What are the effective value and true effective value of a multimeter?
The magnitude of alternating current varies with time, and the instantaneous value (at a certain moment) varies between zero and positive and negative peak values. The maximum value is only a momentary value and cannot reflect the working ability of alternating current.
So the concept of effective value was introduced, which is defined as:
Effective value: defined by heat generation (power), if the heat generated by an AC current through a resistor is equal to the heat generated by another DC current through the resistor at the same time, then the DC voltage value is the effective value of this AC voltage.
True RMS: The definition of RMS is based on heat generation, but it is difficult to measure the RMS voltage using this method in measuring instruments. Therefore, in most voltage measuring instruments, such as multimeters, the measurement method is not based on the "heat generation" defined by RMS. One type of multimeter uses sine waves as a reference and obtains the RMS value (or derives it from the average value) based on the relationship between the peak value of the sine wave and the RMS value, which is twice the root of the sine wave. The RMS value obtained by this method is only correct for the AC voltage of sine wave shapes, and may have deviations for other waveform shapes. Another type of multimeter voltage value is obtained by squaring the effective values of the DC component, fundamental wave, and higher harmonics. This value is similar to the definition of effective value and does not require the shape of the waveform. To distinguish this type of effective value from instruments that obtain effective value through sine waves, it is commonly referred to as "true effective value" in measuring instruments.
