What is the PLC control cabinet?

PLC control cabinet, full name is programmable controller control cabinet, is an indispensable and important part of modern industrial automation control system. It takes programmable logic controller (PLC) as the core, integrates multiple functional modules and electrical components, and forms a compact and comprehensive automation control system.

Definition and composition of PLC control cabinet

PLC control cabinet refers to a control system with PLC as the control core, including PLC body, input and output modules, power modules, communication modules and other electrical components such as operation table, alarm lights, buttons and other control components. These control components are customized according to the actual application environment and operation requirements to realize the control, monitoring and operation of the on-site automation control system. PLC control cabinet not only has good performance, but also has the characteristics of stability, reliability, easy installation and simple operation. It does not require professional technicians, and only simple operations can achieve the effect of automation control.

As the core component of the control cabinet, PLC is responsible for managing the control program and logic functions of the entire system. The input and output module is responsible for inputting the signals of external devices into the PLC, and outputting the signals sent by the PLC to the external device. Other electrical components such as power supplies, switches, relays, timers, counters, etc. are auxiliary equipment of the control cabinet, providing the power supply, protection, control and other functional support required for the normal operation of the control cabinet.

Working principle of PLC control cabinet

The working principle of PLC control cabinet can be summarized into three main steps: signal input, operation processing and signal output.

1. Signal input: PLC receives signals from external devices such as sensors and switches through input modules. These input signals can be digital signals, such as switch status, button actions, etc., or analog signals, such as continuously changing physical quantities such as temperature and pressure. In the input sampling stage, PLC reads all input states and data in sequence in a scanning manner and stores them in the corresponding units in the I/O image area. The sampling results of this stage remain unchanged throughout the entire scanning cycle. Even if the input state and data change, it will not affect the processing results in the current scanning cycle.
2. Operation processing: After completing the input sampling, PLC enters the user program execution stage. In this stage, PLC scans the user program (usually a ladder diagram) in order from top to bottom. When scanning each ladder diagram, the PLC first scans the control circuit composed of various contacts on the left side of the ladder diagram, performs logical operations, and then refreshes the state of the corresponding bit of the logic coil in the system RAM storage area according to the result of the logical operation, or refreshes the state of the corresponding bit of the output coil in the I/O image area, or determines whether to execute the special function instructions specified by the ladder diagram. In this process, only the state and data of the input point in the I/O image area will not change, while the state and data of other output points and soft devices in the I/O image area or system RAM storage area may change.
3. Signal output: When the user program is executed, the PLC enters the output refresh stage. In this stage, the CPU refreshes all output latch circuits according to the corresponding state and data in the I/O image area, and then drives the corresponding peripherals through the output circuit. In this way, the PLC completes a complete scan cycle from signal input to operation processing to signal output. During the entire operation, the CPU of the PLC repeatedly executes the above three stages at a certain scanning speed, thereby realizing continuous automatic control of the equipment.

Types of PLC control cabinets

PLC control cabinets can be divided into many types according to different classification standards.

1. Structural form:
   –Fixed structure: All electrical components are fixed on a panel made of metal or non-metallic insulating materials to form a fixed closed system. The structure is simple and easy to manufacture, but all must be shut down for maintenance.
   Drawer structure: It consists of a certain number of drawer units. Each drawer contains a circuit breaker or contactor and its auxiliary components, which can be pulled out and inserted for operation, which is convenient for maintenance and expansion.
   Combined structure: It is composed of modules with different functions, such as power modules, input and output modules, and intelligent monitors. It has high flexibility and can be customized according to actual needs.
   Rack structure: It is used for the centralized arrangement of multiple devices, with compact structure, space saving, and convenient unified management and control, but it is difficult to maintain and upgrade in the later stage.
2. Purpose:
   General control cabinet: It is mainly used for basic switch control and signal processing tasks, with high cost performance and stability, and is widely used in various industrial sites.
   Special control cabinet: designed for the needs of specific industries or production processes, such as electric furnace control systems in the metallurgical industry, flammable and explosive environment monitoring systems in the chemical industry, etc., to meet specific safety and reliability requirements.

Application of PLC control cabinet

PLC control cabinet has a wide range of applications in the field of industrial automation control, and can be used for factory production line control, robot control, workshop automation control, mechanical automation control and other aspects. It can realize automatic switching, detection, monitoring, control and other functions, and is an advanced automation control system.

1. Factory production line control: PLC control cabinet can realize precise control of various equipment on the production line, including motor start, stop, speed adjustment, etc., to improve production efficiency and reduce energy consumption.
2. Robot control: PLC control cabinet realizes precise control of robots through programming, including motion trajectory, action sequence, speed adjustment, etc., to improve the work efficiency and flexibility of robots.
3. Workshop automation control: PLC control cabinet can realize centralized control and management of various equipment in the workshop, including auxiliary facilities such as lighting, ventilation, air conditioning, etc., to improve the overall automation level of the workshop.
4. Mechanical automation control: PLC control cabinets can be applied to the automation control of various mechanical equipment, such as CNC machine tools, injection molding machines, stamping machines, etc., to improve the operating stability and production efficiency of the equipment.

Environmental conditions of PLC control cabinets

In order to ensure the normal operation of the PLC control cabinet, certain environmental conditions must be met.

1. Temperature: The ambient temperature should be between 0℃-55℃, avoiding direct sunlight.
2. Humidity: The relative humidity of the air should be less than 85%, without condensation, to prevent electrical components from being damaged by moisture.
3. Vibration: Stay away from vibration sources with a vibration frequency of 10-55Hz to prevent vibration from damaging electrical components.
4. Corrosive gas: Avoid equipment in a corrosive and flammable gas environment to prevent electrical components from being corroded or causing fire.
5. Power supply system: The power supply system of the PLC control cabinet is crucial to its normal operation. Under the condition that the general AC voltage fluctuation does not exceed +10% (+15%), the PLC can be directly connected to the AC power grid. Manufacturers will attach great importance to the design and manufacture of power supplies to ensure system stability.

Future development of PLC control cabinets

With the continuous development of science and technology, PLC control cabinets are also constantly improving and improving. In the future, PLC control cabinets will pay more attention to the development of intelligence, networking, modularization, etc.

1. Intelligence: PLC control cabinets will integrate more intelligent algorithms and sensors to realize intelligent monitoring and diagnosis of equipment, and improve the reliability and stability of equipment.
2. Networking: PLC control cabinets will exchange data with other devices through industrial Ethernet or industrial fieldbus networks to achieve remote monitoring and control, and improve the flexibility and scalability of the system.
3. Modularity: PLC control cabinets will pay more attention to modular design, which will facilitate users to customize and develop according to actual needs and reduce development and maintenance costs.

With the continuous advancement of technology, PLC control cabinets will play a more important role in the field of industrial automation control, providing strong support for the production and development of enterprises.