Abstract: Many current PLC models have Pulse Width Modulation (PWM) output modules, which can be used to achieve motor speed control and other functions under industrial field conditions. This paper takes the S7-313C as an example, and elaborates on the functional hardware configuration, programming methods, and precautions for PWM application. Furthermore, this functional module was successfully applied to the wire feeding mechanism of a variable polarity plasma arc welding equipment, achieving precise control of the wire feeding speed under strong arc interference. This paper provides guidance for the development of such systems. Keywords: Programmable Logic Controller (PLC), Industrial Control, PWM, Arc Welding Equipment [b][align=center]Application Research on PWM Module of Programmable Logic Controller Li Zhinning, Zhang Yingtang, Wang Li[/align][/b] Abstract: Many types of PLCs contain a PWM module, which can control equipment in industrial conditions. This paper, e.g., the S7-313C's PWM module, introduces how to set and program the PWM function. Special attentions are also presented while using the PWM module. In order to avoid arc's EMC, the PWM module is used to control the speed of the wire feeder in variable polarity plasma arc welding equipment, and a control voltage experiment is described. This paper is instructive for PWM module control of PLC. Keywords: PLC, industrial control, PWM, Arc welding equipment 1 Introduction Programmable Logic Controller (PLC) is a widely used industrial control device. It has good anti-interference performance and high reliability, and has been widely used in industrial production. With the continuous advancement of PLC manufacturing technology, PLCs are no longer merely combinations of input/output logic relays, but complex devices integrating modules such as A/D, D/A, PROFIBUS, and PWM. They can perform complex industrial process control functions and can be configured into FCS systems according to different fieldbus requirements to achieve automated industrial production control. Many PLC models, such as S7-200, S7-300, FP0, FP1, and CJ1M, integrate PWM function modules, which can be used to easily implement control functions such as motor speed regulation. This paper focuses on the PWM function module of the S7-313C PLC in the S7300 series, studying the hardware and software configuration and programming methods in its PWM function development. Combined with its practical application in variable polarity plasma arc welding equipment, it clarifies the points to note during development, providing guidance for technicians undertaking similar development in the future. For details, please click: Application Research of PWM Function Module in Programmable Logic Controllers