PLC control cabinet refers to a complete set of electrical cabinets that can control motors and switches.

The PLC control cabinet has complete functions and compact structure. It can be combined according to the actual control scale and has functions such as overload and phase loss protection. It can not only realize automatic control of a single cabinet, but also realize a distributed control system composed of multiple cabinets through industrial Ethernet or industrial fieldbus network. It can be adapted to various industrial automation control situations and is widely used in metallurgy, electric power, ports, municipal construction, environmental protection and other industries.

PLC control cabinet can complete equipment automation and process automation control, realize perfect network functions, strong anti-interference ability, stable performance, scalability and other characteristics. It is the core and soul of modern industry.

Components of PLC control cabinet

1. Open

A master air switch is the power control for the entire cabinet.

2. Power supply

A 24VDC switching power supply.

3.PLC

This should be chosen based on the needs of the project. If the project scale is small, the integrated PLC can be used directly; if the project is larger, modules, card types and redundancy may be required.

4. Terminals

Can be configured according to the number of signals. If it is just a simple PLC control cabinet, these things are basically needed. If other equipment in the control cabinet is required, this depends on the situation.

5. Relay

Sometimes the instructions sent by the PLC need to be relayed by the relay first. When the instruction is sent, the relay acts, so that the node of the control loop is connected to the normally open or normally closed point of the relay.

PLC control cabinet usage conditions

Power supply: DC 24V, single-phase AC 220V, (-10%, +15%), 50Hz.

Product functions and features

1. Control with programmable controller.

2. Manual and automatic dual control.

3. Simple wiring and easy operation.

working principle

When the programmable logic controller is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution and output refresh. Completing the above three stages is called a scan cycle. During the entire running process, the PLC's CPU repeats the above three stages at a certain scanning speed.

1. Input sampling stage

In the input sampling stage, the PLC sequentially reads all input status and data in a scanning manner and stores them in the corresponding units of the I/O image area. After input sampling is completed, the user program execution and output refresh phases are transferred. In these two stages, even if the input status and data change, the status and data of the corresponding unit in the I/O image area will not change. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than the scan period to ensure that the input can be read under any circumstances.

2. User program execution stage

During the execution phase of the user program, the PLC always scans the user program from top to bottom. When scanning each ladder diagram, always scan the control circuit composed of the contacts on the left side of the ladder diagram first, and perform logical operations on the control circuit composed of the contacts in the order of first left, then right, first up, then down, and then, According to the result of the logic operation, refresh the state of the corresponding bit of the logic coil in the system RAM memory area; or refresh the state of the corresponding bit of the output coil in the input/output image area.

That is, during the execution of the user program, only the status and data of the input points in the I/O image area will not change, while the status of other output points and software devices in the I/O image area or system RAM storage area will not change. and data may change, and the program execution results of the ladder diagram above will affect the ladder diagram below that uses these coils or data; on the contrary, the status or data of the logic coils refreshed in the ladder diagram below can only be displayed above the ladder diagram program until the next scan cycle.

3. Output refresh stage

After scanning the user program is completed, the PLC will enter the output refresh phase. During this period, the CPU refreshes all output latch circuits according to the corresponding status and data in the I/O image area, and then drives the corresponding peripheral devices through the output circuits. This is the real output of the PLC.