US 4,309,606 AGranted

Measuring plate thickness

AssigneeAktiebolaget Atomenergi

InventorsSimon J. Bjorkman, Georg S. Jonsson, Per S. R. Rundquist

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Abstract

The thickness of a hot metal plate is measured during rolling by determining the absorption by the plate of gamma radiation transmitted through the plate, the gamma radiation having at least one characteristic energy. A measurement value of the intensity of the radiation after passage of the plate is provided by digitally counting pulses generated by a radiation detector. Essentially only pulses which belong to the photopeak of said at least one characteristic energy in the pulse spectrum obtained from the detector are counted. The counted number of pulses is corrected for dead time losses by using a live time counter. Corrected mass absorption coefficients corresponding to partial thickness ranges within the total thickness range are calculated from the measured intensity of radiation passed through calibrating plates of differing thicknesses.

Claims17

Dependent claims

A method of measuring plate thickness by determining the absorption of electromagnetic radiation by the plate, comprising the steps of:

providing a source of electromagnetic radiation having an energy spectrum with at least one characteristic energy;
calculating a plurality of corrected mass absorption coefficients respectively corresponding to partial thickness ranges within the total thickness range to be covered in the measurement process by measuring the intensity of electromagnetic radiation passing through each of a plurality of calibrating plates having different thicknesses lying respectively within said partial thickness ranges;
determining a first normalizing value in association with said calculating step by measuring the intensity of electromagnetic radiation passing through a plate having a predetermined thickness lying within said total thickness range;
determining a second normalizing value prior to a step of measuring plate thickness by measuring the intensity of electromagnetic radiation passing through said plate having said predetermined thickness;
placing a plate whose thickness is to be measured in the path of the electromagnetic radiation from said source and detecting the radiation passing through the plate to be measured;
measuring the intensity of the radiation passing through the plate to be measured by counting only detected radiation pulses lying within a photopeak formed by radiation having an energy level within a predetermined energy interval around said characteristic energy;
normalizing the measured intensity of radiation passing through the measured plate by multiplying the measured intensity by a factor equal to the quotient of said first normalizing value and said second normalizing value;
and
calculating the thickness of the measured plate from the normalized intensity measurement and the corrected mass absorption coefficient corresponding to the partial thickness range within which the measured plate lies.

6 more elements

Apparatus for measuring the thickness of a plate by determining the absorption of electromagnetic radiation by the plate, comprising:

a radiation source emitting electromagnetic radiation with at least one characteristic energy;
radiation detector for generating pulses having amplitudes which are radiation energy level dependent;
means for mounting said radiation source and said radiation detector so that a plate can be placed between them and so that the radiation from the source is directed onto the radiation detector and passes through a thus positioned plate;
a circuit for counting pulses generated by said radiation detector including a radiation pulse counter and pulse amplitude sensitive means for passing to said pulse counter only those pulses having amplitudes within a photopeak corresponding to detected radiation energy in a predetermined energy interval around said characteristic energy, said pulse amplitude sensitive means including means for comparing the amplitudes of generated pulses with at least one reference value, means for detecting amplification related changes in the amplitudes of generated pulses, and means responsive to said detecting means for stabilizing the ratio between the amplitude of each generated pulse corresponding to a specific radiation energy and said reference value;
a diaphragm capable of attenuating the radiation emitted by said source by an amount corresponding to the attenuation introduced by a plate having a thickness within the range of thicknesses to be measured by the apparatus;
means for selectively introducing said diaphragm into the path of radiation between said source and said detector to thereby attenuate the radiation by said amount;
a clock pulse generator;
means responsive to a signal indicating the length of a thickness measurement for counting a predetermined number of clock pulses and for generating an enabling signal during the time of said counting to enable said pulse counter to count pulses from said radiation detector;
live time determination means comprising a counter, responsive to both said enabling signal and the pulses from said radiation detector, for counting clock pulses;
and
data processing means for generating said signal indicating the length of a thickness measurement, for dividing the number of pulses stored in said radiation pulse counter by the number of pulses stored in said live time determination counter to obtain a compensated pulse count, and for normalizing the compensated pulse count in accordance with the ratio of (a) the attenuation produced by said diaphragm at a time when the measuring apparatus is calibrated, and (b) the attenuation produced by said diaphragm at or near the time of the thickness measurement of interest.

8 more elements

Dependencies are inferred from the claim text.