Abstract : Taking Fuji inverters as an example, this paper proposes the application of RS485 bus-based communication protocol macro method in inverter online fault detection technology. Using the CX-Protocol, a communication sequence for monitoring the main parameters of the inverter and displaying alarm information was developed, realizing the function of real-time online detection of various characteristic parameters and operating status of the inverter by a programmable logic controller (PLC) and a touch screen. Practice has proven that this method has achieved satisfactory results in inverter detection and is practically feasible. Keywords : Communication protocol macro; Programmable logic controller; Touch screen; Inverter; Online fault detection 0 Introduction This paper takes Fuji's FRN2.2P11S inverter as the object and establishes a real-time monitoring system composed of a programmable logic controller (PLC) and a touch screen (PT). The communication protocol macro is used to realize online fault detection and status monitoring of the inverter. [b]1. Constructing an Online Monitoring System for Frequency Converters 1.1 Types of Online Monitoring Parameters for Frequency Converters[/b] Frequency converter manufacturers have categorized and integrated the main characteristic parameters that maintain the normal operation of frequency converters, realizing functions such as real-time online fault detection, alarm status monitoring, and provision of peripheral services. Taking Fuji's FRN2.2P11S frequency converter as an example, this frequency converter roughly divides the monitored data into three categories, as shown in Table 1. The first category is parameters that detect the lifespan of the main internal components of the frequency converter, such as the lifespan of the cooling fan. These parameters are crucial to ensuring the normal operation of the frequency converter. The second category is the real-time parameters when the frequency converter alarms, including the effective value of the voltage and the internal temperature at the time of the alarm. The frequency converter stores the latest alarm content in the form of a code as parameter MI6, and the corresponding error information can be found through Table 2. The third category is characteristic parameters that are prompted to peripherals, such as frequency values. [b][align=center]For more details, please click: Application Research of Online Fault Detection Technology for Frequency Converters[/align][/b]