Card controlled beta backscatter thickness measuring instrument

Claim 1

In a beta particle backscatter instrument for non-destructively measuring the thickness of a coating on a substrate by counting beta particle radiation backscattered therefrom comprising: means for counting beta particle radiation backscattered from a coated substrate; memory means for storing data representative of a universal curve describing a relationship between calibration number and multiplied thickness corresponding to a composite relationship of a multiplicity of curves of beta particle backscatter count versus coating thickness for selectable combinations of isotope source, substrate material and coating material; a control card for a particular combination of isotope source, substrate material and coating material incorporating calibration idicia for determining a calibration number for the beta particle backscatter count and multiplier indicia for determining coating thickness for a particular multiplied thickness; means conditioned by the calibration indicia incorporated in the control card to convert particle backscatter count to a corresponding calibration number; means for determining the multiplied thickness corresponding to such calibration number from the universal curve; and means conditioned by the multiplier indicia incorporated in the control card to convert such multiplied thickness to indicia of coating thickness.