01Ladder Diagram (LD)
· Features: A graphical language similar to electrical relay circuit diagrams, suitable for logical control.
· Application Scenarios: Switch logic familiar to traditional electrical engineers (e.g., motor start/stop, interlocking control).
02Instruction List (IL)
· Features: A low-level text language similar to assembly, consisting of operation codes and operands.
· Application Scenarios: Small PLCs or scenarios requiring optimized code efficiency (e.g., maintenance of older equipment).
03Structured Text (ST)
· Features: A high-level text language similar to Pascal/C, supporting complex mathematical operations and algorithms.
· Application Scenarios: Data processing, loop control (e.g., PID algorithms, array operations).
04Function Block Diagram (FBD)
· Features: Graphical modular programming, achieving logic by connecting function blocks (e.g., timers, counters).
· Application Scenarios: Process control, signal processing (e.g., chemical production lines).
05Sequential Function Chart (SFC)
· Features: A low-level text language similar to assembly, consisting of operation codes and operands.
· Application Scenarios: Sequential control (e.g., filling production lines, sorting systems).
06Other Programming Languages
· Continuous Function Chart (CFC)
Non-IEC standard, used for complex control systems (e.g., DCS), supports graphical data flow programming.
· Vendor-Specific Extension Languages
For example, Siemens’ SCL (similar to ST), Mitsubishi’s MELSEC specific instructions.
07Selection Recommendations
· Beginners/Electrical Background: Start with Ladder Diagram (LD).
· Mixed Algorithms: Prefer using Structured Text (ST).
· Process Control: Sequential Function Chart (SFC) is more intuitive.
Different languages can be mixed (e.g., main program in LD, algorithms in ST) and should be flexibly chosen based on PLC model and project requirements.
