Abstract : Based on the discussion of the detection principles of ordinary instruments, and combined with the characteristics of the electrical quantities in various parts of the frequency converter, this paper analyzes the limitations and applicability of using ordinary instruments to measure the voltage and current of the frequency converter, and presents methods for measuring the voltage and current of the frequency converter using ordinary instruments. It introduces the measurement methods for the insulation resistance of the frequency converter and its external circuits, and the measurement techniques for the rectifier bridge and inverter bridge modules of the frequency converter. Finally, a product solution for accurate measurement of the electrical quantities in the frequency converter is given. Keywords : Frequency converter, measuring instrument 1 Introduction Many voltage and current signals in frequency converters are no longer simple DC or power frequency sine wave signals. Faced with the large amount of harmonics, distortion, or non-power frequency electrical quantities in the frequency converter, although the voltage and current in the frequency converter can be directly or indirectly displayed using the frequency converter's own output, and the voltage and current displayed on the frequency converter panel are relatively accurate after hardware filtering and software calculation, many frequency converters can also display voltage and current through two analog outputs of 4-20mA. Some frequency converters also have communication interfaces, such as Schneider Electric's with Modbus and Siemens' with Profibus. The computer communicates with the frequency converter, allowing direct reading of the converter's parameters. These parameters can be read directly via a touchscreen, and then the frequency converter is connected to the computer via an RS232 interface. However, in many cases, such as when a fault occurs in the variable frequency speed control system, it is still necessary to measure the voltage and current in the frequency converter using instruments. Accurate measurement methods utilize instruments with FFT functionality; these instruments are expensive, such as harmonic meters which cost 20,000-30,000 yuan. Most factories lack these advanced instruments and prefer to use ordinary power frequency instruments to measure the electrical quantities of various parts of the frequency converter for simple routine maintenance. Different types of ordinary electrical instruments have different measurement principles and applicable ranges. Different measuring instruments and measurement circuits yield different data. If the measuring instrument is not selected properly, the measurement results will have significant errors, making simple routine maintenance and fault diagnosis impossible; improper measurement methods may even damage the frequency converter. [b][align=center]For more details, please click: Key Points of Frequency Converter Electrical Quantity Measurement Technology[/align][/b]