The ADE7878 datasheet says it calibrates total active energy (net value I assume). Is it possible to calibrate positive and negative power and energy separately in ADE78xx series? I need to store the import and export values in separate registers.
ADE7878 has a single total active energy register (xWATTHR) and a single fundamental active energy register (xFWATTHR). Here, the total means over the entire measurement bandwidth (fundamental energy + harmonic energy). Both are signed registers- they display both positive and negative values.
If you need to store two separate active energy values (positive and negative), you can do so in the MCU by monitoring the sign bit of the energy result from ADE7878. The energy registers update every 8 KHz. So, when you read the energy values (read with reset bit enabled) every 8 KHz, check the sign of the result and store it in a designated register in the MCU.
As an alternative to checking the sign of the bits, interrupts can be used to indicate sign change. There are reverse polarity interrupts available in ADE7878 : REVAPx (bits 6,7,8 of STATUS0 register). These interrupts indicate when the sign change has taken place.
Does this help you? Feel free to post further questions here.
Yes that cleared my doubt. Thanks!
I have another doubt here. The energy registers update every 8 KHz right? And our line frequency is 50 Hz. Does that mean that the power/energy stored in the respective registers can be considered almost instantaneous? Shouldn't the energy be integrated over a few line cycles, to get average value?
Yes, Prathyusha! You are correct! That integration must be done in the MCU where you add all the energy results in a register. If you use line cycle accumulation mode to get energy result over several line cycles in ADE7878, then you lose track of sign changes within that accumulation period.
It is to be noted that the energy results in the xWATTHR and xFWATTHR registers accumulate by default over time (when not in line cycle accumulation mode) and overflow once the register capacity is fully utilized. So, if you do not want to read the energy result every 8KHz, you can let it accumulate for a while and read-with-reset, at a slower rate. It depends on how closely you would like to monitor sign changes and how often you expect reversal of energy flow in application.
Okay got it! Thanks a ton!
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