Here are the instructions using EZ Perdiem. Even if you aren't using it, scroll down to the section with the "red" writing in the link, which is where you will enter your per diem in Turbo Tax.
http://ezperdiem.com/taxes/software_guides/turbotax.php

In Turbo Tax go to:
-"Deductions"
--"Employment Expenses"
---"Any Other Expenses"
----"Meal Expenses covered by Department of Transportation Rules"