What are the key differences between 'ladder logic' and 'structured text' programming languages for PLCs?

Ladder logic and structured text are two common programming languages used for Programmable Logic Controllers (PLCs), but they differ significantly in their structure, syntax, and suitability for different types of control applications. Ladder logic is a graphical programming language that resembles electrical relay circuits. It uses symbols representing contacts, coils, and other electrical components to create a diagram that shows the logical flow of signals. Ladder logic is well-suited for simple control applications involving discrete inputs and outputs, such as interlocking, sequencing, and basic on/off control. It is relatively easy to learn and understand, particularly for electricians and technicians familiar with relay logic. Structured text is a high-level, text-based programming language that resembles Pascal or C. It uses statements, expressions, and control structures to create more complex and sophisticated control programs. Structured text is well-suited for applications involving complex calculations, data manipulation, and advanced control algorithms. It allows for more modular and reusable code, making it easier to develop and maintain large programs. However, it requires a higher level of programming skill than ladder logic. In summary, ladder logic is a graphical language that is easier to learn and use for simple control applications, while structured text is a text-based language that is more powerful and flexible for complex control applications.