PLCspråkene

PLCspråkene refers to the set of programming languages defined for programmable logic controllers (PLCs) within industrial automation. The IEC 61131-3 standard provides a framework for programming PLCs and specifies five languages intended to cover a range of tasks, from simple relay-style logic to complex algorithms. The standard aims to improve portability of programs across different PLC platforms and to accommodate engineers with varying backgrounds.

Ladder Diagram (LD) is a graphical language that resembles electrical relay logic, using rungs and symbols such as contacts and coils. It is popular for discrete control and safety interlocks, as well as for systems that electricians find intuitive to read and modify. LD is well suited for straightforward, bit-level logic and sequencing.

Function Block Diagram (FBD) is also graphical, constructing programs from interconnected blocks that perform specific functions. FBD emphasizes data flow and reuse of function blocks, which can simplify complex control strategies and support modular design. It is commonly used for analog and multi-channel control tasks.

Structured Text (ST) is a high-level textual language similar to Pascal or Ada. It supports complex data structures, advanced algorithms, and large programs, making it a preferred choice for mathematic computations, data handling, and decision logic that are cumbersome in graphical languages.

Instruction List (IL) is a low-level, assembly-like textual language that expresses operations as a sequence of mnemonics. Historically common in older PLCs, IL has declined in popularity and is increasingly deprecated in favor of ST, but may still be present in some systems for legacy compatibility.

Sequential Function Chart (SFC) provides a graphical method for structuring a process as steps, transitions, and actions, aiding the design of process-oriented and state-based control. SFC is often used to organize complex sequences and coordinate multiple control tasks.

Together, these languages offer a spectrum of notation and abstraction levels, allowing engineers to select the most suitable approach for a given automation problem. Many PLCs support multiple languages within a single project, enabling hybrid programming strategies.