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xWATTHR calculation in ADE7878

Question asked by edmont on Nov 10, 2015
Latest reply on Nov 19, 2015 by hmani

I'd like my accumulation registers to reflect real world energy values, with a 1 Wh/LSB constant. Making use of equation 26 on page 50 of the ADE7878 datasheet I get a very high number that makes the registers to be zero all the time.

 

WTHR = PMAX × fs × 3600 × 10^n / (Vfs × Ifs)

 

PMAX = 33516139

fs = 8000

n = 0

Vfs = 447.6 (1 Vpp ADC input)

Ifs = 3.54 (1 Vpp ADC input)

 

The result is 0x08DD69585ED, which makes WTHR0 = 0x009585ED and WTHR1 = 0x00008DD6. If I use those numbers xWATTHR will be zero even after tens of seconds (default read-with-reset enabled), when I apply inputs that generate hundreds of watts in the xWATT registers.

 

However, if I change the xWTHR registers for new values WTHR0 = 0x00000000 and WTHR1 = 0x00000003 I can see some non-zero values in the xWATTHR registers.

 

What I am making wrong in the calculation?

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