WO2022242973A1

WO2022242973A1 - In situ temperature calibration

Info

Publication number: WO2022242973A1
Application number: PCT/EP2022/060384
Authority: WO
Inventors: Dietmar FRÜHAUF; Raphael KUHNEN; Florian Krogmann; Pavo Vrdoljak
Original assignee: Endress+Hauser Wetzer Gmbh+Co. Kg
Priority date: 2021-05-20
Filing date: 2022-04-20
Publication date: 2022-11-24
Also published as: DE102021113198A1

Abstract

The invention relates to an arrangement (1) for in situ calibration and/or validation of a sensor arrangement (3) for determining and/or monitoring the temperature (T) of a medium (M) in a container (2), in particular of a thermometer with at least one temperature sensor (4a), comprising at least one ferromagnetic reference element (5) which has a phase transition between a paramagnetic state and a ferromagnetic state at a given phase transition temperature (T_ph), a magnetic field device (6) for generating a magnetic field (B), and a detection device (7), with the magnetic field device (6) being designed to generate the magnetic field (B) such that it permeates at least the reference element (5), a part of the medium (M) and the detection device (7), with the reference element (5) being arranged and/or designed such that the reference element (5) influences the magnetic field (B) depending on the temperature (T) of the medium (M), and with the detection device (7) being designed to detect the magnetic field (B) and to detect the occurrence of a phase transition in the at least one reference element (5) on the basis of at least one variable that is related to the magnetic field (B).

Description

In situ temperature calibration

The invention relates to an arrangement for in situ calibration and/or validation of a sensor arrangement with regard to the temperature of a medium in a container, in particular a thermometer with at least one temperature sensor.

Calibrations and/or validations related to temperature are mainly performed using calibration baths, ovens or fixed point devices, cf. B. the fixed point cell described in DE102004027072B3. The disadvantage of such methods is that the respective temperature sensor or thermometer must be removed from the process. For example, DE19941731A1 proposed a miniaturized fixed-point cell that is integrated into the thermometer and filled with a fixed-point substance for calibrating a thermometer in the installed state. However, such a procedure is disadvantageous with regard to the sensor dynamics, in particular the response time, and the robustness, since the fixed point substance can escape from the cell.

To determine the temperature of a medium, it has also become known to use specific, characteristic temperature points or characteristic curves. DE19702140A1 discloses a device and a method for measuring the temperature of a rotating carrier part with a temperature sensor which has a ferromagnetic or paramagnetic material which shows a temperature-dependent change in its polarization in the relevant temperature range. The document DE19805184A1 describes the determination of the temperature of a piezoelectric element based on its capacitance. Patent specification DE69130843T2 relates to a method and a device for determining the temperature of a piezoelectric crystal oscillator.

In principle, such characteristic temperature points or curves are also suitable for the calibration and/or validation of thermometers. For example, EP1247268B2 describes a method for in situ calibration of a number of integrated temperature sensors using characteristic curves of one or more reference elements in the form of secondary temperature sensors, which reference elements are built into a thermometer insert in addition to a primary temperature sensor. So that a calibration can take place, the reference elements used in each case differ from the primary temperature sensor in terms of structure and/or the material used in each case, which results in different characteristic curves. The disadvantage here, however, is that the characteristic curves of the reference elements are usually also subject to aging effects and/or sensor drift. To avoid such disadvantages, DE102010040039A1 has disclosed a device and a method for in situ calibration of a thermometer with a temperature sensor and a reference element for calibrating the temperature sensor, in which the reference element consists at least partially of a ferroelectric material which is relevant to the calibration of the temperature sensor Temperature range undergoes a phase transformation at least at a predetermined temperature. The calibration is therefore performed based on the characteristic temperature point of a phase transition of a ferroelectric material, ie based on a material-specific property. Depending on the number of installed reference elements, a so-called 1-point as well as a multi-point calibration and/or validation can be carried out in this way. Other devices and procedures using material -specific properties of reference materials, in particular from ferroelectric, ferromagnetic and/or superconductive materials for calibration or validation regarding the temperature have also become known from DE102015112425A1, DE102016123856A1, DE102017100263A1 or DE10201710026A1 or DEE

Proceeding from the prior art, the present invention is based on the object of specifying an alternative option for in situ calibration and/or validation of a temperature sensor.

