PLATE THICKNESS MEASURING METHOD

PURPOSE:To measure plate thickness accurately by deciding whether or not the calculated value of radiation quantity in a state without material to be rolled in a rolling line is updated according to the counted value prescribed according to the time elapsed from the start-up time of operations. CONSTITUTION:A frame 5 of a thickness meter 2 is provided to the discharge side of a rolling machine 6 so as to hold a steel plate 1 between. A radiation quantity detector 4 is set to an upper side edge part of the frame 5 and a light source 3 of radial rays is set to a lower side part right under thereof. Output of the detector 4 is inputted to an instrument 7 for deciding for and against the updating and a thickness calculator 10. The instrument 7 for decision counts the output of the detector 4 at the time without the plate and calculates a variation rate DELTA1n from this value and the last value, and compares this with an allowable variation rate DELTA10 set for every lapsed time from the start-up of operations to decide for and against the updating of the calculated value 10 of radiation quantity at the time without the plate. Information about the elapsed time is given from a timer 9 and during the prescribed time in operation, the instrument 7 for decision calculates the variation rate DELTA1n, compares it with the allowable variation rate DELTA10 and gives the decided result to the thickness meter 10.