Abstract : A constant pressure control system for multiple pumps in a waterworks was implemented through the combined control of a frequency converter and a PLC. After being put into operation, the system achieved stable water supply pressure, reliable operation, high control accuracy, energy saving, and considerable benefits. Keywords : PLC; variable frequency speed regulation; constant pressure system [b][align=center]Design of Constant Pressure Control System in Waterworks WANG Yu feng, ZHANG Peng, HE Fei (School of Electrical and Control Engineering, Liaoning Technical University, HuLudao 125105, China)[/align][/b] With the improvement of miners' living standards, new requirements have been put forward for water supply quality. In order to change the situation where traditional control systems waste manpower and energy, the mine surface waterworks combined PLC and frequency converter to control a constant pressure control system. This not only saved manpower and energy, but also extended the service life of motors and pumps under the soft start of the frequency converter, basically achieving the expected results. 1. Water Plant System Composition The water plant processes approximately 8000 tons of water per day. The purification process mainly involves underground water extraction (-300m), release of harmful gases from a cascading pool, filtration in a filter bed, chlorination disinfection, and chemical removal of manganese and iron ions. The control system structure is shown in Figure 1. As shown in Figure 1, the central control room consists of one industrial computer and one PLC. The industrial computer is an Advantech industrial control computer, and the PLC is a Siemens S7-300 series. The monitoring software is Beijing Yacon's "KingSCADA 6.51" software. The host computer and the PLC communicate via the RS232 communication protocol. The host computer's control interface enables "three-remote" functions (remote monitoring, remote control, and remote operation) of the controlled objects, allowing real-time monitoring of various systems in the water plant and recording of historical data. The speed-regulating frequency converter is a Siemens MicroMaster430. [b][align=center]For more details, please click: Design of a PLC-based Constant Pressure Control System for a Waterworks[/align][/b]