A sensor arrangement for determining a process variable of a medium in a containment comprises a sensor apparatus, a magnetic field apparatus, and a detection apparatus. The magnetic field apparat produces a magnetic field that penetrates the sensor apparatus, the detection apparatus and partially the medium. The sensor apparatus is embodied such that a magnetic property of a component of the sensor apparatus depends on the process variable, and the magnetic field of the magnetic field apparatus is influenceable by the sensor apparatus as a function of process variable. The detection apparatus is embodied to register a variable related with the magnetic field, especially the magnetic flux density, the magnetic susceptibility or the magnetic permeability, and, based on that variable, to determine the process variable. The sensor apparatus is arranged within an internal volume of the containment and the detection apparatus is arranged outside of the containment.

A method to predict the catalytic activity of a metal oxide of formula M.sub.xO.sub.y where x is a number from 1 to 3 and y is a number from 1 to 8 is provided. The metal of the metal oxide has redox coupled oxidation states wherein the redox transformation is between oxidation states selected from the group consisting of a diamagnetic oxidation state (M.sup.d+) and a paramagnetic oxidation state (M.sup.p+), a paramagnetic oxidation state (M.sup.p+) and a ferromagnetic oxidation state (M.sup.f+), and a paramagnetic oxidation state (M.sup.p+) and an antiferromagnetic oxidation state (M.sup.a+)where d, p, f and a are independently numbers from 1 to 6 and one of the oxidation states (M.sup.d+), (M.sup.p+), (M.sup.f+), and (M.sup.a+) is formed by reduction by the O.sup.2. The magnetic susceptibility of the metal oxide as a sample in an oxygen environment at a specified temperature is correlated with a value of (M.sup.d+ or M.sup.p+ or M.sup.f+ or M.sup.a+)/g (O.sub.2 rich). Then the magnetic susceptibility of the metal oxide as a sample in an oxygen free environment at the specified temperature is measured and correlated with a value of number of (M.sup.d+ or M.sup.p+ or M.sup.f+ or M.sup.a+)/g (O.sub.2 deficient). The catalytic activity is predicted based on the difference of these two numbers.

A method to predict the catalytic activity of a metal oxide of formula M.sub.xO.sub.y where x is a number from 1 to 3 and y is a number from 1 to 8 is provided. The metal of the metal oxide has redox coupled oxidation states wherein the redox transformation is between oxidation states selected from the group consisting of a diamagnetic oxidation state (M.sup.d+) and a paramagnetic oxidation state (M.sup.p+), a paramagnetic oxidation state (M.sup.p+) and a ferromagnetic oxidation state (M.sup.f+), and a paramagnetic oxidation state (M.sup.p+) and an antiferromagnetic oxidation state (M.sup.a+)where d, p, f and a are independently numbers from 1 to 6 and one of the oxidation states (M.sup.d+), (M.sup.p+), (M.sup.f+), and (M.sup.a+) is formed by reduction by the O.sup.2. The magnetic susceptibility of the metal oxide as a sample in an oxygen environment at a specified temperature is correlated with a value of (M.sup.d+ or M.sup.p+ or M.sup.f+ or M.sup.a+)/g (O.sub.2 rich). Then the magnetic susceptibility of the metal oxide as a sample in an oxygen free environment at the specified temperature is measured and correlated with a value of number of (M.sup.d+ or M.sup.p+ or M.sup.f+ or M.sup.a+)/g (O.sub.2 deficient). The catalytic activity is predicted based on the difference of these two numbers.

A device for detection of magnetic permeability () or, alternatively, relative magnetic permeability (r) or, alternatively relative magnetic susceptibility (r-) of a sample is described. The device comprises a sample chamber having at least one opening for introduction of a sample or a sample container holding a sample and an electronic circuit. The device also comprises a coil surrounding said sample chamber, and also an electronic circuit adapted to measure the inductance of said coil. The sample chamber, coil and at least one component of the electronic circuit are placed in a temperature controlled zone. Said at least one component in said electronic circuit is/are selected from the group consisting of capacitors, sensors, precision voltage references, precision regulators, low pass and or high pass filters.

