| 摘要 |
Method to measure the variations in section of a hot rolled bar (12) as it is fed, the method including the generation of a variable frequency magnetic field by at least a generator device (14) defining an inner space (214) for the transit of the bar (12), the variations in section of the bar (12) in transit being measured by a receiver device (15) suitable to monitor the perturbations induced on the magnetic field by the variations in the area of section of the bar (12) in transit, wherein the receiver device (15) is arranged coaxial and inside the generator device (14) and defines inside the same a surface for the transit of the bar (12) which has a transverse section of (As"), the value ("f0") of the frequency of the magnetic field generated by the generator device (14), suitable to minimise the influence of the real temperature of the bar (12) on the measurement, being defined by the formula: f0 = As /.mu.0 .sigma. F .DELTA.02 where - ("As") is the area of section of the surface defined inside the receiver device (15), - ("F") is the filling factor defined by the ratio between the normal nominal area of section of the bar (12) in transit and the value ("As"), - (.mu.0) is the permeability of vacuum, - (.sigma.) is the conductivity of the material which makes up the bar (12) at the average temperature of measurement and - (.DELTA.0) is a coefficient which is a function of the filling factor ("F") and calculated with the following formula: .DELTA.0 = a + bFP - c ¢1 + 1/(1 - F)q!.
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