This object is solved by an arrangement according to claim 1. Advantageous developments are specified in the dependent claims.

The arrangement according to the invention is an arrangement for in situ calibration and/or validation of a sensor arrangement for determining and/or monitoring the temperature of a medium in a container, in particular a thermometer with at least one temperature sensor, comprising at least one ferromagnetic reference element, which a phase transition between a paramagnetic and a ferromagnetic state at a predeterminable phase transition temperature, a magnetic field device for generating a magnetic field, and a detection device.

According to the invention, the magnetic field device is designed to generate the magnetic field in such a way that it penetrates at least the reference element, part of the medium and the detection device. The magnetic field device is thus designed to to generate a magnetic field in the region of the reference element, at least part of the medium and the detection device.

The reference element is arranged and/or designed in such a way that the reference element influences the magnetic field as a function of the temperature of the medium. The reference element is preferably arranged in such a way that it is in, in particular thermal, contact with the medium directly or indirectly, for example by means of a wall of the container. In this regard, arrangements with a single or multiple reference elements are possible. In this case, different reference elements can in particular be designed in such a way that they have different phase transition temperatures.

The reference element can be fastened in particular to an inner wall of the container, for example a container or a pipeline. Both a detachable and a non-detachable, in particular cohesive, attachment can be considered, which attachment can be produced in particular using suitable attachment means. However, the reference element can also be introduced into the interior volume of the container without being attached to a wall. In this case the reference element floats in the medium. An integration of the reference element in the wall of the container, in particular such that the reference element is flush with the inner wall of the container, or attachment to an outer wall of the container is conceivable. The arrangement according to the invention is advantageously designed for in situ calibration and/or validation of a sensor arrangement for determining and/or monitoring the temperature, in particular a thermometer with at least one temperature sensor. The temperature sensor can be arranged together with or separately from the reference element, or the reference element can be part of the thermometer with the temperature sensor. A temperature sensor (primary sensor) is therefore calibrated and/or validated using a secondary sensor (reference element).

At a predeterminable phase transition temperature, ferromagnetic materials exhibit a phase transition from a paramagnetic state to a ferromagnetic state. The ferromagnetic state is characterized by a tendency for the magnetic moments of the atoms of the material to be aligned in parallel. The ferromagnetic material advantageously remains in the solid phase when a phase transition occurs. A material which remains in the solid state is particularly advantageous with regard to structural aspects of the arrangement. The phase transition from the paramagnetic to the ferromagnetic state is a phase transition in which the ferromagnetic material remains in the solid phase, ie, for example, a second-order phase transition according to the Ehrenfest classification. Advantageously, with such a phase transition, no or only a negligible amount of latent heat is released during the phase transition, so that a falsification of the respectively performed calibration and/or validation with regard to latent heat that occurs can be minimized. According to the invention, the detection device is designed to detect the magnetic field and to detect the occurrence of a phase transition in the at least one reference element using at least one variable related to the magnetic field. For this purpose, the arrangement, in particular the detection device, can also have a computing unit which is designed to use the variable related to the magnetic field to detect the occurrence of a phase transition and to calibrate and/or validate the temperature sensor.

The phase transition involves a discontinuity in the second derivative of a thermodynamic quantity such as pressure, volume, enthalpy, or entropy as a function of, for example, temperature. Typically, phase transitions are accompanied by a change in a certain specific material property, for example a change in the crystal structure, or a change in the magnetic, electrical or dielectric properties, in particular the permeability or permittivity. Corresponding material-specific parameters are known for the respective reference element and can be used for a calibration and/or validation of a temperature sensor.

With regard to the quantity related to the magnetic field, when a phase transition occurs, i.e. when passing through the

Phase transition temperature, to a characteristic change, based on which the occurrence of the phase transition can be detected. The temperature of the medium measured essentially at the same time can then be compared with the material-specific phase transition temperature and the temperature sensor can be calibrated and/or validated on the basis of the comparison.

