Different types of PLC programming languages​

The IEC 61131-3 Standard

The IEC 61131-3 standard defines the five main PLC programming languages, providing a unified framework for PLC programming. This standardization allows programmers to easily transition between different PLC platforms, reducing the learning curve and promoting code reusability. The languages defined by this standard are Ladder Diagram (LD), Structured Text (ST), Function Block Diagram (FBD), Sequential Function Chart (SFC), and Instruction List (IL).

Ladder Diagram (LD)

Ladder Diagram (LD), often referred to as Ladder Logic, is the most widely used PLC programming language. Its graphical nature mimics traditional relay logic circuits, making it easy for electricians and technicians familiar with electrical schematics to understand and use. Ladder Logic uses contacts, coils, and other symbols to represent logical operations.

Applications: Simple control tasks, discrete manufacturing, and applications where electricians are primarily responsible for maintenance.

Structured Text (ST)

Structured Text (ST) is a high-level text-based language similar to Pascal or C. It is ideal for complex algorithms, mathematical calculations, and data manipulation. ST allows for structured programming techniques, making code more organized and easier to maintain.

Applications: Complex control algorithms, data processing, batch control, and applications requiring high-level programming constructs.

Example of Structured Text code:

IF Pressure > Setpoint THEN
    Valve := TRUE;
    Temperature := ReadTemperature();
ELSE
    Valve := FALSE;
END_IF;

Function Block Diagram (FBD)

Function Block Diagram (FBD) is a graphical language that uses interconnected function blocks to represent control logic. Each function block performs a specific task, such as PID control, logic operations, or data conversions. FBD is well-suited for process control applications.

Applications: Process control, continuous control, and applications where modularity and reusability are important.

Sequential Function Chart (SFC)

Sequential Function Chart (SFC) is a graphical language used to organize a program into sequential steps. It is ideal for applications with complex sequences of operations, such as batch processing or machine control. SFC uses steps, transitions, and actions to define the program flow.

Applications: Batch processing, machine control, and applications requiring sequential control.

SFC provides a clear and structured way to represent sequential processes, making it easier to understand and maintain complex control logic.

Instruction List (IL)

Instruction List (IL), also known as Assembler, is a low-level text-based language that provides direct access to the PLC's instruction set. While powerful, it is more difficult to learn and use compared to other languages. IL is typically used for performance-critical applications or when fine-grained control is required.

Applications: Performance-critical applications, low-level control, and applications requiring direct access to PLC hardware.

Which PLC Programming Language Is Best to Learn for a Beginner?

For beginners, Ladder Diagram (LD) is generally the best PLC programming language to start with. Its graphical nature and resemblance to electrical schematics make it easier to grasp the fundamental concepts of PLC programming. Once you have a solid understanding of Ladder Logic, you can then explore other languages like Structured Text or Function Block Diagram to expand your skill set.