Chapter 3 - Basics of PLC Programming (1).pdf

PLC introduction

2. 3.1. Program Scan

Internal checks START
‘on memory, speed,
and operation.
Service any | HOUSE:
communication | KEEPING
requests.
PROGRAM
SCAN
OUTPUT

The output image
date is transferred

to the external output
circuits, turning the
output device

ON or OFF.

@ PO

The status of
external inputs
is written to the
input image table
(file or register)

malo

Each ladder rung
is scanned and solved
using the date in the
input file, The resulting
logic is written to the
output image table
(file or register)

INPUT
SCAN

3. 3.1. Program Scan

= The time it takes to complete a scan cycle is a measure of how fast the
controller can react to changes in inputs.

= Ifa controller must react to an input
signal that changes states twice during
the scan time, it is possible that the PLC
will never be able to detect this change.

= The scan time is a function of:
The speed of the processor module
The length of the ladder program
The type of instructions executed
The actual ladder true/false conditions

4. 3.1. Program Scan

Input Input Output | Output
Input _ ata image image | data Output
modules table table modules
file file
Examine Return
data result
| Program |

—

ED I 5
Check/compare/examine
specific conditions

Take some action

5. 3.1. Program Scan

Input Output
instructions instructions
1 A si PL 12
DOS 51 Jr «À = PLA

Rung-in Rung-out
condition condition

GO s2 1k Op
s2

PL2

6. 3.1. Program Scan

Processor memory

Input
module
Input EN
device
13/6
Field-device
power supply

Data
Input Output
image image
table table
file file
> 13/6 a

Output
module

Output

BE device

sl Q:4/7

|

1:3/6
Program

T
ÓN

Field-device
power supply

7. 3.1. Program Scan

Input image table

[oloJoJaTololo[a]o/oT1[oJolol1]o]'

START

JE ©
| O

HAE fon
HR

ET

[olololololo/oTo]olololt]ololtJo}

Output image table

8. 3.1. Program Scan

Vertical versus horizontal sc

RUNG 1 2 3
1 me © e 8 ©

>
u
a
.

: Ç

e... e

o
AA:
o o
E)

4 J e... eee
4 ose ee em 4 . .... . ef
Horizontal scanning order LA A Zu Zu,

Vertical scanning order

9. LC Programming Languages

10. 3.2. PLC Programming Language

PLC programming languages

y y

Textural language Graphical language
Y y Y Y Y

Instruction Structured Ladder Functional Sequential
list text diagram block diagram function chart

Standard IEC 61131 languages associated with PLC programming

11. 3.2. PLC Programming Language

PLC language a

(CRT (CR2) soL
B D Y
E
us)
Hardwired relay control circuit Equivalent ladder diagram program

12. 3.2. PLC Programming Languages

Functional block diagram

Functional block

Ladder logic diagram equivalent
A B AND_BOOL
IE ER O MA È
BD
A
] À OR_BOOL
a re
ji BD
a 8 AND_BOOL
Jete e —
arg

13. 3.2. PLC Programming Language

Caution
PLA
| ES | BAND_ot
| ni |
BAND
Boolean And

Ladder diagram

Sensor 2°. - 2] int
Sensor 32°. cl In2

Equivalent function block diagram

14. 3.2. PLC Programming Language

Sequential function chart (SFC)

lan

like a

Wire
loop

The program is split into steps with
multiple operations happening in
parallel branches.

Initial
Step

Action

Wire

Step 2

Transition

Action

Transition

step 3

Action

Transition

Stop

15. 3.2. PLC Programming Language

7 CRI Ra SOL
—_— He O—
ist
ee

Hardwired relay control circuit

START PB1
AND RI
OR st
AND NOT CR2
OUT SOL

Equivalent instruction
list program

16. 3.2. PLC Programming Language

Sensor 1 Sensor 2 soL
IL iL
dC dt
‘Sensor3 Sensor4 ‘Sensor 5
Ladder diagram

IF Sensor_1 AND Sensor_2 THEN
SOL_1:=1;
ELSEIF Sensor_3 AND Sensor_4 AND NOT Sensor_5 THEN

Equivalent structured text program

17. Relay Type Instructions

18. 3.3. Relay Type Instructions

A

Representations of contacts and coils are the
basic symbols of the logic ladder diagram
instruction set.

19. 3.3. Relay Type Instructions

arme Open Contact i

Associated with each Normally
Open Contact instruction is a
memory bit linked to the status
of an input device or an internal
logical condition in a rung.

20. 3.3. Relay Type Instructions

A 1 corresponds to a true status or on condition.

