Abstract : This paper introduces the hardware structure and control principle of a high-precision automatic position control system based on frequency converter and PLC, which is widely used in the steel industry. Keywords : Frequency converter; Automatic position control system; PLC; Position controller. APC system, short for Automatic Position Controller, automatically moves the controlled object to a pre-given target position at a specified time, ensuring that the difference between the reached position and the target position remains within the deviation range. In the rolling, packaging, and loading processes of steel mills, many processes and packaging require precise positioning, such as setting the roll gap under the rolls, setting the opening degree of the mill guide plate, and controlling the stroke of the trolley. The processing accuracy and control accuracy depend on the control method of the position control system, directly affecting product quality and production speed and efficiency. Therefore, position control plays a very important role in industrial processing. Currently, in many large steel rolling mills, the APC systems used in the position control section mostly consist of a computer or PLC plus a positioning module. The transmission section mostly uses non-speed-adjustable AC drives, while DC speed-regulating transmission systems are used for those requiring higher positioning accuracy and speed. With the rapid development of computer technology, specialized position control products have gradually matured and developed. On the other hand, the performance of frequency converters has gradually improved while their price has gradually decreased, showing a strong trend of replacing DC speed regulation and becoming the preferred product for many manufacturers to upgrade existing position systems and build new control and speed regulation systems. This paper introduces an APC control system based on a frequency converter and position controller. 1. System Hardware Composition The system mainly consists of three parts: a position controller, a frequency converter, and an actuator. The control core is implemented using a PLC. The hardware block diagram is as follows: [b][align=center]For more details, please click: Application of APC System Based on Frequency Converter in the Steel Industry[/align][/b]