PLC control system design content and design steps - Database & Sql Blog Articles

1. PLC Control System Design Content

(1) Based on the design task book, analyze the process and determine the control plan, which serves as the foundation of the entire design.

(2) Select input devices such as buttons, switches, sensors, and output devices like relays, contactors, and indicator lights.

(3) Choose the appropriate PLC model, considering factors like model type, capacity, I/O modules, power supply, and more.

(4) Assign the I/O points of the PLC and create the hardware wiring diagram for the system.

(5) Develop and debug the program to ensure it meets the control requirements.

(6) Design the control console, electrical cabinet, and related installation wiring diagrams.

(7) Prepare the design manual and user instruction guide.

2. Design Steps

(1) Process Analysis

Gain a deep understanding of the process, working characteristics, and control requirements of the system. Break down the control stages, identify their features, and define the transition conditions between them. Draw a control flowchart or functional block diagram to visualize the process.

(2) Selecting the Right PLC Model

When choosing a PLC, consider the following:

1. Function Selection: For small PLCs, focus on I/O expansion modules, A/D and D/A modules, and command functions like interrupts or PID control.

2. I/O Point Determination: Count the number of switching and analog inputs/outputs, and add 10%–20% for future expansion to determine the required I/O points and output specifications.

3. Memory Estimation: The memory needed depends on the number of I/O points, control complexity, and program structure. A general formula is: Memory = (Switching Input Points × 10) + (Switching Output Points × 8) + (Analog Channels × 100) + (Timers/Counters × 2) + (Communication Interfaces × 300) + Spare Capacity.

(3) I/O Point Assignment

Assign the input and output points of the PLC, prepare an I/O distribution table, or draw the wiring diagram for the terminals. This step is essential before programming and on-site construction of the control panel or cabinet.

(4) Programming

For complex systems, create a control flowchart or functional block diagram based on the production process. Then design the ladder logic and write the corresponding instruction list. Simulate and test the program, making adjustments until all control requirements are satisfied.

(5) Design and On-Site Construction

Plan the layout of the control cabinet and operation console, including the installation wiring diagram. Design the electrical interlock diagram for each part of the system and perform on-site wiring according to the drawings, followed by thorough checks.

(6) Overall System Debugging

If the system has multiple components, start with partial debugging before moving to full integration. For multi-step programs, debug in segments and then combine them for final testing.

(7) Prepare Technical Documentation

Technical documentation should include external wiring diagrams, electrical layout plans, component lists, sequential function charts, annotated ladder diagrams, and user instructions.