110V AC to 3V AC for harmonic analysis
If the constraint is &quot;faithfully reproduce&quot; then one of the 1st things you need to consider is to what harmonic. The more harmonics you capture the closer to the actual waveform the data you acquire will be. This means higher and higher ADC rates.
A good rule of thumb is the sampling rate needs to be at least 10x higher than the frequency of interest. This is related to Nyquist sampling theorem but remember you do not have a perfectly band-limited signal and Nyquist never stated to use twice the sampling frequency in such situations ;).
10x will mean you can reconstruct the highest frequency of interest with a gain of 0.99 and a phase of 5.7 degrees. The closer your sampling frequency is to the frequency of interest, the further the quality to degrade until eventually you will hit aspects of Nyquist sampling theorem
How to measure? An isolated voltage divider would be the best option.
A resistor chain feeding an SAR would be the simplest but you then need isolated power and isolated signals. TI (and analog) have some nice digital isolators with integrated isolated DCDC which are good for a a reasonable amount of mA