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How do I convert between dBA, dBV and RMS values? For example, I have used a current probe (clamp) with a gain of 100mV = 1A to measure a series of currents in dB and I would like to know the equivalent RMS current values.

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up vote 2 down vote accepted

I'll assume dBA is for amperes and not the 'A weighted' dB sound pressure level measurement.

Zero dBA will therefore mean 1A RMS and 6dBA will mean 2A RMS. Strictly speaking 2A is closer to 6.021dBA but everyone accepts that if you double the current (or voltage) it increases by 6dB

0dBV is 1V RMS and by the reasons above 2V is 6dBV

RMS values are always implied unless otherwise stated.

Calculating: if your meter read 13.5dBA, divide by 20 to get 0.675 and take the inverse log (base 10) to get 4.732A

Or dBA = 20 log(I)

EDIT - if your meter read 13.5dBV it actually measures 4.732V and if your clamp has a gain of 100mV per amp, the current flowing will be 47.32A. All values RMS.

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What if the meter read 13.5dBV, and the gain of the clamp is 100mV = 1A? I want the current in dBA and RMS please. –  Jacob May 16 '13 at 12:15
    
13.5 dBV is equal to 4.732 volts. If 100mv (0.1v) = 1A, then the current is 47.32 A or 33.50 dBA. It is assumed that all the values are RMS as most meters are either true RMS reading (therefore independent of waveshape) or are calibrated to read RMS (assuming the waveshape is sinusoidal). –  Barry May 16 '13 at 23:03
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