THE MEASUREMENT CHI-SQUARE (CHI(M)2) APPROACH FOR DUAL NUCLEAR GAUGES

A new unified approach called the Measurement Chi-Square (chi(M)2) App roach is described and demonstrated for on-line use, evaluation and op timum design of dual nuclear gauges. Dual nuclear gauges have been use d to eliminate or minimize measurement interferences such as sample co mposition or position for a number of common measurements such as dens ity, component fraction (most often hydrogen or water), and thickness for at least 30 years. However, no unifying common approach has been p ut forward for on-line use, evaluation and optimum design of this tech nique. The present chi(M)2 approach is demonstrated here for the alumi num thickness measurement application with x-ray gauges in the presenc e of unknown sample composition variations. The approach is shown to b e valid, easy to implement, and to have the advantages that it is form ulated in the most straightforward and general way, automatically yiel ds the best possible accuracy, and can be used on-line to determine th e source of gauge malfunctions. It should prove very useful for the al uminum thickness measurement application and other future dual nuclear gauge applications.