dedicated applications
26

27. Evolution
•
Expansion of capabilities
¾
Oper
ator communication
¾
Analog
contr
o
l
¾
Positioning control
¾
Machine fault detection
™
Installations expand into
minicomputer equiv
a
lent
applic
a
tions
27

28. Evolution
™
Installation of manufacturing lines controlled by PLC networks
28

29. Evolution
™
The year of PLC “Downsiz
ing”
¾
Micr
oproc
essor
-
b
ased PLCs now cost effective in
small-scale applications
¾
Space-efficient, high-density I/O
29

30. Evolution
™
The year of PLC “Downsiz
ing”
¾
Micr
oproc
essor
-
b
ased PLCs now cost effective in
small-scale applications
¾
Space-efficient, high-density I/O
30

31. Evolution
™
Introduction of fourth and future generations of PLCs providing continuing improvements in cost/performance effectiveness
¾
Improved operator communication
¾
Expanded capabilities
¾
Extensive inter-control communication
31

32. Evolution
™
The advent of distributed control
¾
Data Highways
¾
Peer-to-peer PLC networks
¾
Applic
ations:
¾
Material handling/tracking
¾
Decentralized process control
32

33. Evolution
™
Smart I/O, more distributed intelligence
¾
Proces
sing power in I/O interfac
e
¾
Microprocessor CPUs incr
ease functionality, at
lower cost
¾
PID control
¾
Graphic operator
inter
f
aces
33

34. Evolution
™
PLCs functionality expands into computer-like capability
¾
Instruction sets expand
to incl
ude floating point math, Boolean
file manipulations
¾
Microprocessor-based I/O perfo
rms sophisticated closed loop
control
¾
Use of Data Highways ex
pand throughout industry
34

35. 4.The Changing Face of Industrial Control
35

36. Business Is Driving the Integration of Plant Floor & Information
INFORMATION
CONTROL
ERP
MRP II
MES/Ba
tch
MMI/
SCADA Control System Devices
1960
1970
1980
1990
2005
TIME
Fixed
Co
ntrol
Programmable
Co
ntrol
Networked
M
a
n
u
facturing
Systems
Machin
e
Enterprise
Plant Floor
Network
e
d
Business and

M
a
nufacturing Systems

37. Distributed Control Market Trends
Distributi
n
g control
l
e
rs to
improve performanc
e
Device Element
•
Distribution of Control
•
Control migrating into other devices
•
Increased Importance of Networking
Control Element
Distributi
n
g I
/O t
o

reduce w
i
ring costs
I’
m op
en
Distributi
n
g devices to
eliminate I/O an
d red
u
ce w
i
ring
I’
m op
en
& I’
m

OK
!
Devices w
i
th
diag
n
o
stics to
improve proce
s
s av
ailability
L
o
g
ic capable devices to
improve performanc
e and
reduce costs

38. Information Flow…
I/OI/O
Thin Cli
e
nt
HMI
Thin Cli
e
nt
HMI &
Dat
a
S
e
rv
er
S
w
itch /
Rout
er
Se
r
v
e
r
Cli
e
nt
Te
rmin
al
Cli
e
nt
Te
rmin
al
Cli
e
nt
Te
rmin
al
Cli
e
nt
Te
rmin
al
Cli
e
nt
Te
rmin
al
Web S
e
rv
er
&
Fir
e
w
a
l
l
In
tern
e
t
In
tern
e
t
Re
m
o
t
e
Cli
e
nt
Re
m
o
t
e
Cli
e
nt
Re
m
o
t
e
Cli
e
nt
Re
m
o
t
e
Cli
e
nt
Control Networ
k
Data
Networ
k/
Intr
an
et
ERP MIS
HMI/SC
A
D
A
CRM
De
v
i
ce
s
Control System
Information Control
Fie
l
dbu
s
F
ie
ldbu
s
PLC
PLC
Fi
el
d
D
e
v
i
ces
Fi
el
d
D
e
v
i
ces
I/O Bus
I/O Bus
I/O
Fi
el
d
D
e
v
i
ces
Fi
el
d
D
e
v
i
ces
I/O

39. Information Flow…
In
tern
e
t
In
tern
e
t
Modbus
Ethernet TCP/I
P
Ethernet TCP/I
P
Se
r
v
e
r
Web S
e
rv
er
&
Fir
e
w
a
l
l
S
w
itch/Router
Bus
X
Bus
X!
!
!
Em
a
il
fro
m
PL
C
-
1
F
a
ilur
e
R
e
por
t
Information
Webcast
Control
ASi

40. Open Communications…
Ethernet
ERPERP
B
u
si
ness
La
y
e
r
B
u
si
ness
La
y
e
r
Fir
e
w
a
ll
Intern
et
SCADA
Pow
e
r Monitorin
g
Soft
w
a
re
SMS
TM
Sy
m
b
o
l
s
Sy
m
b
o
l
s
tab
l
e
s
tab
l
e
s
=S= Leads In Web Automation
I/
O
I
/
O
I/
O
Serip
l
ex
Ethernet
PH
ASE
ME
T
E
R
S
MI
N
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X
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[S
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t
u
p
]
MO
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PH
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(
A-
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B(
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)
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Ethernet
Modb
us
Bridge

