Device and method for the in-situ calibration of a thermometer

Abstract

The present disclosure relates to a device for determining and/or monitoring temperature of a liquid, comprising a temperature sensor, a reference element for in-situ calibration and/or validation of a temperature sensor and an electronics unit, wherein the reference element is composed at least partially of a material, in the case of which at least one phase transformation occurs at at least a first predetermined phase transformation temperature in a temperature range relevant for calibrating the temperature sensor, in which phase transformation the material remains in the solid phase. According to the present disclosure, the electronics unit is embodied to supply the reference element with a dynamic excitation signal. Furthermore, the present disclosure relates to a method for calibration and/or validation of a temperature sensor based on a device of the invention.

Claims

1. An apparatus for determining and/or monitoring a temperature of a liquid, comprising: a temperature sensor; a reference element for in-situ calibration and/or validation of the temperature sensor; and an electronics unit, wherein the reference element is composed at least partially of a material in which a phase transformation occurs at a first predetermined phase transformation temperature in a temperature range relevant for calibrating the temperature sensor, wherein the material is ferroelectric material, and the phase transformation includes a change in a permittivity of the ferroelectric material; or the material is a ferromagnetic material, and the phase transformation includes a change in a magnetic permeability of the ferromagnetic material; or the material is a superconducting material, and the phase transformation includes a change in a conductivity of the material, wherein in the phase transformation the material remains in the solid phase, and wherein the electronics unit is embodied to: supply the reference element and the temperature sensor with a dynamic excitation signal that is a time-varying alternating electrical current or a time-varying alternating voltage; receive a dynamic signal from the temperature sensor and determine the temperature of the liquid therefrom; receive a dynamic signal from the reference element and detect the phase transformation in the reference element therefrom by detecting the change in the permittivity of the ferroelectric material or the change in the magnetic permeability of the ferromagnetic material or the change in the conductivity of the superconducting material; and when the phase transformation is detected, compare the phase transformation temperature with the determined temperature and perform a calibration of the temperature sensor based on the comparison of the phase transformation temperature and the determined temperature.

2. The apparatus as claimed in claim 1, wherein the excitation signal and/or a received signal received from the reference element is, in each case, a sinusoidal, rectangular, triangular, sawtooth-shaped, or pulse-shaped electrical current or voltage signal.

3. The apparatus as claimed in claim 1, wherein the electronics unit is embodied to vary the frequency and/or the amplitude of the excitation signal.

4. The apparatus as claimed in claim 1, wherein the material is the ferroelectric material, and wherein the reference element is a capacitor element having a dielectric composed at least partially of the material in which the phase transformation occurs.

5. The apparatus as claimed in claim 1, the material is the ferromagnetic material, and wherein the reference element includes a coil arrangement having at least one coil and a magnetically conductive body, wherein the magnetically conductive body is composed at least partially of the material in which the phase transformation occurs.

6. The apparatus as claimed in claim 1, wherein the electronics unit is further embodied to ascertain an impedance, or a variable dependent on the impedance, of at least one component of the reference element, and to detect the phase transformation based on the impedance, or the variable dependent on the impedance, based on a line or a curve of the impedance, or the variable dependent on the impedance, as a function of time and/or temperature.

7. The apparatus as claimed in claim 1, the material is the ferroelectric material or the ferromagnetic material, and wherein the electronics unit is further embodied to ascertain a capacitance, an inductance, or a variable dependent on the capacitance and/or the inductance, of at least one component of the reference element, and to detect the phase transformation based on the capacitance, the inductance or the variable dependent on the capacitance and/or the inductance, based on a line or a curve of the capacitance, the inductance or the variable dependent on the capacitance and/or the inductance, as a function of time and/or temperature.

8. The apparatus as claimed in claim 1, wherein the electronics unit includes a bridge circuit, including a Wien bridge or a Wien-Maxwell bridge, and the reference element is a component of the bridge circuit.

