Simultaneously Reading Two Analog Inputs with Arduino

AbdulMoizFarooq:

Robin2:
Given that you can't read from 2 pins at the same time then what is the maximum amount of time between readings that would be acceptable in order to get useful data?

I am not sure, what is the minimum time I can get??

The minimum sample rate required is a pretty essential part of specifying any discrete time sampling system. If you're just looking for a fundamental imbalance then twice the rotational rate of your spindle is the lower bound per the Nyquist Theorem. There may be higher order vibrations in a particular system that need be taken into account.