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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)

 

if:

 

(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

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