Difference Between Average Response Multimeter and True RMS Multimeter
Digital multimeters and clamp meters have average response and true RMS. For example, the 110 series true RMS multimeters and 170 series true RMS multimeters are introduced in the data, but only 15B and 17B digital multimeters are introduced for 15B and 17B; then their What is the difference between How should the user make a choice?
What is a valid value?
The heat generated by an alternating current i passing through a pure resistance circuit R in a period T is equal to the heat generated by a direct current I passing through the same resistance 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, which is also the form factor of the sine wave. So for a sine wave, the average rectification principle can be used to measure the effective value. The average value is multiplied by 1.11 to get the rms value. This technique is also known as "average reading, calibrated by rms value". The problem is that this measurement method only works with pure sine waves.
True RMS measurement principle:
For the waveform in the figure below, the form factor = effective value / average value = 1.82. If the average response method is used to measure, the average value will still be multiplied by 1.11. There is a large error between the obtained effective value and the real effective value, so it must be Measured by the true effective value method, 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 the true RMS and average response meters can measure accurately, but for distorted waveforms, or typical non-sinusoidal waves such as square waves, triangle waves, and sawtooth waves, only true RMS meters can be accurate Measurement.
