When designing a PLC application system, the first step is to perform functional design, which involves defining the necessary tasks and required conditions of the system based on the functions and technological requirements of the controlled object. Next, functional analysis of the PLC application system is conducted. This involves analyzing the system's functions to determine the structural form of the PLC control system, the types and quantities of control signals, and the system's scale and layout. Finally, based on the results of the system analysis, the specific PLC model and system configuration are determined.
PLC control system design steps:
1. Familiarize yourself with the controlled object and develop a control plan.
Analyze the technological process and working characteristics of the controlled object, understand the coordination between the mechanical, electrical, and hydraulic systems of the controlled object, and determine the control requirements of the controlled object for the PLC control system.
2. Determine the I/O devices
Based on the system's control requirements, determine the user's required inputs (such as buttons, limit switches, selector switches, etc.) and output devices (such as contactors, solenoid valves, indicator lights, etc.), thereby determining the number of I/O points for the PLC.
3. Select PLC
The selection process mainly includes choosing the PLC model, capacity, I/O modules, and power supply.
4. Assign I/O addresses to the PLC
Based on the needs of the production equipment site, determine the control buttons, and select the models, specifications, and quantities of various input/output devices such as switches, contactors, solenoid valves, and indicator lights; based on the selected PLC model, list the correspondence table between the input/output devices and the PLC input/output terminals to facilitate the drawing of the PLC external I/O wiring diagram and the programming.
5. Design software and hardware, including PLC programming, control cabinet (unit) and other hardware design and on-site construction.
Because program and hardware design can be carried out simultaneously, the design cycle of a PLC control system can be greatly shortened, whereas for a relay system, all electrical control circuits must be designed before construction design can proceed.
6. Online debugging
Online debugging refers to performing unified online debugging on a program that has passed analog debugging. Initially, debugging is performed without any output devices (contactor coils, signal indicator lights, etc.). The programmer's monitoring function is used, employing a segmented debugging method. After each part is debugged normally, an actual load is applied for operation. If it does not meet requirements, adjustments are made to the hardware and program. Usually, only a portion of the program needs modification. After all debugging is complete, it is put into trial operation. After a period of operation, if it works normally and the program does not require modification, it should be burned into the EPROM to prevent program loss.
7. Organize technical documents
This includes design specifications, electrical installation diagrams, a list of electrical components, and user manuals.
