PLC programming languages are defined by the international electrotechnical commission (IEC) under sections 61131-3 standards are explained below.
1. Ladder logic (LD)
● Modeled from relay logic panel.
● Easy to understand and troubleshoot.
● Difficult for motion and batching programming
2. Sequential function chart (SFC)
● Language is similar to flow charts.
● The process can be broken into steps.
● To have direct access to the logic for a piece of equipment fault.
● Minimal programming effort and greater clarity through graphic programming.
● Excellent legibility for maintenance personnel.
● Less time in the commissioning phase thanks to the graphical programming interface.
● Minimal implementation effort because there are few possibilities for errors when generating code.
● High availability of the machine through process diagnostics functions (interlock and supervision).
● Fast error detection through PLC code display and criteria analysis on the HMI.
3. Functional block diagram (FBD)
● FBD describes functions between inputs and outputs that are connected by connection lines.
● It is in the graphical form language with repeated blocks.
● It is good for motion control programming.
● It can combine many lines of the program into a single block.
● But it is difficult to troubleshoot using this language.
4. Structured text (ST)
● Similar to C language, this language uses instructions like- for, while, if, else, case, if-else, etc.
● Very organized and good for computing large mathematical calculations.
● It covers some instructions that are not available in the ladder diagram.
● It is difficult to edit online.
5. Instruction List (IL)
● Instruction list language consists of predefined instructions, which are used to program a PLC.
● The use of instructions makes this program very compact.
● It is difficult to edit online.