The difference between an average response multimeter and a true effective value multimeter
FLUKE's digital multimeter and clamp meter have a distinction between average response and true effective value. For example, in the information section, the 110 series true effective value multimeter and 170 series true effective value multimeter are introduced, while only the 15B and 17B digital multimeter are introduced; So what are the differences between them? How should users make choices?
What is a valid value?
If the heat generated by AC current i through a pure resistance circuit R in one cycle T is equal to the heat generated by a DC current I through the same resistance at the same time T, then the value of I is called the effective value of i.
Principle of average response measurement:
For a sine wave, the peak value is 1.414 times the effective value, and the effective value is 1.11 times the average value, which is also the waveform factor of the sine wave. So for sine waves, the principle of average rectification can be used to measure the effective value. After measuring the average value and multiplying it by 1.11 to obtain the effective value, this technique is also known as "average reading, calibration according to the effective value". The problem is that this measurement method is only applicable to pure sine waves.
Principle of true effective value measurement:
For the waveform shown in the figure below, the waveform factor is equal to the effective value/average value=1.82. If the average response method is used for measurement, the effective value obtained by multiplying the average value by 1.11 will still have a significant error compared to the true effective value. Therefore, the true effective value method must be used for measurement, which is expressed by the formula: this measurement principle determines that the effective value can be directly measured for all characteristic waveforms.
Conclusion:
For pure sine waves, both true RMS and average response instruments can accurately measure, but for distorted waveforms or typical non sinusoidal waves such as square waves, triangular waves, and sawtooth waves, only true RMS instruments can accurately measure.
