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. Another brand specific issue is the names for the instructions and functions. 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. Many PLC ladder logic program examples are available for download, and you will have to install the PLC programming software to view the example ladder. This is another article of the free Siemens PLC programming series. This programming language is also used heavily in highly sophisticated automation systems such as electronics and car factories. In this video, you’ll learn how to write a PLC program to start and stop an electric motor and test it using PLCSIM. The programming language is quite useful for programming simple yet critical systems or for reworking old hard-wired systems into newer programmable ones. Ladder diagram programming allows PLCs to perform several different types of tasks, including Boolean logic, timing, counting, arithmetic, and special functions. Ladder logic is widely used in industrial settings for programming PLCs where sequential control of manufacturing processes and operations is required. 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. By executing the loop quickly enough, the effect still seems like a simultaneous and immediate execution within the required time tolerance.

It mimics the relay logic (combination of switches, relays, coils and contacts). But if the program is applied to PLCs, the rules are executed sequentially through software and in a continuous loop. Ladder Logic is the main programming method used for PLC’s. Each 'rung' in the ladder represents a rule, so when implemented to relays and various electromechanical devices, these rules execute simultaneously and immediately. Ladder logic is described as a rule-based language rather than a procedural or imperative one.

Plc ladder logic program