An implantable susceptometry marker (1001) for use in surgical guidance comprising one or more ferromagnetic elements (1004a, 1004b, 1004c); and at least one diamagnetic element (1003); wherein the one or more ferromagnetic elements are formed of at least one ferromagnetic material having an initial relative permeability of at least about 10,000 and a saturation induction Bs of less than about 1.5 T, and the at least one diamagnetic element is formed of at least one diamagnetic material having a bulk susceptibility of at least about ?0.16?10.sup.?4; and wherein the total volume of diamagnetic material in the marker is about 100-10,000 times greater than the total volume of ferromagnetic material.

An implantable susceptometry marker (1001) for use in surgical guidance comprising one or more ferromagnetic elements (1004a, 1004b, 1004c); and at least one diamagnetic element (1003); wherein the one or more ferromagnetic elements are formed of at least one ferromagnetic material having an initial relative permeability of at least about 10,000 and a saturation induction Bs of less than about 1.5 T, and the at least one diamagnetic element is formed of at least one diamagnetic material having a bulk susceptibility of at least about ?0.16?10.sup.?4; and wherein the total volume of diamagnetic material in the marker is about 100-10,000 times greater than the total volume of ferromagnetic material.

A method to detect a decrease of the demagnetization of permanent magnets of the generator of a wind turbine, wherein a frequency converter is able to adapt to the variable frequency of the generator output voltage to the frequency of a power grid, wherein the AC/DC converter or the DC/AC converter of the frequency converter is been disabled, the electrical connections between the generator and the frequency converter are switched on via circuit breakers, the generator speed is determined; the generator output voltage is determined by a voltage sensor which is part of the frequency converter, the magnetic flux density of the generator is calculated depending on the generator speed and the generator output voltage, a demagnetization event is determined by comparing the resulting flux density value with a predetermined flux density value is provided.

A method to detect a decrease of the demagnetization of permanent magnets of the generator of a wind turbine, wherein a frequency converter is able to adapt to the variable frequency of the generator output voltage to the frequency of a power grid, wherein the AC/DC converter or the DC/AC converter of the frequency converter is been disabled, the electrical connections between the generator and the frequency converter are switched on via circuit breakers, the generator speed is determined; the generator output voltage is determined by a voltage sensor which is part of the frequency converter, the magnetic flux density of the generator is calculated depending on the generator speed and the generator output voltage, a demagnetization event is determined by comparing the resulting flux density value with a predetermined flux density value is provided.

Method and apparatus for measuring an amount of superparamagnetic material in an object, the method including a) applying a magnetic field having a first component alternating with a first period to the object and a magnetic field strength lower than a magnetic field strength at which the superparamagnetic material is driven in saturation; b) measuring a first magnetic susceptibility of the object with a detection coil; c) applying a static second component to the magnetic field for a second period being equal or larger than the first period, the strength of the magnetic field during the second period is such that the superparamagnetic material is driven towards saturation; d) measuring a second magnetic susceptibility of the object with the detection coil during the application of the static second component; and e) determining the amount of superparamagnetic material from a difference between the measured first and second susceptibility of the object.

Method and apparatus for measuring an amount of superparamagnetic material in an object, the method including a) applying a magnetic field having a first component alternating with a first period to the object and a magnetic field strength lower than a magnetic field strength at which the superparamagnetic material is driven in saturation; b) measuring a first magnetic susceptibility of the object with a detection coil; c) applying a static second component to the magnetic field for a second period being equal or larger than the first period, the strength of the magnetic field during the second period is such that the superparamagnetic material is driven towards saturation; d) measuring a second magnetic susceptibility of the object with the detection coil during the application of the static second component; and e) determining the amount of superparamagnetic material from a difference between the measured first and second susceptibility of the object.