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Introduction into IEC 61131- 4
User Guidelines

Scope

This Technical report (TR) IEC 61131-4 is to introduce the end-users of PLC to the IEC 61131 standard, and to assist the end-users in selection and specifying their equipment requirements according to the IEC61131standard.

This TR has as its main audience the PLC users. As depicted in Figure 1 the users consist of System integrators and End-users. The Vendor of PLC is required by the IEC 61131 standard to furnish appropriate product information to the user. The user needs to supply applications requirement and specifications to the vendor in order to receive suitable products and services from the vendor. The object of this TR then is to assist in this communication, especially from the end-user's perspective. Accordingly, this TR does not detail all the requirements of each and every part of IEC 61131 standard, such as conformance tests. The user should refer to the individual parts of the standard when needed.

The International Standard IEC61131 applies to programmable controllers (PLC) and their associated peripherals. PLCs and their associated peripherals are considered as components of a control system. Therefore, this standard does not deal with the automated system in which the programmable controller system is but one component. However, when applying this User guidelines an overall system architecture evaluation is recommended.

Since PLCs are component devices, overall automated system safety is beyond the scope of this standard.


Table of content – IEC 61131-4

1 General 9
1.1 Scope 9
1.2 References 10
1.3 Use of this report 10
2 Definitions 10
2.1 Application program (user program) 10
2.2 Automated system 11
2.3 PLC-system 11
2.4 Programmable controller (PLC) 11
2.5 Programmable controller system (PLC-system) 11
3 Key elements of IEC 61131-1, Part 1: General information 11
3.1 PLC hardware model 11
3.2 Basic functional structure of a PLC system 12
3.3 CPU function 13
3.4 Programming languages 13
3.4.1 Textual languages 13
3.4.2 Graphical languages 14
3.4.3 Sequential Function Chart (SFC) 14
3.5 Availability and reliability 14
3.6 Re-start of PLC operating system 15
3.7 Documents supplied to the user 15
4 Key elements of IEC 61131-2: Part 2 - Equipment requirements and testing 15
4.1 Scope of Part 2 15
4.2 Definitions 16
4.2.1 Digital input types 16
4.2.2 Earth, functional Earth, Protective Earth 16
4.2.3 Equipment class 16
4.2.4 Hazardous voltage 16
4.2.5 Operator 16
4.2.6 Pollution degree 17
4.2.7 Protective Extra-Low Voltage (PELV) circuit 17
4.2.8 Safety Extra-Low voltage (SELV) circuit 17
4.2.9 Type of test 17
4.3 Functional requirements 17
4.3.1 Power supply ratings 17
4.3.2 Power supply harmonics 17
4.3.3 Power back up for memory 18
4.3.4 Digital I/Os 18
4.3.5 Special output modules 19
4.3.6 Analog I/Os 19
4.3.7 Communication Interfaces 19
4.3.8 Main Processing Unit(s) and Memory(ies) 19
4.3.9 Remote input/output stations (RIOSs) 20
4.3.10 Peripherals (PADTs, TEs, HMIs) 20
4.3.11 Self-Tests and Diagnostics 20
4.3.12 Marking requirements 21
4.3.13 External wiring terminals identifications 21
4.4 Electromagnetic compatibility (EMC) requirements 21
4.4.1 Electromagnetic emission requirements 21
4.4.2 Immunity zones 22
4.4.3 EMC performance criteria 24
4.5 Safety requirements for PLC equipment 24
4.5.1 Protection against electric shock 24
4.5.2 Protection against spread of fire 25
4.5.3 Protection against hazardous temperature 25
4.6 Information to be provided by the manufacturer 26
4.6.1 Information on type and content of documentation 26
4.6.2 Information on compliance with this standard 26
4.6.3 Information on reliability 26
4.6.4 Information on EMC 26
4.6.5 Information on safety 26
4.6.6 Information on evaluation of enclosures for open equipment 27
4.6.7 Information on mechanical terminal connection 27
4.6.8 Information on other conditions 27
4.6.9 Information on AC and DC power supply 27
4.6.10 Information on digital inputs (current sinking) 27
4.6.11 Information on digital outputs for alternating currents (current sinking) 28
4.6.12 Information on digital outputs for direct current (current sourcing) 28