9. The apparatus as claimed in claim 1, wherein the electronics unit includes an electrical oscillatory circuit, and the reference element is a component of the oscillatory circuit.

10. The apparatus as claimed in claim 9, wherein the electronics unit is further embodied to detect the phase transformation based on a change of a resonant frequency of the oscillatory circuit.

11. The apparatus as claimed in claim 1, further comprising: a means for applying an electrical field or a magnetic field, wherein the electronics unit is further embodied to measure over time an output voltage of the electronics unit and to plot the measured output voltage as a function of the dynamic excitation signal to form a hysteresis diagram, and wherein the electronics unit is further embodied to detect the phase transformation based on the hysteresis diagram.

12. A method for in-situ calibration and/or validation of an apparatus for determining and/or monitoring a temperature of a liquid, comprising: providing the apparatus for determining and/or monitoring the temperature of the liquid, including: a temperature sensor; a reference element for the in-situ calibration and/or validation of the temperature sensor; and an electronics unit, wherein the reference element is composed at least partially of a material in which a phase transformation occurs at a first predetermined phase transformation temperature in a temperature range relevant for calibrating the temperature sensor, wherein the material is ferroelectric material, and the phase transformation includes a change in a permittivity of the ferroelectric material; or the material is a ferromagnetic material, and the phase transformation includes a change in a magnetic permeability of the ferromagnetic material; or the material is a superconducting material, and the phase transformation includes a change in a conductivity of the material, wherein in the phase transformation the material remains in the solid phase, and wherein the electronics unit is embodied to: supply the reference element and the temperature sensor with a dynamic excitation signal that is a time-varying alternating electrical current or a time-varying alternating voltage; receive a dynamic signal from the temperature sensor and determine the temperature of the liquid therefrom; receive a dynamic signal from the reference element and detect the phase transformation in the reference element therefrom by detecting the change in the permittivity of the ferroelectric material or the change in the magnetic permeability of the ferromagnetic material or the change in the conductivity of the superconducting material; and when the phase transformation is detected, compare the phase transformation temperature with the determined temperature and perform a calibration of the temperature sensor based on the comparison of the phase transformation temperature and the determined temperature; supplying the reference element and the temperature sensor with the dynamic excitation signal; receiving the dynamic signal from the temperature sensor and determining the temperature of the liquid therefrom; receiving the dynamic signal from the reference element and detecting the phase transformation in the reference element therefrom by detecting the change in the permittivity of the ferroelectric material or the change in the magnetic permeability of the ferromagnetic material or the change in the conductivity of the superconducting material; and when the phase transformation is detected, comparing the phase transformation temperature with the determined temperature and performing the calibration of the temperature sensor based on the comparison of the phase transformation temperature and the determined temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in greater detail based on the appended drawing. Equal elements of the device are provided with equal reference characters. The figures of the drawing show as follows:

(2) FIG. 1 shows a schematic representation of a thermometer having a temperature sensor and a reference element for in-situ calibration and/or validation of a temperature sensor according to the state of the art,

(3) FIG. 2 shows a schematic representation of a calibration and/or validation of a temperature sensor based on the reference element,

(4) FIG. 3 shows a second embodiment of a device of the present disclosure with two temperature sensors and a reference element according to the present disclosure,

(5) FIG. 4 shows a schematic representation of an embodiment of the reference element as (a) a capacitor element and (b) as a coil arrangement

(6) FIG. 5 shows a schematic representation of an electronics unit with a bridge circuit for a reference element (a) in the form of a capacitor element and (b) in the form of a coil arrangement,

(7) FIG. 6 shows a schematic representation of an electronics unit in the form of an oscillatory circuit for a reference element (a) in the form of a capacitor element and (b) in the form of a coil arrangement, and

(8) FIG. 7 shows a schematic representation of an electronics unit, which is suitable for detecting a phase transformation based on a hysteresis diagram, for a reference element (a) in the form of a capacitor element and (b) in the form of a coil arrangement.

