ADE7758: Line cycle energy accumulation method

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 ?

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

Hi Angel

Accurate source is a source which can generate a known voltage and current signal and it must have an error less than the expected error of the ADE7758 measurements.

The method of calibration is just to remove meter-to-meter variations and to find the constant of conversion of register values to real-world values. So, it is independent of the method that you will be using to measure energy after calibration. While calibrating, it is recommended to select one particular method and follow the same method till you finish calibrating the meter. After that, you are free to use any method possible to comprehend energy and RMS readings.

Regards

hmani

Hi Hmani,

Thank you very much for the explanations given so far.

I have some other doubts regarding the SPI communication of ADE7758.

What is the minimum and maximum SCLK frequency required for ADE7758(considering CLKIN as 10MHz) ?

From the timing characteristics(Data-sheet pg.no. 6), with a 10MHz CLKIN frequency, the SCLK ON/OFF time is minimum 50nS min. That means, SCLK frequency of 10 MHz.

Am I correct ?

Hi Angel

Yes. That corresponds to 10 MHz max SCLK frequency.

Regards

hmani

Hi Hmani,

Ok, so what is the minimum SCLK frequency required ?

I am interfacing the ADE7758 with a PIC16LF1938, which is working in 10MHz.

And it gives out an SCLK frequency of Fosc/4, which is 2.5 MHz.

Is it fine to give this frequency to ADE7758?

Thanks & Regards,

Angel

Hi Hmani,

     Please give me your suggestion on this....

Waiting for your reply.

Thanks & Regards,

Angel