Bit_ is 1413121109 8 7 6 5 4 3 2 1 0
number
[ 1 FF Status

11/4

Instruction interpreted

as true
1/4

CESSES

If the instruction memory bit is a 1 (true) this instruction will
allow rung continuity through itself, like a closed relay contact.

21. 3.3. Relay Type Instructions

A 0 corresponds to a false status or off condition.

15 14 13 12 # 10 9 876543210
0

Eva

E

Instruction interpreted
as false

o——_—_}
EV4

T
ÉCOLOS

If the instruction memory bit is a 0 (false) this instruction will
not allow rung continuity through itself and will assume a
normally open state, just like an open relay contact.

22. 3.3. Relay Type Instructions

Variable na Variable Va] Data Type [memory al nal Val Variante 10] — Used | Comments
fm ‚© Boo 0000 VR
EL Boot [401020 VaR

sm m
Row 0 WE &

Row 5

jeececcecocccccce

23. 3.3. Relay Type Instructions

e Normally Closed Contact inst Symbol
tes normally dre
dt. - _ This instruction asks the PLC’s processor to
o 3 >| 1) examine if the contact is open.
| It does this by examining the bit at the memory
“ | 110) location specified by the address for a 0 or 1.

24. 3.3. Relay Type Instructions

As with any other input the memory bit is set to 1 or 0 depending on the status of the input.
A 1 corresponds to a true status or on condition.

Bit
number 5141312 1109876543210
4 [ Status
E 11/4
a)
2
[1
a Instruction interpreted
lia as false
11/4 jal

The instruction is interpreted as false when the bit is 1
and will not allow rung continuity through itself.

25. 3.3. Relay Type Instructions

AO corresponds to a off condition.

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 O

o.
17a
ia
|
L E
| Instruction interpreted
72,9 3 as true
Eva e]
e)

The instruction is interpreted as true when the bit is
0 and will not allow rung continuity through itself.

26. 3.3. Relay Type Instructions

Variable Wal Variable Va] Data Type [Memory Ai ital Vatu Variable Ki[ Used | Comments
ne la
aaa eee =
= =

| ]

| m
Row 2 er

3
| H
cub ¿
¿
| -
¿
A :
¿
¿

20 Allan loa

ms | “LEE em Ce a

27. 3.3. Relay Type Instructions

Symbol

— >— Output energize

This instruction signals the PLC to energize (switch on)
or de-energize (switch off ) the output.

The instruction is associated with a memory bit that energizes the output
when set to 1 and de-energizes the output when reset to 0.

28. 3.3. Relay Type Instructions

Coil instruction is set to 1 to output 43 12 11 10 9 8 7 6
energize the output. — de

Program

1
a y

A true logic path is established by
the input instructions in the rung.

Input
module

29. 3.3. Relay Type Instructions

r ed Coil

[Variable Na] Variable Valu] Data Type [Memory All initial Value] Variable Ki] Used [Comments
1 0 BOOL__IX0.0.0 VAR
2 [swe 0 BOOL 7861%0.01 VAR
EL 0 BOL | 40X020 VAR

30. 3.3. Relay Type Instructions

Bit
status

Ladder logic program

FALSE

[Core

>[o

A signal present makes the
NO bit (1) true; a signal
absent makes the NO bit
(0) false. The reverse is
true for an NC bit.

Lia]

Ladder logic program

TRUE
A OUTPUT
où )—|
à
Ÿ—Corr)-
FALSE

Button actuated

31. 3.3. Relay Type Instructions

Variable Na] Variable Val Data Type | Memory Al] intial Value] Variable Ki] Used | Comments]
=
ao II ry
Row [mar MS == =. == =
=
|| 5 :

Cal al al El eal al Ec [es © Talv

sal

32. 3.3. Relay Type Instructions

is to control

Each contact or coil symbol is referenced with an address that identifies what is being
evaluated and what is being controlled.

Inputs Outputs
The same contact instruction can

be used throughout the program 1 i
whenever that condition needs to L >
be evaluated. Rong?) oy

Not place the same addressed Coil

instruction on multiple rungs within v2 va or
the same program. Rung 1 Y ] [ O

33. 3.3. Relay Type Instructions

Rung O —} F T ï | iO) |

A complete closed path is referred |
to as having logical continuity. — Rung! 7 @) |
When logical continuity exists => Rung2—| F y Tr | o.

in at least one path, the rung |
condition and Coil instruction LE 07

are said to be true.

34. 3.3. Relay Type Instructions

Py E 7

are 27]

… E =
DE >
al E N

Arq Ey
eorcacorecones

E

35. Input Instructions Output instruction The logic states (0 or 1) indicate whether an
NO, Ne a instruction is true or false and is the basis of

) ( 4 controller operation.