41. 2.The Micro PLC

42. Development of the PLC
™
The driv
ing force behind the devel
opment of the Micro PLC was the
demand by OEM for a PLC.
Desired Features of Micro PLC •
R
elay Logic Instructions.
•
M
ath capabilities, +,-,*,/,Sq-root,=,<,>
•
T
imers--
On/Off Del,Retentive
•
D
ata Handling instructions
•
U
p/Down Counters
•
H
igh-speed counting
•
BCD to Binary conversion routines
•
D
rum timer and sequencer functionality
•
S
ubroutines and interrupts
•
P
rogrammed with a personal computer
•
C
ommunication with other electronic devices
•
A
nalogue Handling

43. What makes micro PLC a micro?
™
Micro PLC’s
a
re self-contained units with
Processors,Power supply & I/O’s in one package …. Hence often called Packaged Controller
.
General Characteristics are -- ™
Number of Inputs and Outputs </= 32 I/O’s.
™
Cost in four figures.
™
Physical Size --
ever competing.
Modicon
TSX Nano
10E/S
16E/S
24E/S
60mm (2.36”)
85mm (3.35”)
105mm (4.13”)
135mm (5.32”)
16
5mm (6.50”)

44. 3.
Micro
PLC Operation

45. PLC Components Overview
CR
???????
Central
Processor
MEMORY
progra
m
data
Low
V
o
lta
g
e
POW
E
R SUPPL
Y
Output
Circuits
Input
Circuits
Programming / Communication
Devices
Optical
Isolation
Barrier
Optical
Isolation
Barrier

46. Input Devices
™
Pushbuttons
™
Selector Switches
™
Limit Switches
™
Level/Pressure/Temperature Switches
™
Photoelectric Sens
ors
™
Proximity Sensors
™
Motor Starter Contacts
™
Relay
Contacts
™
Thumbwheel Switches
™
Trans
ducers/Transmitters
™
Encoders/Tachos/Resolvers
•
120 VAC
•
24 VDC

47. Points to know about Input Modules.
™
Can be
Discrete
or Analogue
.
™
Can be varying voltages/ currents.
™
Field signals
are unfiltered. Conditioning of the signals are required
because the internal components of
a PLC operate on 5V DC. This
minimizes the possibility of
damage by shielding them.
™
To
electrically isolate
the internal components from the input
terminals, PLC employ an optical
isolator --
a dev
ice which uses
light to couple signals from
one electrical device to another.
™
The field signal needs to be qualified as valid which means
it needs
to be distinguished from the electrical nois
e
.
™
This activity is done by Input Filt
ers which determine the validity of
the signal of
a signal by it’s durat
ion --
they wait to confirm that a
signal is a reference from an inpu
t device rather than an electrical
noise.
™
Some
PLC’s
have adjustable filter
time ??( Question Higher/Lower)

48. Output Devices
Relays
•
120 VAC/VDC
•
240 VAC/VDC
•
24 VAC/VDC
Triac
•
120 VAC
MOSFET
•
24 VDC
™
Valves
™
Motor Starters
™
Solenoids
™
Control Relays
™
Alarms
™
Lights
™
Fans
™
Horns

49. Points to know about Output Modules.
™
Can be
Discrete
or Analogue.
™
Can be varying voltages/ currents.
™
Output circuits operate in a manner
similar to the input circuits –
signals from the CPU pas
ses thr
ough an isolation barrier before
energising
outputs.
™
Output Circuits can be
¾
--
..Relays ---can be either for AC/
DC, handle higher amp,slow,
wear & tear.
¾
---
Transistors --Switches DC Power,Fast
,lower Amp handling
typically 0.5A.
¾
Triacs
--
Switches AC Power,other featur
es same as Transistors.
™
Note
¾
--
Solid State Outputs (
T
riacs
&

Transistors) can be damaged by
ov
er voltage or over
curr
ent.

50. Points to know about CPU’s
™
CPU,the primary component is made of a microprocessor & a memory syste
m.
™
CPU reads the inputs,executes logic as dictated by the
APPLICATION
PROGRAM
,performs calculations & controls the outputs accordingly.
™
PLC users work with 2 areas of the CPU :
Program Files
&
Data Files
.
™
Program File stores an user applic
ation program,subroutines & the error
files.
™
Data files store data associated wi
th the program,such as I/O status,
counter/timer preset /accumulated va
lues & other stored constants or
variables.
™
Together the above 2 areas are call
ed Application or User Memory.
™
CPU also has an executive program
or system memory that directs &
performs “operation” activities of
the internal functions of the
C
PU’s. This
System Memory is Programmed by the manufacturer cannot be accessed by the user.

51. Points to know about Application Memory
™
Memory is a physic
a
l space inside the
CPU where
the

Program files
&
Data
information
are stored & manipulated.
™
Memory are 2 types --
volatile & non-
volatile.
¾
Volatile memory
can be easily altered
or er
as
ed, it can be written to & read
from.Without backup,the programmed contents will be lost
in absence of
Power. Best known form is RAM & is typically backed up by battery or

capacitor.
¾
Non-volatile
memory retains its
programmed contents without a backup. The EEPROM offers the same flexibility as RAM.
MEMORY
PROG
RAM
FILESDATA FILES

52. Knowing about Data, Memory & Addressing
™
Data
is a pattern of Electrical charges
that represent a numerical value.
™
A bit
is the smalles
t
unit of memory available
.
It is a dis
c
r
ete loc
a
tion
within a silicon chip that has a vo
ltage present(1--On) or absent (0--off).
™
16 bit
groups
is known as a
WORD
.
Generally CPU
’s process & store
data in words, but the data can be manipulated at the bit level.
™
Each
WORD
has a specific, physical location
in the CPU called an
address or a register.
™
The address is related to the
terminal
where
input &
output devices
are connected.
™
Thumbwheel switches require 4 bits per wheel
since they
communicate in BCD format.
T
hus any PLC used with a thumbwheel
must be able to accept a BCD input.

