I could only work from the data you supplied, so I looked at the graph. What you post, more often than not, determines who and how good the answer is.
I still think that the damping of your measurement system will be critical to effective and accurate measurement as well. Check out the following http://www.tedea-huntleigh.com/ They supply accros the world. I think you should get the actual weigh system from them or similar. If the assistance if usefull, then you could help others by rating the answers. Good luck.
