Can the multimeter be used to measure the output signal of the frequency converter?
It depends on the measurement purpose and the measurement principle of the multimeter:
1. Usually we say that the output of the inverter is 380V, 50Hz, which means that its fundamental wave (sine wave) is 380V, 50Hz. The actual output waveform of the frequency converter is a PWM wave, which includes a carrier signal in addition to the fundamental wave. The frequency of the carrier signal is much higher than the fundamental wave, and it is a square wave signal, which contains a large number of high-order harmonics.
2. Ordinary multimeters can 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 it can be used for frequency conversion measurement and testing. In fact, this is not the case, because the measurement results of this meter include both the fundamental wave and the carrier wave. For example, when the frequency converter mentioned above has a 380V output, the measurement result is generally above 400V.
3. The instrument used for frequency conversion test 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 sample sequences, and then perform discrete Fourier on the sample sequences Leaf transformation, the amplitude and phase of the fundamental wave and the amplitude and phase of each harmonic are obtained.
4. There is also an idea that the calibration average value can replace the effective value of the fundamental wave component in the inverter output PWM signal.
The quasi-average value (MEAN) is theoretically equal to the true rms value of the sine wave, equal to the fundamental rms value of the sinusoidally modulated PWM waveform, and is simple to implement; therefore, MEAN is used in many instruments to replace the rms value of the positive harmonic ( RMS) or PWM fundamental effective value (H01) measurement.
However, in recent years, the frequency conversion speed regulation technology is changing with each passing day, and the application of non-sinusoidal modulation PWM is more and more, and the frequency converter users usually do not know what modulation mode their frequency converter adopts, and the MEAN value is more limited in PWM measurement. bigger and bigger.
5. The AnyWay broadband power test 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 performs spectrum analysis on the sampled signal, and calculates the fundamental effective value (H01) of the measured signal in real time. This method is suitable for the effective value test of PWM signals of any modulation mode and other arbitrary sinusoidal and non-sinusoidal signals.
AnyWay takes the fundamental effective value test as the basic test mode, and at the same time, provides measurements such as true effective value (RMS), calibration average value (MEAN), rectified average value (RMEAN), and arithmetic average value (DC, mainly used for DC measurement) mode for user reference.