53. Memory & Data
MEMORY
™
Bit
1
or 0
™
Nibble
4
bits
™
Byte
2 nibbles
™
Word
2 bytes
™
Double Word
2 words
™
Long Word
2 D words
DATA
•
Octal
0-7
•
BCD
0-9
•
HEX
0-F (15)
•
Integer (signed)
-32767/ +32768
•
Unsigned Integer
65,535
•
Floating Point IEEE
+/-
3
.45x10
38
to
+/-1.17x10
-38

54. What' happens in an operating cycle
Ba
s
e
d on the data in
the output image file the PLC energises or de-energi
s
es it’s output
circuits,controlling external devi
ces
.
1.Input Scan
3. Output
Scan
START
-
--
-
PLC
OPERATING
CYCLE
TYPICALLY
1 to 25 ms.
During the input scan PLC examines the external input
devi
ces

On or Off.
The status of the inputs is
temporaril
y
stored in an input ima
g
memo
ry file.
Th
e PLC s
c
ans the instru
ctions in the ladder
logic pro
g
ram,us
es
the input status from the
input image file & determ
ines if an output w
ill
be energis
e
d.
The resulting
status of the outputs
is written to the output image memo
ry
file.
-
2. Program
Scan

55. Speed of a PLC or “the through put time”
™
The throughput time includes the ti
me for actuation of the physic
a
l
input ; time for PLC’s input circuit
to sense the signal;time for input
scan, program scan and output scan; ti
me for actuation of the output
circuit & corresponding field
device;and time for the CPU’s
housekeeping or overhead functions.
™
Therefore the formula is -- Input scan time+Output scan time+housek
eeping time
+
pr
ogram
scan
t
ime(addition of instructio
n execution times when all
instructions are True)
+
PLC input circuit filter time+PLC output
circuit turn on time.
Advanced Micros offer functions
of high speed counting with
direct control of outputs & im
mediate I/O update instructions.
These functions enable the micro
controller to detect & react
quickly to
changing conditions.

56. Power Supplies
™
PLC
Power supplies are typically desi
gned to meet normal operation of +10
to -15%.
Fluctuation
in voltage.
™
Converts the inc
o
ming voltage
to a useable form for t
he internal electronics
™
Protects
the PLC
‘s components from volt
age spikes
.For voltage condition
that are unstable insist on a CVT
between PLC & primary power source.
™
Operates either on 120VAC/ 240 VAC/
24VDC
.
™
PLC’s
Power Supply is designed to
meet short power losses without
affecting the operation of the system.
PLC can operate for several “ms”
without line power before the PS signals
the processor that it can no longer
provide adequate DC Power to the syste
m. The CPU executes a controlled
shut down whic
h saves the users program & data in memory
™
The other factor affecting
the function of the PLC is
EMI or electrical
noise
.Us
e
an isolation transformer, take
care of shielding from Drives,
ensure proper earthing & cabling practices.

57. Programming Devices & HMI
™
Personal Computer
¾
Run PLC Pr
ogr
a
mming Softwar
e
¾
It creates, edits,
document,
store and troubleshoot ladder
diagrams, and generates printed reports.
™
Hand Held Programmer
¾
Mainly a troubleshooting tool.
¾
On factory floor you can modify the pr
ogr
a
m, stor
e the
program and transfer the prog
ram to multiple machines.
™
Operator Interfaces
¾
These are not programming devices but graphic or alphanumeric displays & contro
l panels that consolidate all
the functions of traditional operat
or interface devices into a
single panel
.
These product
s co
mmunicat
e wi
th the PLC through a RS
232
communication port & thereb
y I/O’s are not sacrificed.

58. SOURCING vs. SINKING DC I/O (General)
+VDC
DC
Power Supply
-+
DC COM

59. SOURCING vs. SINKING DC I/O (General)
SINKING Pushbutton
SOURCING Pushbutton
DC
Power Supply
DC
Pow
e
r
Supply
-
+VDC
+
-
DC COM
+

60. SOURCING vs. SINKING DC Inputs
DC
Input Module IN1
DC
Input ModuleIN1
DC
Power Supply
-
Field Device
Field Device
DC
Pow
e
r
Supply
-
+VDC
+
+
DC COM

61. SOURCING vs. SINKING DC Outputs
DC
Power Supply
-
DC COM
DC
Pow
e
r
Supply
+ -
Field Device
Field Device
DC
Output Module
OUT1
DC
Output Module
OUT1
+VDC
+VDC
+
DC COM

62. RULES
Field devices on the positive side
(+VDC) of the fie
l
d powe
r
supply
are
sourcing
field devices.
Field devices on the negative side
(DC COM) of the field power
supply are
sinking
field devic
e
s.
Sourcing field devices must be c
onnected to sinking I/O cards and
vice versa. Sinking field devices must be conn
ec
ted to sourcing I/O cards and
vice versa.
) ) ) )

63. PLC Fundamentals Review

64. 4. Ladder Logic Fundamentals

65. Programming Language
™
A
Program
is a user developed series of instructions or commands that directs the
PLC to execute actions.
™
A
Programming Language
provides rules for combining the instructions so that
they produce the desired actions.
™
The most commonly used Programming Language is
‘LADDER LOGIC’
™
Other Languages occasionally used to program the
P
LC’s
include BASIC, C and
Boolean. Why ladder logic?
•
T
he Ladder logic programming language is an adaptation of an
electrical relay wiring diagram, also known as ladder diagram.
•
L
adder Logic is a graphical system of symbols and terms even
those not familiar with relay wiring diagram can easily learn it.

