Measuring device for the "contactless" measurement of large thicknesses, for metal materials above the Curie temperature

Claim 2

A measuring device for the "contactless" measurement of the thickness of materials above the Curie temperature, characterised by comprising a sensor constituted by a magnetic core with pole pieces which can be made to approach the wall to be examined and by an electric coil wound on the body of said core, means for supplying a sinusoidal current to said coil, means for measuring the impedance of said coil, and processing means for obtaining the thickness of the wall under measurement from the measured value of said impedance.

Claim 3

A thickness measuring device as claimed in claim 1, characterised in that said core is either of ferromagnetic material or not, or air.

Claim 4

A thickness measuring device as claimed in claim 1, characterised in that said means for supplying a sinusoidal current comprise a sinusoidal generator able to provide the sinusoidal feed current for the coil and to provide a reference voltage, and said impedance measurement means comprise two synchronous detectors able to rectify the voltage developed across the coil in accordance respectively with said reference voltage and with a voltage the phase of which is shifted through 90° relative to said reference voltage, the outputs of said detectors being fed to a processor for calculating the wall thickness.

Claim 5

& thickness measuring device as claimed in claim 1, characterised in t tat said means for supplying a sinusoidal current comprise a double sinusoidal generator able to provide the sinusoidal feed current for the coil and to provide an identical feed current for an inluctor having a coefficient equal to that of the coil when the wall is absent, and said impedance measurement means comprise a differential amplifier able to obtain the difference between the two resultant voltages and a phase comparator able to make a phase comparison between said difference and a reference voltage provided by said generator.

Claim 6

A thickness measuring device as claimed in claim 1, characterised in that said means for supplying a sinusoidal current comprise a sinusoidal generator able to provide the sinusoidal feed current for the coil, and said impedance measurement means comprise a detector able to rectify the voltage developed across the coil; the output of said detector being fed to a processor for the calculation of the wall thickness.

Claim 7

A thickness measuring device as claimed in claims 3 to 5, characterised in that the frequency of the sinusoidal current generator can be varied as a function of the thickness of the material to be examined.

Claim 8

A thickness measuring device as claimed in claim 1, characterised by being cooled, and protected from the flames and fumes which accompany the material.

Claim 9

A thickness measuring device as claimed in claim 1, characterised in that the magnetic core or the coil can be of any shape, such as C shape, E shape, Erotation shape, 9 shape or I shape.

Claim 10

A thickness measuring device as claimed in claim 1, characterised by comprising more than one winding, which are separate or in the form of an autotransformer.

Claim 11

A thickness measuring device as claimed in claim 9, characterised in that the sensor is constituted by an exciter coil and two secondary measurement coils constituting two branches of a Wheatstone bridge.

Claim 12

A thickness measuring device as claimed in claims 1 and 10, characterised in that the two measurement coils are obtained from the exciter coil by means of an autotransformer tap.

Claim 13

A thickness measuring device as claimed in-claims 1 and 10, characterised in that the core is of 4 shape, and the exciter coil is mounted on the central branch and the two bridge coils are mounted on the adjacent vertical branches of the

Claim 14

A thickness measuring device as claimed in claim 1, characterised in that the thickness signal is obtained from the modulus and/or from the real part and/or from the imaginary part of the voltage across the coil, while this latter is fed by a current- controlled generator.

Claim 15

A thickness measuring device as claimed in claim 1, characterised by being able to make measurements in short time periods of down to 1 ms.

Claim 16

A thickness measuring device as claimed in claims 1 to 14, able to determine the distance between the measuring device itself and the wall of the material subjected to measurement.

Claim 17

A measuring device as claimed in claim 15, characterised in that the signal dependent on the sensor-wall distance is obtained by the use of one or more different higher frequencies (either simultaneous or not simultaneous with the first).

Claim 18

A measuring device as claimed in claim 15, characterised in that the sensor-wall distance is deduced, together with the thickness value, from two of the three components (modulus, real part and imaginary part) of the inductance.

Claim 19

A measuring device as claimed in claim 1, characterised in that the sensor-wall distance is measured independently by a further sensor (capacitive, optical, microwave, eddy current, for example).

Claim 20

A measuring device as claimed in claims 1 to:18, characterised by being used for measuring the thickness of tubes of ferrous material above the Curie temperature, the tube being either at rest or moving relative to the sensor.

Claim 21

A measuring device as claimed in claim 19, characterised in that by locating one or more sensors in motion or at rest around the tube it is possible to determine the eccentricity of said tube.

Claim 22

A measuring device as claimed in claim 20, characterised in that the tube eccentricity measurement is made by opposing sensors fed by the same sinusoidal generator, and using means for measuring the variations in the impedance differences between the two coils of the opposing sensors.

Claim 23

A measuring device as claimed in claims 1 to 18, characterised by being used for measuring the thickness of ferrous plate above the Curie temperature, the plate being either at rest or moving relative to the sensor.

Claim 24

A measuring device as claimed in claim 22, characterised in that one or more sensors facing a ferrous plate above the Curie temperature are able to determine the transverse profile and/or the planarity of said plate.

Claim 25

A measuring device as claimed in claims 1 to 18, characterised by being used for measuring the diameter of ferrous rod above the Curie temperature, the rod being either at rest or moving relative to the sensor,

Claim 26

A thickness measuring device as claimed in claims 1 to 24, characterised in that said ferrous material above the Curie temperature is of dia and/or paramagnetic type.

Claim 27

A thickness measuring device characterised in that the sensor is the inductive part of an oscillating circuit whose self frequency variation is measured to deduce wall thickness.

Claim 28

A thickness measuring device characterised in that the sensor is the inductive part of an oscillating circuit whose self frequency variation is measured to deduce wall thickness.