The Howdy Glossary

Ladder logic is a graphical programming language primarily used to program Programmable Logic Controllers (PLCs). It visually represents electrical circuits through rungs of logic operations and symbols, mimicking current flow in electrical circuits from left to right and top to bottom. Rooted in relay-based control systems, ladder logic employs symbols for inputs/outputs and instructions for logical operations such as AND, OR, timers, counters, and mathematical functions. This design simplifies creating automation sequences for industrial engineers who may not have extensive software development expertise but are familiar with electrical schematics.

Originally introduced by Dick Morley in the 1970-1980s for General Motors Hydramatic Manufacturing Systems Division, ladder logic revolutionized industrial automation by offering a straightforward method of programming PLCs. It allows engineers and technicians accustomed to electrical schematics to easily translate real-world circuits into functional automation applications. Despite the emergence of other PLC programming languages like Function Block Diagram (FBD), Structured Text (ST), Instruction List (IL), and Sequential Function Charts (SFC), ladder logic remains popular due to its simplicity and visual appeal.

Competing languages offer unique features tailored for different needs: FBD emphasizes modular blocks; ST provides a text-based approach suitable for complex tasks; IL offers mnemonic coding akin to assembly language; SFC focuses on sequential steps. These alternatives cater to varying preferences in industrial contexts but lack the universal familiarity of ladder logic among electricians and technicians. The visual nature of ladder logic makes it particularly accessible for users with an electrical background yet limited programming knowledge, ensuring its enduring relevance in PLC programming by enabling intuitive translation from traditional relay-based systems into modern automated solutions.