4.6.13 Information on analog inputs 28
4.6.14 Information on analog outputs 28
4.6.15 Information on communication interface 29
4.6.16 Information on main processing unit(s) and memor(ies) of the PLC system 29
4.6.17 Information on remote input/output stations (RIOSs) 29
4.6.18 Information on peripherals (PADTs, TEs, HMIs) 30
4.6.19 Information on self tests and diagnostics 30
4.7 Compliance with IEC 61131-2 standard 30
5 Key elements of IEC61131-3: Part 3 - Programming Languages 31
5.1 Technical contents of Part 3 31
5.2 Common Elements 31
5.2.1 Data typing 31
5.2.2 Variables 32
5.2.3 Configuration, resources and task 32
5.2.4 Programs 33
5.2.5 Functions 33
5.2.6 Function Blocks (FB) 33
5.2.7 Sequential Function Chart (SFC) 33
5.3 Programming languages 34
5.3.1 Instruction List (IL) 35
5.3.2 Structured Text (ST) 36
5.3.3 Ladder diagram (LD) 37
5.3.4 Function Block Diagram (FBD) 37
5.4 Applications program development 39
5.4.1 Top-down and bottom-up program development 39
5.4.2 Program layout and structure 40
5.4.3 Programming with Sequential function chart (SFC) 40
5.4.4 Derived Function Block (DFB) 41
5.5 Implementation 42
6 Key Elements of IEC61131-5, Part 5 - Communication 42
6.1 Scope of Part 5 42
6.2 Technical contents of IEC61131-5 and the PLC model 43
6.2.1 Technical contents of Part 5 43
6.2.2 PLC communication model 44
6.3 Communication Model 45
6.3.1 Client-server model 45
6.3.2 Communication relating to PLC hardware model 45
6.4 PLC communication services 46
6.4.1 PLC subsystems and their status 46
6.4.2 PLC summary status 47
6.4.4 Status of I/O subsystem and Processing Unit 49
6.5 Application functions 50
6.5.1 Device verification 51
6.5.2 Data acquisition 51
6.5.3 Parameter Control 51
6.5.4 Alarm reporting 51
6.5.5 Application program execution and I/O control 52
6.5.6 Application program transfer 53
6.5.7 Connection management 53
6.6 Communication function blocks 53
6.6.1 Communication function and block representation 53
6.6.2 Example for the use of Communication Function Blocks 54
6.7 Compliance 55
7. Key elements of IEC61131-7, Part 7 - Fuzzy Logic programming 56
7.1 General outline of Part 7 56
7.2 Integration of fuzzy control application into the programmable controllers 56
7.3 Fuzzy Control Language (FCL) 57
7.3.1 Function Block interface 57
7.3.2 Fuzzification 57
7.3.3 Defuzzification 58
7.3.4 Rule block 59
7.4 Exchange of fuzzy control programs 60
7.5 Compliance 61
7.5.1 Compliance classes of Fuzzy Control Language (FCL) 61
7.5.2 Data check list 62
8 General rules for installation 63
8.1 Environmental conditions 63
8.2 Field wiring 64
8.3 Electromagnetic compatibility 65
8.4 User system markings 66
9 PLC in Functional safety applications 66
9.1 Using a PLC in a safety-related application 66
9.2 Safety-related system – Safety requirements 67
9.3 PLC requirements in a safety-related system 68
9.4 Integration of PLC into safety-related system 68
Annex A User checklists 70
A.1 Equipment data 70
A.2 General information checklist 71
A.3 Equipment requirements checklist 71
A.4 Checklist on programming languages 73
A.5 Checklist on communication 73
A.6 Checklist on Fuzzy control language 74
A.7 Checklist on installation 74
A.8 Checklist on safety-related application 74
Annex B Comparism of EN and IEC61131 75
C1 Advance Planning 76
C2 Variable Naming Conventions / Methodologies 77
C2.1 Naming Methodologies 77
C2.2 Use of Upper & Lower Case 77
C2.3 Consistent Project Prefixes, Suffixes and Acronyms 77
C2.4 Sequential Function Chart (SFC) step naming 77
C3 Structure / Organization 78
C3.1 Program Structure by area / process flow 78
C3.2 Structured Variables (Data Types) for multiple devices 78
C3.3 Data Arrays for data storage & Manipulation 79
C4 Use of the Appropriate Language 79
C5 DFB requirements 79
C5.1 Device Control 79
C5.2 Frequently used Functions 79
C5.3 Special Functions 79
Annex C Example of PLC software implementation 79
Annex D Example of PLC communications implementation 80
Annex E Example of PLC fuzzy control language implementation 81
Annex F Example of a PLC system in safety-related application 82
Annex G Reference standards 83