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So what is True-RMS and why is it important to us? RMS is the Root Mean Square, or effective heating value of any ac voltage or current waveform. RMS is the equivalent DC heating value of an AC waveform.
A true-rms device is one of three tools that can measure alternating current (ac) or ac voltage:
1. True-rms digital multimeters (or clamp meter)
2. Average-responding digital multimeter (or clamp meter)
3. Oscilloscope
Only the first two are commonly used, and both can accurately measure standard (pure ac) sinusoidal waveforms.
With an average responding meter, it takes the average of a signal, multiplies it by 1.11 and displays the RMS. This only works for linear loads or perfect sinusoidal waves. If an average responding meter were to measure an electronic load such as drives or simple lighting controls, the average responding meter will give you inaccurate readings distorted by harmonics.
Distorted waveforms or non-sinusoidal waves are caused by non-linear loads, which include virtually electrons loads. Hence why a true-rms digital multimeter or true-rms clamp meter is widely preferred because only they can accurately measure both pure waves and the more complex non-sinusoidal waves. Waveforms can be distorted by nonlinear loads such as variable speed drives or computers. An averaging meter attempting to measure distorted waves can be up to 40% low or 10% high in its calculations.
Successfully troubleshooting electrical problems relies equally on good tech manuals from the manufacturer and a high quality, true-rms test tool.
Fluke True-RMS tools: bit.ly/2JD3a8Z
More on True-RMS: bit.ly/2IIogkQ
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