In one embodiment, the quantity related to the magnetic field was magnetic flux density, magnetic susceptibility, or magnetic permeability. In one configuration, the magnetic field device comprises at least one coil and/or one permanent magnet. In addition, a coil core, in particular made of a material with high permeability, can also be present. On the one hand, it is possible to apply a magnetic field that is essentially constant over time. However, it is also possible to modulate the magnetic field, in particular with regard to a frequency and/or amplitude. Such a modulation is particularly advantageous for reducing the influence of interference signals.

It is also advantageous if the detection device is arranged outside of the container. The detection device can on the one hand be attached to an outer wall of the container or arranged at a distance from it. In particular, however, the detection device can also be part of a separate unit which can be brought into the vicinity of the container in each case in order to detect the process variable and/or characteristic variable of the medium. The magnetic field device can also be arranged outside of the container, in particular together with the detection device.

One configuration of the sensor device includes the ferromagnetic material being arranged in a housing. For example, it can be a medium-tight encapsulation, in particular made of a non-magnetic material, z. B. stainless steel act. In this way, for example, compatibility with the respective medium can be achieved. Such an embodiment is also advantageous in the case of a sensor device floating in the medium. In addition to the reference element, the temperature sensor for detecting the temperature of the medium of the sensor arrangement can also be arranged in the housing.

In one configuration of the arrangement, the detection device comprises a magnetic field sensor. The magnetic field sensor is used to detect the magnetic field outside the container, which is influenced by the reference element inside the container depending on the temperature of the medium, or to detect the variable related to the magnetic field.

In one configuration, the magnetic field sensor is a Hall sensor or a GMR sensor.

In an alternative embodiment, the magnetic field sensor is a quantum sensor. Quantum sensors, in which a wide variety of quantum effects are used to determine various physical and/or chemical measured variables, relate to various recent developments in the field of sensor technology. In the context of industrial process automation, such approaches are particularly important with regard to increasing efforts towards miniaturization simultaneous increase in the performance, in particular the measuring accuracy, of the respective sensors.

Quantum sensors are based on the fact that certain quantum states of individual atoms can be very precisely controlled and read out. In this way, for example, precise and low-interference measurements of electric and/or magnetic fields and gravitational fields with resolutions in the nanometer range are possible. In this context, various spin-based sensor arrangements have become known, for which atomic transitions in crystal bodies are used to detect changes in movements, electric and/or magnetic fields or gravitational fields. In addition, various systems based on quantum-optical effects have also become known, such as quantum gravimeters, NMR gyroscopes or optically pumped magnetometers, the latter in particular being based on gas cells, among other things.

An embodiment of the magnetic field sensor in the form of a quantum sensor thus includes the magnetic field sensor being a gas cell. With a quantum sensor in the form of a gas cell, atomic transitions and spin states are optically detected, for example to determine magnetic and/or electrical properties. A gas cell typically includes a gaseous alkali metal and a buffer gas. Magnetic properties of a medium surrounding the gas cell can be determined using Rydberg states generated in the gas cell.

Gas cells are often used in quantum-based standards that determine physical variables with high precision, for example in frequency standards or atomic clocks, as is known from EP 0 550 240 B1. In addition, US Pat. No. 10,184,796 B2 describes a chip-sized atomic gyroscope in which a gas cell is used to determine the magnetic field. An optically pumped magnetometer based on a gas cell is known from US Pat. No. 9,329,152 B2. By manipulating the atomic states in gas cells, further fields of application of gas cells can be opened up. For example, JP 4066804 A2 describes the use of gas cells to determine absolute path lengths. In addition, gas cells are also used as the starting point for microwave sources, as described in EP 1 224 709 B1.

An alternative embodiment of the magnetic field sensor in the form of a quantum sensor means that the magnetic field sensor is a sensor comprising at least one crystal body with at least one defect. In such spin-based quantum sensors, atomic transitions in different crystal bodies are used to detect even small changes in movements, electric and/or magnetic fields or gravitational fields. Typically, diamond with at least one silicon or nitrogen defect, silicon carbide with at least one silicon defect or hexagonal boron nitride with at least one defect color center is used as the crystal body. In principle, the crystal bodies can have one or more defects. In the case of several defects, a linear arrangement of the defects is preferred.

