The difference between an average response multimeter and a true RMS multimeter
FLUKE's digital multimeters and clamp meters are divided into average response and true RMS. For example, the 110 series true RMS multimeter and the 170 series true RMS multimeter are introduced in the information, but only the 15B and 17B digital multimeters are introduced; then What are the differences between them? How should users make choices?
What are valid values?
If the heat generated by the alternating current i passing through the pure resistance loop R in one period T is equal to the heat generated by the direct current I passing through the same resistor in the same time T, then the value of I is called the effective value of i.
Average response measurement principle:
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. This value is also the form factor of the sine wave. So for sine waves, the average rectification principle can be used to measure the effective value. The average value is measured and multiplied by 1.11 to obtain the effective value. This technique is also called "average reading, calibrated to effective value." The problem is that this measurement method only works for pure sine waves.
True effective value measurement principle:
For the waveform in the figure below, crest factor = effective value/average value = 1.82. If measured using the average response method, the average value will still be multiplied by 1.11. There is a big error between the obtained effective value and the true effective value, so it must be The true effective value method is used for measurement, and the formula is expressed as: This measurement principle determines that the effective value can be directly measured for all characteristic waveforms.
in conclusion:
For pure sine waves, both true RMS and average response instruments can measure accurately. However, for distorted waveforms, or typical non-sinusoidal waves such as square waves, triangle waves, and sawtooth waves, only true RMS instruments can accurately measure them. Measurement.
