Ladder diagrams (LD)
Ladder diagrams also called with ladder logic. This programming languages visualized electrical contact (NO/NC, etc), same as the relay contact. These contact can be arranged to form more complex logic. It is the most common and most used PLC programming language. LD also the simplest form of PLC programming language especially for an introduction to PLC programming language.
Structured Text (ST)
As it name, this programming language is based on the text. It is more similar to high-level language structured like Basic and Pascal. For somebody who already gets used to Basic and Pascal, maybe it is better to program PLC with ST.
Instruction List (IL)
It is a low-level language and resembles assembly. This programming language is pretty compact. Because of it, it is not common in use and only suitable for a small project.
Functional Block Diagram (FBD)
FBD is a graphical language that defines the function between input and generates output. There can be a combination of several blocks, with several inputs and outputs. As regular network/line, the data will be carried from the left, through the block and pass it to the right. By using FBD, it is much easier to program and do trouble shoot if something is wrong.
Sequential Function Chart (SFC)
SFC is also a graphical language, that can works in a parallel operation, mean that it doesn't follow a single path like an ordinary flowchart. It can combine FB (function block) and ST (structured text) to form a function chart for the control system. It is also possible to add LD (ladder diagram) in the SFC, This show that SFC is very flexible PLC programming language and make it easier to improve or maintain when something is wrong in the program.
From 5 types of PLC programming language, LD is recommended for an introduction to PLC Programming. Still, when you already get used with one programming language, it is not easy to convert to another programming language. So, if it's not necessary to learn or convert to another language, mastering one programming language is already enough. Not every PLC type and manufacturer will include all of those PLC programming languages, but basically, LD and ST are included.
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