Alternator Charging Rate?

Some cases show that alternator eventually fails (or dying?) even if it delivers around 14V to the battery, so from voltage alone it is hard to tell apart normal and faulty alternator (only after battery dies).
Could we then tell the difference through the charging rate?
What is the normal charging rate (Ampere) of an alternator during engine idling at 1kprm?
Is there any diagram that shows engine rpm vs charge rate maybe?
Also assume that there are no other loads.

note:
Battery is 60Ah, standard alternator on 1.6L 02 Lancer ES/Cedia.

thanks.