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Difference of PLC and Relay (2)

Here's the 2nd part introducing the difference of PLC and Relay. If you want to review the 1st part, click here:

4. Time-limited control: The 
difference of PLC and Relay is that relay control logic uses the hysteresis action of the time relay to perform time-limited control. Time relays are generally classified into air damping type, electromagnetic type, and semiconductor type. The timing accuracy is not high, and the timing time is susceptible to environmental humidity and temperature changes, and the adjustment time is difficult. Some special time relays are complicated in structure and inconvenient to maintain.
difference of PLC and Relay
The PLC uses a semiconductor integrated circuit as a timer. It is the difference of PLC and Relay. The time base pulse is generated by a crystal oscillator with high accuracy. The timing range is generally from 0.1 s to several minutes or even longer. The user can set the timing value in the program as needed, and then the software. And the hardware counter to control the timing time, the timing accuracy is less than 10 ms and the timing time is not affected by the environment.
5. counting control: the difference of PLC and Relay is that PLC can realize counting function, and relay control logic generally does not have counting control function.
6. Design and construction: The use of relay control logic to complete a control project, its design, construction, commissioning must be carried out in sequence, long cycle, and difficult to modify. The bigger the project, the more prominent it is. The difference of PLC and Relay is that PLC is used to complete a control project. After the system design is completed, the on-site construction and control logic design (including the ladder program design) can be performed at the same time, the cycle is short, and debugging and modification are very convenient.
difference of PLC and Relay
7 Reliability and maintainability: Relay control logic uses a large number of mechanical contacts, and there are many connections. When the contacts are opened and closed, they are damaged by the arc, mechanical wear, and short life, so the reliability and maintainability are poor. The difference of PLC and Relay is obvious.
The PLC adopts microelectronic technology, and a large number of switching actions are performed by non-contact semiconductor circuits, which have small body, long life and high reliability. The PLC is also equipped with self-test and supervision functions, which can detect its own faults and display them to the operator at any time. It can also dynamically monitor the execution of the control program, which provides convenience for on-site commissioning and maintenance.

8. Price: The relay control logic uses mechanical switches, relays and contactors, and the price is relatively cheap. The difference of PLC and Relay is PLC use medium-sized integrated circuits, which are more expensive.
These are the difference of PLC and Relay. Hope it is more clear for you in PLC and Relay after reading this news. 
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