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From the hardware structure of High performers, PLC can be divided into five basic structural forms: integral fixed I/O type, basic unit plus expansion type, modular type, integrated type, and distributed type. Next, let's take a look at the composition of PLC.
Here is the content list:
Central Processing Unit (CPU)
Memory
Input and output interface (I/O module)
Communication Interface
Power supply
The central processing unit (CPU) is the control center of the PLC. It's the core of the PLC and acts as the whim-whams center. Each set of PLC has at least one CPU. It receives and stores the stoner program and data entered from the programmer according to the functions given by the PLC system program; Checks the status of power force, memory, I/ O, and watchdog timekeeper, and can diagnose syntax crimes in the stoner program. When the Integrated solution for automation and operation is put into operation, it first receives the status and data of each input device on-site by scanning and storing them in the I/O image area respectively. Then read the user program one by one from the user program memory, and send the results of logic or arithmetic operations to the I/O image area or data register according to the instructions after the command is interpreted. After all the user programs are executed, the output status of the I/O image area or the data in the output registers are finally transmitted to the corresponding output devices, and the cycle runs like this until it stops running. To further improve the reliability of PLCs, dual CPUs are used to form a redundant system for large PLCs, or a voting system with three CPUs is used. In this way, even if a certain CPU fails, the entire system can still operate normally. CPU speed and memory capacity are important parameters of PLC, which determine the working speed, I/O quantity, and software capacity of PLC, thus limiting the control scale.
The system program memory is the memory for storing the system software; the user program memory is for storing the PLC user program application; the data memory is used to store the intermediate state and information when the PLC program is executed, which is equivalent to the memory of the PC.
The interface between the PLC and the electrical circuit is completed through the input and output part (I/O). The I/O module integrates the I/O circuit of the PLC, its input temporary register reflects the state of the input signal, and the output point reflects the state of the output latch. The input module transforms the electrical signal into a digital signal and enters the programmable logic controller system, and the output module does the opposite. I/O is divided into digital input (DI), digital output (DO), analog input (AI), analog output (AO), and other modules.
The main function of the communication interface is to realize data exchange (communication) between PLC and external outfits. There are various forms of communication interfaces, the most basic ones are standard serial interfaces such as UBS, RS-232, RS-422/RS-485, etc. Connections can be made via multi-core cables, twisted pairs, coaxial cables, fiber optic cables, etc.
The PLC power supply provides working power for the Wide Range of Quality Products at Great Prices circuit and plays a very important role in the entire system. The main function of the communication interface is to realize data exchange (communication) between PLC and external outfits. Generally, the AC voltage fluctuation is in the range of +10% (+15%), and the PLC can be directly connected to the AC grid without taking other measures. The power input types are AC power supply (220VAC or 110VAC), and DC power supply (commonly used is 24VDC).
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