DETAILED DESCRIPTION

(9) FIG. 1 is a schematic view of a thermometer 1 with a protective tube 2 and an electronics unit 4 according to the state of the art, which thermometer is suitable an in-situ calibration and/or validation. The portion of the protective tube 2 facing the liquid 5 is also referred to as the sensor head 3. The internal volume of the sensor head 3 is filled with a filler 6, especially an electrically insulating filler 6, especially a cement. Furthermore, arranged in the interior of the sensor head 3 are a temperature sensor 7 and a reference element 8, each of which is contacted, especially electrically contacted, by means of at least two connection wires, 9,10 and connected with the electronics unit 4. Temperature sensor 7 is, for example, a resistance element or a thermocouple. Reference element 8 is, in turn, composed at least partially of a material, in the case of which at least one phase transformation at least of second order occurs at at least one predetermined phase transformation temperature within the temperature range relevant for operation of the device. The number of needed connection wires 9,10 for contacting the reference element and the temperature sensor 7,8 can vary, depending on type of applied measuring principle. In the illustrated embodiment, the temperature sensor 7 and the reference element 8 are arranged mutually spaced within the same sensor head 3. They can, however, likewise directly contact one another and, for example, be soldered together.

(10) Calibration and/or validation of the temperature sensor 7 by means of the reference element 8 is illustrated in FIG. 2. The upper graph represents the curve of a characteristic physical or chemical variable G used for detecting the phase transformation. If a phase transformation occurs in the reference element 8, then there occurs in the illustrated example an abrupt change of the variable G.

(11) The point in time, at which the abrupt change of the variable is detected, is the phase transformation point in time t.sub.ph, at which the reference element 8 has the phase transformation temperature T.sub.ph.

(12) In the lower graph, the sensor temperature T is ascertained by means of the temperature sensor 7 as a function of time t. For calibration and/or validation of a temperature sensor 7 based on the reference element 8, for example, that measurement point in time t.sub.m is ascertained, which has the shortest time separation from the phase transformation point in time t.sub.ph. The sensor temperature T.sub.m corresponding to the measurement point in time t.sub.m is compared with the phase transformation temperature T.sub.ph. Using the comparison, then a calibration and/or validation can be performed. Moreover, in the case of a difference ΔT=T.sub.m(t.sub.m)−T.sub.ph(t.sub.ph) above a predeterminable limit value, the thermometer 1 can be adjusted and/or a report concerning the occurrence of a difference generated and/or output.

(13) Three possible embodiments for the reference element 8 are shown in FIG. 3 by way of example. Suited in the case of a ferroelectric material, for example, is an embodiment of the reference element 8 in the form of a capacitor element, as shown in FIG. 3a. The material 11, in which the phase transformation occurs, forms the dielectric in this case. The reference element 8 includes, furthermore, two electrodes 12a and 12b, which in the example shown here is arranged directly on two oppositely lying, lateral surfaces of the material 11, which is embodied as an essentially cuboidal body and electrically contacted by means of the two connection lines 10a and 10b, in order, for example, to detect the capacitance C.sub.ref of the reference element 8 and based on an especially abrupt change of the capacitance C.sub.ref to detect the phase transformation. For other details of this embodiment of the reference element 8 in the form of a capacitor element, reference is made to disclosure document DE102010040039A1.

(14) In the case of a reference element 8 comprising a ferromagnetic material 15, beneficial is an embodiment in the form of a coil arrangement, such as shown, by way of example, in FIGS. 3b and 3c. An opportunity for detecting a phase transformation in the case of such an embodiment of the reference element 8 lies in detecting a change of the inductance L.sub.ref of the arrangement. Upon a phase transformation from the ferromagnetic to the paramagnetic state, the magnetic resistance of the material 15, in which the phase transformation occurs, changes, and, thus, for example, also the inductance L.sub.ref of the arrangement.

