# xWATTHR Calculations

Question asked by DavidX on Sep 9, 2016
Latest reply on Sep 13, 2016 by dlath

Hello,

i set up my Meter with following Values (Load= 1 Light bulb 100W):

Vn = 233.8 V

In = 0.445 A

xVRMS = 2620539 @ Vn

xIRMS = 49297 @ In

Setting GAIN values:

xVGAIN 15872780

xIGAIN 15960936

After setting xVGAIN / xIGAIN registers i get good values

2338000 xVRMS  => 233.8 Volt

44500 xIRMS => 0.445 Ampere

Setting

THR = 54931641

CF1DEN = 1

Now i see energy pulses on CF1 Output every ~36ms

36ms  => 100000 Pulses per Hour.

1 Impulse => 0,001Wh

As far as good, but now i try to calibrate the Meter AWGAIN register as described

on Page 7 of AN-1076.

WATTHRref = ( (Vn x In) / (10a x 3600) ) x (LINECYC / 2) * (Period / 256 *10^3)

LINECYC = 30000 ( 20ms per Full wave Line cycle -> 10 Minutes )

Period = 5116   (19.9ms -> 50 Hz)

a = 10^-3 ?

WATTHRref = ( (233.8V x 0.445A ) / (10-3 x 3600) ) x (30000 / 2) * (5116 / 256 *10^3)

= 8663.309

What is wrong with my calculation?

Thank you