DE102011079854A1 - Sensing unit for use in measurement device for detection of e.g. temperature of substance, has conductor element comprising reflectance locations, where partial reflection of signal occurs at locations based on measured variable - Google Patents

Abstract

The unit (1) has a conductor element (2) comprising reflectance locations (A) that are discretely arranged along a longitudinal axis, where partial reflection of an electromagnetic signal (EM) and impedance alteration of the conductor element occur at the locations based on a chemically and/or physically measured variable. Two portions of the conductor element exhibit a dielectric constant (epsilon1) and another dielectric constant, respectively. The locations exhibit different reflectance behavior that is changed based on temperature or pressure in environment of the conductor element. The electromagnetic signal is high frequency signal, a continuous wave signal and/or pulse-type signal. An independent claim is also included for a method for determining a chemically and/or physically measured variable.

Description

The invention relates to a sensor element for detecting a chemical and / or physical measured variable, comprising a conductor element, in which electromagnetic signals can be coupled, and to a measuring device with such a sensor element.

The invention also relates to a method for determining a chemical and / or physical measured variable, wherein electromagnetic signals are coupled into a conductor element.

For the measurement of temperatures, there are a variety of methods, but almost all have the property of being able to determine a temperature only selectively. If you want to measure a temperature distribution, so you have only very few methods of measurement to choose from such. B. the fiber optic temperature measurement.

For example, from the patent US 3938385 a temperature sensor in the form of a coaxial cable has become known. The temperature dependence of the conductor elements of the coaxial cable is exploited in order to determine a temperature distribution along the cable by means of time domain reflectometry.

Furthermore, from the patent US 3938385 a chain of temperature-dependent resistors known. For this purpose, several temperature-dependent resistors are fastened close to one another on a steel chain. The electrical signals of the individual sensors are then transmitted to a data processing system.

Another way to measure a temperature distribution is the present invention.

The object is achieved by a sensor element, a measuring device and a method.

With regard to the sensor element, the object is achieved in that the conductor element has discrete reflection points arranged along its longitudinal axis, at which an at least partial reflection of the electromagnetic signal occurs as a function of the measured variable.

The invention is based on the fact that one or more high-frequency or pulsed signals propagating in a line with constant line impedance are reflected at points at which, for example, an impedance change occurs. The conductor element thus serves to conduct electromagnetic signals. The conductor element in which the electromagnetic signals propagate can have one or more reflection points, at which a reflection of the electromagnetic signals occurs. It is an idea of the invention to exploit the reflection of signals at these reflection points in order to determine, for example, the temperature distribution or the pressure distribution along the sensor element, which, for example, is located in a tank in which a medium is located. Generally speaking, the conductor element can therefore consist of materials whose physical properties change in such a way depending on the measured variable that the reflection behavior of electromagnetic waves also changes. Is the conductor element made of different materials, which vary depending on their dependence, d. H. the change in their physical properties, differ from the measured variable, the reflection behavior of the electromagnetic signals also changes at the transition between the materials. The different materials and / or reflection points are, for example, along the longitudinal axis of the sensor element adjacent to each other or arranged successively. For this purpose, for example, two or more, in particular three, materials may be used from which the conductor element consists.

In one embodiment of the sensor element, an impedance change of the conductor element as a function of the measured variable takes place at the reflection points. An impedance change at a position in the conductor element as a function of the measured variable also causes a change in the reflection behavior of the electromagnetic signals propagating in the conductor element. For example, a measuring element which changes its impedance as a function of the measured variable can be connected to the conductor element at such a reflection point. The point at which the measuring element is connected to the conductor element then forms a reflection point. A change in the impedance of this measuring element, which is, for example, a temperature-dependent resistor, then causes at the reflection point, via which the measuring element is connected to the conductor element, for example. An impedance change, so that the reflection behavior of an electromagnetic signal at this Reflection point changes. Electromagnetic signals are therefore at the reflection point as a function of the reflection behavior, which is dependent on the measured variable, reflected to different degrees. In an alternative embodiment, the conductor element consists of several adjoining sections, wherein adjoining sections, for example, differ from each other in terms of their permittivity.

In a further embodiment of the sensor element, the conductor element has a plurality of discrete sections along the longitudinal axis, which differ from one another with regard to their reflection behavior as a function of the measured variable and form reflection points. For example, these sections may consist of materials whose physical properties change in different ways depending on the measured variable.

Furthermore, the sensor element can be designed so that all reflection points in the conductor element have a substantially equal reflection behavior at a certain temperature or generally at a certain value of the measured variable. Alternatively, the reflection points have a different reflection behavior as a function of a value of the measured variable.