66. Electrical Ladder Diagram
Electri
cal Continuity
L1
L2
PB1 Stop
PB2 Start
M1
M1
Motor
Power Bus
Power Bus
Auxiliary Holding
Contac
t
R
un
g
™
Ladder Logic is evolved from
electrical ladder diagrams
, which represents
how electrical current flows thru the devices to complete an electrical circuit.
™
An electrical diagram consists of two vertical bus lines or power lines, with current flowing from left bus to the right bus.
™
Each electrical circuit in the diagram is considered a
rung.
™
Every rung has two components
¾
It contains at least one de
vice that is controlled
¾
It contains the condition(s) that control the device.

67. Ladder Logic Program
™
Ladder Logic
closely resembles
electrical ladder diagrams
™
A Ladder logic program exists only in the PLC’s software.
™
In ladder Logic it is not the actual
flow of current thru circuits.
™
In
electrical diagram
the dev
ices are described as open or closed
(ON or
OFF),
where as in
Ladder Logic
, instructions are either
TRUE or FALSE
.
™
In Ladder Logic Program must
contain at least one
control instruction
(output)
and usually contains one or more
conditions (inputs).
Logical Continuity
L1
L2
PB1 Stop
PB2 Start
Motor-
M1
Control Instruction
Auxiliary Contac
t
Rung
% I 1
% I 2
Conditi
on Instruction
% Q 1
% Q 1

68. Ladder Logic Instructions
™
The instructions in PLC la
dder logic program are the
Normally

open (N.O.)
instructions, the
Normally closed (N.C.)
instructions,
and the
Output energized
instruction.
Normal
ly
Op
en
In
st
ruc
t
ion
Control Instruction
Condition Instruction
Normal
ly
Op
en
In
st
ruc
t
ion
Output E
n
ergize
In
st
ruc
t
ion
Normal
ly
Clo
s
e
In
st
ruc
t
ion

69. Normally Open Instruction (--I I--)
™
A Normally Open instruction examines a PLC memory location for an ON condition. If PLC detects ON condition, the instruction is True and has Logical continuity.
™
Let us take an example of a Push Button PB1.
When PB1 is
Pressed(ON)
Output Terminal on PLC
Status of Output ON
% Q4
True
% I3
Ladd
er
P
r
ogram
True
% Q4
PB1
Input Terminal on PLC
Input Device
% I3
Fal
s
e
% I3
Ladd
er
P
r
ogram
Fal
s
e
% Q4
PB1
Input Terminal on PLC
Input Device
% I3
When PB1 is
Released(OFF)
Output Terminal on PLC
Status of Output OFF
% Q4

70. Normally Close Instruction (--I\I--)
PB1
Input Terminal on PLC
Input Device
% I4
PB1
Input Terminal on PLC
Input Device
% I4
When PB1 is
Pressed(ON)
When PB1 is
Released(OFF)
True
% I4
Ladd
er
P
r
ogram
True
% Q5
Fal
s
e
% I4
Ladd
er
P
r
ogram
Fal
s
e
% Q5
™
A Normally Open instruction examin
es a PLC memory location for
an OFF condition. If PLC detects
OF
F condition, the instruction is
True and has Logic
a
l continuity.
™
Let us take an example of a Push Button PB1.
Output Terminal on PLC
Status of Output ON
% Q5
Output Terminal on PLC
Status of Output OFF
% Q5

71. Output Energize Instruction (--( )--)
™
When Logical continuity exists on
a rung, the On condition (binary 1)
is written to the loc
a
tion in the
memory associated with the output
energize instruction. Higher Level Instruction
•
W
hile relay logic is suitable for simple On/Off sensing and
control, many applications requi
re more powerful instructions.
•
T
hese instructions deals with numerical data beyond simple 1s
or 0s by manipulating data in bytes or words.
•
E
xamples of higher level instructions include Counters,
Timers, Sequencers, Math, Comparison and other operations.

72. Combining Instructions
™
Two fundamental logic operations
–
A
ND and OR provide the rules
for governing how the instructions are combined.
AND Logic
( )
X
YZ
( )
X Y
Z
OR Logic

73. Logical AND Construction
IF
input 004
AND
input 005 have power
THEN
energize output 1
( )
%Q 1
| |
%I 4
| |
%I 5

74. Logical AND Construction
IF
input
4
A
ND
input
5
have power
THEN
energize output
1
( )
%Q 1
| |
%I 4
| |
%I 5
T
TT
Logic
a
l Continuity

75. Logical OR Construction
IF
input
4
OR
input
5
have power
THEN
energize output
1
| |
%I 4
| |%I 5
( )
%Q 1

76. Logical OR Construction
IF
input
1OR
input
2
have power
THEN
energize
output
1
( )
%Q1
Logical Continuity
T
| |
%I 1
%I 2
T
F
| |

