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ADE7953 - issues with active/reactive power values

Question asked by ksrm on May 24, 2016
Latest reply on Jun 1, 2016 by dlath

For certain loads, it seems the values in the apparent, active and reactive power registers do not obey the relationship S^2 = P^2 + Q^2.

 

Load 1 (fan):

S (apparent): 169891

P (active): 167197

Q (reactive): 29829

sqrt(P^2 + Q^2) = 169836, very close to the expected apparent power

Power factor: 0.98

 

Load 2 (LED lamp powered by a SMPS):

S: 62420

P: 36097

Q: 10045

sqrt(P^2 + Q^2) = 37468, only 60% of the apparent power register value

Power factor: 0.58

 

Load 3 (same lamp at a higher brightness):

S: 203410

P: 132787

Q: 29443

sqrt(P^2 + Q^2) = 136012, 67% of S

Power factor: 0.65

 

Why would this be? For the values to be meaningful, the above relationship must certainly hold for the real units (expressed in VA/W/var) and I think it should also hold for the LSB values, as the conversion factor from LSBs to real unit should be the same or very similar for all three registers.

 

Have I made a stupid mistake, or are the values I'm getting incorrect?

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