With the continuous improvement of frequency conversion technology, frequency converters are being used more and more widely, especially in coal mine production in recent years. According to surveys, frequency conversion technology accounts for more than 55% of coal mine technological transformation projects. Currently, they are used in mine hoists, belt conveyors, coal mining machines, fans, water pumps, compressors, etc., and the development trend is good. However, due to the limited knowledge of frequency converter technology among field technicians and their insufficient understanding of methods for measuring the electrical characteristics of frequency converters, improper selection and use of measuring instruments can lead to significant difficulties in diagnosis and repair should equipment malfunctions occur. Having worked in frequency converter research, application, and development for many years, I have accumulated considerable experience in the methods for measuring the electrical characteristics of frequency converters and the selection of measuring instruments, which I offer as a reference for field technicians during maintenance, fault diagnosis, and parameter measurement. For equipment inspection or energy-saving testing, it is more effective to focus on measuring the input and output power of the frequency converter, supplemented by data such as voltage, current, power factor, and efficiency, for comparison, analysis, and judgment, rather than measuring the internal components of the frequency converter. Electrical instruments are typically manufactured for measuring power frequency waveforms (50Hz, 60Hz sine waves). Therefore, if the measured waveform is a rectangular wave or approximately sine wave, the instrument's reading will differ from that of the power frequency power supply. This discrepancy is particularly pronounced when the measurement frequency is lower or significantly higher than the power frequency (depending on the type of instrument). Currently, there are no standardized measuring instruments for use with frequency converters. Data obtained using a Fast Fourier Series Analyzer (FFT) is relatively accurate, but its application in factories and enterprises is limited. Therefore, correctly selecting a measuring instrument appropriate for the application is crucial. Measurement Location and Instruments The input side of a frequency converter is a rectifier circuit, which has non-linear characteristics, thus generating high-order harmonics. These harmonics distort the voltage and current waveforms of the input power supply. The output side of the frequency converter uses PWM control, which also generates high-order harmonics. Its output voltage and current waveforms are not standard sine waves, as shown in Figure 1. Therefore, different measuring instruments are selected depending on the measurement location. The measurement circuit is shown in Figure 2. [b][align=center]For details, please click: Measurement of Inverter Parameters and Selection of Instruments[/align][/b]