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ADE7816 24-bit raw V waveform data units

Question asked by dBC on May 29, 2015
Latest reply on Jun 15, 2015 by dlath

It looks like all the 24-bit instantaneous waveform data, peak detection values and over-voltage thresholds are all after the VGAIN register.  Is this correct?

 

I'd like to derive an formula for converting raw 24-bit values to real world voltage readings at the input to my meter.  The datasheet tells me an approximate way of doing it is:

 

reading/5,989,256 * 0.5V  * D

 

where D is my meter's voltage divider ratio, but this is subject to the variations in my 1% resistor divider.

 

I've used precision equipment to calibrate VGAIN so the the 7816's VRMS readings give me real world values.  1 LSB of the VRMS represents 62.5uV  (1/16th of a mV) at the input to my meter.  Given I've done that, it seems it must be possible to come up with a formula to convert a raw 24-bit voltage reading to a real-world voltage also.

 

Maybe some real live numbers will help explain what I'm after:

 

My resistor divider is 880K/1K

I've configured a voltage gain of x 1.2108  (i.e. the VGAIN register is written with 0x1afd11)

Now 234V RMS ideal input to my meter gives me a VRMS(*) reading of 3,744,000

Then I configure VPEAK detector to give me the peak over 255 half cycles.

A typical VPEAK reading I get back is 5,253,231

 

I'm looking for a way to calculate what divider I should use to turn that back into real world volts at the meter input.  Empirically I can determine that the answer must be about 15,874, i.e 5,253,231 / (234 * sqrt(2)), but it seems that given I've used VGAIN to turn VRMS into real-world units, I should be able to calculate what I need to do to turn a raw 24-bit value into real-world units as well.  Is it as simple as dividing by 16,000?

 

(*) All VRMS readings are done via the recommended large averaging technique to remove any ripple.

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