In this context, DE 3742878 A1, for example, discloses an optical magnetic field sensor in which a crystal is used as a magnetically sensitive optical component. DE 10 2017205 099 A1 discloses a sensor device with a crystal body having at least one defect, a light source, a high-frequency device for applying a high-frequency signal to the crystal body, and a detection unit for detecting a magnetic-field-dependent fluorescence signal. Further sensors using defects in crystal bodies are described in DE 102017 205 265 A1, DE 10 2014 219 550 A1, DE 10 2018 214 617 A1, or DE 102016 210 259 A1.

From the previously unpublished German patent application with the file number 10 2020 123 993.9, a sensor device has also become known which uses a fluorescence signal from a crystal body with at least one defect to determine a process variable of a medium and which also uses a variable that is characteristic of the magnetic field to monitor the status of the respective medium process is carried out. A limit level sensor is also known from the previously unpublished German patent application with the file number 10 2021 100223.0, in which a statement about a limit level is determined on the basis of the fluorescence.

With regard to the detection device with a quantum sensor with a crystal body with at least one defect, it is advantageous if the detection device also has an excitation unit for optically exciting the defect, a device for detecting a magnetic field-dependent fluorescence signal from the crystal body and a

Evaluation unit for determining the variable related to the magnetic field based on the fluorescence signal.

The excitation unit for the optical excitation of the defect can be, for example, a laser or a light-emitting diode (LED). The detector, in turn, can be a photodetector or a CMOS sensor, for example. In addition, the detection unit can have additional optical elements, such as various filters, lenses or mirrors. The excitation unit and the detector can be arranged on the one hand in the area of the crystal body, or three-dimensionally be separated from the crystal body. In the second case, optical fibers can be present for conducting the excitation light and fluorescence signal.

In addition, the detection device can have a unit for exciting high-frequency or microwave radiation. This allows electrons to be excited to higher energy levels.

Various variants are also conceivable with regard to the evaluation unit for determining the variable related to the magnetic field using the fluorescence signal. For example, the evaluation unit can include a lock-in amplifier.

In one configuration, the arrangement comprises a magnetic field device and at least two detection devices, with the magnetic field device being arranged and/or designed in such a way that at least a first and a second partial magnetic field are formed, with the reference element being arranged in the region of the first partial magnetic field, and wherein a first detection device is arranged in the area of the first partial magnetic field and a second detection device is arranged in the area of the second partial magnetic field. No reference element is arranged in the area of the second partial magnetic field. For example, an air gap can be present in this area.

The first partial magnetic field penetrates the first detection unit, at least part of the medium and the reference element, while the second partial magnetic field penetrates the second detection unit, at least part of the medium and possibly the air gap. The first and second partial magnetic fields preferably only overlap in an area which surrounds the magnetic field device, but not in areas in which the detection units or the reference element or, if applicable, the air gap are arranged. It is also advantageous if a specifiable reference temperature is selected, with a dimension, in particular a diameter, of the air gap being selected in such a way that, at the specifiable reference temperature, the variables recorded for the first and second partial magnetic field are related to the respective partial magnetic field essentially have the same value, i.e. have the same effect. The definable reference temperature is preferably greater than the phase transition temperature.

It is also advantageous if, to determine the process variable and/or characteristic of the medium, the second partial magnetic field is subtracted from the first magnetic field or the variable related to the second magnetic field is subtracted from the variable related to the first magnetic field, or when the based on the first and second partial magnetic field respectively determined values for the quantities related to the respective magnetic field are subtracted from each other. For this purpose, for example, the computing unit of the arrangement or also the evaluation unit of the detection device can be suitably designed. In this way, the calibration and/or validation is advantageously carried out using a differential measurement principle, by means of which advantageously possible interferences or also parasitic interference effects of the arrangement can be compensated, eliminated or minimized.

In this context, it is also advantageous if the magnetic field device comprises a coil and a coil core, in particular a coil core designed in the form of an M or egg geometry, with a first part of the coil core in the region of the first partial magnetic field and a second part of the coil core is arranged in the area of the second partial magnetic field. By using a core, the partial magnetic fields can be separated from one another in a particularly simple manner.

The first and second parts of the coil core are preferably designed in the same way.

Alternatively, the use of two identically designed coil cores, in particular arranged next to one another, with a single coil is also conceivable.

