Is a multimeter used to measure the output signal of a frequency converter
1. Usually, when we talk about the output of a frequency converter at 380V and 50Hz, it means that its fundamental wave (sine wave) is 380V and 50Hz. The actual output waveform of the frequency converter is PWM wave, which includes not only the fundamental wave but also the carrier signal. The frequency of the carrier signal is much higher than the fundamental wave, and it is a square wave signal that contains a large number of high-order harmonics.
2. A regular multimeter can generally only measure AC sine waves of 45-66Hz or 45-440Hz. The measurement frequency range of some true effective value multimeters is much wider, and many people believe that they can be used for frequency conversion measurement and testing. Actually, it's not the case because the measurement results of this type of meter include both the fundamental and carrier waves. For example, when the frequency converter mentioned above outputs 380V, the measurement result is generally above 400V.
3. The instrument used for frequency conversion testing should have the ability to decompose its fundamental wave in various PWM waveforms. Strict measurement requires the use of digital signal processing, that is, high-speed sampling to obtain a sample sequence, and then performing discrete Fourier transform on the sample sequence to obtain the amplitude, phase, and amplitude and phase of each harmonic of the fundamental wave.
4. There is also a train of thought that calibrating the average value can replace the effective value of the fundamental component in the PWM signal output by the frequency converter.
The quasi average value (MEAN) is theoretically equal to the true effective value of a sine wave and the fundamental effective value of a sine modulated PWM waveform, and is easy to implement; Therefore, MEAN is used in many instruments to replace the effective value (RMS) of positive harmonics or the fundamental effective value (H01) of PWM for measurement.
However, in recent years, frequency conversion speed regulation technology has been advancing rapidly, and the application of non sinusoidal modulation PWM is increasing. Moreover, frequency converter users usually do not know what modulation mode their frequency converter adopts, and the MEAN value is becoming increasingly limited in PWM measurement.
5. The AnyWay broadband power testing system provides users with a professional overall solution for frequency conversion measurement and testing, including sensors and instruments.
On the basis of high-speed sampling, AnyWay conducts spectral analysis on the sampled signal and calculates the fundamental effective value (H01) of the measured signal in real time. This method is suitable for testing the effective value of PWM signals with any modulation method and other sinusoidal and non sinusoidal signals.
