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True RMS


Kevin Weddle
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Hi Kevin,
Check the frequency response of your meter with sine-waves on each voltage range of it. You will probably find that the response drops-off above only a few hundred Hz, especially at high voltage ranges.
The frequency response of my premium true-RMS-reading DMM is down 3dB (0.707 of the correct voltage) at 17Hz and 17KHz. My cheap DMM is down 3dB at 58KHz and perfect at 10Hz (my lowest frequency). The lowest range on my good meter is 400mV and is 200V on my cheap one which explains the difference in frequency response between them.

Therefore you should use an oscilloscope to measure the level of clock signals if they are at a high frequency.

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