CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims the priority benefit of German Patent Application No. 10 2017 100 264.2, filed on Jan. 9, 2017 and International Patent Application No. PCT/EP2017/081686 filed on Dec. 6, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a device for determining and/or monitoring temperature of a liquid, comprising a temperature sensor and a reference element. Furthermore, the present invention relates to a method for in-situ calibration and/or validation of a device of the invention.

BACKGROUND

The calibration of thermometers is currently usually performed in calibration baths, ovens or fixed point systems. A corresponding fixed point cell is described, for example, in DE102004027072B3. However, in the case of these methods, usually the thermometer must be deinstalled from the measuring point. In order, in contrast, to be able to calibrate a thermometer in the installed state, DE19941731A1 discloses a miniaturized fixed point cell provided in a thermometer. The fixed point cell is filled with a fixed point substance, e.g. a metal or a eutectic alloy. In this case, however, an additional cell is required for encapsulating the fixed point substance, which lessens the dynamic range of the sensor, especially deteriorates response time to a temperature change. Moreover, it could happen, in given cases, that the fixed point substance could escape from the cell, which could lead to damage or even destruction of the thermometer.

It would thus be desirable to be able to perform a calibration and/or validation of a thermometer in the installed state, thus in-situ, in the case of which the mentioned disadvantages would not occur.

In principle for determining a temperature, the most varied of physical and/or chemical, temperature dependent, material properties can be used. In such case, the property can be either a change, especially an abrupt change, of a particular property, occurring at a certain characteristic temperature point or a continuous change of a property in the form of a characteristic line or curve. For example, the Curie temperature of a ferromagnetic material is a characteristic temperature point for the material. In this regard, known from DE 4032092C2 is a method for ascertaining the Curie temperature, in the case of which by means of a differential scanning thermal analyzer an abrupt change of the absorbed amount of heat is detected in the region of the Curie temperature. In DE19702140A1, in turn, described are a device and a method for measuring the temperature of a rotating support part with a temperature sensor, which has a ferro- or paramagnetic material, which exhibits a temperature dependent change of its polarization in the temperature range of interest. Thus, a characteristic line or curve of temperature dependent polarization is taken into considering for determining temperature.

A further example known from DE19805184A1 describes the ascertaining of temperature of a piezoelectric element based on its capacitance. Similarly, DE69130843T2 concerns a method and a device for determining temperature of a piezoelectric crystal oscillator.

The use of certain characteristic temperature points or characteristic line or curves is suited basically also for calibrating and/or validating thermometers.

Thus, in EP1247268B2, for example, a method for in-situ calibration of a plurality of integrated temperature sensors based on characteristic lines or curves of one or more reference elements in the form of secondary temperature sensors is described. The reference elements are installed in a thermometer insert supplementally to a primary temperature sensor. In order that a calibration can occur, the utilized reference elements differ from the primary temperature sensor with reference to construction and/or applied material. This results in different characteristic lines or curves. Disadvantageous in such case, however, is that the characteristic lines or curves of the reference elements are usually subject to aging effects and/or sensor drift.

For preventing such disadvantages, known from DE102010040039A1 are a device and a method for in-situ calibration of a thermometer having a temperature sensor and a reference element for calibrating the temperature sensor, in the case of which the reference element is composed at least partially of a ferroelectric material, which experiences a phase transformation at at least one predetermined temperature in the temperature range relevant for calibrating the temperature sensor. The calibration is thus performed based on the characteristic temperature point of a phase transformation of a ferroelectric material, thus based on a material-specific property. Depending on number of installed reference elements, in this way, both a so-called 1-point- as well as also a multipoint-calibration and/or validation can be performed. A similar device, especially suitable for multipoint calibrations, is, furthermore, known from this applicant's German patent application No. 102015112425.4, filed Jul. 29, 2016, and unpublished at the date of first filing of this application. The thermometer described there includes at least one temperature sensor and at least two reference elements contacted via exactly two connection wires. The reference elements are composed at least partially of two different materials, each of which has in the temperature range relevant for calibrating the temperature sensor at least one phase transformation at least of second order at, in each case, a predetermined phase transformation temperature. DE 102010040039A1 (U.S. Pat. No. 9,091,601) as well as DE 102015112425.4 (US 2018217010) are incorporated here by reference.

SUMMARY

Starting from the state of the art, an object of the present invention is to provide an alternative for in-situ calibration and/or validation of a temperature sensor.

The object is achieved by a device for determining and/or monitoring temperature of a liquid as defined in claim1as well as by a method for in-situ calibration and/or validation of a device of the invention as defined in claim14.

As regards the device of the invention, the object is achieved by 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. 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 the phase transformation, the material remains in the solid phase. According to the invention, the electronics unit is embodied to supply the reference element with a dynamic excitation signal.

The thermometer of the invention is advantageously embodied for in-situ calibration and/or validation of at least a first temperature sensor. For this, the temperature sensor (primary sensor) is calibrated and/or validated using a secondary sensor (reference element).