In a further embodiment of the sensor element, the conductor element has a first dielectric in a first section and a second dielectric in a second section, wherein the first dielectric differs from the second dielectric in terms of its permittivity as a function of the measured variable. Preferably, therefore, at least one material is used whose permittivity changes as a function of the measured variable. For example, materials are known whose permittivity changes as a function of the temperature or the pressure. The sensor element therefore preferably consists of different dielectrics.

In a further embodiment of the sensor element, a plurality of segments consisting of the first and the second section are in particular arranged directly next to one another. A reflection point is formed, for example, from the transition between two different materials or sections with different permittivity. These two sections of the conductor element then form a segment of the conductor element. A conductor element may consist of several such segments. Between these segments, the conductor element can also consist of other materials or sections with different permittivity.

In a further embodiment of the sensor element, the reflection behavior changes as a function of the temperature or the pressure. Furthermore, a change in the reflection behavior can also be attributed to a change in length of the materials used. By means of this change in length (s), it is likewise possible, for example by means of transit time analysis of a signal coupled into the conductor element and reflected, to detect changes in the measured variable. Thus, for example, the permittivity of the materials used may be substantially constant or independent of the measured variable, but the length expansion may be dependent on the measured variable.

In a further embodiment of the sensor element, reflection sites are formed by the at least one first section and the at least one second section, at which an at least partial reflection of the electromagnetic signals occurs. Your reflection of one or more electromagnetic signals in the conductor element occurs at the interface between the two sections.

The object is further achieved by a measuring device with a sensor element according to at least one of the previous embodiments. For this purpose, the sensor element can be connected to a measuring transducer which serves to generate and / or evaluate the electromagnetic signals which are coupled into or out of the sensor element. The measuring device comprises, for example, a sensor element according to one of the described embodiments and a measuring transducer.

The object is also achieved by a method for determining a chemical and / or physical measurand, wherein at least one electromagnetic signal is coupled into a conductor element, which signal is at least partially reflected as a function of the measured variable at discrete reflection points of the conductor element, and by means of at least the reflected Signal the measured variable is determined.

In one embodiment of the method, the distribution of the measured variable along the sensor element is concluded by means of the reflected signal.

In a further embodiment of the method, high-frequency signals, in particular continuous signals, so-called continious-wave signals, and / or pulsed signals are used as electromagnetic signals.

In a further embodiment of the method, a sensor element according to at least one of the proposed embodiments is used as the conductor element.

In a further embodiment of the method, based on the reflection of the electromagnetic signal at the at least one reflection point, a temperature distribution and / or a pressure distribution along the conductor element is determined.

In a further embodiment of the method, the duration of the electromagnetic signals and / or the amplitude and / or the phase relationship between the electromagnetic signals used.

The invention will be explained in more detail with reference to the following drawings. It shows:

1 FIG. 2: a schematic representation of a first embodiment of the proposed invention with a sensor element consisting of different dielectrics, FIG.

2 FIG. 2: a schematic representation of a second embodiment of the proposed invention likewise consisting of sections of different dielectrics, FIG.

3 FIG. 2 shows a schematic illustration of a third embodiment of the proposed invention in which temperature-dependent resistors are connected to the conductor element of the sensor element at discrete locations, FIG.

4 : a schematic representation of an alternative arrangement of the temperature-dependent resistance elements according to the third embodiment of the proposed invention in which temperature-dependent resistors are connected to the conductor element of the sensor element at discrete locations,

5 FIG. 2: a schematic representation of a section of a conductor element of a sensor element, FIG.

6 FIG. 2: a schematic representation of a sensor element with a plurality of discrete reflection sites according to the third embodiment of the proposed invention, FIG.

7 FIG. 2 is a schematic representation of a fifth embodiment of the proposed invention, FIG.

8th FIG. 2: a schematic representation of a signal course of an electromagnetic signal coupled or reflected in a proposed sensor element, and FIG

9 : A schematic representation of the waveform of reflected signals in a proposed sensor element.

