Thank you very much.
This is a drawing that illustrates my idea.http://www.flickr.com/photos/34955071@N02/5045191279/
I want to get that flat steel plate to have that convex in the middle by using high pressure.
But, the height of that convex has to be regulated to a specific height.
That's why i was thinking of using proximity sensor to measure it.
But, it seems that arduino and proximity or any other electronic device can't be worked in that condition.
There must be some other way to measure that height of convex, but I don't know how.