Upon a phase transformation in a material, which remains in the solid phase, involved, for example, according to the Ehrenfest classification, is a phase transformation at least of second order. In contrast with a phase transformation of first order, no or only a negligible amount of latent heat is released during the phase transformation. When no or only a negligible amount of latent heat is released, it can—basically and independently of the selected classification for phase transformations—, among other things, be advantageously assured that the temperature measured by means of the temperature sensor at the point in time of the occurrence of a phase transformation, is not corrupted, especially not by released, latent heat.

In an additional classification of phase transformations significantly more usual in the present state of the art, it is distinguished only between discontinuous (first order) and continuous (second order) phase transformations [compare e.g. Lexikon der Physik, Spektrum Akademischer Verlag, Heidelberg, Berlin, Vol. 4, under the entry “Phasenübergänge and andere kritische Phänomene” (Phase Transformations and Other Critical Phenomena)]. According to this classification, various ferroelectric materials can be associated with both phase transformations of first as well as also second order, wherein in both cases the particular material, for which a phase transformation occurs, remains in the solid phase during the phase transformation.

The remaining in the solid phase is important for the present invention independently of the selected classification of a phase transformation. A material remaining in the solid state is especially advantageous with reference to structural aspects of the system, especially the monitoring unit.

A phase transformation includes a discontinuity in the second derivative of a thermodynamic variable, such as, for example, the pressure, the volume, the enthalpy, or the entropy as a function, for example, of temperature. Typically, phase transformations involve the change of a certain specific material property, for example, alternation in the crystal structure, or alternation in the magnetic, electrical or dielectric properties. Corresponding material-specific parameters are known for the particular reference element and can be taken into consideration for a calibration and/or validation of a temperature sensor. In such case, the at least one reference element can have one or more phase transformations, especially phase transformations in the solid phase of the utilized material. Each phase transformation occurs at a certain characteristic, fixed and long term stable, temperature value, so that, in principle, no drift and/or no aging effects need to be taken into consideration for the reference element.

Since the reference element is supplied with a dynamic excitation signal, especially an excitation signal dynamic with respect to time, other characteristic parameters can be taken into consideration for detecting the occurrence of the at least one phase transformation, characteristic parameters which are not available in the case of a static excitation signal.

During the phase transformation, depending on embodiment of the reference element, typically changing, for example, is the permittivity, or the magnetic permeability, of the material, in which the phase transformation occurs. These characteristic parameters can, depending on embodiment of the reference element, be registered by means of various measuring principles, for example, based on capacitance or inductance. In the case of considering the capacitance or inductance, the permittivity, or permeability, results from real- and imaginary parts. The 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. The supply of electrical power to the reference element by means of a dynamic excitation signal permits, thus, advantageously, the direct registering of phase transformation dependent, characteristic parameters.

The electronics unit is, furthermore, preferably embodied, based on a received signal received from the reference element, to detect the occurrence of the at least one phase transformation. Using a comparison of the phase transformation temperature with a temperature of the liquid measured essentially at the same time by means of the temperature sensor, then a calibration and/or validation of a temperature sensor can be performed. Especially, the received signal is likewise a dynamic received signal, especially a received signal dynamic with respect to time.

In an embodiment, 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 signal, especially an electrical current- or voltage signal. It is, thus, for example, an alternating electrical current or an alternating voltage.

In an advantageous embodiment of the device of the invention, the at least one material, of which the reference element is composed at least partially, is a ferroelectric material, a ferromagnetic material or a superconducting material, especially a high temperature superconductor. Correspondingly, the at least one phase transformation is a phase transformation from the ferroelectric into the paraelectric state or vice versa, from the ferromagnetic state into the paramagnetic state or vice versa, or from the superconducting state into the normally conducting state or vice versa. The phase transformation temperature is correspondingly, for example, the Curie temperature of a particular material or the so-called critical temperature.

Another embodiment provides that the electronics unit is constructed to vary the frequency and/or the amplitude of the excitation signal. The electronics unit is thus suitable especially for performing an impedance-spectroscopy and/or for performing a frequency-sweep, in the case of which especially a predeterminable frequency range is systematically moved through with discrete frequencies for the excitation signal. If one considers, for example, polarization, or a variable dependent or derived from polarization, as characteristic parameter for detecting the phase transformation of a particular material, of which the reference element is at least partially composed, the polarization can have different causes. For example, it can be an electronic, a molecular, a dipolar or also an ionic polarization. Since a suitable frequency is selected for the excitation signal, individual mechanisms underpinning the polarization can be selected with targeting. The occurrence of a phase transformation is thus detectable based frequency dependently on a polarization.

For the reference element of the invention, many different embodiments are possible, which all fall within the scope of the present invention. The two options for embodiment of the reference element to be described here are, thus, by way of example, and to be seen, in fact and form, in no way as an exclusive listing.

In a first preferred embodiment, the reference element is a capacitor element having a dielectric, wherein the dielectric is composed at least partially of the material, in the case of which of the at least one phase transformation occurs. For this embodiment, it is correspondingly expedient to detect the occurrence of the at least one phase transformation based on a capacitance or on a variable dependent on the capacitance.