77. Logical OR Construction
IF
input
1
OR
input
2
have power
THEN
energize output
1
| |
(
)
| |
%I 1
%I 2
%Q1
Logical Continuity
T
F
T
| |
(
)
| |
%I 1 %I 2
%Q1
Logical Continuity
T
F
T

78. Combining Instructions contd
…
..
Combining Series and Parallel Logic
™
AND and OR logic (series and parallel circuits) can be combined on a single rung.
( )
W
Y
Z
X
( )
W
Y
Z
X

79. Combining Instructions contd
…
..
™
The Function of a branch is to
allow both condition and control
instructions to be programmed in parallel in a single rung
¾
Condition inst
ructions programmed
in parallel are the equivalent
of
an OR operation.
¾
Control instructions programmed in
parallel are the equivalent of an
AND oper
ation.
Branch Operations
( )
DOOR A
KEY PRESENT
DOME LIGHT
DOOR B
DOOR C DOOR D
( ) BE
LL

80. Program Execut
i
on
The total loop is the throughput time of the PLC.
Start of N
e
xt Sweep
Start of Sweep Housekeeping
Input Scan
Run
Mode
?
Logic Solution
I/O
Enabled
?
Output Scan Programmer
Communications
User Program
Checksum Calculation
No
Yes
No
Yes
No
Yes
I/O
Enabled
?
Diagnostics
Housekeeping
Data Input Program Execution
Data Output
Programmer Service
Scan time of PLC

81. 5. What’s Networking & the Parlance

82. Schneider Communication Network Terms
™
RS-232
™
RS-422
™
RS-485
™
CL-20
™
Fibre
O
ptic
™
Modbus
™
Unitelway
™
Modbus
P
lus
™
FIPIO
™
Fipway
™
Ethernet TCP IP
™
Profibus DP
™
Interbus
™
Lon Works
What the hell do all these mean?

84. 5. How to apply a micro PLC?

85. Do I need a Programmable Controller
1.
Do you have any equipment or
process
controlled by 10 or
more relays?
2.
Are you satisfied with the reliability and up
time of r
e
lay contro
lled machine tools and
processes?
3.
Are you experiencing e
xcessive downtime due to
electrical problems?
4.
Do relay control panels occupy fl
oor space needed for
other
purposes?
5.
Do existing relay control panel
put a drain on ener
gy consumption?
6.
Do control requir
e
ments change frequently, say, once
a month, and require rewiring or
logic
changes?
7.
Is it must that you have to
monitor
operations presently cont
rolled to detect and repor
t

malfunctions, par
t counts, machine uptime, etc.?
8.
Does existing equipment have
pr
ovisions for
adding monitoring capability without major

rework?
9.
Do you operate equipment on a multi-
shift basis, shortening relay life?
10.
Do you anticipate extending, or
having to
extend, the capability
of existing control by
modifying them or
by adding har
dware?
11.
Do you have any highly repetitive oper
ations being per
for
m
ed by
employees?
12.
Do you have any operation repetitive in
nature being handled by workers in an
uncomfor
t
able or
haz
ardous environment?

86. Do I need a Programmable Controller
13.
Do you inspect large quantities of raw
materials or
finished goods visually?
14.
By
weight?
15.
By
v
o
lume?
16.
By dimensions?
17.
Would automatic tabulation of inspection r
e
su
lts be valuable under
such circumstances?
18.
Do you have pr
ocess type oper
ations requiring
continuous or
periodic monitoring of the
pressure, flow rates, vacuum, leakage,
spills, temperature,or
humidity?
19.
Is contr
o
l of such variables required?
20.
Is your
maintenance staff knowledgeabl
e in troubleshooting relay
equipment?
21.
Can you readily train new employees
to use and maintain relay controls?
22.
Do you use conveyor systems
or

stacker
cranes for
material handling?
23.
Is speed of star
t up of new equipment critical?
24.
Do you have a need to fine t
une or
optimize the per
f
or
ma
nce of existing equipment to
increase productivity?
25.
Do present control systems permit equi
pment to be econom
ically optimized?
26.
Do you require data stor
age capabilities?
27.
Do you plan to convert more
than one or
two machines to
PCs at the time of re-
mechanization?
28.
Do you expect to add more PCs wi
thin the next three to five years?

87. What type of Programmable Controller do I need?
™
Will your small
e
st co
n
t
rol a
ppl
ica
t
ion
req
u
ir
e
fewer th
e 20 i
n
p
u
ts/ outp
u
ts (I/O)?
™
20 to 40 I/Os?
™
Will your l
a
rgest control a
p
p
licati
on req
u
ir
e 40 to 12
0 I/Os?
™
Mor
e
tha
n
10
00 I/Os?
™
Do yo
u re
q
u
ire o
n
ly di
gital I/O ca
pa
bility?
™
W
ill your
cont
rol applicat
ion r
equir
e
analog I/
O
capability?
™
Will your application in
volve pulse within a confined area
, say,
within a radius of 100 ft?
™
Do you pl
an to incl
ude, or add at so
me future date, reporting or
data displa
ying equi
pment such as CRT terminals
or li
ne pri
n
ters?
™
Is there th
e
possi
bility the PC
will be con
nected to a con
t
rol co
mp
uter in a hi
erarch
ica
l system?
™
Will the application require
programming equipment
to diagnose faults, display status, generate documentation, or
handle off-l
ine programming?
™
Will the controller need to ha
ve full range ac/dc capability?
™
Will you require protection or
limited access to information stored in the memory?
™
Must the control retrofit to
an existing machin
e or operati
o
n?
™
Will you do the engineering insta
llation, programming, and checko
ut using in-house personnel?
™
Will you contract some of the work?
™
Most of the
work?
™
All f the work?
™
Do you presently have perso
nnel know
ledgeabl
e i
n
PC, or
who can readily trained?
™
Do you have service/maintenance personne
l famili
ar w
ith ladder di
agram l
o
gi
c?
™
Do you have any severe environmental
conditions w
h
ic
h may effect
equi
pment?
™
Must you produce a cost
justification to get t
he approval of purchase?
™
Do you have any i
n
herent resistance
with in your pl
ant towards the use of
PC
s such as fear of programming,
mai
n
te
na
n
c
e, or l
o
sin
g
me
mory
in
the event of a power outage?