One configuration of the arrangement includes the magnetic field device being configured to modulate the magnetic field strength, in particular at low frequency, with a definable modulation frequency. A low-frequency magnetic field is advantageous in particular in connection with metallic containers, through which a frequency-dependent damping of the magnetic field takes place. Basically, the modulation of the magnetic field allows an evaluation of the fluorescence signal based on the frequency and, associated therewith, an evaluation that can be implemented in a simple manner, in particular with a reduced influence of interference signals.

In this regard, it is advantageous if a magnetic field strength that is constant over time is superimposed on the modulated magnetic field strength. For example, the magnetic field device for generating the modulated magnetic field strength can have a coil, with a time-constant magnetic field strength being generated by means of a permanent magnet. However, the magnetic field device can also exclusively have one or more coils. A suitable offset can be added to the modulated, magnetic field strength by means of the magnetic field strength, which is constant over time.

With regard to the modulation of the magnetic field, it is also advantageous if the variable related to the magnetic field is the amount of the magnetic field or the magnetic flux density, with the detection device being designed for this purpose is to detect the occurrence of the phase transition based on the presence of at least one harmonic in the magnitude of the magnetic field or in the magnetic flux density as a function of frequency. This procedure advantageously allows detection in the frequency domain and, associated therewith, detection of the occurrence of a phase transition in a particularly simple and precise manner.

Finally, a further configuration of the arrangement includes the arrangement, in particular the processing unit, being configured to determine how a wall of the container influences the magnetic field, in particular based on the thickness of the wall and/or based on the material from which the container is made and to take into account the influence of the wall of the container during calibration and/or validation. In this way, influences of different materials and different thicknesses of different containers on the magnetic field, which lead in particular to a container-dependent damping of the magnetic field, can be taken into account, which also leads to increased accuracy.

The object on which the invention is based is also achieved by an arrangement for determining and/or monitoring the temperature, comprising a sensor arrangement with at least one temperature sensor, for example in the form of a resistance element or thermocouple, and an arrangement according to at least one of the configurations described above. The device is preferably a thermometer. The temperature sensor and the reference element can be arranged together, for example in a common housing or on a common carrier, or separately from one another.

In summary, the present invention allows a sensor arrangement for determining and/or monitoring the temperature to be calibrated and/or validated in a simple manner. In particular, no openings or windows are required within the container for the installation of a reference element. The invention is based on the finding that a magnetic field, which is influenced by the temperature by means of a ferromagnetic reference element, can be detected from outside the container, ie through the wall of the container. The invention accordingly provides a high-performance, simple and robust arrangement which is particularly advantageously also low-maintenance. With the arrangement according to the invention, the intervention in the process required for installing the same can advantageously be minimized, since only the reference element has to be introduced into an inner volume of the container. In addition, use of the arrangement in an explosive atmosphere is also readily possible. The invention and its advantageous configurations are explained in more detail below. It shows:

1: an arrangement according to the invention with a reference element fastened to the container wall;

2 shows an arrangement according to the invention with a separately arranged detection device and magnetic field device;

3 shows an arrangement according to the invention with a magnetic field device with a coil with a core and a permanent magnet;

4: an arrangement according to the invention for generating two partial magnetic fields;

Fig. 5: a simplified energy scheme for a negatively charged NV center in diamond;

6 shows a schematic arrangement of a detection device for a quantum sensor with a crystal body with at least one defect; and

7: two schematic diagrams to explain the detection of the phase transition in the case of a modulated magnetic field.

In the figures, the same elements are provided with the same reference symbols.

1 schematically shows a first embodiment of an arrangement 1 according to the invention for calibrating and/or validating a sensor arrangement 3 for determining and/or monitoring a temperature T of a medium M in a container 2, which is designed here in the form of a container. The sensor arrangement 3 includes a temperature sensor 4a for detecting the temperature T, which protrudes into an inner volume V of the container 2 medium M, and can be a resistance element or a thermocouple, for example. Here, the sensor arrangement 3 also includes electronics 4b for determining the temperature T using a temperature signal detected by the temperature sensor 4a. The arrangement 1 is used for in situ calibration and/or validation of the sensor arrangement 3 or the temperature sensor 4a. The arrangement 1 comprises a reference element 5 made of a ferromagnetic material, which is fastened to the wall W within the inner volume V of the container 2 . At a predeterminable phase transition temperature _Tph , the reference element 4 has a phase transition between a paramagnetic and a ferromagnetic state, which is used for calibration and/or validation of the temperature sensor 4a or the sensor arrangement 3 can be used.

