Abstract: This paper introduces two control methods for frequency converters, namely local control and remote control, using a high-pressure water descaling control system as a specific example. The schematic diagram of the parameter setting system and part of the control program are also provided. Keywords: High-pressure water descaling; Frequency converter; Local control; Remote control 0 Introduction Before entering the sizing mill, the iron oxide scale on the surface of hot-rolled seamless steel pipes not only adversely affects the surface quality of the sizing pipe but also increases the wear of the sizing rollers and reduces their service life. Therefore, removing the iron oxide scale from the outer surface of the steel pipe before sizing is particularly important. In the descaling system, high-pressure water generated by a high-pressure water pump enters the descaling nozzle. Under the action of the nozzle, the high-pressure water forms a fan-shaped water jet with a large impact force, which is sprayed onto the surface of the steel pipe. Under the action of this high-pressure fan-shaped water jet, the iron oxide scale undergoes a process of being cut, rapidly cooled and contracted, peeled off from the base material, and washed away from the surface of the steel pipe. Therefore, the impact force of the high-pressure water is the most important factor affecting the descaling effect. High impact force ensures thorough crushing of iron oxide scale, creating sufficient cracks, which is a prerequisite for descaling. The high-pressure water required for descaling is supplied by three 110kW high-pressure water pumps (two in operation and one on standby), using a "high-flow high-pressure pump + unloading valve + Siemens MM440 frequency converter" system. The frequency converter adjusts the flow rate of the high-pressure water pumps to meet different requirements, achieving energy and water conservation. 1. Overview of the High-Pressure Water Descaling Control System This control system utilizes the Profibus network and BICO control functions of the MICROMASTER440 series frequency converter. Through an industrial control computer and PLC, it uses both Profibus network control and external terminal control of the frequency converter for automatic and manual control. Under normal conditions, the first command data group (CDS) is used for Profibus network control—automatic control. In case of network failure, the second command data group, i.e., external terminal control of the frequency converter—manual control—is used. In practical applications, all frequency converters are equipped with a Profibus template and a BOP operation panel. In terms of hardware configuration, digital input 1 serves as the enable signal for the first command data group; digital input 2 serves as the inverter start/stop signal for the second command data group; digital input 3 serves as the inverter electric potentiometer acceleration signal for the second command data group; and digital input 4 serves as the inverter electric potentiometer deceleration signal for the second command data group. [b][align=center]For more details, please click: Application of Frequency Converters in High-Pressure Water Descaling[/align][/b]