Hi Hmani,
Thank you for the clear explanation regarding the AGND/DGND connections, very helpful.
For the voltage monitoring, the application is for a utility, and the input power will vary, in some instances it will be a "Phase" and "Neutral" connection (120V), in other instances the input will be 240V connection with no Neutral. Changing the design to use an isolated supply would require a complete redesign.
The full bridge rectified input, effectively puts the local system ground (GND & AGND) at a potential mid way between the two inputs, whether they be "Line" and "Neutral", or "Phase1" and "Phase2". The voltage attenuator uses identical resistive dividers (499K and 499 Ohms) to AGND, from each input.
Testing, so far, has shown a suitable signal at the V2P and V2N inputs to the meter, and reasonable values being read from the meter. We have not yet gone though the calibration process to understand if the voltage readings are as accurate as should be expected.
Best regards,
Ian