PLC ladder diagram design six principles - Database & Sql Blog Articles

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1. Contact Arrangement

In ladder diagrams, contacts should be drawn on horizontal lines rather than vertical branches. This ensures clarity and makes the circuit easier to follow.

2. Series and Parallel Processing

When multiple series circuits are connected in parallel, the one with the most contacts should be placed at the top of the diagram. Similarly, when parallel circuits are connected in series, the one with the most contacts should be positioned on the left side for better readability and logical flow.

3. Coil Placement

Coils should only be placed to the right of contacts. You cannot draw a contact after a coil, as this would violate the standard structure of ladder logic.

4. No Double Coil Output

Using the same coil more than once in a single program is known as double coil output. In such cases, only the last instance of the coil will take effect, making the previous ones invalid. It's best to avoid this to prevent unexpected behavior in your control system.

5. Circuit Redesign

For complex circuits, it's often helpful to restructure them by reusing certain contacts to create an equivalent simplified version before programming. This can save time and reduce errors during implementation.

6. Programming Order

When working with complicated programs, break them into smaller, manageable blocks. Start each block from the leftmost contact, proceed from top to bottom, and then connect the segments logically. This method helps maintain a clear and organized structure throughout the program.