Abstract: This paper introduces a constant pressure water supply control system based on PLC and frequency converter, and elaborates on the system composition, system function, working principle and safety measures. The control system is stable and reliable, and has been successfully applied to the water supply system of a power plant, achieving constant pressure water supply. Keywords : Frequency converter; PLC; Constant pressure water supply 0 Introduction Traditional water tower water supply methods have many problems: secondary water pollution, imbalance between peak and off-peak water usage, easy damage to pipes and valves, and high maintenance costs, etc. With the development and improvement of control technology, the reliability of frequency converters and PLCs is increasingly widely used in various industries, and their flexibility has been recognized by users. This paper introduces a constant pressure water supply control system using PLC and frequency converter. The following sections elaborate on the system composition, system function, working principle and safety measures. This control system has been successfully operating in the water supply system of a power plant for many years, achieving constant pressure water supply. 1 System Composition The structure of the constant pressure water supply control system is shown in Figure 1. The water supply system consists of four large pumps (22KW) and one small pump (5KW); the control system uses a Siemens S7-200 series CPU226 PLC and a TD200 text display; the frequency converter is a Mitsubishi FR-A540 series with a power of 22KW. [b][align=center]For details, please click: Constant Pressure Water Supply Control System Based on PLC and Frequency Converter[/align][/b]