Multi Objective optimization?

I am optimizing an Multi objective function with different ranges of values for objectives considered.......

for example..... let there are 3 objectives

for Case1:

First objective: 100

Second objective: 0.2

Third objective: 0.004798

for Case2:

First objective: 0.100

Second objective: 0.05892

Third objective: 798

If I use weighted sum approach to normalize the objectives............. then I need to vary weights for each case.......... so that they are normalized thereby multi objective optimization can be made.

Can I vary the weights for each case.......... if so I don't know how my objectives will vary in magnitude for another case.

Kindly let me know..........................