Hello,

I am working with an ADE7880 and I successfully get the Current, Voltage, PowerFactor, ApparentPower and ActivePower.

I am able to compute the real values of the Current, Voltage, PowerFactor, ApparentPower and ActivePower with the values I read in the ADE's registers.

Now I try do to the same thing with the Energy. I choose to use the energy accumulation mode and my accumulation number of half periods is 10.000. As I am working with 50Hz signals the duration of my accumulation is T = 1*10000 / (50 * 2) = 100 seconds.

I know the average power I have during thoses 100 seconds but I can't figure how can I compute the value of one LSB of the xWATTHR register.

On page 49/104 of the ADE7880's datasheet it's written that "Note that line cycle active energy accumulation uses the same signal path as the active energy accumulation. The LSB size of these two methods is equivalent."

I am considering this simple case : my voltage is 0.5V and my current is 0.5A when the ADE's ADC are at full scale (I am doing simulations with a function generator as I don't have big currents available at the office).

So one LSB[Whr] = (PMAX * 1024000 * 3600 * 100[sec] / (0.5[V] * 0.5[A] * 2^27) in Watt hours ? So one LSB [J] = LSB [Whr] / 3600 ?

I hope I explained my problem correctly.

Thanks for your help.

Pierre

Hi Pierre,

Our ADE7880 Calibration Application Note (AN-1171) is very useful for setting up a meter.

http://www.analog.com/static/imported-files/application_notes/AN-1171.pdf

Page 12, "Calibrating Using the Energy Registers", is helpful for the configuration of the ADE7880 when calibrating by directly reading the register values. The first equation on page 13, section "Establishing the Wh/LSB Constant" shows the calculation of Wh/LSB. For this let's assume that part is setup with the nominal voltage being 220V and nominal current being 10A, then this gives the Load(W), the accumulation time could be the 100 seconds you specified, xWATTHR is the register value when in line cycle accumulation mode. This then gives you Wh/LSB, it is recommended to calibrate at working voltage and current.

For testing purposes in the lab where you do not have high voltage, the 220V and 10A can be correlated to what the part would see in that situation, let's say that 220V is seen by the part as a +/-250mV peak wave and 10A is +/- 100mV peak wave then these 50Hz low voltage waves can be used as inputs. I would suggest using a smaller accumulation time such as 1 second (LINECYC = 100 at 50Hz) just to speed up this process.

From the equation:

Wh/LSB = (220V * 10A) *1second / (6598 *3600) = 9.6262 *10^-5

This is assuming we treat the inputs as if we were reading 220V and 10A.

Please let me know if I did not answer your question or if you have any further question on this and I will help you out.

Regards,

David