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ADE7858: need help to calculate VARTHR Register

Question asked by Bachmann on Sep 17, 2013
Latest reply on Sep 20, 2013 by hmani

Hello,

 

i need some help to calculate the right values for following registers:

WTHR0, WTHR1, VARTHR0, VARTHR1, VATHR0, VATHR1

 

i want to have an LSB of 1varh / 1Wh.

so i took the equation of the datasheet: VARTHR = (PMAX x fs x 3600 x 10^n) / (Vfs x Ifs)

 

1varh -> n = 0

Vfs = 196,006Vrms when ADC has 0,5Vpp

Ifs = 11,048Arms when ADC has 0,5Vpp

 

so i get the following values:

VARTHR = (33516139 x 8000 x 3600 x 1) / (196,006 x 11,048)

VARTHR = 0x67C8E5EA45

 

VARTHR0 = WTHR0 = VATHR0 = 0xE5EA45

VARTHR1 = WTHR1 = VATHR1 = 0x67C8

 

but when i'm measuring energy the result seems to be incorrect!

is anything wrong with my calculation?

 

regards,

Stefan

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