There are two basic variables that are needed. First is a representation of load. Usually described in lbs. per foot or Kg per meter. The other variable is belt travel in feet or meters per second. By combining both signals you can get lbs. per second or alternately kg per second. If you accumulate this combined signal based on distance travelled you can get a total weight. There are alot of influences on get both of these signals correct, and if you have any specific questions, post away! There are a number of experienced people that read this forum.
Kaskaskia Valley Scale Co.