PLC Ladder Design Principles

PLC ladder design principles

PLC ladder design six principles

1.Contact arrangement

Ladder contacts should be drawn on a horizontal line,not on vertical branches.

2.Series and parallel connection processing

When there are several series circuits in parallel,the series circuit with the most contacts should be placed on the top of the ladder diagram.When there are several parallel circuits in series,place the parallel circuit with the largest number of contacts on the far left of the ladder diagram.

3.Coil arrangement

Do not draw the contacts on the right side of the coil,but only on the right side of the contact.

4.Do not allow double coil output

If the coils of the same component are used two or more times in the same program,they are called dual coil outputs.At this time the front output is invalid,only the last one is valid,so should not appear double coil output.

5.Rearrange the circuit

If the circuit structure is more complex,you can re-use some contacts to draw its equivalent circuit,then it is easy to program.

6.Programming sequence

For complex programs,the program can be divided into several simple program segments.Each segment starts from the leftmost

contact and is programmed from the top to bottom then to right,then connect program by segment.