The difference between PLC control system and elec

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Differences between PLC control system and electrical control system

compared with electrical control system, PLC control system has many similarities and differences. The differences are mainly in the following aspects:

1) from the perspective of control method, the control logic of electrical control system adopts hardware wiring, and uses the series or parallel connection of relay mechanical contacts to form control logic. Its wiring is many and complex, with large volume and power consumption. After the system is formed, it is difficult to change or add functions. In addition, the number of contacts of the relay is limited, so the flexibility and scalability of the electrical control system are greatly limited. PLC adopts computer technology, and its control logic is stored in the memory in the way of swing bar alignment and vertical marking program. To change the control logic, you only need to change the program, so it is easy to change or add system functions. The system has less wiring, small volume and low power consumption, and the so-called "soft relay" of PLC is essentially the state of memory unit. Through the use of our products, the number of contact plasticizer points of "soft relay" is unlimited, and the flexibility and scalability of PLC system are good

2) in terms of working mode, in the relay control circuit, when the power is turned on, all relays in the circuit are in a restricted state, that is, the relay that should be pulled in is pulled in at the same time, and the relay that should not be pulled in cannot be pulled in due to certain conditions. This working mode is called parallel working mode. The user program of PLC is executed circularly in a certain order, so all soft relays are in the process of periodic cycle scanning, and the action order of each relay restricted by the same condition depends on the program scanning order. This working mode is called serial working mode

3) in terms of control speed, the relay control system relies on the action of mechanical contacts to achieve control. The revenue of the global 3D printing material market is expected to reach $2.5 billion. The frequency is low, and the mechanical contacts will shake. PLC controls the semiconductor circuit through program instructions, which is fast, the execution time of program instructions is microseconds, and there will be no contact jitter

4) in terms of timing and counting control, the electrical control system adopts the time delay action of the time relay for time control. The time delay time of the time relay is easily affected by the ambient temperature and temperature changes, and the timing accuracy is not high. While PLC uses semiconductor integrated circuit as timer, clock pulse is generated by crystal oscillator, with high precision and wide timing range. Users can set the timing value in the program according to their needs, which is convenient to modify and is not affected by the environment. Besides, PLC has counting function, while electrical control system generally does not have counting function

5) in terms of reliability and maintainability, the electrical control system uses a large number of mechanical contacts, which have mechanical wear, arc burns, etc., short service life, and many system connections, so the reliability and maintainability are poor. A large number of switching actions of PLC are completed by contactless semiconductor circuit, which has long service life and high reliability. PLC also has self diagnosis function, which can detect its own fault, display it to the operator at any time, and dynamically monitor the implementation of the control program, providing convenience for on-site debugging and maintenance. (end)

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