What is a True RMS Multimeter
The quantities that describe the magnitude of alternating current are: peak value (and peak-peak value), average value, and effective value. The peak value is the maximum value; Called the root mean square value (the formula on the first floor).
Effective value: pass the direct current and alternating current through two identical resistance devices, if they generate equal heat in the same time, then take the voltage and current of the direct current as the effective value of the alternating current. Therefore, people generally say that the voltage and current refer to the effective value when there is no special statement.
There is a certain relationship between the three: the ratio of the effective value to the average value is called the form factor KF; the ratio of the peak value to the effective value is called the crest factor KP.
For a sine wave, the crest factor KP=root 2 (constant), and the form factor KF=2 times root 2nd row (constant). And for non-sine waves the value will change.
Obviously, what people are most concerned about is the effective value, but it is not easy to measure, and the average value and peak value are easy to measure, so ordinary multimeters (including voltmeters, etc.) measure the effective value indirectly by measuring the average value or peak value (press sine wave relationship). For example, if the peak value is measured on the meter, if the measured value is 10V, it will be displayed as 7.07V (effective value). These two types of meters display effective values, but they measure "false" effective values. Obviously, it is relatively accurate to use this type of meter to measure sine waves, but it is wrong to measure non-sine waves.
A more advanced meter can directly measure the effective value (there are many methods), that is to say, it displays the effective value and measures the effective value, so the result of this kind of meter is correct no matter which waveform is measured. In order to distinguish the first two tables, it is called true effective value.
