Ladder Logic

Ladder logic is described as a rule-based language rather than a procedural or imperative one. Each "rung" in the ladder represents a rule, so when implemented to relays and various electromechanical devices, these rules execute simultaneously and immediately. But if the program is applied to PLCs, the rules are executed sequentially through software and in a continuous loop. By executing the loop quickly enough, the effect still seems like a simultaneous and immediate execution within the required time tolerance. The capabilities of the PLC being used have to be considered during programming as the electromechanical nature of the devices connected to it might not be able to keep up with the instructions, and it may seem that some rules are being skipped when the devices really just cannot keep up.

Ladder logic is widely used in industrial settings for programming PLCs where sequential control of manufacturing processes and operations is required. The programming language is quite useful for programming simple yet critical systems or for reworking old hard-wired systems into newer programmable ones. This programming language is also used heavily in highly sophisticated automation systems such as electronics and car factories.

The idea behind ladder logic is that even personnel without programming backgrounds can quickly program since it makes use of conventional and familiar engineering symbols for programming. But this advantage is quickly negated since manufacturers of PLCs often also provide ladder logic programming systems with their products, which sometimes do not use the same symbols and conventions as those made for other models of PLCs from other manufacturers; in fact, the programming system is usually meant only for specific models, so the programs cannot be ported easily to other PLC models or must be outright rewritten.