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Measurement of VRMS - ADE7758

Question asked by NicoSalvay on Jul 5, 2013
Latest reply on Jul 7, 2013 by mkaiserm

Hello, I'm starting with the first measurements of VRMS and I can not interpret the reading.


I did the following steps:


- The WAVMODE register was configured to sample the voltage for phase A.

- I used the internal reference voltage of 2.42 V.

- The PGA2 was configured with gain equal to 1.

- I wrote the AVRMS register to read the VRMS.

- I get the value of 3 bytes corresponding to the VRMS of phase A.


The calculation used to interpret this value is:


LSB of ADC = Vref / (2 ^ 16-1)




(2 ^ 16-1) bits ------------------------------------------------------------------- 2.4 V

Number of bits read from AVRMS register / 256 ------------------ = XVRMS of ADC input



Then, as my input to the ADC has a resistive divider as shown in the picture:


VA input.png


Real VRMS = xVRMS of ADC input * (1M + 1K) / 1K


I need to know if my procedure is complete, or if there is something to add?



Thanks in advance


Nicolás Salvay