The most prominent advantage of PLC is the use of "soft relay" instead of "hard relay". Replace "hardware routing logic" with "software programming logic." PLC programming languages are ladder diagrams, Boolean mnemonic languages, and more. Especially the first two are commonly used.
1. Each ladder diagram consists of multiple steps.
2. The vertical lines on the left and right sides of the ladder diagram represent imaginary logic power supplies. When the logical operation result of a certain step is "1", an imaginary current passes.
3. The relay coil can only appear once, and its normally open, normally closed contacts can appear countless times.
4. The result of each step is immediately used by the subsequent steps.
5. The input relay is controlled by an external signal. Only contacts appear and no coils appear.