What does a true RMS multimeter look like?
The quantities that describe the size of alternating current include: peak value (and peak-peak value), average value, and effective value. The peak value is the maximum value; the average value is the average of the highest peak value of alternating current (that is, after rectification) within one cycle; the effective value is also It is called the root mean square value (the formula on the first floor). Effective value: Direct current and alternating current pass through two identical resistive devices respectively. If the heat generated by them is equal in the same time, then the voltage and current of the direct current are regarded as the effective value of the alternating current. Therefore, people generally say that voltage and current refer to the effective value unless otherwise stated. There is a certain relationship between the three: the ratio of the effective value to the average value is called the crest 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 crest factor KF = 2 times the root 2/2 (constant). For non-sinusoidal wave values it will change. Obviously, what people are most concerned about is the effective value, but it is difficult to measure. The average value and peak value are easy to measure, so ordinary multimeters (including voltmeters, etc.) indirectly measure the effective value (according to the method of measuring the average value or peak value). sine wave). For example, on a peak value 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 measure "false" effective values. Obviously, it is more accurate to use this type of meter to measure sine waves, but it is wrong to measure non-sinusoidal waves. A more accurate 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 what kind of waveform it measures. In order to distinguish the first two tables, it is called true effective value.