An alternative preferred embodiment includes that the reference element is a coil arrangement having at least one coil and a magnetically conductive body, wherein the body is composed at least partially of the material, in the case of which of the at least one phase transformation occurs. In the case of this embodiment, it is, in turn, expedient to detect the at least one phase transformation based on an inductance or a variable dependent on the inductance.

The choice of the special embodiment of the reference element depends, on the one hand, on the particular embodiment of the thermometer. Furthermore, the embodiment of the reference element depends also on the characteristic parameter referenced for detecting the phase transformation, or the suitable characteristic variable depends on the particular embodiment of the reference element.

In the case of a dynamic excitation signal, especially an excitation signal dynamic with respect to time, and depending on embodiment of the reference element and the particular thermometer, especially the electronics unit, which, for example, includes an, especially electronic, measurement circuit suitable for registering a particular variable, suitable characteristic parameters include, for example, the capacitance, the inductance, the impedance or also the loss angle.

Thus, in an especially preferred embodiment, it is provided that the electronics unit is 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 occurrence of the phase transformation based on the impedance, or the variable dependent on the impedance, especially based on the line or curve of impedance or the variable dependent on the impedance as a function of time and/or temperature.

Another especially preferred embodiment includes that the electronics unit is embodied to ascertain a loss angle, or a variable dependent on the loss angle, of at least one component of the reference element, and to detect the occurrence of the phase transformation based on the loss angle or the variable dependent on the loss angle, especially based on the line or curve of the loss angle, or the variable dependent on the loss angle, as a function of time and/or temperature.

Still another especially preferred embodiment includes that the electronics unit is embodied to ascertain a capacitance, an inductance, or a variable dependent on the capacitance and/or inductance, of at least one component of the reference element, and to detect the occurrence of the phase transformation based on the capacitance, the inductance or the variable dependent on the capacitance and/or inductance, especially based on the line or curve of the capacitance, the inductance, or the variable dependent on the capacitance and/or inductance, as a function of time and/or temperature.

Also for the utilized measuring circuits, or the electronics unit, the most varied of embodiments are available, by means of which the different characteristic parameters can be registered. A series of especially preferred examples of embodiments is presented below. Of course, these are in no way to be considered an exclusive listing. Rather, many other suitable measuring principles in the state of the art are available, which likewise fall within the scope of the present invention.

In an embodiment, the electronics unit includes a bridge circuit, especially a Wien bridge or a Wien-Maxwell bridge, wherein the reference element is a component of the bridge circuit. The measuring principles underpinning such a bridge circuit are known per se from the state of the art and are, consequently, not explained here in further detail. Advantageously, a bridge circuit is suited also for registering the temperature of a particular liquid, when the temperature sensor is embodied, for example, in the form of a resistance element. In contrast with bridge circuits for application with static excitation signals, especially excitation signals static with respect to time, in the case of bridge circuits for dynamic signals, especially signals dynamic with respect to time, such as, for example, alternation signals, no thermovoltages arising within such a bridge circuit corrupt the measurement result, or received signal. In the case, in which both the phase transformation is detected, as well as also the temperature of the liquid ascertained, by means of the bridge circuit, such is a constructively especially simple embodiment of the present invention. A bridge circuit can especially preferably be applied for determining the phase transformation dependent impedance.

In another embodiment, the electronics unit includes an electrical oscillation circuit, wherein the reference element is a component of the oscillatory circuit. The oscillatory circuit can be, for example, an RL-, RC, or RCL oscillatory circuit. Also by means of an oscillatory circuit, temperature can basically be ascertained, for example, based on a temperature sensor embodied as a resistance element. In the case of an oscillatory circuit, suitable, for example, for detecting the phase transformation is the registering of a time constant, based on which for a reference element embodied as a capacitor element, or as a coil arrangement, for example, the capacitance or inductance is determinable.

For this embodiment, it is, furthermore, advantageous that the electronics unit be embodied to detect the occurrence of the at least one phase transformation based on a change of a resonant frequency of the oscillatory circuit. The characteristic parameter for these embodiments is thus the resonant frequency of the oscillatory circuit, which experiences a change, especially a jump-like change, upon the occurrence of the at least one phase transformation.

Finally the device includes in an embodiment means for applying a field, especially an electrical, or magnetic, field, wherein the electronics unit is embodied to detect the occurrence of the at least one phase transformation based on at least one hysteresis diagram.

Independently of the particular embodiment of the reference element, the particular embodiment of the electronics unit and the, in each case, characteristic variable referenced for detecting the phase transformation, it is, finally, advantageous that the electronics unit be embodied to supply the temperature sensor with a dynamic excitation signal. Such an embodiment is distinguished advantageously by an especially simple construction. Depending on concrete embodiment, both the reference element as well as also the temperature sensor can be operated and read-out simultaneously by means of an electronic arrangement.

The object of the invention is, furthermore, achieved by a method for in-situ calibration and/or validation of a device of the invention, wherein a reference element is supplied with a dynamic excitation signal.

The embodiments explained in connection with the device can also be applied mutatis mutandis for the proposed method.