The sensor arrangement 1 also includes a magnetic field device 6 for generating a magnetic field B at least in part of the medium M and in the region of

Detection device 7. The magnetic field B thus penetrates the detection device 7 and the medium. The magnetic field B is also influenced by the reference element 5, so that based on the detected or detected by the detection device 7 magnetic field B, or based on a detected or detected with the magnetic field B-related variable, the occurrence of a phase transition in the

Reference element 5 can be detected. The detection device 7 and the magnetic field device 6 are arranged outside of the container 2 . Furthermore, the sensor arrangement 3 is separated from the arrangement 1 for the embodiment shown here. In other configurations, however, a joint arrangement of both components 1 and 3 can also be provided.

A further configuration for a sensor arrangement 1 according to the invention is shown in FIG. In contrast to the embodiment from Fig. 1, the detection device 7 and the magnetic field device 6 are arranged together in a separate unit E and can each be brought into the immediate vicinity of the reference element 5 if a calibration and/or validation of the temperature sensor 4a of the Sensor array 3 is required. For this configuration, the reference element 5 is assigned to the sensor arrangement 3 and is arranged together with the temperature sensor 4a.

It should be pointed out that in addition to the exemplary configurations shown here for an arrangement according to the invention or an arrangement and a sensor arrangement for determining and/or detecting the temperature T, numerous other configurations are conceivable, all of which also fall under the present invention.

The arrangement 1, in particular the detection device 7, can advantageously also be designed to determine an influence of the wall W of the container on the detected magnetic field B, in particular based on a thickness of the wall and/or based on the material from which the container 2 is made. to be determined and taken into account during calibration and/or validation. For this purpose, for example, suitable reference curves or calculation specifications for different materials of the containers 2 and/or wall thicknesses can be stored, for example in a calculation unit that is not shown here. 3 shows a further preferred embodiment for an arrangement 1 according to the invention. The magnetic field device 6 includes here, for example, a permanent magnet 8 and a coil 9 with a core 9a, which consists of two L-shaped elements. In a gap between the two elements of the core 9a, the detection device 7 is arranged, which has a magnetic field sensor 10 and a

Arithmetic unit 11 includes. The magnetic field sensor 10 can be a Hall sensor, a GMR sensor or a quantum sensor, for example. A variable related to the magnetic field B can be detected by means of the arithmetic unit 11 and the occurrence of a phase transition can be detected on the basis of this variable.

Such a configuration of the magnetic field device 6 is suitable, among other things, for generating a modulated magnetic field B. In this case, for example, the coil 9 can be used to generate a modulated magnetic field strength, while the permanent magnet 8 can be used to generate a magnetic field strength that is constant over time.

A further preferred embodiment is the subject of FIG. 4. The arrangement comprises a magnetic field device 6 with a coil 9 [not shown separately] and a core 9a, as well as two detection devices 7a and 7b. The core 9a of the coil 9 has an El geometry such that the arrangement of the coil 9 relative to the core 9a forms two partial magnetic fields B1 and B2. The reference element 5 and the first detection device 7a are arranged in the area of the first partial magnetic field B1 and are not penetrated by the second partial magnetic field B2. The second partial magnetic field B2 serves as a reference magnetic field and penetrates the second detection device 7b, which in turn is not penetrated by the first partial magnetic field B1. There is an air gap 12 at a position equivalent to the position of the reference element 5 within the area penetrated by the second partial magnetic field B2. In this way, to detect the phase transition, the variable related to the second partial magnetic field B2 by the second detection device 7b and first detection device 7a detected variable related to the first partial magnetic field B1 or the two partial magnetic fields are subtracted from each other. In this way, interference can be minimized or compensated for. Particularly advantageous configurations of the present sensor arrangement relate to detection devices 7 in which magnetic field sensors 8 in the form of a quantum sensor 13 are used. These are characterized by great compactness with very high performance and precision. The use of magnetic field sensors 10 in the form of quantum sensors 13 is an example below Example of a quantum sensor 13 in the form of a sensor 14 comprising at least one crystal body 15 with at least one defect explained.

