PLC control cabinet is generally composed of these parts:

1. PLC cabinet

The exquisite workmanship of the PLC cabinet is the external image of the complete PLC control system. It should be economical and high-end atmospheric, and must also take into account the requirements of waterproof, dustproof, reasonable structure and easy component installation.

2. Air switch

1) AC220V total power switch, which is necessary for every PLC control cabinet. If the power supply of external instruments and electrical equipment needs to be sent from the PLC cabinet, each circuit should be equipped with a power switch in a single way.

2) DC24V power main switch, which is necessary for each PLC control cabinet. If the power supply of external instruments and electrical equipment needs to be sent from the PLC cabinet, each circuit should be equipped with a power switch in a single way.

3) The main power switch, if the PLC control cabinet is also installed with contactors, frequency converters and other equipment, this switch is necessary.

3. Trunking

The trunking groove is used for wiring in the PLC cabinet. The size of the trunking groove is determined by the number of cables in the cabinet.

4. DC24V switching power supply

Most PLCs have their own DC24V power supply. If more DC24V power supply circuits are required, the input AC220V / output DC24V high-quality switching power supply module must be configured separately.

5. Programmable Logic Controller (PLC)

The PLC brand of programmable logic controller is usually selected according to engineering needs. Stable performance, reliable operation, high cost performance, simplicity and practicality, easy expansion and strong compatibility are the basic elements for choosing PLC. If the project is relatively large or important occasions need to consider PLC redundancy (that is, the two sets are used interchangeably).

6. Intermediate relay

In principle, the DO output of the programmable controller in the PLC control cabinet does not directly enter the external control loop, and should be relayed by a high-performance intermediate relay (such as OMRON brand, coil voltage DC24V), which is beneficial to prolong the service life and safety of the PLC DO output module. The number of intermediate relay contacts can be selected as two normally open / two normally closed types or four normally open / four normally closed types as required.

7. Terminal

The number of wiring terminals is determined by the number of input and output circuits.

8. Signal isolator and distributor

The signal of the on-site two-wire transmitter is converted into a 4-20mA signal by the distributor and sent to the AI input terminal of the programmable controller; the external 4-20mA, 0-5V, 0-20mA and other signals are converted by the signal isolator The 4-20mA signal is sent to the programmable logic controller AI input. The use of signal isolators and power distributors can improve the anti-interference ability and system stability of the entire system.

9. Safety barrier

If the AO output or DI output of the programmable controller needs to be sent to a hazardous area, the corresponding safety barrier should be selected as required.

10. Other equipment

PLC cabinets are usually equipped with contactors, buttons, frequency converters, switches, human-machine interface touch screens and other equipment, depending on engineering requirements.

The PLC control cabinet generally contains: circuit breaker equipment, fuses, switching power supplies, transformers, PLC body modules and I / O expansion modules, signal isolation modules, surge protectors, HMI man-machine interface, button indicators, wiring terminals, Intermediate relays, wiring ducts, cabinet lights, limit switches, etc. Of course, many of the equipment inside are optional, and there are no listed ones that are matched with actual engineering projects, all of which are different.