ADE7758: Line cycle energy accumulation method

Hi All,

I am using ADE7758 Poly phase energy metering IC for my project. I went through the data sheet of the ADE7758 IC, and some of the topics were quite confusing for me. Especially the "Energy accumulation mode" and "Line cycle energy accumulation mode".

What I could understand is, in Line cycle energy accumulation mode, the value in the value in Energy accumulation registers(eg. AWATTHR) gets updated gets updated when the number of half-line cycles becomes equal to the Line cycle (LINECYC) register count.

And in Energy accumulation mode, the value in Energy accumulation registers(eg. AWATTHR) gets updated at every 0.52 Sec.(WDIV=0).

Is this correct ?

In both the methods, before reading the Energy accumulation registers(eg. AWATTHR), do I have to wait for a Zero-cross detect for ensuring that the value has been updated ?

Or should I be waiting for the LENERGY interrupt to occur in Line cycle energy accumulation mode ?

Please help me to understand these concepts clearly.

Thanks & Regards,

Angel

  • 0
    •  Analog Employees 
    on Jan 23, 2013 7:02 PM

    Hi Angel

    Energy accumulation mode is the basic mode of operation. The energy registers get updated every 0.4 microseconds and their value reaches the maximum limit of the register at 0.524 sec( for WDIV=0) and overflows.

    In order to read the registers, just read after 0.4 us every time. There is an interrupt AEHF that indicates when the energy register is half full. If needed, you can use it as well.

    Coming to the line cycle accumulation mode, the registers get updated only after the LINECYC number of half-line cycles have been completed and LENERGY interrupt signals the end of the accumulation.

    Regards

    hmani

  • Hi Hmani,

    Thank you very much for your explanation. I could understand it well.

    Regards,

    Angel

  • Hi Hmani,

    I have another doubt regarding the xWATTHR register value.

    I am not able to understand how to convert the xWATTHR 16-bit register value into actual Watt Hr energy.

    Currently if i consider all default settings of ADE7758 values.

    How to do the conversion of xWATTHR register value to the real time Watt Hr units ?

    Can you please explain it with an example ?

  • 0
    •  Analog Employees 
    on Jan 31, 2013 12:39 AM

    Hi Angel

    To convert register values to real world units, you will have to calibrate the meter and find out the respective constant. Multiplying that constant with the register value will then result in the required result.

    For example, say you get 0x0030 in the AWATTHR 16-bit signed register. Convert that to decimal : d48. If your constant is found to be 2.9 * 10^-4 KWh/LSB, then your register value will correspond to 48 * 2.9 * 10^-4 = 0.01392 KWh or 13.92 Wh.

    One point to remember is that the register is a signed register. So if the number is negative( MSB is 1), take 2's complement of the register reading and then convert to decimal, to get the exact value.

    Now, to understand about the calibration process and to find the required constant, refer to the datasheet-page 42.

    Kindly get back to me if you have any further doubts.

    Regards

    hmani

  • Hi Hmani,

    Thank you for the explanation.

    I still have to go through the calibration section thoroughly.

    But from the first point, to choose the right method for calibration out of two, I wanted to know few things.

    In the line cycle accumulation method, what does the "accurate source" exactly mean ? Is it just a source with known voltage and current with a particular load ?

    And, if I am using Line cycle accumulation method for calibration, is it necessary that I should use the same mode for the energy accumulation as well ? or I can switch between the modes when necessary(while calibrating) ?

    Thanks & Regards,

    Angel