Analysis of PLC Control Cabinet and core technology

 

PLC Cabinet Components are a complete set of electrical cabinets that integrate various electrical components to achieve control functions for motors, switches, and other equipment. It has core protection functions such as overload, short circuit, and phase loss protection, with a compact structure and stable operation. The functional configuration can be flexibly combined according to the actual control scale. It can achieve independent automatic control of a single cabinet, and can also form a distributed control system through industrial ethernet or industrial fieldbus networks, which can adapt to different scales of industrial automation control scenarios. It has a wide range of applications in various industrial fields such as power, metallurgy, chemical, papermaking, and environmental wastewater treatment.

 

As the core equipment of modern industrial automation control, Application Cabinet can complete equipment automation and process automation control, with excellent network communication functions, as well as stable performance, strong scalability, and outstanding anti-interference ability. Users can customize the design of PLC Based Control Cabinet, frequency conversion cabinets, etc., according to their actual control needs, and when combined with a human-machine interface touch screen, it can achieve convenient operation. Its typical application scenarios include constant pressure water supply, air compressor control, fan and pump speed regulation, central air conditioning regulation, port machinery operation and maintenance, machine tool processing control, boiler operation management, paper and food machinery automation, and many other fields.

 

 

 

The composition of the PLC System Cabinet for Sewage needs to be configured according to control requirements, and the core components include the following key components. The Air switch (circuit breaker) is mainly used to cut off and connect the power supply of the control cabinet. To ensure the reliable operation of important electrical components, independent circuit breakers can be set up according to the function of the components, such as dedicated circuit breakers for PLC and contactor circuits. As the core control unit, a PLC can achieve simple logic control through contactors; If it involves automatic control functions or complex logical operations, a PLC must be configured. When selecting, small projects can use integrated PLCs, while large projects can choose modular PLCs according to their needs.

 

The 24VDC switching power supply is also an important component of the Electric Cabinets PLC Panel Cabinet. Its power transistor operates in a high-frequency switching state above 20kHz. With technological upgrades, the current switching frequency can reach several hundred kilohertz or even several megahertz. The core component is the DC converter, which can be divided into self-excited and separately excited types according to the way the power switching transistor is excited. If the PLC power input is DC type, a separate switch power supply needs to be configured. Most PLCs come with a 24VDC power output, and whether to additionally configure a switch power supply needs to be determined based on the actual application scenario.

 

The configuration of relays is closely related to the output type of the Explosion-proof PLC Cabinet. Relay output PLC can directly drive AC loads or power loads (different models have different driving capabilities) without the need for additional intermediate components; If a transistor output type PLC needs to drive AC loads or power loads, it needs to use external relays to control the relay coil through PLC output signals, and then drive the load to run through the relay contacts. At this time, the relay plays an intermediary role in signal conversion and amplification. As the core accessory for achieving electrical connections, terminal blocks belong to the category of connectors. With the improvement of industrial automation and the increasing demand for control accuracy, their usage in control cabinets continues to grow. If the control cabinet needs to be additionally connected to a small control box for power supply or various instruments, supporting components such as air switches can be added according to demand.

 

 

The stable operation of Industrial PLC Cabinet requires specific usage conditions, and the power supply can use two-phase AC 220V (50Hz) or DC 24V; the protection level usually needs to reach IP20 or IP41; In terms of environment, it is necessary to stay away from strong vibration sources, avoid frequent or continuous vibrations of 10-55Hz, prevent direct sunlight exposure, control the working environment temperature between 0 ℃ -55 ℃, and stay away from corrosive and flammable gases. The relative humidity of the air should be less than 85% (no condensation).

 

The basic structure of the integrated Programmable Logic Controller Cabinet mainly includes four core parts: power supply, central processing unit (CPU), built-in memory, and input/output interface circuit. The power module is the basic guarantee for the stable operation of PLC. Its design usually supports direct connection to the AC power grid without additional measures when the AC voltage fluctuates within ± 10% (± 15%) range. Common power conversion methods include AC 220V to DC 24V and DC 24V direct power supply. The central processing unit (CPU) serves as the control center of the Electrical Control Cabinet, with core functions including receiving and storing user programs and data, checking power, memory, I/O interfaces, and alert timer status, diagnosing user program syntax errors, and achieving automated control by scanning input signals, executing user programs, and outputting control results during runtime.

 

The built-in memory of Automation Control Cabinet is divided into two types: system program memory and user program memory, which are used to store system software and application software, respectively. The input/output interface circuit is the key to the interaction between PLC and external devices. The input interface circuit is responsible for transmitting signals generated by external devices such as buttons, travel switches, sensors, etc. to the CPU. According to the power supply type, it can be divided into DC input circuit and AC input circuit. The DC input circuit has a short delay time and can be directly connected to electronic input devices such as proximity switches and photoelectric switches, while the AC input circuit is suitable for harsh environments such as oil mist and dust; The output interface circuit is responsible for converting the CPU output signal into a signal that can drive external execution components, and realizing the on/off control of electrical appliances such as contactor coils. To ensure the safety of internal circuits, optical coupling isolation technology is usually used for input-output interface circuits. Common types of output interface circuits include relay output, transistor output, and thyristor output. For modular Enclosed PLC Cabinet, in addition to the core components, functional modules, communication modules, and other extension components can also be configured according to requirements.

 

The working process of PLC is centered around the scanning cycle. After being put into operation, it needs to complete three stages in sequence: input sampling, user program execution, and output refresh. The CPU will repeat these three stages at a fixed scanning speed. In the input sampling stage, the Dustroof PLC Cabinet reads the status and data of all input terminals one by one in a scanning manner, and stores them in the input image register. After the end of this stage, regardless of whether the input signal changes, the data in the input image register remains unchanged. Therefore, if the input is a pulse signal, its width needs to be greater than one scanning cycle to ensure that the signal is reliably read.

 

During the execution phase of the user program, Custom PLC Cabinet scans the user program in a top-down order. For each ladder diagram, it first scans the control circuit composed of the left contacts, completes logical operations in the order of left to right and top to bottom, and then refreshes the status of the logic coil in the system RAM storage area or the output coil in the corresponding bit of the I/O mapping area based on the operation results, or executes special function instructions. In this stage, only the state and data within the input image area remain stable, while the state and data of other output points and software devices may change. The execution result of the upper ladder diagram will have an immediate impact on the program using the relevant coils or data in the lower layer, and the update of the state or data in the lower layer program needs to wait for the next scanning cycle before it can be applied to the upper layer program. If the immediate I/O instruction is used in the program, the I/O point can be accessed directly without going through the mapping area. The input immediate instruction directly takes values from the I/O module, and the output immediate instruction will immediately refresh the output mapping register.

 

In the output refresh stage, after completing the user program scan, the Modular PLC Cabinet will refresh all output latch circuits according to the status and data in the I/O image area, and then drive external peripherals through the output circuit to complete the actual output action of the PLC.

 

 

If you have customized requirements or technical consultation for PLC Control Cabinet, please feel free to contact us at any time. Looking forward to communicating and cooperating with you to provide you with professional industrial automation control solutions.