Abstract : This paper analyzes the connection method of frequency converter and PLC, proposes precautions for design, installation and use, and gives some methods for anti-interference. Keywords : frequency converter, PLC, anti-interference [b]1 Introduction[/b] Frequency converter speed control technology is a high-tech technology that integrates automatic control, microelectronics, power electronics and communication technology. Due to its excellent speed control and energy-saving performance, it has been widely used in various industries. Programmable Logic Controller (PLC) is an industrial control device that has developed rapidly and has a wide range of applications in recent years. It is a digital electronic system designed specifically for industrial environments. It uses a programmable memory to store user instructions and performs defined logic, sequence, timing, counting, operation and some defined functions through digital or analog input/output to control various types of machinery or production processes. It has advantages such as small size, flexible assembly, simple programming, strong anti-interference ability and high reliability. Many fields of modern industrial production combine frequency converters and PLCs. The following issues should be noted in the design, installation and operation of such systems. [b]2 Input/Output Circuit of the Frequency Converter 2.1 Input of Operating Signals[/b] The input signals of the frequency converter include: run, stop, forward/reverse, micro-motion, and other digital input signals. The frequency converter typically uses relay contacts or open-collector transistors to connect to the host computer and obtain these operating signals, as shown in Figure 1. [b][align=center]For more details, please click: Discussion on the Connection and Usage Methods of Frequency Converters and PLCs[/align][/b]