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IEC 61131-3 Format – Explanation
June 6th, 2010 | Posted in Web Design.The nonprofit group International Electrotechnical Commission or IEC published the IEC 61131-3 standard in 1993. The IEC 61131-3 standard is comprised of eight different sections: General information, Equipment requirements and tests, Programming languages, User guidelines, Messaging, Communications, Fuzzy logic control, Guidelines implementation.
Programmers are most concerned with Part 3 of the standards. It encompasses programming languages as well as some common elements applied in programming. Common elements of the IEC 61131-3 standard include: Variables, Configuration, Resources, Tasks, and Data Types. Data types may be standard (Boolean, Byte, Integer, word, string, float, etc.) or User Defined Type (UDT). UDT enables combination and grouping of standard data types to create other more customized application-specific types, making it an effective way of organizing and transferring data.
Programming units can be divided into three separate categories: functions, function blocks, and programs. Functions are logics that do not require pre-allocated memory. A function block is encapsulated logic with I/O modules that has the capability of retaining memory between scans. Programs are parts of code with specific execution criteria. A program’s logic can be cyclical (fast running and looping), periodic (time-based), or event driven (triggered by an event).
Five programming languages are supported by the IEC 61131-3 standard, including: Instruction List, Function Block Diagram, Structured Text, Ladder Diagram, and Sequential Function Charts.
Instruction list and assembly code are similar. It is ideal for the lowest level operations and can be constructed to run very fast in specific situations. Although it may be difficult to read, it does have the advantage of being text-based.
FBD utilizes a set of interconnected graphical blocks that show logic flow. FBD is similar to that of Boolean logic diagrams.
Structured Text (ST) is a text-based language that is utilized for construction of high-level logic functions. ST is also suitable for math, string, and array operations.
LD resembles electrical relay logic diagrams and is a graphical representation. In the US it is widely used and easy to learn. It is perfectly matched for bit logic involving digital inputs and outputs. It is not good for use with array operations or complex data manipulations.
Sequential Function Charts (SFC) is a graphical language resembling flow charts. It is a high-level language meant for sequential operations and is suitable for debugging.
The best choice of a language is one that best solves the problem at hand.
IEC 31131-3 standard has many benefits including debugging, reduced training, and maintenance time and code reusability which reduces costs for subsequent systems. It is also more beneficial for consistency and reducing errors that occur as a result of standardization. Multiple languages can be used in the same program allowing easy collaboration.
For an outline of the IEC-61131-3 Standard, check out iec-61131-3.com – a website loaded with useful info on IEC-61131-3 Standard
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