(1) high reliability. Since PLC mostly uses single-chip microcomputer integration high, coupled with the corresponding protection circuit and self-diagnosis function, improve the reliability of the system.

(2) easy programming. PLC programming mostly adopts relay control ladder diagram and command statement, the number of which is much less than microcomputer instruction. Except for medium and high-grade PLC, there are only about 16 small PLC. Because trapezoidal graphics are simple, they are easy to master and use, and even can be programmed without computer expertise.

(3) flexible configuration. Because PLC adopts building block structure, users can flexibly change the function and scale of the control system only by simple combination, so it can be applied to any control system.

(4) input/output function modules are complete. One of the biggest advantages of PLC is that it aims at different field signals (such as DC or AC, switching value, digital quantity or analog quantity, voltage or current, etc.), each template can be directly connected to industrial devices (such as buttons, switches, sensor current transducer, motor starters or control valves) and connected to the CPU motherboard through a bus.

(5) easy installation. Compared with the computer system, the installation of PLC requires neither special data center nor strict shielding measures. When using, you only need to correctly connect the detection device with the I/O interface terminal of the actuator and PLC to work normally.

(6) fast running speed. Because PLC control is executed by program control, no matter its reliability or running speed, relay logic control cannot be compared.

In recent years, the use of microprocessor, especially with the extensive use of single chip microcomputer, has greatly enhanced the ability of PLC, and made the difference between PLC and microcomputer control system smaller and smaller, especially high-grade PLC.^[6]