The status of the instruction is

Ifthe ar table bit | \ormally Open Contact | Normally Closed Contact Coil
Logic O False True False

Logic 1 True False False

36. Input instructions

LE u

Output instruction

Coil

The time aspect relates to the repeated scans

of the program, wherein the input table is
updated with the most current status bits.

Instruction outcome Input bit status
Time NO NC Coil NO NC Coil
# (initial) False True False o 0 o
ta True False Goes false 1 1 o
ta False False Remains false o 1 o

38. 3.4. Branch Instructions

The rung will be true |
if either instruction A >
1
]

or Bis true.

39. 3.4. Branch Instructions

on of

JE

Either A and not B, or C provides logical continuity and energizes output D.

40. 3.4. Branch Instructions

41. 3.4. Branch Instructions

Output branching a

path tc

Either A or B provides a true logical path to | ( )
all three output instructions: C, D, and E. D |

| LH

€
\
PA

E Additional input instructions can be
WH programmed in the output branches.

42. 3.4. Branch Instructions

to all three

43. 3.4. Branch Instructions

nested to avoid re

me.

| ] ] If CY |
| ] dL ai \, |
] ] LY
dt | \/
Anested branch starts or e
ends within another branch. | [E IL

44. 3.4. Branch Instructions

In some PLC models, the A 8 (e Y
programming of a nested - F E EX
branch be done 5
directly. MN
~~ A branch within
E a branch
It is possible, however, tr 8 (93 A
to program a E (
branching D a
condition. Bd
> Contact
instruction C
E
repeated

45. 3.4. Branch Instructions

« Maximum 10 contacts >

HAHAHAHAHA KH HE O
HHAHAHHHAHHHHHHHHH
{HEHEHE HEHEHE
HAHAHAHHHAHHHHHHHHH

Maximum 7 |
parallel lines.

Aie oi
Lo Co LL LL Lo

46. 3.4. Branch Instructions

A D Y

The PLC will not allow for programming | ( >
of vertical contacts. => Fa 2

A D Y B E

] [ ] [ ©) Boolean equation: Y = (AD) + (BCD) + (BE) + (ACE)

B ie D |

8 E

] [ ] [ Reprogrammed to eliminate

A = = vertical contact.

47. 3.4. Branch Instructions

The processor examines the ladder logic rung

A B €
for logic continuity from

EE HO
I

If programmed as shown, contact
combination would be

F

A 8 € y 1,
EE |

Boolean equation: Y = (ABC) + (ADE) + (FE) + (FDBC)
A D E

eLo

circuit,

F D 8 €

48. Internal Relay Instructions

49. 3.5. Internal Relay Instructions

MW0.0

The advantage of using internal outputs is that there are many situations in
which an output instruction is required in a program but no physical connection
to a field device is needed.

50. 3.5. Internal Relay Insti

Internal relay

t n

es more series contacts than

Discrete inputs

1 2@ 83 10.0

4 5 6 7 «uw
This PLC allows for only Rung 1 HO

7 series contacts when pee! |
12 are required for the |

Discrete inputs call
Programmed logic. “wos 9 10 M 12

ro AAA O

Internal Discrete
relay output

51. 3.5. Internal Relay Instruction

[Variable Val Data Type | Memory Au] (£2
BOOL_ 5410.00

BOL 1%000.1

BOOL |#00.0.10

‘BOL /%400.0.11

-
12 0 BOOL 2.
E = SERIE

52. he Pump (M) is started b
pped when Stop button is p

n the Selector switch (Manual/Auto) is i
the Solenoid valve (SV)

e automatic position, the

e Pressure switch

53. reversing workpiece
moto
Se a | Forward Rovers
| ‘Conveyor ©
= O) (Shs ee
Reverse
e left and r to the right when the Start button is
1 it > rightmost limit (LS2), the Motor at ratically reverse

e back to the leftn

The Reverse pushbutton f
leftmost limit (LS1) can ta

Stop button is use

, and the

rotor

54. 3.5. Internal Relay Instructions

-
Oo
o»

he Conveyor when Start button is momentari
top the Conveyor when Stop button is momentarily pre

Energize the Run status light when the process is

Energize the Standby status light

re Solenoid
the Level

valve and
sensor g

gize the Full light

55. Modes Of Operation

56. 3.6. Modes Of Operation

modes of
un mode.

program mode

=
A three-position keyswitch may be Sc
used to select different processor a=

modes of operation. RUN REM PROG

57. 3.6. Modes Of Operation