Hi

We are using ADE7880 and have a question regarding the value of the threshold registers (WTHR, VARTHR, VATHR). I read the datasheet and AN-1171 calibration document and found that the value of these three registers can all be calculated using the equation...

I understand all the parameters in the equation except the exponent 'n'. The description says...

Its value depends

on how much energy is assigned to one LSB of watt-hour registers.

Supposing a derivative of Wh [10n Wh], n as an integer, is

desired as one LSB of the xWATTHR register, WTHR is

computed using the following equation:

Could you please give me a real example of how to determine what value to use for 'n'?

Thanks

Hello Abdullah_Ghamdi,

You can significantly adjust the N value for example:

Supposed you computed already a value of

WTHR = 593979 X 10 ^ N(dec) in your formula using the other parameters.N = 0 gives Wh = 593979 or 9103B (hex)

N=1 give 10 Wh = 5939790 or 5AA24E (hex)

N=2 gives 10^2 Wh = 59397900 or 38A570E (hex)

N= -2 gives 10 ^ -2 = 5939.79 or 173 (hex)

N= -4 gives 10^-4 = 59.3979 or 3B (this is already 8 bits)

and so on....

If you try to input your values and try to change the N integer one at a time you will find out that your amount is adjusting at a multiple or fraction of a ten. N depends on your preference and also on the size of your computed 1 LSB of xWATTHR.

This is important in making sure that what will you compute as WTHR in hex is enough to fit the 8 bits allowable value. If not, you have to adjust the N.

There is also a default value for WTHR which is 03. Any values lower than 3 is not recommended. Take note that as you increase values greater than WTHR = 3 (hex) the longer time it takes to get the information out from DSP as it accumulates larger values of xWATTHR.

For more information you can read http://www.analog.com/media/en/technical-documentation/data-sheets/ADE7880.pdf on page 49.

Regards,

aheredia