To this end, a simplified energy scheme for a negatively charged NV center in diamond is shown in FIG. In this way, the excitation of the defect and the detection of the fluorescence can be explained as an example. The following considerations apply equally to other crystal bodies with corresponding defects. In diamond, each carbon atom is typically covalently bonded to four other carbon atoms. A nitrogen vacancy center (NV center) consists of a defect in the diamond lattice, i.e. an unoccupied lattice site, and a nitrogen atom as one of the four neighboring atoms. In particular, the negatively charged NV centers are important for the excitation and evaluation of fluorescence signals. In the energy scheme of a negatively charged NV center, in addition to a triplet ground state ³ A, there is an excited triplet state ³ E, each of which has three magnetic substates m _s =0,±1. Furthermore, there are two metastable singlet states ¹ A and ¹ E between the ground state ³ A and the excited state ³ E. Excitation light LA from the green region of the visible spectrum, ie excitation light LA with a wavelength of 532 nm, finds a Excitation of an electron from the ground state ³ A to a vibrational state of the excited state ³ E takes place, which returns to the ground state ³ A by emitting a fluorescence photon LF with a wavelength of 630 nm. An applied magnetic field with a magnetic field strength B leads to a splitting (Zeeman splitting) of the magnetic sub-states, so that the ground state consists of three energetically separated sub-states, each of which can be excited. However, the intensity of the fluorescence signal LF depends on the respective magnetic substate from which the excitation took place, so that the distance between the fluorescence minima can be used, for example, to calculate the magnetic field strength B using the Zeeman formula.

However, other options for evaluating the fluorescence signal are also possible, such as evaluating the intensity of the fluorescent light, or an electrical evaluation, for example via photocurrent detection of magnetic resonance (PDMR), which also fall within the scope of the present invention.

An exemplary detection device 7 for use with such a quantum sensor 10 in the form of a sensor 14 with a crystal body 15 with a Finally, the defect is shown in FIG. The detection device 7 has an excitation unit 16 for generating the excitation light LA, and a device 17 for detecting the magnetic field-dependent fluorescence signal LF from the crystal body 15. In addition, the detection device 7 has an evaluation unit 18 for determining the variable related to the magnetic field B based on the fluorescence signal LF.

For the embodiment shown in FIG. 6, there is also a unit 22 for exciting high-frequency or microwave radiation. In addition to a lock-in amplifier 19, the evaluation unit 18 also includes a control/processing unit 20 and a modulator 21 for modulating the magnetic field B.

Finally, a schematic representation for the detection of a phase transition in the case of a modulated magnetic field B is given in FIG. In FIG. 7a, the magnetic flux density B is a function of the magnetic field strength H for two different reference elements 5a and 5b with the two

Phase transition temperatures Ta _Ph and Tb _Ph shown. The magnetic field strength H is made up of a magnetic field strength H _mod modulated over time with the modulation frequency Wi and a magnetic field strength H _offset that is constant over time. The time-constant magnetic field strength H _0ffset is selected in such a way that an interval for the magnetic field strength H _m0d used for the modulation lies in a non-linear range of the characteristic curve B(H).

The phase transition can then be detected in a simple and precise manner in the frequency domain, as illustrated with reference to FIG. 7b. In the schematic

Diagram of the absolute value of the magnetic field strength | detected by means of the detection device 7 B | As a function of the frequency f, a harmonic O _a and O _b occurs in the frequency domain when a phase transition is passed in the respective reference element 5a or 5b. The occurrence of a phase transition can therefore be detected based on the presence of a harmonic O _a or O _b . Reference List

1 arrangement

2 container

3 sensor arrangement

4 temperature sensor (4a) and electronics (4b)

5 (5a, 5b) reference element(s)

6 magnetic field device

7 (a,b) detection device(s)

