Can a multimeter be used to measure the inverter output signal?
It depends on the purpose of measurement and the measurement principle of the multimeter:
1. Usually when we say that the inverter outputs 380V, 50Hz, it means that its fundamental wave (sine wave) is 380V, 50Hz. The actual output waveform of the frequency converter is a PWM wave, which in addition to the fundamental wave, also contains the carrier signal. The carrier signal frequency is much higher than the fundamental wave, and it is a square wave signal containing a large number of higher harmonics.
2. Ordinary multimeters can generally only measure AC sine waves of 45~66Hz or 45~440Hz. The measurement frequency range of some true RMS multimeters is much wider, and many people think that they can be used for variable frequency measurement and testing. In fact, this is not the case, because the measurement results of this kind of meter include both the fundamental wave and the carrier wave. For example, when the above-mentioned inverter outputs 380V, the measurement result is generally above 400V.
3. The instrument used for frequency conversion testing should have the ability to decompose the fundamental wave in various PWM waveforms. Strict measurement requires the use of digital signal processing, that is, high-speed sampling to obtain the sample sequence, and then discrete Fourier analysis of the sample sequence. Leaf transform is used to obtain the amplitude and phase of the fundamental wave and the amplitude and phase of each harmonic.
4. There is also a way of thinking that the calibrated average value can replace the effective value of the fundamental wave component in the PWM signal output by the inverter.
The quasi-average value (MEAN) is theoretically equal to the true effective value of the sine wave, equal to the effective value of the fundamental wave of the sinusoidal modulated PWM waveform, and is simple to implement; therefore, MEAN is used to replace the effective value of the positive harmonic in many instruments and meters ( RMS) or the measurement of the fundamental effective value (H01) of PWM.
However, in recent years, variable frequency speed control technology has been advancing rapidly, and non-sinusoidal modulation PWM has been increasingly used. Moreover, inverter users usually do not know what modulation mode their inverter uses, and the MEAN value has become more and more limited in PWM measurement. Come bigger.
5. AnyWay broadband power test system provides users with a professional overall solution for frequency conversion measurement and testing, including sensors and instruments.