88. What are the Application’s Requirements?
™
The first step in approaching a control situation is to specify the application’s requirements. This includes determining :
¾
Input and Output
device requirements
.
¾
The need for
s
p
ecial operation
in additi
on t
o
discret
e ( ON/
O
FF ) logic,
including:
¾
Timing
¾
Counting
¾
High speed counting
¾
Sequencing
¾
Data acquisition
¾
Data calcul
ati
o
ns
¾
The
ele
c
trical require
ments
for inputs, outputs, and system power.
¾
How fast the control system must operate
(
speed of operation
).
¾
If the application requires sharing
data outside the process, i.e.
communication.
¾
If the system needs
operator control or interaction
.
¾
The
physical environment
in which the control system will be located.

89. Example
Let us take an example, imagine
designing a control system for a
parking garage with a 500 car ca
pacity. The first step is to
define and describe the car parking process.

90. What is the desired operation for the parking garage?
™
The car approaches an automated ticket machine at a gate.
™
The driver pushes a button on the ti
cke
t
machine to
receive a
ticket.
If there is space left in the garage,
the driver will receiv
e a ticket.
The machine should not provide a ticke
t if the garage is full or
if the
gate is already up.
™
Removing the ticket raises the gate and turns on a green “enter”light.
™
After the car clears the gate, the gate lowers and the green light shuts off.
™
The number of vehic
les in th
e garage needs to be known at any
time.
™
If maximum capac
ity is reached, a “G
arage Full” sign is illuminated,
the
ticket ma
chine will not provide a
ticket, an
d the
gate
will no
t
raise.
™
An alarm must sound when the gate is obstructed.

91. 1.Inputs and Output requirements From the description, the following I/O requirements can be listed;
Functions(inputs) •Ticket request •Ticket taken •Car cleared gate •Car departed garage •Gate obstruct
ed
•Gate in up position •Gate in down
position
Device •Push Button •Limit switch •Photoelectric sensor •Photoelectric sensor •Motor overload contact •Proximity sensor •Proximity sensor
Functions(outputs) •Provide Ticket •Garage Full sign •Green Light •Alarm •Raise gate •Lower Gate
Device •Solenoid •Light •Light •Horn •Gear motor forward •Gear motor reverse
The system requires seven inputs and six outputs

92. 2.Advance Function Requirements
Use •
Co
unts cars entering garage
•
Counts cars leaving garage
Functions(inputs) •
Up counter
•
Down counter
When determining the electrical requirements of a system, consider three items ™
incoming power(power for the control system)
™
Input device voltage
™
Output voltage and current
To decide what type of voltage
to use, consider the following:
™
What type of power is available(e.g. 24Vdc, 120Vor 240V ac)?
™
How will the machine or process controlled be used?
™
Will people come in contact with the machine?
™
What power do the field devices use?
™
What electrical codes apply?
3.Electrical Requirements

93. 3.Electrical Requirements
c
ontd…
Summarizing the electrical requirements for the parking garage:
Functions(inputs) •Ticket request •Ticket taken •Car cleared gate •Car departed garage •Gate obstructed •Gate in up position •Gate in down position Functions(outputs) •Provide Ticket •Garage Full sign •Green Light •Alarm •Raise g
a
te
•Lower Gate Advanced Functions •Up counter •Down counter
Device •Push Button •Limit switch •Photoelectric sensor •Photoelectric sensor •Motor overload contact •Proximity sensor •Proximity sensor Device •Solenoid •Light •Light •Horn •Gear motor forward •Gear motor reverse
Voltage •
24V dc
•
24V dc
•
24V dc
•
24V dc
•
24V dc
•
24V dc
•
24V dc
Voltage •
24V dc
•
24V dc
•
24V dc
•
24V dc
•
120 V ac
•
120 V ac
Device •To be determined •To be determined
Voltage •
TBD
•
TBD

94. 4.Speed of Operation
When determining the speed of oper
ation, consider these points
:
™
How fast does the process
occurs or
machine operates?
™
Are there “time critical “ operations
or events that must be detected?
™
In what time frame must the fa
stest action occur(input device
detection to output device activation)?
™
Does the control system need to
count pulses
from an encoder or
flow meter and respond quick
ly?
™
The control system selected needs
to meet the speed demands
of
the process or machine, so know
ing these criteria is important.

