Three situations of the effective value of a multimeter
The Meaning of Effective Values in a Multimeter
For alternating current, its voltage is a changing waveform, and its voltage value is usually described as its effective value. As for 220V power supply, its peak voltage is over 311 volts, and its peak to peak voltage is over 600 volts.
1. Effective value: defined by heat generation (power), where a certain alternating current generates heat through a resistor and another continuous current passes through the resistor. If the heat generated within the same time period is equal, then the DC voltage value is the effective value of the AC voltage.
2. True RMS: The definition of RMS is defined by heating, but it is difficult to measure RMS voltage using this method in measuring instruments. Therefore, in most voltage measuring instruments, such as a multimeter, the measurement method is not based on the "heating" defined by RMS. One type of multimeter uses a sine wave as a reference, The effective value is obtained by the relationship between the peak value of a sine wave and the effective value that is twice the root sign (or derived from the average value). The effective value obtained by this method is only correct for the AC voltage of the sine wave type, and will cause deviation for waveforms of other shapes.
The voltage value of another type of multimeter is calculated by the square of the effective values of the DC component, fundamental wave, and various higher harmonics. This value is similar to the definition of effective value, and there is no requirement for the shape of the waveform. To distinguish this type of effective value from the effective value obtained from a sine wave instrument, it is commonly referred to as the "true effective value" in the measuring instrument table.
3. Root mean square value: Another term for the effective value (which should be the true effective value on a measuring instrument).
There are three scenarios for the effective value of a multimeter:
1. Calibration average value method, the calibration average value is also called the correction average value, or the Average rectified value calibrated to the effective value. Its principle is to change the AC signal into the DC signal through the rectification and integration circuit, and then multiply it by a coefficient according to the characteristics of the sine wave. For the sine wave, the result is equal to the effective value of the sine wave after multiplying the coefficient. Therefore, this method is limited to sine wave testing.
2. Peak detection method uses a peak detection circuit to obtain the peak value of the AC signal, and then multiplies it by a coefficient based on the characteristics of the 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.
3. The true effective value method uses a true effective value circuit to convert AC signals into DC signals for measurement. This method is suitable for testing the true RMS of any waveform. Most multimeters use the first two methods. And there are significant limitations on the frequency of the signal
