In the PLC ladder logic diagram, there are certain rules and conventions for the placement of contacts.
According to the information I have, in the PLC ladder logic diagram, contacts should not be placed vertically, but should be drawn on the horizontal line.
The following is a specific explanation of this view:
Contact placement principles
1. Horizontal placement: The contacts of the ladder diagram should be drawn on the horizontal line, not on the vertical branch. This is to ensure the clarity and readability of the ladder diagram, so that programmers can understand and maintain the program.
2. Series and parallel:
- When there are several series circuits in parallel, the series circuit with the most contacts should be placed at the top of the ladder diagram.
- When there are several parallel circuits in series, the parallel circuit with the most contacts should be placed on the far left of the ladder diagram.
The impact of vertical placement
Although the vertical placement of contact graphics in electrical schematics is a common representation method used to show the switching status of electrical equipment and the connection status of electrical circuits, this rule does not apply to PLC ladder logic diagrams. In ladder logic diagrams, vertical placement of contacts may lead to unclear logic and increase the difficulty of programming and maintenance.
Other considerations
1. Coil placement: The contact point cannot be drawn on the right side of the coil, and the coil can only be connected to the right side of the contact point. This is to avoid logical confusion and errors.
2. Double coil output: Double coil output should be avoided, that is, in a program, the same output coil should not be used twice or more. If a double coil appears, the previous output is invalid, and only the last one is valid.
3. Program structure: For complex programs, it can be divided into several simple program segments, each starting from the leftmost contact, programming from top to bottom to right, and then connecting the program segment by segment.
In summary, the contacts in the PLC ladder logic diagram should not be placed vertically, but should follow the principle of horizontal placement to ensure the clarity and readability of the program.