PLC logic can be programmed in different languages, including high-level visual programming languages. One of the most popular visual programming languages for PLC control logic and configuration is Ladder Logic (LL), which is mirrored in Ladder Diagrams (LDs).The main advantage of Ladder Logic is that it provides a visual interface, which significantly reduces the PLC programming learning curve. In addition, the structure of Ladder Logic and Ladder Diagrams is similar to that of relay circuits, which makes them easy for electromechanical and industrial engineers to understand and use. Similarly, familiarity with bitwise operators and Boolean logic helps in understanding and using ladder logic.
From a programming perspective, ladder logic uses symbolic representations to express logical operations. As a result, ladder logic programs contain batches of mathematical logic in symbolic positions, i.e., they are based on bit logic operations and are structured similarly to ladder diagrams. This is the reason and rationale behind the name "ladder logic". This makes it a standardized programming language. However, ladder logic was not invented for traditional programmers of high-level programming languages. Instead, it was designed primarily for technicians, electricians and electrical engineers familiar with electrical signals. As a result, ladder symbols look like electrical signals such as contacts and relays. These symbols map to Boolean and symbolic logic in the context of a ladder logic program.
Ladder logic is the most popular PLC programming language, but it is not the only way to program PLCs. Other popular languages include Sequential Function Chart (SFC), Function Block Diagram (FBD), Structured Text (ST), and Instruction List (IL). These languages have conceptual and syntactical similarities to ladder logic, as well as a smooth learning curve for engineers and technicians familiar with electrical concepts.
