Apparatus for measuring thickness of metals on a rolling mill

A system for continuously determining the thickness of a material by measuring the radiation transmission through the material, comprising:

• source means for generating a polychromatic X-radiation beam through the material;
• and
• detector means for detecting a plurality of energy bands of a received polychromatic X-radiation beam which has penetrated through the material, and for producing output electrical signals representing the intensity of each of said detected energy bands of said received polychromatic radiation beam;
• said detector means having an ion chamber containing at least one gas having a plurality of stages of different specified lengths sequentially arranged according to length, such that the stage with the smallest length is positioned closest to said source means and the stage with the longest length is positioned farthest from said source means.

A method for continuously measuring the thickness of a sheet material with a variable composition, comprising the steps of:

• directing a polychromatic radiation beam through the sheet material, said polychromatic radiation beam having a plurality of energy bands;
• detecting said polychromatic radiation beam with a length absorption filter after said radiation beam has penetrated through the sheet material;
• selecting a specific plurality of energy bands to measure such that the elemental determination condition is satisfied;
• measuring the intensity of said plurality of energy bands, the quantity of said measured energy bands being equivalent to the quantity of elements contained in said sheet material;
• producing a sheet transmission ratio for each of said measured energy bands of radiation flux transmitted through the sheet material to radiation flux transmitted through the air in the absence of the sheet material;
• calculating the percentage amount of all elements of the sheet material as a function of said transmission ratios and the absorption coefficients of the elements, comprising the steps of:
• equating the measured intensity through the material in each of said measured energy bands, resulting in as many equations as there are elements in said material, and
• simultaneously solving said equations for the percentage of each element in said material;
• and
• calculating the thickness of the sheet based on said percentage amounts and said absorption coefficients of said plurality of elements present.