(15) In the embodiment of FIG. 3b, the reference element 8 includes a coil 13 with core 14, and a magnetically conductive body 15, which is composed of the ferromagnetic material. The magnetically conductive body 15 is arranged in such a manner that it is located at least partially in a magnetic field B emanating from the coil 13 with the core 14. The magnetic field is indicated by the sketched field lines. Upon a phase transformation in the magnetically conductive body 15, the magnetic field B changes, which is detectable, for example, based on a change of the inductance L of the arrangement.

(16) The use of a core 14 for the coil 13 is, however, optional. A possible embodiment of the reference element 8 as a coil arrangement without core is correspondingly shown in FIG. 3c. Sketched in this Fig. is, furthermore, by way of example, on the one hand, the magnetic field B.sub.1, which reigns, when the material 15 is located in the ferromagnetic state. Moreover, shown in dashed lines is the magnetic field B.sub.2, which reigns, when the material 15 is located in the paramagnetic state.

(17) In the case of supply of electrical power to the reference element 8 with a dynamic excitation signal U.sub.E,dyn, especially an excitation signal dynamic with respect to time, different characteristic parameters of the reference element 8 can be taken into consideration for registering the at least one phase transformation, especially such, which would not be available in the case of a static excitation signal.

(18) Upon a phase transformation in a reference element 8 embodied as a capacitor element as shown in FIG. 3a, for example, the permittivity of the material changes, which, in this case, is present as a dielectric. Suited as characteristic parameter is correspondingly, for example, the capacitance C.sub.ref. Upon a phase transformation in a reference element 8 embodied as a coil arrangement, as shown in FIG. 3b or FIG. 3c, in contrast, the permeability of the material, here the magnetically conductive body 15, changes. In this case, in turn, the inductance L.sub.ref is a suitable characteristic parameter. In the case of considering the capacitance C.sub.ref or inductance L.sub.ref, the permittivity, and permeability, are directly linked with corresponding imaginary parts. These imaginary parts can, in turn, in the case of supply of electrical power to the reference element by means of a dynamic excitation signal, be directly registered.

(19) Besides the capacitance C.sub.ref or inductance L.sub.ref, other characteristic parameters, which in the case of supply of electrical power to the reference element 8 can preferably be registered for detecting the occurrence of a phase transformation, are, for example, the impedance Z or the loss angle δ, such as illustrated in FIG. 4. Although the invention is in no way limited to the mentioned characteristic parameters for detecting a phase transformation, the following description for purposes of simplification concerns the mentioned variables—the inductance L, the capacitance C, the impedance Z as well as the loss angle δ.

(20) For detection of the phase transformation based on the impedance Z or based on the loss angle δ, the reference element 8 can be embodied, for example, corresponding to one of those shown in FIG. 3. FIG. 4a represents the magnitude of the impedance, thus of the alternating current resistance, schematically as a function of temperature. At the phase transformation temperature T.sub.ph, the impedance is minimum, so that, for example, based on the line or curve of the magnitude of the impedance as a function of time the occurrence of a phase transformation in the reference element 8 can be detected. The loss angle δ, which is the ratio of resistive power to reactive power, is, in contrast, maximum at the phase transformation temperature T.sub.ph, as shown schematically in FIG. 4b. Also based on the line or curve as a function of time for the loss angle δ, thus the occurrence of a phase transformation can be detected.

(21) If the impedance Z and/or the loss angle δ are, moreover, measured with at least two different excitation signals U.sub.E,dyn,1 and U.sub.E,dyn,2 having at least two different frequencies f.sub.1 and f.sub.2, and the ratio of the impedances Z(f.sub.1)/Z(f.sub.2) or loss angles δ(f.sub.1)/δ(f.sub.2) formed, the phase transformation can likewise be registered based on either of these ratios. These ratios are advantageously independent of particular absolute values of particular excitation signals U.sub.E,dyn,1 and U.sub.E,dyn,2.

(22) Some especially preferred embodiments of an electronics unit 4 of the invention, which can be used for registering various characteristic parameters, such as the capacitance C, the inductance L, the impedance Z or the loss angle δ, will now be presented in the following figures.