95. 6. Operator Interfaces and Communication
™
Operator Interfaces
¾
I
n
order t
o
c
o
nv
ey i
n
f
o
rmati
o
n about
ma
c
h
ine or process stat
us, or t
o
all
o
w
an operator to input data, many applicat
ions require operator interfaces.
¾
Traditi
onal I
n
t
e
rfac
es i
n
cl
udes

push button, thumbwheel switches, pilot
lights
and
LED numeric displays
. Elec
tronic Operat
or int
e
rf
ac
e devices like
Magelis displays message
about machine status, di
splays part count and
track al
arms. They
are also us
ed f
o
r d
a
t
a
i
npu
t.
™
Communication
¾
Communication involves sharing applicat
ion data or status with another
de
vice
s su
ch
as co
mpute
r
o
r
a mon
ito
r
.
¾
Communic
a
ti
on t
a
k
e
s plac
e l
o
c
a
lly t
h
ru a
twisted pair wire
or rem
o
t
e
ly
via
telephone or radio modem.
™
The parking control system does not require operator interface beyond the ticket request push button, the green light and the alarm horn.
™
However communication capabilities could have provided the benefit, as if the portion of the garage was being repaired and 50 parking space were eliminated, it would be advantageous fo
r the garage operator to change the
capacity parameters from 500 to 450.

96. 7.Environment
™
Consider the environment where the
control system will be loc
a
ted.
Will it be subjected to Temperat
ure extremes? Water? Humidity?
Salt? Shock? Dust? Vibration?
™
In harsh environments, house the c
ontrol system in an appropriate
NEMA-
o
r IP-
r
ated enc
los
u
re.
™
For parking garage, the control system loc
a
ted in the ticketing
machine needs to be housed into an
enclosure to protect it against
moisture and dirt.

97. Selecting a control Method
™
The System des
igner can select from
three types of control system:
Relay, PLC’S, Wired(SBC).
™
For the control method selection,
the best method is to develop a
chart
which integrates applic
ation requirements with control
methods.
No
Yes
No
0
No
Operator i
n
terface
Yes
Yes
No
0
No
Communications
Yes
Yes
No
0
No
Data acquisition
Yes
Yes
No
0
No
Data Calculations?
Yes
Yes
No
0
No
High Speed required?
Yes
Yes
Yes
1 up/down
Yes
Counters
Yes
Yes
Yes
0
No
Timers
Yes
Yes
Yes
6
Yes
Outputs
Yes
Yes
Yes
7
Yes
Inputs
SBC
PLC
Relay
Ca
n the control method accomplish task?
Quantity
Re
quired?
Application
Characterist
i
cs

98. Selecting a control Method
™
All the three control methods can ac
complish the task, so the control
system cannot be selected on the app
lication requirement alone.
™
To differentiate between contro
l methods, we need to evaluate the
relativ
e
cost
impact of each met
hod using the following criteria.
********
*/**
Not app
l
icable
PLC
**
***
Maintenance
**
****
Modifying Logic
**
****
Documenting Logic
*
****
Duplicati
n
g Application
***
***
Impl
em
enting Logic
*
***
Panel
Space
*
***
Panel
Assem
b
ly
*
**/***
Control System hardware
****
Not app
l
icable
System design and development
SBC
Relay
Application Characteristics
* = Low, ** = Moderate, *** = High, **** = Very High

99. Result of the Selection
™
From the comparis
on we can see that
PLC’s are the easiest control system
to support.
Assistance for programm
i
ng and troubleshooting
is available
at reasonable costs from many sources.
™
And if the PLC fails, a
replacement
PLC can be purchased off the shelf from
the nearest industrial elec
trical supp
lier---
t
here is no need to wait for a
shipment from the factory. Furthermore, the
ruggedness
of the PL
C
s

compared to SBCs giv
e
s them a defin
ite advantage in harsh environment or
when durability is a primary consideration.
™
For all the criteria by which th
e control system are evaluated ---
Cost, Size,
Flexibility, and Supportability
–
m
icro PLC provide the user with distinct,
advantages over other control options fo
r many control applic
ations. Thus, a
micro PLC has been selected to provi
de the logic for the parking
garage.

100. What are the PLC Specifications?
™
After determining application requi
rements and selecting a method for
providing system control, the next step
is to determine specifications of a
control system. Categories that c
an be considered for determining the
PLC spec
ifications are as follows
:
¾
Total number of I/
O
¾
Electrical requirements
¾
Output c
i
rcuits
¾
Memory requirements
¾
Speed of operation
¾
Communication
¾
Operator interfaces

101. Defined Specifications
™
Total number of I/
O
¾
7 Inputs and 6 Outputs
™
Electrical requirements
¾
Incoming Power
–
24 VDC
¾
Input Voltage
–
24 VDC (7 Devices)
¾
Output Voltage
–120VAC (2 Devices) –
24VDC (4 Devices)
™
Output c
i
rcuits
¾
Relay Outputs
™
Memory requirements
¾
13 I/O +1I/O = 14 I/O, 14 x 10 Words= 140 estimated words of memory required. Worksheet
™
Speed of operation
¾
Simplified program increases the performance.
™
Communication
™
Operator interfaces

102. Program Develop
m
ent
Procedures
Three steps to develop a sequence of operation: ™
Define the rules of operation for each control point.
™
Identify and label inputs and outputs.
™
Convert the rules of operation to ladder logic.