8 permanent magnet

9 coil, 9a core

10 magnetic field sensor

11 unit of account

12 air gap

13 quantum sensor

14 Sensor comprising a crystal with a defect

15 crystal bodies

16 excitation unit

17 Device for detecting the fluorescence signal

18 evaluation unit

19 lock in amplifier

20 control/processing unit

21 modulator

22 Unit for generating high-frequency or microwave radiation M Medium

W wall

B magnetic field, B1, B2 partial magnetic fields, magnetic flux density

V internal volume

E unit

LA excitation light

LF fluorescent light

Tph phase transition temperature

H magnetic field strength

O harmonics f _mod modulation frequency

H _mod modulated magnetic field strength

H _offset temporally constant, superimposed magnetic field strength

Claims

patent claims

1 . Arrangement (1) for in situ calibration and/or validation of a sensor arrangement (3) for determining and/or monitoring the temperature (T) of a medium (M) in a container (2), in particular a thermometer with at least one temperature sensor (4a) , comprising at least one ferromagnetic reference element (5) which has a phase transition between a paramagnetic and a ferromagnetic state at a predeterminable phase transition temperature (Tp _h ), a magnetic field device (6) for generating a magnetic field (B), and a detection device (7 ), wherein the magnetic field device (6) is designed to generate the magnetic field (B) in such a way that it penetrates at least the reference element (5), part of the medium (M) and the detection device (7), the reference element (5) is arranged and/or designed in such a way that the reference element (5) influences the magnetic field (B) as a function of the temperature (T) of the medium (M), and di e detection device (7) is designed to detect the magnetic field (B) and to detect the occurrence of a phase transition in the at least one reference element (5) using at least one variable related to the magnetic field (B).

2. Arrangement (1) according to claim 1, wherein the variable related to the magnetic field (B) is the magnetic flux density, the magnetic susceptibility or the magnetic permeability.

3. Arrangement (1) according to claim 1 or 2, wherein the magnetic field device (6) comprises at least one coil (9) and/or a permanent magnet (8).

4. Arrangement (1) according to at least one of the preceding claims, wherein the detection device (7) is arranged outside of the container (2).

5. Arrangement (1) according to at least one of the preceding claims, wherein the detection device (7) comprises a magnetic field sensor (10).

6. Arrangement (1) according to claim 6, wherein the magnetic field sensor (10) is a Hall sensor or a GMR sensor.

7. Arrangement (1) according to claim 6, wherein the magnetic field sensor (10) is a quantum sensor (13).

8. Arrangement (1) according to claim 7, wherein the magnetic field sensor (10) is a gas cell.

9. Arrangement (1) according to claim 7, wherein the magnetic field sensor (10) is a sensor (14) comprising at least one crystal body (15) with at least one defect.

10. Arrangement (1) according to claim 9, wherein the detection device (7) also has an excitation unit (16) for optical excitation of the defect, a device (17) for detecting a magnetic field-dependent fluorescence signal (I_F) from the crystal body (15), and a Evaluation unit (18) for determining the characteristic of the magnetic field (B) variable based on the fluorescence signal (I_F).

11. Arrangement (1) according to at least one of the preceding claims, comprising a magnetic field device (6) and at least two detection devices (7a, 7b), wherein the magnetic field device (6) is arranged and/or designed in such a way that at least form a first (B1) and a second partial magnetic field (B2), with the reference element (5) being arranged in the area of the first partial magnetic field (B1), and with a first detection unit (7a) in the area of the first partial magnetic field (B1) and a second Detection unit (7b) is arranged in the region of the second partial magnetic field (B2).

12. Arrangement (1) according to claim 11, wherein the magnetic field device (6) comprises a coil (9) and a coil core (9a), in particular a coil core configured in the form of an M or El geometry (9a), wherein a first part of the coil core (9a) in the area of the first

Partial magnetic field (B1) and a second part of the coil core (9b) is arranged in the region of the second partial magnetic field (B2).

13. Arrangement (1) according to at least one of the preceding claims, wherein the magnetic field device (6) is designed to modulate the magnetic field strength, in particular at low frequency, with a predeterminable modulation frequency (W.

14. Arrangement (1) according to claim 13, wherein the quantity related to the magnetic field (B) is the magnitude of the magnetic flux density (B) as a function of the modulation frequency (W), and wherein the detection device (7) is designed to detect the occurrence of the phase transition based on the presence of at least one harmonic (O _a , O _b ) in the magnetic flux density (B) as a function of the modulation frequency (W.