Eee3420 lecture03 rev2011

EEC3420 Industrial Control
Department of Electrical Engineering
│ Lecture 3 │
Basic Programmable Logic Controller
(PLC) Programming
© Vocational Training Council, Hong Kong. Week 1

EEE3420 Industrial Control
© Vocational Training Council, Hong Kong. Week
2
Learning Objectives
 Know different types of programming languages used in
PLC
 Understand the basic programming techniques of PLC

3
IEC 61131 standards for PLC
 the use of PLC has been standardized by the IEC
 developed with the input of vendors, end-users and
academics, IEC 61131 consists of five parts:
 General information
 Equipment and test requirements
 PLC programming languages
 User guidelines
 Communications

The IEC 61131-3 programming language
 the international standard for programmable controller
4
programming languages
 specifies the syntax, semantics and display for the
following suite:
 Ladder diagram (LD)
 Sequential Function Charts (SFC)
 Function Block Diagram (FBD)
 Structured Text (ST)
 Instruction List (IL)

5
Ladder diagram (LD)
 widely spread graphical programming language for
PLCs
 a programmatically replacement for relays and coils
which can be combined using AND and OR operations
 best suited to compute Boolean expressions
 IEC 61131-3 defines a complete LD set of instructions,
consisting of different types of contacts and coils

6
Ladder diagram (LD)
 contacts lead (according to their type) the power
from the left to the right
 coils store the incoming value
 both, contacts and coils, are assigned to Boolean
variables
 an LD network can be supplemented by jumps,
returns, labels and comments

Sequential Function Charts (SFC)
 SFC is the IEC 61131 -3 method to program
7
sequential controls
 actions may contain Boolean variables or entire
networks, networks are programmed in Ladder
Diagram, true action associations from several
steps, several concurrent SFC networks in one
diagram

8
Function Block Diagram (FBD)
 FBD defined in IEC 61131-3 consists of different
functions and function blocks that are either linked or
connected to variables
 in FBD networks, jumps, labels and returns can be used
 similar to the creation of functional diagrams or block
diagrams, with the control logic being created by simply
connecting blocks and elements
 frequently used in the process industry due to the flow-oriented
properties of function blocks

9
Structured Text language (ST)
 similar to the high-level language PASCAL or BASIC
 uses statements like IF...THEN or FOR…NEXT
 concerned compiler is responsible for syntactically
correct insertion of the language constructions
 text editor simplifies the programming work through
syntax highlighting
 syntax and the set of instructions of ST are optimally
suited for mathematical calculations and data
manipulations

10
Instruction List (IL)
 an assembler type textual programming language
 large (and mostly incompatible) sets of instructions
have been created by many vendors
 the IEC 61131 Instruction list reduced this set to a
minimum and favours the usage of functions and
function blocks for more complex tasks
 code in IL consists of a sequence of instructions
separated by lines, which consist of one operator
("command"), one operand (variable, constant or
instance name) and one optional modifier respectively

11
 jumps and labels can be used
 concerned assembler is responsible for syntactically
correct insertion of the language constructions
 text editor simplifies the programming work through
syntax highlighting (colour marking of language
elements)
 mainly used if the processing speed of the PLC
program has high priority

12
Basic instructions used in Allen Bradley PLC
Mnemonic Function Mnemonic Function
LD Load ANDN And Not
LDN Load Not ORN Or Not
ST Store MPS Memory Push
STN Store Not MPP Memory Pop
AND And MRD Memory Read
OR Or MCR Master Control Relay
ANB And Block
ORB Or Block
Note: The instruction mnemonic may vary across different series of the Allen
Bradley PLCs.

13
Basic instructions used in Omron PLC
LOAD Load NOP No Operation
LOAD NOT Load Not TR Temp. Register
OUT Out IL InterLock (eq. to MC)
AND And ILC InterLockClear(eq. to
MCR)
AND NOT And Inverted
AND LD And Block
OR Or
OR NOT Or Not
OR LD Or Block

14
Basic instructions used in Mitsubishi PLC FX series
LD Load NOP No Operation
LDI Load Inverted MPS Memory Push
OUT Out MPP Memory Pop
AND And MRD Memory Read
ANI And Inverted MC Master Control
ANB And Block MCR Master Control Reset
OR Or
ORI Or Inverted
ORB Or Block

IL, LD and its associated logic equation
operation labeled
with circle 1 is
performed first as it
is the deepest
nested term, and
operations proceed
with circle 2,circle 3
and circle 4
consecutively
(Mitsubishi PLC
codes)
15

A list of commonly used IL operators defined in IEC 61131-3
16

example of IL using the syntax defined in IEC 61131-3
17

18
example of IL using
the syntax defined
in IEC 61131-3

19
example of IL program using
the instructions MPS, MPP &
MRD to implement multiple
outputs using the syntax
defined in IEC 61131-3

20
example demonstrating
the use of TR instruction
(similar to MPS, MPP &
MRD instructions defined
in IEC 6113-3) in Omron
PLC

