Products > Test Equipment

DMM with THD capabilities

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Brianf:
To protect your soundcard, http://pmillett.com/ATEST.htm

Kleinstein:

--- Quote from: bson on January 03, 2023, 08:44:26 pm ---If you insert a 1kHz notch filter and apply a 1kHz test tone, then the DMM set to ACV RMS will measure THD+N RMS.  Divide by the test tone RMS level and you have it as a fraction.

--- End quote ---
The method with the notch is the standard method.  However the notch is usually not perfect and one would still use a scope (e.g. with FFT function) to look at the residual signal.
One can use the scope also to trim the notch or generator frequency if needed.
The notch extends the test range to lower distortions - unless the notch itself adds distortion.
Using RMS for THD+N only works if the notch is near perfect, which is rare (higher order). One still needs the very good generator.

DrGeoff:
Look for an AWA F242A Noise And Distortion Meter.

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