Dynamic alloy correction gauge

An apparatus for calculating the thickness of a sheet material comprising a source of photons located on one side of said sheet material, adapted to direct a beam of photons from said photon source against said sheet material, a first detector located on the same side of said sheet material as the photon source for detecting reflected radiation from said sheet material and a second detector located on the opposite side of the said sheet material as the photon source for detecting transmitted radiation, the first detector concentrically surrounding the photon beam source, computing means for combining the signals of transmitted and reflected photon beams and computing and signal processing means for measuring and processing the data from both detectors for a number of calibrating samples using a polynomial in two variables employing a best-fit method, and whereby the thickness of the sheet material is obtained as a function of the detected data and the function is applied to determine the unknown thickness of a sample.

A method of calculating the thickness of a sheet material comprising directing a beam of photons against the sheet material from a photon source located on one side of said sheet material, detecting reflected radiation from said sheet material in a first detector located on the same side of said sheet material as the photon source and detecting transmitted radiation in a second detector located on the opposite side of the said sheet material from the photon source, combining the signals of transmitted and reflected photon beams, measuring and processing the data from both detectors for a number of calibrating samples using a polynomial in two variables employing a best-fit method, wherein the polynomial is of the form:

• X=.SIGMA.a.sub.ij I.sup.i I.sup.bj, and obtaining the thickness as a function of the detected data and applying this function to determine the unknown thickness of a sample.