Types of PLC Programming Language
PLC user
program is under the control system designer process control requirements,
through the establishment of PLC
programming language design. Developed by the International Electro
technical Commission standard industrial control programming language (IE PLC
user program is under the control system designer process control requirements,
through the establishment of PLC programming language design.
The five
languages in the IEC Standard 61131-3 are:
Instruction
List (IL): A
low-level language very similar to assembly language. The code is compact and
suitable for small projects. It is not very powerful. The other languages are
easier to use and document. It has been years since I have used it and do not
miss it.
Structured
Text (ST): A high
level language structured like Pascal. Users trained in high level text
languages would be comfortable with ST.
Ladder
Diagrams (LD): Also,
commonly known as Ladder Logic, modelled after the electrical wiring of
contacts and relays used to create logic. It made the transition from Relay
logic (using actually electrical relays) to the PLC easier. It falls short when
tasks become complex. Not the best for modular PLC
programming. This language will look very familiar to Electricians.
Function
Block Diagram (FBD):
The blocks contain procedures or functions to act on the input “wires” and
output the result. It lends itself readily to standardizing, modulating, and
maintaining programs. I prefer this over LD, and many are coming to realize its
advantages. Ladder Diagrams will die a slow death.
Sequential
Function Chart (SFC):
This graphic language is great for concurrent parallel sequential operations.
It is self-documenting. It very useful pulling together in a flow chart form
the other PLC programming elements such as function blocks (FB) or structured
text (ST). Its format shows overall program flow very well making it faster and
easier to understand what the program is doing, Easy to identify the section of
interest for troubleshooting and program improvement.
A common
belief is that you would be able to quickly convert between the above
languages. This is false. Although they have common elements, they also have
differences that preclude the possibility.
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