You actually just have a data formatting problem. You're using tabs to separate devices by departments instead of simply creating a department field/column and putting everything in one tab. The data was likely delivered to you that way, but don't let the delivery format define the true working format of the data.
Combine everything in one tab, and then you'll be able to use the data in a pivot table just fine.
If you have more data than will fit in a tab, put it in a database such as MS Access, MS SQLServer or mySQL, and then tell excel to use the database as the pivot table source.