Abstract: This paper introduces the Siemens S7-200 series PLC, as well as the application of frequency converter technology and touch screen human-machine interface in the electrical control system of a combing machine. Keywords : Combing machine, PLC, frequency converter, touch screen 1 Introduction The Siemens S7-200 series programmable logic controller (PLC) features a compact design, good expandability, and powerful computing capabilities. Therefore, this series of PLCs can meet a variety of automation control needs. Furthermore, combined with the Hitachi SJ300 frequency converter and PWS1711 touch screen, which offer good price advantages, it is highly adaptable to solving practical industrial automation problems for users. 2 Composition of the Combing Machine Electrical Control System As shown in Figure 1, the electrical control system mainly consists of a programmable logic controller (PLC), an LCD touch screen, and a frequency converter. The PLC completes all data calculations and the logic control of the entire machine's process actions. The display screen displays and sets process parameters such as self-stop time, sliver length, output, and sliver exit speed, and also has fault alarm and display functions. The frequency converter, through communication with the PLC, controls the main motor to complete process requirements such as low speed, high speed, and predetermined long deceleration. 3. Modular PLC Software Design The entire program adopts a modular design, with different process actions calling corresponding subroutines. The calling process is based on the priority of the subroutines, with those having higher real-time requirements being called first. [b][align=center]For details, please click: Application of Frequency Conversion Technology in the Electrical Control of Combing Machines[/align][/b]