1 shows a generator G, which is connected to a directional coupler. From the directional coupler leads a line in this case with a coaxial structure to a terminating impedance Z ₀ . The line consists of several sections, with adjoining sections consisting of different dielectrics. In this case, line sections having a first dielectric ε ₁ , a line impedance Z ₀ . A second line segment has a second dielectric ε ₂ , which has a high dependence on the physical variable to be measured in comparison to the first dielectric. Since the line impedance Z _{L of} the line is dependent on the dielectric used, it is therefore also dependent on the size to be measured. This makes it possible to measure different physical quantities. The following examples are limited to the measurement of temperature. The line sections with ε ₂ thus have an impedance z. B. depends on the ambient temperature. As soon as Z _L differs from Z ₀ , a reflection of the high-frequency or pulse-shaped electromagnetic signal fed from the generator G occurs at these points. The degree of this reflection depends directly on the impedance change Z _L - Z ₀ , and thus on the quantity to be measured. The quantity to be measured is thus represented in the amplitude of the reflected signal. The reflected signal is fed via the directional coupler to a signal analyzer, which determines the measured variable from the amplitude of the signal.

Since only a small part of the injected electromagnetic signal EM is reflected by the impedance transitions, ie the reflection points A, an arrangement of several sections with ε ₂ in succession is possible. The signal analyzer S can thus conclude the local distribution of the measured variable along the conductor element or the sensor element on the basis of the different signal propagation times of the reflected signals.

2 shows a structure according to the structure 1 , However, in this measuring principle, a dielectric ε _{2 is} used, which has the smallest possible temperature dependence, but nevertheless differs from the dielectric ε ₁ , so that reflections occur in the cable. As with a change in temperature, a longitudinal expansion of the conductor element 2 , in particular the different sections of the conductor element 2 , which is designed here as a cable, is accompanied by the measurement of the transit times t ₁ (transition ε ₁ -ε ₂ -ε ₁ ) and t ₂ to the temperature in this region of the conductor element 2 getting closed.

3 shows one too 1 alternative embodiment. According to 3 the sections that consist of the dielectric ε ₂ , replaced by discrete, temperature-dependent resistors. Since reflections also occur at the transitions from Z ₀ to R (T), the temperature of the measuring elements can be determined by the amplitudes of the reflections analogously to the measuring method as described in the description of the figures 1 described. The difference to measuring method according to 1 and 2 is that the temperature-dependent resistor R (T) practically no local expansion has and thus only one reflection per resistance element R occurs. This means that for the subsequent sections of the ladder element 2 a stronger signal is available.

Depending on the resistance value, the temperature-dependent resistors can also be used as in 4 can be arranged, where they also serve to conduct the electromagnetic signals EM in the conductor element.

wobei Zo die Wellenimpedanz der Leitung und Z, die angeschlossene Impedanz ist. Daraus ergibt sich:

5 shows a single (lossless) cable segment with a termination impedance Z _L. The reflection factor is defined by the ratio of the reflected signal Vr to the forward signal Vf.

where Zo is the wave impedance of the line and Z is the connected impedance. This results in:

6 shows several segments extended, the following relationship applies to Z _L1 :

It should be noted that the full signal generator Vf ₀ no longer reaches the following segments, but only the signal Vf ₁ which is reduced by Vr ₁ . This means for Z _L2 :

Generalized, this means for any segment n:

By the installation of a constant reference element all measurement results can be further calibrated and corrected and thereby parasitic effects of the conductor element 2 be minimized.

Will the conductor element 2 , which is, for example, a measuring cable, not terminated at the end with a line resistance, but short-circuited or left open, it is formed at the end of the conductor element 2 a total reflection of the transmission signal. By measuring the signal amplitude of this total reflection, the measurement accuracy can be increased.

7 shows a sensor element into which a square pulse, generated by the generator G and having a pulse duration of 2 nsec (nanoseconds), is fed. The signal, ie the rectangular pulse, is fed via a resistor R4 into a coaxial cable with sections T1, T2, T3 and T4. After a cable length of 1 m, a resistor R1 of 1 kΩ is placed. This segment consisting of T1 and R1 is repeated three times, represented by components and reference numerals T2-R2, T3-R3. At the end, the cable is terminated with a resistor R5. At point T1-P1, the signal reflected in the line is tapped. The reflection points A, to which the resistor R1, R2, R3 is connected to the coaxial cable, are shown enlarged.

8th shows a typical waveform of the transmit pulse (large positive pulse) and the reflections on the resistors (small negative pulses) using the example of the in 7 shown conductor element.

As in the enlargement in the 9 can be seen, the three reflected signals have a different amplitude. In this case, the resistance R2, for example, was changed by a temperature change by 100 Ω to 1.1 Ω. The change in the signal curve of the reflected signal relative to the segments T1-R1 and T3-R3 which occurs as a result of the impedance change of 100Ω at R2 in the segment T2-R2 is clearly visible.

