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 system 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, including its type, capacity, I/O modules, power supply, and other necessary components.

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

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

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

(7) Prepare the design documentation and user manual for the system.

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 flow chart or functional block diagram.

(2) Selecting the Right PLC Model

When choosing a PLC, consider the following key factors:

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

- I/O Point Calculation: Count the number of digital and analog I/O points in the system, and include a buffer of 10%–20% for future expansion when selecting the PLC's I/O specification.

- Memory Estimation: The memory size required depends on the number of I/O points, control complexity, and program structure. A general formula is: Storage Capacity = (Number of Digital Inputs × 10) + (Number of Digital Outputs × 8) + (Number of Analog Channels × 100) + (Number of Timers/Counters × 2) + (Number of Communication Interfaces × 300) + Spare Capacity.

(3) Assigning I/O Points

Allocate the input and output points for the PLC, prepare an I/O distribution table, or draw the wiring diagram for the I/O terminals. This allows for programming and on-site construction of the control panel or console.

(4) Programming

For complex systems, first create a control flow chart or functional block diagram based on the production process. Then, develop a ladder diagram and write the corresponding instruction list program. Simulate, test, and modify the program until it fully satisfies the control needs.

(5) Design and On-Site Construction of the Control Panel or Console

Design the layout and wiring diagram for the control panel and operator console. Create interlock diagrams for each part of the system and perform on-site wiring according to the drawings, ensuring proper connections and checks.

(6) System-Level Debugging

If the system consists of multiple parts, start with partial debugging before moving to full system testing. For programs with many steps, break them into segments and test each one before integration.

(7) Preparing Technical Documentation

The technical documentation should include external wiring diagrams, electrical layout plans, component lists, sequence function charts, annotated ladder diagrams, and user instructions for the programmable controller.