dear IA:
your project need a mechanical system with loadcell to apply the weighing data in motion ,about this part check out the National Scale Men's Association for detail;
i got a handbook when i visited USA in 197x (which's an very old one -197X) so if you need just let me know I'll get you some copys with your needs but go chech this out first they're doing all these kind of measuring, in that time a 12 bits A/D conerter do the anloge and 8051 do the caculation ,display, data transmition (rs232)
so Up still the most importen thoing in this kind of project.