Differences and Similarities between PLC Control and Traditional Electrical Control
Time:2023-05-20
Views:116
There are many similarities and differences between PLC control systems and electrical control systems.
The similarity is that PLC is a product of combining traditional relay contactor control systems with computer technology. It is a technology that combines software and hardware, and there is a trend to replace traditional relay contactor control systems in the future.
Compared to electrical control systems, PLC has the following differences:
(1) Different control methods
The control logic of the electrical control system adopts hardware wiring, which combines the series or parallel connection of relay mechanical contacts to form control logic. The wiring is numerous and complex, with large volume and high power consumption. After the circuit is composed, it is difficult to modify or expand its functions. In addition, the limited number of contacts in the relay limits the flexibility and scalability of the electrical control system. PLC adopts computer technology, and to change the control logic, only the program needs to be changed, making it easy to change or add system functions. The system has few connections, small size, and low power consumption, and the number of contacts for relays is limited, which varies depending on the production process.
(2) Fast control speed, no jitter
The electrical control system relies on the action of mechanical contacts to achieve control, and the working frequency is low, and mechanical contacts may also experience shaking problems. The PLC controls the semiconductor circuit through program instructions, with fast speed, program instruction execution time at the US level, and no contact jitter problem.
(3) Timing accuracy and counting function
The electrical control system adopts a delay action of a time relay for time control, which is easily affected by temperature changes, has low timing accuracy, and generally has no counting function; The PLC adopts an electronic integrated circuit timer, and the clock pulse is generated by a crystal oscillator. The timing is accurate and has a wide range. Users can set the timing value in the program according to their needs, which is easy to modify and not affected by temperature changes. The PLC also has a counting function.
(4) High reliability and good maintainability
Due to the use of a large number of mechanical contacts in the electrical control system, there may be mechanical wear, arc burns, etc. during operation, resulting in a short lifespan and multiple connections in the system, resulting in poor reliability and maintainability. A large number of switch actions in PLC are completed by contactless point circuits, which have a long lifespan and high reliability. In addition, PLC also has self diagnosis function, which can detect its own faults, display them to operators at any time, and dynamically monitor the execution of control programs, providing convenience for on-site debugging and maintenance.
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