(23) In the embodiment in FIG. 5, the electronics unit 4 includes a bridge circuit with four impedances Z.sub.1-Z.sub.3 and Z.sub.ref. The reference element 8 forms at least one component of the bridge circuit, especially the impedance Z.sub.ref, and at least one of the impedances Z.sub.1-Z.sub.3 includes at least one electronic component of electrically adjustable size. Depending on embodiment of the reference element 8, the individual impedances Z.sub.1-Z.sub.3 and Z.sub.ref can each be a resistance R, a capacitance C, an inductance L or an arrangement of at least two of the elements R,C,L connected at least partially in series and/or at least partially in parallel.

(24) In the case of embodiment of the reference element 8 in the form of a capacitor element, such is suited, for example, for implementing a so-called Wien bridge. In the case of a reference element 8 embodied as a coil arrangement, the electronics unit 4 comprises, in contrast, preferably a so-called Wien-Maxwell bridge circuit. The measuring principles underpinning these two measuring circuits are known per se in the state of the art, because of which these are not explained here in detailed.

(25) The electronics unit 4, especially the bridge circuit, is excited by means of the dynamic excitation signal U.sub.E,dyn. The phase transformation dependent impedance Z of the bridge circuit can then be ascertained based on the diagonal voltage U.sub.det. If the bridge circuit is located in the balanced state, then the diagonal voltage U.sub.det is zero, which leads for the particular bridge circuit to a formula, from which, using the known impedances Z.sub.1-Z.sub.3, the unknown impedance Z.sub.ref can be calculated. If the impedance Z.sub.ref changes, for example, as a result of a phase transformation in the reference element 8, then the bridge circuit is unbalanced and the diagonal voltage U.sub.det is not zero. For detection a change of the phase transformation dependent impedance Z.sub.ref, one can, for example, rebalance the bridge or instead use a non-zero U.sub.det. Both methods are known per se in the state of the art.

(26) In the rebalancing method, at least one component of at least one of the known impedances Z.sub.1-Z.sub.3 is changed, until a balance is achieved anew and the unknown impedance Z.sub.ref can be calculated by means of the formula for the balanced condition. Advantageously in the case of such method, only a detection of the zero voltage state of the diagonal voltage U.sub.det is necessary. However, the adjustment of the impedances Z.sub.1-Z.sub.3 and Z.sub.ref is comparatively complicated. By utilizing a non-zero U.sub.det, in contrast, no balancing of the bridge circuit occurs. Instead, the unknown impedance Z.sub.ref is ascertained from the measured diagonal voltage U.sub.det. In this case, however, a more exact voltage measurement is required.

(27) In contrast with bridge circuits for static signals, especially signals static with respect to time, thus, for example, direct voltage measurement bridges, there occurs in the case of alternating voltage bridge circuits advantageously no negative influencing of a particular measurement signal by thermovoltages occurring within the measurement circuit. A further advantage of a bridge circuit for application with a dynamic excitation signal, especially a signal dynamic with respect to time, is that likewise a resistance can be determined by means of a corresponding circuit, besides a parameter characteristic for the reference element 8. In the case, in which the temperature sensor 7 is embodied in the form of a resistance element, thus by means of the same bridge circuit the temperature of a particular liquid 5 can be determined. Such an embodiment is distinguished advantageously by an especially compact construction.

(28) Another opportunity (not illustrated based on a FIG.) for determining the loss angle δ is, for example, to supply the reference element 8 by means of a dynamic excitation electrical current signal, thus by means of an alternating current, and to detect across a suitably selected measuring resistance a received voltage signal, especially an alternating voltage, phase shifted relative to the excitation electrical current signal. Alternatively, it is also possible to use an excitation signal in the form of an alternating voltage and to tap a phase shifted, received signal in the form of an alternating current.

