Abstract: The main factors affecting the reliability of PLC control system were analyzed, the design method and principle of hardware anti-interference measures of PLC control system were studied, and these measures were applied to the anti-interference design of PLC control system of bearing special grinding machine SMZ203D. Keywords: PLC control system anti-interference design, planning, work and application 1 Introduction PLC (Programmable Logic Controller) is an industrial automatic control device based on microprocessor and integrating computer technology, automatic control technology and communication technology. As a new generation of industrial control computer, PLC is widely used in the industrial field because of its advantages such as small size, strong function, good versatility, strong practicality, complete hardware, simple and easy-to-learn program design and convenient maintenance. Since PLC is a control device designed specifically for industrial production environment, it can generally be used directly in industrial environment without taking any special measures. However, if the environment is too harsh, such as strong magnetic field, strong corrosion, high dust, strong radiation, violent impact and vibration, it cannot guarantee the normal and safe operation of PLC. Therefore, the study of anti-interference design of PLC control system has very important practical significance [1]. 2. Main factors affecting the reliability of PLC control system The reliability of PLC control system is usually measured by mean time between failures (WIBF). It represents the average time interval between the repair of a system failure and the next failure. The PLC device itself is very reliable, while the interference of PLC control system is mainly caused by external links and improper hardware configuration. First, the power frequency interference on the power supply side, which enters the PLC device through the power supply and causes the system to work abnormally; second, the electrostatic or magnetic field coupling interference in line transmission, as well as the radiation interference of surrounding high frequency power supply. Electrostatic coupling is through the parasitic capacitance between the signal line and the power line, magnetic field coupling occurs on the parasitic mutual inductance between the middle lines of long wiring, and high frequency radiation is through the parasitic capacitance between the high frequency alternating magnetic field and the signal; third, the interference caused by improper grounding system of PLC control system. Therefore, in actual design, the following aspects are often considered [1]: 1) protection of program and data; 2) adaptability to industrial production environment; 3) fault safety principle, system independence principle and redundancy and fault tolerance structure; 4) real-time and continuity during operation. 3. Anti-interference Design of PLC Control System Based on the main factors affecting the reliability of a PLC control system, the development and design of a PLC control system should consider both system software and hardware to improve its reliability and anti-interference capability. In practical production applications, the hardware anti-interference design of the control system is the primary consideration. The 3MZ203D machine tool is a bearing ring internal grinding machine. Based on actual production requirements and years of practical experience, relevant measures were taken for the hardware anti-interference design and application of the PLC control system for this 3MZ203D internal grinding machine. These measures are described below. For details, please click: Anti-interference Design and Application of PLC Control System