- The maximum DC voltage ADc can measure is 3.3 volts. You are taking 3 volts as the maximum voltage.
- The "Gain" block connected to the ADCs should have a gain of 3.3/4095.
- I guess the "Constant" blocks with values 1.25 and 1.28 are the offsets you want to remove from the measurement. Ensure the value is correct and in the same unit as the measurement, i.e., volts.
- Ensure you are using the pins from the same ADC module ("C" in this case) on the board for measurement.
- Check if there are any wrong values set for the ADC block parameters. You can go through this documentation to do the same.