21
example
demonstrating
the use of MCR
instruction in
Allen Bradley
PLC

22
example
demonstrating the
use of MC & MCR
instructions in
Mitsubishi PLC
(N0 is the nested
number, maximum
7,i.e. a total of 8
nested levels; SP
means “space”)

23
example
demonstrating
the use of IL &
ILC instructions
in Omron PLC

Conversion of more complex logic gates
24

25
Multiplexer

Time Related Instruction – the Latch
26
• a latch in ladder logic uses one
instruction to latch, and a
second instruction to unlatch
• the output with an L inside will
turn the output D on when the
input A becomes true
• D will stay on even if A turns off
• D will turn off if input B
becomes true

27

a typical timing diagram, ignoring the brief pulse
28

The SR (Set-Reset) Flip Flop
Latches are not used universally by all PLC vendors,
others such as Siemens use flip-flops
29

the SR Flip Flop may be implemented by using AND-OR
functions
30

the SR Flip Flop may also be implemented by using SET-RESET
31
functions

32
implement the SR Flip Flop in Omron PLC

33
The Timers
• four fundamental types
• on-delay timer will wait for a set time after a line of
ladder logic has been true before turning on, but it
will turn off immediately
• off-delay timer will turn on immediately when a line
of ladder logic is true, but it will delay before turning
off
• retentive timer will sum all of the on or off time for a
timer, even if the timer never finished
• non-retentive timer will start timing the delay from
zero each time

Operation of a TON (non-retentive) Timer
34

Operation of a RTO (retentive time on) timer
35

Operation of a TOF (non-retentive t-off)
timer
36

37
Timers in Mitsubishi PLCs
• in FX1N and FX2N series, there are four types of
timers
• T0 ~ T199 are non-retentive time on timer with
timing interval of 100 ms
• T200 ~ T245 are non-retentive time on timer with
timing interval of 10 ms
• T246 ~ T249 are retentive time on timer with timing
interval of 1 ms
• T250 ~ T255 are retentive time on timer with timing
interval of 100 m

Using non-retentive time on timer in
Mitsubishi FX series PLC
38

39
Timers in Omron PLC
• in CP series, there are 48 timers/counters with
timing range running
• from 0.1s to 999.9s if it is set as common timer
• or 0.01s to 99.99s if it is set as high speed timer

40
Timers in Omron PLC

41
The Counters
• two basic counter types:
count-up and count-down.
• when the input to a count-up counter goes true the accumulator
value will increase by 1, if the accumulator value reaches the
preset value the counter DN bit will be set
• a count-down counter will decrease the accumulator value until the
preset value is reached

An up-down counter in Allen Bradley PLC
42

Counter operation in Mitsubishi PLC
43

44
Counter operation in Omron PLC

The Edge Triggering Instructions
in Mitsubishi FX series PLC, there are two edge
triggering instructions, namely, PLS (PuLSe) and PLF
(PuLse Falling)
45

in Mitsubishi FX series PLC, there are two edge
triggering instructions, namely, PLS (PuLSe) and PLF
(PuLse Falling)
46

in Omron PLC, there are similar edge triggering
instructions, namely, the DIFU (DIFferentiate Up) and the
DIFD (DIFferentiate Down)
47

in Omron PLC, there are similar edge triggering
instructions, namely, the DIFU (DIFferentiate Up) and the
DIFD (DIFferentiate Down)
48

Applications of Time Related Instructions
The timers and the counters find their
applications in many industrial process controls
49

Pulse generator circuit
50

Fixed width pulse generator circuit
51

Delay off timer - Many PLCs such as Mitsubishi do not
provide delay off timer, but this function can easily be
built by the delay on timer
52

Light flasher
53

Variable delay on/variable delay off circuit with Mitsubishi
PLC
54

Variable delay on/variable delay off circuit with Omron
PLC
55

Summary of Basic PLC Programming
․ The Instruction List programming language uses stack
operation to perform the operations specified.
․ Logic can be represented with basic Boolean operations
56
AND, OR, NOT.
․ Boolean equations can be converted to and from ladder
logic or instruction list.
․ The MPS, MPP and MRD enable intermediate results to
be pushed, pop and read to facilitate multiple outputs.
․ Use of the MC/MCR instructions simplifies the
organization of the ladder logic.
․ The time related instructions realize the sequential
functions.

57
Basic PLC Programming
End of Lecture 3
 Revision
Mitsubishi PLC FX series hardware handbook.
Allen Bradley PLC handbook
Omron PLC manual

Eee3420 lecture03 rev2011

Recommended

Recommended

More Related Content

What's hot

What's hot (13)

Similar to Eee3420 lecture03 rev2011

Similar to Eee3420 lecture03 rev2011 (20)

More from benson215

More from benson215 (20)

Recently uploaded

Recently uploaded (20)

Eee3420 lecture03 rev2011