What is a true effective multimeter?
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.
Root Mean Square Value: Another term for the effective value (which should be the true effective value on a measuring instrument).
How to measure the effective values of voltage and current with a multimeter
The effective value of a multimeter usually refers to one of the following three situations:
1. The method of calibrating the average value, also known as the corrected average value or the rectified average value calibrated to the effective value, is based on the principle of converting an AC signal into a DC signal through rectification and integration circuits, and then multiplying it by a coefficient according to the characteristics of a sine wave. For a sine wave, the result of multiplying by this coefficient is equal to the effective value of the sine wave. Therefore, this method is limited to sine wave testing only.
2. Peak detection method obtains the peak value of an AC signal through a peak detection circuit, and then multiplies it by a coefficient based on the characteristics of a sine wave. For a sine wave, the result of multiplying by this coefficient is equal to the effective value of the sine wave. Therefore, this method is limited to sine wave testing only.
3. The true effective value method uses a true effective value circuit to convert AC signals into DC signals before measurement. This method is applicable for testing the true effective value of any waveform.
Most multimeters use the first two methods. And there are significant limitations on the frequency of the signal.
