Basis weight gauging apparatus system and method

Claim 1

A basis weight gauging method for measuring the weight per unit area of a material having scanning head means for carrying a radiation source and a radiation detector and providing a gap therebetween for said material, the radiation source providing radiation in the form of a succession of events having a plurality of different energy levels, where the detector receives said radiation having said plurality of different energy levels after it has come into contact with said material and counts the radiation events received to provide a digital count, I, proportional to the number of said events indicative of radiation absorbed by said material, and where a reference sample of said material is used having a known basis weight, X1, said method comprising the steps of a. placing said reference sample in said gap and obtaining an initial digital count measurement, I1o, b. removing all material from said gap leaving only air and obtaining an initial measurement, Iao, c. obtaining the mass absorption coefficient, Mu , of said radiation source and material by Mu (-1/X1) loge (IO/Ioao) d. scanning said predetermined material to obtain a measurement, I, and periodically during said scanning removing all material from said gap to obtain Ia, which is an updated Iao which takes changing ambient conditions into account including the effect of decay of said source, air density change due to temperature variation and dirt build-up on the window of the radiation source, and in addition from Ia obtaining an updated I1o, namley I1, by I1 Ia (I1o/Iao) and e. obtaining the actual basis weight, X, of said material by X X1 - (1/ Mu ) loge(I/Il).