The document discusses the benefits of standardizing PLC software. It describes how standardization improves productivity, quality, and reliability by reducing development costs. It then provides an overview of IEC 61131-3, the international standard for PLC programming, including its data types, languages like ladder logic and structured text, and programming concepts like function blocks. The document advocates for using standardized software and languages to improve reliability, productivity, and maintenance efficiency for industrial automation systems.

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IEC 61131 Basics
Presented by
Bill Lydon, Director PLCopen North America
Automation Industry Consultant
blydon@PLCopen-NA.org

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Why standard software?
Standardization
Improves Productivity
Quality & Reliability

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Percentage of Software development costs in
production systems (source: McKinsey)
0%
20%
40%
60%
80%
100%
1970 1980 1990 2000
Mechanic Electric Software

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Software Functions Increasing
Complexity Increases Exponentially

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“… the never ending story of software ”
enhancements…..
new requirements ...
new functionalities ….
new wishes ...
Typically software enhancements &
maintenance cost are 2 times the
initial development investment.

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Conceptual
Design
Specification
Functional
Design
Verification
CodingTesting
Refining
Commissioning
Maintenance
Standard Software Advantages

7. Page 7 www.PLCopen.org
PLCopen®
for efficiency in automationStandard Software Advantages
 Improved Software Reliability – Common Design
Architecture
 Improved Productivity
 Common Base of Understanding & Training
 Improves Maintenance Efficiency
• Emergency Bug Fixes & Corrective Bug Fixes
• Adding Features & Functions
• Mandatory Changes ( Law, Safety,...)
• Enhancements
• Studies show software maintainers spend about 50% their time
understanding the code.
Lifecycle Maintenance = 2 X Initial Development

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IEC 61131-3 - International Electrotechnical Commission (IEC)
Open Programmable Logic Controller Standard
1st published 1993 - 3rd edition published 2013
 Defined application program development environment
 Strong data typing for error prevention
 1 Structuring Tool – Sequential Function Chart (SFC)
 4 programming languages: 2 Textual & 2 Graphical
 Program Organization - Program Structuring & Reuse
What is IEC 61131-3 ?

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IEC 61131-3 Strong Data Types
 BOOLEAN
 REAL
 INTEGER
 STRING
 TIME
 ARRAY
 STRUCTURES
 USER DEFINED

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Languages
 Instruction List (IL)
 Structured Text (ST)
 Ladder Logic/Diagram (LD)
 Function Block (FB)
 Sequential Function Chart (SFC)

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A B C
-| |--|/|----------------( )---[Function[---
Ladder Diagram (LD)
Standardized set of relay ladder programming
symbols and terminology
• Electrical Flow
• Large base of users
• Boolean equations
• Function Blocks
• Easy rules

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for efficiency in automationLadder Diagram (LD)

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LD A
AND B
ST C
• Single accumulator based execution model
• Low Level Programming
• One operation such as storing a value in the
accumulator register, is allowed per line
Instruction List (IL)
Single statements, or instructions, written and
executed in a line-by-line format.

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C:= A AND NOT B
If A = FALSE THEN ...
CASE Select OF ....
• High level language, block structured
• Syntax resembles PASCAL, C, C+
• Complex statements and nested instructions
possible
• Support for
• Iteration loops (REPEAT-UNTIL; WHILE-DO)
• Conditional execution (IF-THEN-ELSE; CASE)
• Functions (SQURT(); SIN())
Structured Text (ST)

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for efficiency in automationStructured Text (ST)

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AND
A C
B
• Graphical Language
• Program elements appear as blocks to be
“wired” together
Function Block Diagram (FB)
Function Examples: ADD, SQRT, SIN, COS, AND, OR, CASE, etc.

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Inputs Outputs
Function Block
• Explicit Data
• Variables
• Tag Names
• Logic
• Actions/Calculations
Self Contained Building Blocks
Function Block
Inherent Data Integrity Checks

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Inputs Outputs
Function Examples
• AND, OR, XOR, GATE…
• PID, SELECT, LIMIT…
• SQUARE ROOT, COS…
• ADD, SUB, DIV, MUL…
Function Block
Self Contained Building Blocks

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Inputs Outputs
Send/Receive Email
Serve UP WEB Pages
Send Messages (SMS)
Send SOAP Messages
Send XML Messages
OPC UA Communication
PEER to PEER
Self Contained Building Blocks

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BUILD
YOUR OWN
FUNCTIONS
Function Block
Encapsulation

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Built from standard blocks ...
Inputs Outputs
User Created
Object
Encapsulation

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Ladder Logic Instruction List Structured Text
Build your own function blocks
with Ladder Logic, Instruction
List, or Structured Text
Standardization
Reuse Tested Code
Easily Understood
Self Documenting
Password Protect
Inputs Outputs
Your Own
Function Block

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for efficiency in automationSequential Function Chart (SFC)
Step 1
Transition
Step 2
Transition
Action 1
Action 2
Action 1
• Sequential Controls
• Procedural Controls
• Structured
• Describes Process
• Logic Driven
• Partition Control Functions
• Rapid Visual Diagnostics

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• Serial & Parallel Processes
• Process Synchronization
• Application examples
• Startup Sequences
• Shutdown Sequences
• Presses
• Productions Lines
• Process Automation
• Packaging technology
• Machine tools
• Batch Process Control – S88
• Flexible Manufacturing
Sequential Function Chart (SFC)

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• Multiple Automation and Control Disciplines
• Process Design
• Logic Simulation
• Automatic Documentation
• Engineering Tools
• Online Debug Environment
• Breakpoints
• Watch Windows
• Strip chart Recorder
• Integrated HMI
IDE - Integrated Design Environment (IDE)
IEC 61131 Controller

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29. Page 29 www.PLCopen.org
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for efficiency in automationPLCopen Extensions
 Vendor Independent, Not for Profit Organization
 Extends IEC 61131-3 Functionality

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More Information...
www.PLCopen.org
Electronic Newsletter
Application Examples
Specifications
Compliant Products
Bill Lydon, Director PLCopen North America
Automation Industry Consultant
blydon@PLCopen-NA.org

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