103. Program Develop
m
ent
Procedures
Defining Rules of Operations
Recalling from t
he earlier
section, the control for

Garage control system
wa
s
described like this
™
The car approaches an automated ticket machine at a gate.
™
The driver pushes a button on the ticket machine to receive a ticket. If there is space left in the garage, the driver will receive a ticket. The machine should not provide a ticket if the garage is full or if the gate is already up.
™
Removing the ticket raises the gate and turns on a green “enter”light.
™
After the car clears the gate, the gate lowers and the green light shuts off.
™
The number of vehicles in the garage needs to be known at any time.
™
If maximum capacity is reached, a “Garage Full” sign is illuminated, the ticket machine will not provide a ticket, and the gate will not raise.
™
An alarm must sound when the gate is obstructed.

104. Program Develop
m
ent
Procedures
Inputs •Ticket request
pushbutton
•Ticket taken
limit switch
•Car cleared gate
photo sensor
•Car departed garage
photo sensor
•Gate obstruct
ed
(Motor overload contact)
•Gate in up position
proxim
ity sen
s
or
•Gate in down
position
proximity sensor
Outputs •Provide Ticket •Raise gate •Lower Gate •Garage Full sign •Green Light •Alarm

105. Program Develop
m
ent

rung 1
Ladder Logic Development
The rules of operation converts easily to a ladder logic program, as follows:
Rules of Operation
Control Point:
->>
The ticket machine will provide a ticket
Conditions:
->>If the driver presses the ticket request pushbutton ->>AND the “Full” sign is NOT on ->>AND the gate is lowered
Gate is Lowered
L1
L2
Ticket R
e
qu
est P
B
Garage Full
Provide Ticket Solenoid Control Instruction
Run
g
1
% I 1
% I 2
Conditi
on Instruction
% Q 1

106. Program Develop
m
ent

rung 2
Control Point:
->>
Raise the gate un-till fully up
Conditions:
->>After the driver takes the ticket ->>AND the gate is NOT up ->>AND the “Full” sign is NOT on
% Q 1
Gate is Up
L1
L2
Ticket has been

taken
Limit S
w
it
ch
Garage Full
Raise Gate
Control Instruction
Run
g
2
% I 1
% I 2
Conditi
on Instruction
% Q 1

107. Program Develop
m
ent

rung 3
Control Point:
->>
Vehicle Present latch
Conditions:
->>Vehicle has been detected. ->>AND the vehicle has NOT cleared the gate
% Q 1
L1
Vehic
l
e
Photo

Sens
or
(gat
e)
Vehic
l
e clear
of Gate
Vehicle present
Lat
c
h
Control Instruction
Run
g
3
% I1
% I 2
Conditi
on Instruction
% Q 1

108. Program Develop
m
ent

rung 4
Control Point:
->>Vehicle clear of Gate
Conditions:
->>Vehicle present latch is on. ->>AND a vehicle is NOT detected ->>AND the ticket request push button is NOT pressed
Vehic
l
e is Clear of Gate
L1
Vehicle P
r
esent
Lat
c
h
Vehic
l
e
Photo

Sens
or
(gate)
Vehic
l
e is Clear of
Gate
Control Instruction
Run
g
4
% I 1
% I 2
Conditi
on Instruction
% Q 1
Ticket R
e
qu
est
PB
% I 2

109. Program Develop
m
ent

rung 5
Control Point:
->>Lower the Gate until fully down
Conditions:
->>If the Gate is up ->>AND the car has cleared the Gate ->>AND the Gate is NOT down
->>AND the Gate is not obstructed
Lo
wer Gate
L1
Gate is
Up
Vehic
l
e is
clear of Gate
Lo
wer Gate
Control Instruction
Run
g
5
% I 1
%
I 2
Conditi
on Instruction
% Q 1
Gate is
Lo
wered
% I 2
% I 2
Gate is
Obstruc
t
ed

110. Program Develop
m
ent

rung 6
Control Point:
->>Turn On the Green light
Conditions:
->>If the Gate is up
L1
Gate is
Up
Green (G
O)
Light
Control Instruction
Run
g
6
% I 1
Conditi
on Instruction

111. Program Develop
m
ent

rung 7
Control Point:
->>Count cars entering/turn on full sign at 500
th
car
Conditions:
->>If the Gate has been lowered
->>If accumulated counter value >/preset value of 500
Run
g
7
Conditi
on Instruction
Control Instruction
L1
Lo
wer
Gate
Num
b
er of Vehicl
es
in the Garage
CU
Co
un
te
r Up
Cou
n
te
r
Preset 500
DN

112. Program Develop
m
ent

rung 8
Control Point:
->>Turn On the Full sign
Conditions:
->>If accumulated counter va
lue >= preset value of
500
L1
DN
Garage is
ful
l
Control Instruction
Run
g
8
C5:10
Conditi
on Instruction

113. Program Develop
m
ent

rung 9
Control Point:
->>Decrement the counter (count departing vehcile)
Conditions:
->>If a vehicle departs the garage
Run
g
9
Conditi
on Instruction
Control Instruction
L1
Vehicle P
h
oto Sensor
(Departing Gara
ge)
Num
b
er of Vehicl
es
in the Garage
CU
Count Down
Preset 500
DN

114. Program Develop
m
ent

rung 10
Control Point:
->>Sound Alarm
Conditions:
->>If the gate is obstructed
L1
Gate is obstru
cted
Ala
r
m
Sounded
Control Instruction
Run
g
10
Conditi
on Instruction