Abstract : This paper introduces the application of Siemens S7 series PLC, TP270 touch screen, and Micromaster420 frequency converter in the control system of a pharmaceutical coating machine. The system design is described from both hardware and software perspectives, with a focus on the software flow and continuous PID function block of the TP270. In practical applications, the system improves product quality and production efficiency, proving the rationality of the design. Keywords : Coating machine; Touch screen; Frequency converter; Control 1 Introduction With the continuous improvement of the performance and the decreasing price of Programmable Logic Controllers (PLCs), their application in industrial control is becoming increasingly widespread. They can not only achieve complex logic control but also complete various closed-loop controls. The system has high reliability, strong anti-interference ability, low maintenance, and can easily communicate with the human-machine interface. 2 Controlled Objects and Control Requirements 2.1 Controlled Objects The pharmaceutical coating machine system consists of five sets of equipment: a main unit, a hot air blower, an exhaust fan, a peristaltic pump, and a spray gun solenoid valve, as shown in Figure 1. The peristaltic pump and spray gun solenoid valve are integrated with the main unit. During the production process, the hot air blower and exhaust fan are first turned on, and the air intake volume is adjusted to meet production requirements; the exhaust volume is adjusted to ensure the negative pressure of the roller reaches the negative pressure standard for pharmaceutical production; and the air intake temperature is adjusted to achieve the optimal standard for pharmaceutical quality. Then, the peristaltic pump is turned on to spray syrup onto the pharmaceuticals, and simultaneously, the main roller is turned on to coat the pharmaceuticals. Once coating is complete, the spray gun solenoid valve is turned on to dry the coating. 2.2 Control Requirements As can be seen from the process, a total of 5 sets of equipment need to be controlled: the main roller, hot air blower, exhaust fan, peristaltic pump, and spray gun solenoid valve. The control of each piece of equipment is divided into manual and automatic modes. [b][align=center]For details, please click: Application of PLC in the Control System of Pharmaceutical Coating Machines[/align][/b]