PLC migration design method programming steps - Database & Sql Blog Articles

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1. Analyze the Original System

Start by understanding how the existing system operates. Study the process and mechanical behavior of the equipment being controlled, and analyze the working principle of the control system based on the relay circuit diagram. This step is crucial to ensure a smooth transition during the PLC implementation.

2. Assign PLC I/O Points

Identify all input and output devices in the system and assign them to the appropriate I/O points on the PLC. Create a wiring diagram that shows the external connections for the PLC. This helps in visualizing the entire system and ensures proper integration.

3. Establish Component Correspondence

Determine how each component in the original relay circuit corresponds to the internal components of the PLC. This includes mapping intermediate relays, time relays, and other elements to auxiliary relays and timers within the PLC. This step is essential for accurate translation of the logic into the new system.

Key considerations during this process include:

• Actuators like contactors, solenoid valves, and lights should be mapped to output relays in the PLC.
• Input devices such as Switches, buttons, and sensors correspond to input relays. The thermal relay’s contacts can either be used directly as inputs or placed in the external circuit, depending on the availability of PLC input points.
• Intermediate relays from the relay circuit map to auxiliary relays in the PLC.
• Time relays must be matched with timers or counters in the PLC. Note that time relays have both power-on and power-off delay types, while PLC timers typically only support power-on delay.

4. Design the Ladder Logic Program

Using the established correspondence, translate the relay circuit into a "quasi-ladder diagram." Then refine it into a structured and efficient ladder diagram following standard programming rules. For complex systems, break the process into smaller parts, convert them individually, and then integrate the results.

5. Review and Debug the Program

After completing the ladder logic, carefully review and test the program to ensure it accurately replicates the functionality of the original system. This step is critical to avoid errors and ensure reliable operation once the system is deployed.