Programmable Logic Controller (PLC) is an industrial digital computing device that helps us to monitor inputs and outputs and make some decisions for industrial processes. Everyone have a doubts on that how the PLC knows the process sequence. PLC is act like a slave. Inside the PLC we can store a process sequence as the form of program. Next our doubts about how that type programs are developed ? What are the languages been used? . International Electrotechnical Commission defines some standards for PLC programming languages under the code named IEC 61131 – 3. Five programming languages has proposed under the standard those are
Text based programming languages
1. Structured Text (ST)
2. Instruction List (IL)
Graphical based programming languages
1. Sequence Function Chart (SFU)
2. Function Block Diagram (FBD)
3. Ladder Diagram (LD)
Problem Condition for Reference Photo: Both Proximity sensors are in same state Motor should be ON otherwise it’s OFF.
Programming Software: Codesys V2.3
Structured Text (ST):
Structured Text is a high level text based programming language. It seems like Pascal and Basic. You have some knowledge about Conditional, Loops, Repeat and Function statements, You could easily understand the structured text language. Some peoples have not interested with this language for a single reason ‘It’s Text based’. The C programming structure is the best example of this.
Instruction list (IL):
Instruction List programming language is different from other programming languages that contains text based instructions. Instruction List programming is similar to Assemble language that we used in 8051 microcontroller programming in our college days. Instruction List is known for executing quickly due to having low overhead. In my experience Keyence PLC ladder instructions like Addition, move till follow the assembly level concepts.
Sequence function Chart (SFC):
Sequence Function Chart is a graphical based programming language. It is similar to a flowchart of a process. SFC is help to divide high & complex processes in to small pieces that help programmers to achieve their goal. Sequence Function Chart contains Logic Conditions, Transitions, Step wise actions & Links. In my college days i draw that Sequence Function Chart diagram before to write a C program
Function Block Diagram (FBD):
Function Block Diagram is a graphical based programming language. In this programming language the functions are described by using elementary blocks.Every block having its own input and output terminals. Input and Output variables are connected to blocks by connection lines. Loops, Functions, Structures and everything has in the form of blocks. Lab VIEW & Matlab simulink softwares programming concepts like this.
Ladder Diagram (LD):
Ladder diagram is a schematic based programming language. Ladder diagram Basic tools and concepts are derived from electrical relay diagram. Ladder Programming is the easiest one because we can solve complex programs using Logical method. Most of the Programmable Logic Controller programmers were from electrical Base. The ladder diagram only used in PLC programming. Yet I don’t saw it any other programming softwares.