MEASUREMENT OF THICKNESS OF STEEL PLATE

PURPOSE:To enable correct plate thickness to be accurately measured in correspondence with steel plates slightly different in component values from one another by determining the density and the mass absorption coefficient of each steel plate to be measured based on the result of the analysis of a steel component structure for the steel plate. CONSTITUTION:A measuring instrument is composed of a radiation source 3 for emitting a radiation 3 to a steel plate 1, a radiation dose detector 4, a radiation thickness gage 5, a computer 7 and the like. When the rolling of the steel plate 1 is initiated at a step (S) (1), a radiation transmission quantity is detected at S(2) and a detected radiation quantity I0 in the absence of the plate and a detected radiation quantity It in the presence of the plate are outputted. On the other hand, prior to above, the analysis of the steel component structure of the steel plate to be measured is conducted at S(3) and a resulted analytical value is stored in a computer at S(4). Before the detection at said S(2), based on the analytical value stored at S(4), the mass absorption coefficient mum and the density rho of the steel plate to be measured are calculated with a prescribed expression at S(5). The thickness (t) of the steel plate is measured at S(6) based on I0 and It at S(2) and mum and rho at S(5).