Six Principles of PLC Ladder Diagram Design
1. Contact point arrangement
The contact points of a ladder diagram should be drawn on horizontal lines, not on vertical branches.
2. Processing of series and parallel connections
When several series circuits are connected in parallel, the series circuit with the most contacts should be placed at the top of the ladder diagram. When several parallel circuits are connected in series, the parallel circuit with the most contacts should be placed at the far left of the ladder diagram.
3. Coil Arrangement
The contact point cannot be drawn to the right of the coil; the coil can only be connected to the right of the contact point.
4. Dual-coil output is not permitted.
If the coil of the same component is used two or more times in the same program, it is called a double-coil output. In this case, the previous outputs are invalid, and only the last one is valid, so double-coil output should not occur.
5. Rearrange the circuit
If the circuit structure is complex, you can reuse some contacts to draw its equivalent circuit, and then programming it will be easier.
6. Programming order
For complex programs, you can first divide the program into several simple program segments. Each segment starts from the leftmost contact and is programmed from top to bottom to right. Then connect the program segments one by one.
