What functions does a PLC control cabinet have?

Release time:

2022-07-28

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Abstract

The PLC control cabinet has maintenance functions such as overload, short circuit, and phase loss protection. The equipment is compact, operates stably, and is fully functional. This system can be combined according to the actual control scale, allowing not only for automatic control of the cabinet but also for distributed control (DSC) of multiple cabinets through industrial Ethernet or industrial fieldbus networks.

　　PLC control cabinetIt has maintenance functions such as overload, short circuit, and phase loss protection. The equipment is compact, operates stably, and is fully functional. The system can be configured according to the actual control scale, allowing for automatic control of the cabinet and distributed control (DSC) of multiple cabinets through industrial Ethernet or industrial fieldbus networks. PLC control cabinets can be applied in various scales of industrial automation scenarios and are widely used in industries such as power, metallurgy, chemical engineering, papermaking, environmental protection, and wastewater treatment.

1. Air switch: The main air switch controls the power supply of the entire cabinet, and each cabinet must have one.

2. PLC: Should be selected based on project needs. For example, if the project is small, the PLC can be directly integrated; however, if the project is large, modules and cards may be needed, or redundancy (i.e., two sets of backup applications) may be required.

3. 24VDC power supply: 24 VDC switching power supply. Most PLCs have their own 24VDC power supply. Whether this switching power supply is needed depends on actual requirements.

4. Relay: Generally, a PLC can send commands directly to the control circuit but can also transmit through a relay first. For example, if the output port of the PLC is charged at 24V DC but the node in the control circuit requires a PLC power supply of 220VAC, a relay must be added to the output port of the PLC. This means that when a command is issued, the relay will act, but the node in the control circuit will connect to either the normally open or normally closed point of the relay. The use of relays is also chosen based on circumstances.

5. Terminal block: A must-have for every cabinet. It can be configured according to the number of signals. If a simple PLC control cabinet only needs these components, additional items can be added based on circumstances. For example, if power may be needed for certain scenarios or small control boxes, increasing the number of open spaces may be necessary. If you want to connect the PLC to a host computer, you may need to add a switch or other components.

A programmable logic controller is essentially a computer specifically designed for industrial control. Its hardware structure is fundamentally similar to that of microcomputers. The basic structure of a PLC control cabinet consists of the following components:

1. Power supply

The power supply of the PLC plays a very important role in the entire system. Without a good and reliable power supply system, it cannot operate normally. Therefore, PLC manufacturers also pay great attention to the design and manufacturing of power supplies. Typically, AC voltage fluctuates between 10%-40%; within this range (15% and below), the PLC can be directly connected to the AC grid without any additional measures.

2. Processor CPU

The processor CPU is the control center of the PLC. It receives and stores user programs and data inputs from programmers according to functions specified by the PLC system program; checks the status of power supply, memory, IO, and alarm timers; and diagnoses syntax errors in user programs. When a programmable logic controller is put into operation, it first receives and stores the status and data from each input device in a scanned form in the IO image area; then it reads user programs one by one from user program memory and sends results from logical or arithmetic operations based on instructions to either the IO image area or data registers. After executing user programs, it inputs output states from the IO image area or data from output registers into corresponding output devices and continues this cycle until stopped.

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