1. Calibration average method. The calibration average is also called the corrected average, or the rectified average calibrated to the effective value. Its principle is to convert the AC signal into a DC signal through the rectification and integration circuit, and then according to the characteristics of the sine wave, Multiply by a factor that, for a sine wave, equals the effective value of the sine wave. Therefore, this method is limited to sine wave testing.

2. Peak detection method, through the peak detection circuit, obtain the peak value of the AC signal, and then multiply it by a coefficient according to the characteristics of the sine wave. For the sine wave, after multiplying by the coefficient, the result is equal to the effective value of the sine wave. Therefore, this method is limited to sine wave testing.

3. True RMS method, which uses a true RMS circuit to convert the AC signal into a DC signal before measuring. This method is applicable to the true effective value test of arbitrary waveforms.

For alternating current, its voltage is a changing waveform. Usually the voltage value we describe refers to its effective value. For example, when we say 220V power supply, its peak voltage is more than 310 volts, and the peak-to-peak voltage is twice the peak value. It is more than 600 volts.