Theoretically, an infinite number of measuring points formed by the reflection points A, in a conductor or sensor element 1 . 2 will be realized. Due to the geometry of the structure of the sensor element 1 can, for example, consisting of a cable conductor element 2 thus very well adapted to most measurement tasks, whereby a high cable length is possible.

LIST OF REFERENCE NUMBERS

G

signal generator

Z ₀

Line impedance of the first dielectric

Z _L

Temperature-dependent line impedance of the second dielectric

Z _L1

Line impedance for a two-segment line element

Vf ₀

first forward signal

Vf ₁

second forward signal, after transmission via ZL1

Vr ₁

reflection signal

ε ₁

first dielectric

ε ₂

second dielectric

S

signal analyzer

I ₁ (T)

Temperature-dependent length of a section consisting of a dielectric of the second type

I ₂ (T)

Temperature-dependent length of another section consisting of a dielectric of the second type

t1 (T)

Running time of the electromagnetic signal through a section consisting of the second dielectric

t2 (T)

Running time of the electromagnetic signal through another section consisting of the second dielectric

t

Time

R (T)

temperature-dependent resistance

R1

first temperature-dependent resistance

R2

second temperature-dependent resistance

R3

third temperature-dependent resistance

R4

fourth temperature-dependent resistance

T1

first section of serving as a conductor element coaxial cable

T2

second section of serving as a conductor element coaxial cable

T3

third section of serving as a conductor element coaxial cable

T4

fourth section of a serving as a conductor element coaxial cable

1

sensor element

2

conductor element

A

Relexionsstelle

EM

electromagnetic signal

L

longitudinal axis

RK

directional

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 3938385 [0004, 0005]

Claims (14)

Sensor element ( 1 ) for detecting a chemical and / or physical measurand, comprising a conductor element ( 2 ), in which at least one electromagnetic signal can be coupled, wherein the conductor element ( 2 ) discrete along its longitudinal axis (L) arranged reflection points (A), at which an at least partial reflection of the electromagnetic signal (EM) occurs as a function of the measured variable. Sensor element ( 1 ) according to the preceding claim, wherein at the reflection points (A) an impedance change of the conductor element ( 2 ) takes place as a function of the measured variable. Sensor element ( 1 ) according to the preceding claim, wherein the conductor element ( 2 ) has a plurality of discrete sections along the longitudinal axis (L), which differ in terms of their reflection behavior as a function of the measured variable from one another and form reflection points. Sensor element ( 1 ) according to the preceding claim, wherein the conductor element ( 2 ) in a first section, a first dielectric (ε ₁ ) and in a second section, a second dielectric (ε ₂ ), and the first dielectric (ε ₁ ) of the second dielectric (ε ₂ ) with respect to its permittivity as a function of the measured variable different. Sensor element ( 1 ) according to the preceding claim, wherein a plurality of the first and the second section existing segments (T1, T2, T3) are in particular directly lined up. Sensor element ( 1 ) according to the preceding claim, wherein the reflection behavior at at least one reflection point (A) in dependence of the temperature or the pressure, preferably in the vicinity of the conductor element, changes. Sensor element ( 1 ) according to the preceding claim, wherein by the at least one first portion and the at least one second portion reflection points (A) are formed, at which an at least partial reflection of the electromagnetic signals (EM) occurs. Measuring device with a sensor element ( 1 ) according to one of the preceding claims. Method for the determination of a chemical and / or physical measurand, whereby electromagnetic signals (EM) in a conductor element ( 2 ), which signals (EM) as a function of the measured variable at discrete reflection points (A) of the conductor element ( 2 ) are at least partially reflected, and by means of at least the reflected signals, the measured variable is determined. Method according to the preceding claim, wherein by means of the reflected signals on the distribution of the measured variable along the Leierelements ( 12 ) is closed. Method according to one of claims 9 or 10, wherein as electromagnetic signals (EM) high-frequency signals, in particular continuous signals, so-called. Continuious-wave signals, and / or pulse-shaped signals are used. Method according to one of claims 9 to 11, wherein as conductor element ( 2 ) a sensor element ( 1 ) according to one of claims 1 to 7 is used. Method according to one of claims 9 to 12, wherein based on the reflection of the electromagnetic signal at the at least one reflection point, a temperature distribution and / or a pressure distribution along the conductor element is determined. Method according to one of claims 9 to 13, wherein for the evaluation of the transit time of the electromagnetic signals (EM) and / or the amplitude and / or the phase relationship between the electromagnetic signals (EM) is used.

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