ADE7758 xWATTHR Measurement:

Hello All,

I have communicated with ADE7758 with my Host MCU.

SPI Works fine and to Read/Write Default Values. From HOST ADE7758 to Host MCU.

I am giving 0 to +/- 500mV to Voltage  and 0 to  +/- 500mV to Current channel(s)

And able to read xVRMS and xIRMS resgiter.

I have able to read xWATTHR with

1) LCYCMODE Register  , RSTREAD =1 Default Mode

2) LCYCMODE Register  , RSTREAD =0, LWATT = 1 and LINECYC  = 0x10.

But I am unable to understand ..

1)How to Convert xWATTHR in to real Watt. With Line Accumulation or With RSTREAD in Default.

2) Or If suppose, AVRMS = 0x1243412 and AIRMS = 0xCBCD12. What should be in AWATTHR Register.

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Thanks..

  • Thanks.. But Asking again..

    Again...

    But I am unable to understand ..

    1)How to Convert xWATTHR in to real Watt. With Line Accumulation or With RSTREAD in Default. ??

    2) Or If suppose, AVRMS = 0x1243412 and AIRMS = 0xCBCD12. What should be in AWATTHR Register. ??

  • Getting WATT information from WATTHR might not be the best method. Since power is mostly an instantaneous measurement, you are going to obtain an average power over accumulation time.

    Moreover, you need to activate the line accumulation mode LCYCMODE (not ON by default) and RSTREAD=1

     

    To reply to your question, you should obtain your conversion constant Wh/LSB, VARh/LSB, and VAh/LSB by performing gain calibration:

    1. eq.50-51-52 in the datasheet with Calibration Using Pulse Output 

    2. eq 66-67-67 in the datasheet with Calibration Line Accumulation  (e you perform calibration math that you have:

    Then:

    conversion constant [Wh/LSB] * WATTHR = Energy accumulated.

    and

    WATT = Energy accumulated *1000/3600

     

  • Using Equations 66,67,68 in rev E of the datasheet are good for getting LSB/Wh type values using line cycle accumulation, but there's no guidance for how to get the xWG, xVAG, xVARG values _without_ using frequency outputs.

    The whole win of using linecycle accumulation mode is surely that we don't need to use frequency outputs and compare them to another frequency output.

    Have you got any guidance on working out the _nominal_ xWATTHR -> Wh/lsb based on system design (voltage divider and CT ration) so that you can work out both the WH/LSB _and_ the gain calibration?