Method for measuring the thickness and temperature of a moving metal sheet by means of eddy currents
AssigneeCegedur Societe de Transformation de l'Aluminium Pechiney
InventorJacques Charpentier
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Abstract
A non-contacting, eddy current, measuring method for determining the thickness and temperature of a moving metal sheet as in a metal rolling operation. Two separate magnetic fields are generated by applying two voltages of differing frequencies to a primary winding on one side of the sheet to induce two voltages in an opposed secondary winding on the other side of the sheet. The generated voltages are used to determine the calibration constants required to calculate the thickness and temperature of the moving sheet.
Claims10
A method for the non-contacting measurement of the thickness (e) and temperature (.theta.) of a thin metal sheet while in motion during a manufacturing operation comprising:
- generating on the same side of the sheet two separate magnetic fields by applying to at most two primary windings (A1) and (A2) a voltage V1 of a frequency N1 and a voltage V2 of a frequency N2 so as to develop respectively the induced voltages V'1 and V'2 in at most two secondary windings (B1) and (B2) placed on the other side of the sheet and respectively facing (A1) and (A2);
- determining a voltage U1 in volts in the electrical circuit using V1 and V'1 and a voltage U2 in the circuit using V2 and V'2 where U1 and U2 are directly related to V1, V'1 and V2, V'2 respectively;
- establishing the relationship U=K/e+C where K and C are constants which is obtained by measuring the voltage U.sup..theta. 1 generated by a field of frequency N1 when it passes through sheets of different thicknesses but at a constant temperature the likewise the voltages U.sup..theta. 2 for a frequency N2, and deducing the values of the constants C1 and C2 respectively correspondng to two values of C for the frequencies N1 and N2, it being known that the 0 of the volage measuring apparatus has been regulated to a reference thickness e.sub.0 and a temperature .theta..sub.0 ;
- establishing the relationship U=b+a.theta. where b and a are constants which is obtained by measuring the voltages U.sup..theta. 1 generated by a field of frequency N1 when it passes through sheets of different temperatures but of constant thickness and likewise for the voltages U.sup..theta. 2, the zero of the voltage measuring apparatus also being regulated for e.sub.0 and .theta..sub.0 and deducing the values of the constants a1, a2, b1, b2, whose indices 1 and 2 correspond to the frequencies N1 and N2;
- using the values of said constants a, b and c to determine the values of other constants A1, A2, B1 and B2 from the following equations:
- ##EQU4##
- and
- determining the values of e and .theta. by introducing the values of the constants A1, B1, C1, A2, B2, C2 and the values of U1 and U2 observed on the metal sheets to be measured into the following formulae:
- e=[A1B2-A2B1]/[(U1-C1)B2-(U2-C2)B1] and
- .theta.=[A2(U1-C1)-A1(U2-C2)]/[B1(U2-C2)-B2(U1-C1)].
Dependencies are inferred from the claim text.