(29) In the case of this embodiment, it is possible, furthermore, based on the amplitude ratio of the instantaneous values of electrical current and voltage to ascertain the impedance Z=U(t)/I(t). Alternatively to the previously described embodiments, the reference element 8 can, for example, embodied in the form of a capacitor element or in the form of a coil arrangement of FIG. 3, be provided in an electrical oscillatory circuit within the electronics unit 4, such as illustrated in FIG. 6. Available as characteristic parameter for detecting the phase transformation, in this case, is preferably a time constant for the reference element 8 or a resonant frequency f.sub.0 of the oscillatory circuit.

(30) For the case of a reference element 8 formed as a capacitor element with capacitance C.sub.ref, as shown in FIG. 6a, for example, an RC oscillatory circuit with the resistance R.sub.1 is implementable, which is suitably selected as a function of the reference element 8. In the case of an embodiment of the reference element 8 as a coil arrangement with the inductance L.sub.ref, as shown in FIG. 6b, in contrast, suited is, for example, an RCL oscillatory circuit with the resistance R.sub.1 and the capacitance C.sub.1, both of which are selected as a function of the reference element 8. Besides the two shown variants, there are, however, still numerous other embodiments for oscillatory circuits, which likewise fall within the scope of the present invention.

(31) The occurrence of a phase transformation changes the resonant frequency f.sub.0 of the oscillatory circuit, so that a change of the resonant frequency f.sub.0 of the oscillatory circuit basically can be taken into consideration for detecting the phase transformation at the phase transformation temperature T.sub.ph.

(32) For ascertaining a time constant, one can, in contrast, for example, proceed in the following way: used as excitation signal is preferably a rectangular signal. In the case of a reference element 8 formed as a capacitor element, then, for example, the time for charging the capacitor element to a predeterminable voltage threshold value is measured. In the case of a reference element 8 embodied as a coil arrangement, in contrast, for example, the time, until an electrical current through the coil sinks below a predeterminable electrical current threshold value, or the time, until a voltage across the coil sinks below a predeterminable voltage threshold value, can be ascertained. The measured time, in each case, is a measure for the capacitance C.sub.ref, or the inductance L.sub.ref, of the reference element 8.

(33) Another opportunity is to determine a phase shift between the excitation signal and the received signal, based on which phase shift, for example, likewise the capacitance C.sub.ref or the inductance L.sub.ref of the reference element 8 can be determined. Finally, it is likewise possible to perform an amplitude modulated measurement in the case of a fixed resistance R.sub.1. The amplitude change of the received signal is, in such case, likewise a measure for the capacitance C.sub.ref, or the inductance L.sub.ref.

(34) In the case, in which the at least one phase transformation is, in contrast, detected based on a hysteresis diagram, finally, for example, a measurement circuit corresponding to one of the embodiments of FIG. 7 can be used. As in the case of the preceding figures, the reference element 8 is part of an electrical measurement circuit within the electronics unit 4.

(35) For registering a hysteresis diagram, the change of the polarization of a particular material, in which the phase transformation occurs, is registered by applying a time dynamic voltage U.sub.E,dyn. The particular hysteresis diagram results from plotting voltage U.sub.1 as a function of U.sub.E,dyn. The occurrence of a phase transformation can be detected, for example, based on a change of the ratio of the voltages U.sub.E,dyn and U.sub.1.

(36) For the embodiment of FIG. 7a, the reference element 8 is a capacitor element with the capacitance C.sub.ref, such as, for example, in FIG. 3a. Correspondingly, a phase transformation is from the ferroelectric into the paraelectric state or vice versa. Such a measurement circuit is a so-called Sawyer-Tower circuit, which is per se well known from the state of the art and therefore is not described in detail here.

(37) An electrical circuit for detecting a phase transformation in the case of a reference element 8 in the form of a coil arrangement with the inductance L.sub.ref, such as, for example, in one of the figures, FIG. 3b or FIG. 3c, each of which includes ferromagnetic material, is, in contrast, shown in FIG. 7b. The capacitance C.sub.1, as well as the resistances R.sub.1 and R.sub.2 are, in each case, matched to the applied reference element 8.