Method and apparatus for electromagnetically measuring parameters of electrically conductive high temperature materials

Claim 1

An apparatus for electromagnetic quantity measurement of at least one of the resistivity, temperature, dimension and spatial location of an electrically conductive material at high temperature, comprising: a transmitter coil for generating an electromagnetic alternating field in the electrically conductive material, an a.c. source for supplying the transmitter coil with alternating current at a frequency such that the electromagnetic alternating field penetrates to a depth δ in the electrically conductive material; a receiver coil located a distance D from the electrically conductive material wherein the ratio (δ/D) lies between 0.1 and 3, for detecting secondary electromagnetic alternating fields dependent upon the measured parameter and generated by induced currents in the electrically conductive material; and signal processing means connected to the receiver coil for detecting and processing alternating voltage signals induced therein by said secondary electromagnetic alternating field and for distinguishing changes in the measured parameter from changes in other parameters, said signal processing means including means for selectively detecting the magnitude of alternating voltage signal components induced in the receiver coil which are phase-shifted relative to the alternating current supplied to the transmitter coil, said selective detecting means including a synchronous demodulator coupled to the receiver coil and to the a.c. source via a phase shifting circuit for substantially eliminating the effects of ambient surroundings on the electromagnetic field generated by the transmitter coil.

Claim 2

An apparatus for electromagnetic quantity measurement of at least one of the resistivity, temperature, dimension and spatial location of an electrically conductive material at high temperature, comprising: a transmitter coil for generating an electromagnetic alternating field in the electrically conductive material, an a.c. source for supplying the transmitter coil with alternating current at a frequency such that the electromagnetic alternating field penetrates to a depth δ in the electrically conductive material; a receiver coil located a distance D from the electrically conductive material wherein the ratio (δ/D) lies between 0.1 and 3, for detecting secondary electromagnetic alternating fields dependent upon the measured parameter and generated by induced currents in the electrically conductive material; and signal processing means connected to the receiver coil for detecting and processing alternating voltage signals induced therein by said secondary electromagnetic alternating field and for distinguishing changes in the measured parameter from changes in other parameters, said signal processing means including means for selectively detecting the magnitude of alternating voltage signal components induced in the receiver coil which are phase-shifted relative to the alternating current supplied to the transmitter coil, said selective detecting means including a synchronous demodulator coupled to the receiver coil and to the a.c. source via a phase shifting circuit for substantially eliminating the effects of ambient surroundings on the electromagnetic field generated by the transmitter coil.

Claim 10

A method of measuring a parameter of a metal that is at least near its molten state, comprising the steps of: generating a primary alternating electromagnetic field at a frequency such that the field penetrates into the metal a depth δ, to thereby induce electrical currents in the metal; and detecting the magnitude of a component of a secondary alternating electromagnetic field which is generated by the induced electrical currents and which is dependent upon the measured parameter of the metal, said detected component being phase-shifted in relation to the phase of the primary generated electromagnetic field to thereby substantially eliminate the effects on the primary electromagnetic field of disturbing fields which result from the ambient surroundings, said detection taking place at a location spaced a nominal distance D from the electrically conductive material wherein the ratio (δ/D) lies between 0.1 and 3 so that the effect of a change of the measured parameter can be distinguished from changes in other parameters.

Claim 11

A method of measuring a parameter of a metal that is at least near its molten state, comprising the steps of: generating a primary alternating electromagnetic field at a frequency such that the field penetrates into the metal a depth δ, to thereby induce electrical currents in the metal; and detecting the magnitude of a component of a secondary alternating electromagnetic field which is generated by the induced electrical currents and which is dependent upon the measured parameter of the metal, said detected component being phase-shifted in relation to the phase of the primary generated electromagnetic field to thereby substantially eliminate the effects on the primary electromagnetic field of disturbing fields which result from the ambient surroundings, said detection taking place at a location spaced a nominal distance D from the electrically conductive material wherein the ratio (δ/D) lies between 0.1 and 3 so that the effect of a change of the measured parameter can be distinguished from changes in other parameters.

Claim 14

A method as claimed in claims 9, 10 or 11, characterized in that a component of the total electromagnetic alternating field is detected at said location of detection, said component being phase-shifted substantially 90° in relation to the phase of the primary generated electromagnetic alternating field at the place of detection.

Claim 19

A method of measuring at least two independent parameters of a metal that is at least near its molten state, comprising the steps of: generating a primary alternating electromagnetic field at a frequency such that the field penetrates into the metal a depth δ, to thereby induce electrical currents in the metal; detecting the magnitude of a first component of a secondary alternating electromagnetic field which is generated by the induced electrical currents and which is dependent upon one of the parameters to be measured, said detected component having a predetermined phase relationship relative to the primary generated electromagnetic field, said detection taking place at a location spaced a nominal distance D from the electrically conductive material wherein the ratio (δ/D) lies between 0.1 and 3; and detecting a second component of said secondary electromagnetic field, said second component corresponding solely to currents induced in depth in the electrically conductive material, to determine the value of the second parameter to be measured.

Claim 20

A method of measuring at least two independent parameters of a metal that is at least near its molten state, comprising the steps of: generating a primary alternating electromagnetic field at a frequency such that the field penetrates into the metal a depth δ, to thereby induce electrical currents in the metal; detecting the magnitude of a first component of a secondary alternating electromagnetic field which is generated by the induced electrical currents and which is dependent upon one of the parameters to be measured, said detected component having a predetermined phase relationship relative to the primary generated electromagnetic field, said detection taking place at a location spaced a nominal distance D from the electrically conductive material wherein the ratio (δ/D) lies between 0.1 and 3; and detecting a second component of said secondary electromagnetic field, said second component corresponding solely to currents induced in depth in the electrically conductive material, to determine the value of the second parameter to be measured.