The Five(05) IEC Programming Languages that Every Automation & Control Professional Should Know About

What are the Five(05) IEC Programming Languages that Every Automation & Control Professional Should Know About

Background

Given below are the five IEC languages that apply to all platforms for the implementation of discrete control logic/programming: 

1. Function Block Diagram 
2. Structured Text 
3. Instruction List 
4. Sequential Function Chart 
5. Ladder Logic 

Historically Ladder Diagram was originally developed for the programming of PLC as a replacement of relay logic system and Function Block Diagram (FBD) was originally developed for the distributed control system (DCS). However, nowadays,  a PLC is not limited to ladder logic and a DCS is not limited to the function block. 

1. Function Block Diagram (FBD)

Back in the 1970s with the evolution of DCS, this programming language was typically to program the PID loops and associated functions and logic. In this programming language, numerous blocks are used and logic is developed through the interlocking of these blocks

2. Structured Text (ST)

Do you have experience working on FORTRAN? If yes, then this language won't be much different from it. It is a high-level language having similar syntax to FORTRAN having a complete set of instructions for variable assignment, loops, conditional statements, and function block calling, etc. It has an advantage in the easier implementation of intensive calculation functions and relatively complex functions that are cumbersome while using other programming languages. 

     3. Instruction List (IL)

While studying the engineering course, a student comes across with assembly language or machine language. Instruction list is a low-level language similar to assembly language. It has a set of instructions to variable definition, assignment, conditional statements, reiterations, simple arithmetic calculations, etc. It has its own syntax for coding and implementation. 

    4. Sequence Functional Chart (SFC)

The Sequential Function Chart (SFC) is the basic design tool for sequential control applications. Its implementation can be done through texts, graphical or semigraphical formats. However, the graphical format is widely used across the automation world. The graphical form basically consists of Steps, transition conditions, and actions against each step.  The IEC 61131-3 SFC language is derived from the IEC 848 function chart standard.

    5. Ladder Logic 

Being an automation and control professional, it is well known to everyone that electromechanical relays were used for the automation of the telegraph industry back in the 1800s. PLC came as a replacement for this relay basic control implementation. The programming language closely resembles the wiring diagram implementation for relay logic. Initially for ladder programming, simple logic circuits are converted to relay logic and then to ladder logic or ladder diagram. 

For Further Reading:

• IEC 61131-3:2003. Programmable Controllers – Part 3: Programming Languages Geneva 20 – Switzerland: IEC (International Electrotechnical Commission)
• IEC 848:1988. Preparation of Function Charts for Control Systems