Analysis of the hardware and software composition and working principle of PLC

A programmable controller (PLC) is a computer device designed specifically for industrial control environments. Its structure is similar to that of an ordinary computer, but it is specially optimized for industrial application scenarios. The hardware architecture of PLC is closely centered around control requirements and can achieve stable and reliable operation in a variety of automation scenarios. The hardware system usually consists of a host computer and several peripheral devices. The host computer realizes the interconnection of various functional modules through different buses to form a complete control system. In terms of hardware organization, PLC can choose an integral structure, which integrates all components into a single chassis; it can also choose a modular structure, which encapsulates each functional component into independent modules and interconnects through racks and cables to enhance the flexibility of system configuration. In order to adapt to harsh industrial environments, related equipment is often equipped with Control cabinet or Electrical control cabinet for centralized installation and protection.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PLC hardware consists of a host computer and peripherals. The host computer includes units such as CPU, memory, I/O modules, power supply, and communication interfaces. As the control center, the CPU is composed of a microprocessor and a controller and is responsible for logical operations, mathematical processing and system coordination to ensure precise control of field equipment. The memory is divided into Enclosed PLC cabinet system memory (the solidified system management program) and user memory (storing custom applications and work data). It supports read-only, programmable read-only and other types to meet different data storage needs.

 

The I/O module is a bridge connecting field devices: the input module collects switching signals (supports DC, AC or both AC and DC) and converts the external state into a level that can be recognized by the PLC; the output module converts the TTL control signal generated by the CPU into a drive signal adapted to the field device to achieve actuator control. The Custom PLC cabinet unit converts the external 220V AC power into the stable working voltage required by the internal circuit, and adopts a switching voltage stabilizing design to ensure power supply reliability. The peripheral interface supports the connection of programmers, text displays and other devices, and realizes program editing, status monitoring and networking functions through RS-485 and other interfaces.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The PLC operates in a cyclic scanning mode in Automation control cabinet, with a single cycle taking milliseconds to ensure real-time performance and reliability. The scanning process is divided into three stages: the input sampling stage, in which all input states are read in sequence and stored in the I/O image area. In this stage, the input data is locked until the next cycle; the user program execution stage, the user program is scanned line by line in the order of "first left, then right, first up, then down" to complete logical operations and data processing; the output refresh stage, the output latch circuit is updated according to the user program results to drive external device actions. Affected by the scanning mechanism, there is an inherent lag in input and output, but the millisecond-level cycle can meet the needs of most industrial control scenarios.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PLC software is divided into system programs and user programs. The system program is solidified in the system memory by the manufacturer and is responsible for the underlying logic management and hardware scheduling. It cannot be modified directly by the user. The user program is written by the developer according to the control requirements and uses a dedicated programming language to implement the device control logic. This type of language is optimized for electrical technicians. It has the characteristics of graphical instruction structure, clear variable definition and simplified program framework, which lowers the development threshold and improves debugging efficiency.

 

 

The company focuses on the R&D and manufacturing of PLC System Enclosure. Whether it is standard or customized, our control cabinets can be seamlessly adapted to various PLC systems to ensure reliable protection, heat dissipation and wiring management of the hardware in complex industrial environments. Welcome to contact us for selection support and overall solutions.