EP3063511A1

EP3063511A1 - Device for determining or monitoring the fill level of a medium in a container

Info

Publication number: EP3063511A1
Application number: EP14755827.4A
Authority: EP
Inventors: Thomas Blödt; Peter KLÖFER
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2013-10-31
Filing date: 2014-08-28
Publication date: 2016-09-07
Also published as: DE102013112025A1; CN105705913B; CN105705913A; US20160265959A1; WO2015062765A1

Abstract

The invention relates to a device for determining or monitoring the fill level (h, H) or a specified limit level of a medium (3) in a container (2), comprising a self-excited system, which consists of an oscillation generation unit for generating electromagnetic waves within a specified frequency band, at least one sensor (1) having an electrode (4), which sensor is arranged at a specified angle to the longitudinal axis of the container (2), wherein the electromagnetic waves are applied to the electrode (4), wherein the at least one sensor (1) is arranged in relation to the medium (3) in such a way that the phase position of the electromagnetic waves reflected at the boundary surface of the medium (3) changes under the influence of the medium (3), and a feedback circuit, which feeds the electromagnetic waves back to the at least one sensor (1), whereby the frequency of the self-excited system is determined, comprising a frequency detector, which detects the frequency of the electromagnetic waves, and comprising an evaluating unit (28, 29), which determines the relative permittivity (DK_mess) dependent on the particular fill level (h) and/or determines the permeability of the medium (3) on the basis of the detected frequency and which determines the fill level (h) or the reaching of the specified limit level of the medium (3) in the container (2) on the basis of the determined relative permittivity (DK_mess) or the permeability of the medium (3).

Description

Device for determining or monitoring the level

a medium in a container

The invention relates to a device for determining or monitoring the level or a predetermined limit level of a medium in a container.

The Applicant offers a variety of level gauges for industrial automation technology and sold. To determine the level of a medium in a container

used different measuring principles. For example, radar measuring instruments determine the fill level of a product in a container over the duration of ultrasonic signals or microwave signals. In these so-called. Run-time method, the physical law is exploited that the running distance is equal to the product of transit time and propagation speed of the waves. In the case of level measurement, the running distance is twice the distance between the antenna and the surface of the medium. The level itself can then be determined from the difference between the known distance of the antenna from the bottom of the container and the distance determined by the measurement of the surface of the medium from the antenna.

The disadvantage of radar level gauges is shown when they are used in small containers, in particular smaller than 1 m. The spatial resolution, ie the measurement accuracy, is then relatively low and the blocking distance is large. Block distance is understood here to be the minimum distance from the antenna, starting at - below

Consideration of the radiation characteristic of the antenna - a reliable measurement is possible in the first place. The influence of the blocking distance can be partially compensated by suitable signal conditioning, e.g. by using a reproducible guided wave propagation. Corresponding level measuring devices have become known under the name TDR (Time Domain Reflectometry) devices.

Laser measuring devices can also be used with a short measuring distance, but their realization is cost-intensive.

Furthermore, capacitive probes or hydrostatic pressure probes are used for continuous level measurement. On capacitive probes can

Deposits reduce the accuracy of measurement. Hydrostatic pressure probes are relatively strongly influenced by pressure changes, which occur in particular when filling small containers. Furthermore, there are indirect methods for determining a level. To name in this context, for example, a dropper, which on a

Infusion bag is attached. An inexpensive system for level measurement consists of a plurality of interconnected limit switches, each covering a defined height range of the container. If a fixed number of limit switches are distributed over the height of the container, the larger the container, the greater the measurement inaccuracy. If 1 1 limit switches are used, the system can dissolve in steps of 10%. In addition, several point level measuring points are costly depending on the measurement method; they can also affect each other in principle.

The invention has the object to provide a device for determining the level or the level of a medium in a container, which is also suitable for use in small containers.

The object is achieved by a device for determining or monitoring the level or a predetermined limit level of a medium in a container with a self-excited system consisting of

- A vibration generating unit for generating electro-magnetic

Waves within a given frequency band,

- At least one sensor having an electrode which is arranged at a predetermined angle to the longitudinal axis of the container, wherein the electrode is acted upon by the electromagnetic waves, wherein the at least one sensor with respect to the medium is arranged such that the phase position of the at the interface of the medium reflected electromagnetic waves under the influence of the medium changes, and

a feedback circuit which feeds back the electromagnetic waves to the at least one sensor, whereby the frequency of the self-excited system is determined,

with a frequency detector which detects the frequency of the electromagnetic waves, and

with an evaluation unit, which determines the relative permittivity (DK _mess ) or the permeability of the medium on the basis of the detected frequency, and which uses the determined relative permittivity (DK _mess ) and / or the

Permeability of the medium determines the level or reaching the predetermined level of the medium in the container. The refractive index - also called refractive index - corresponds to the ratio of the speed of light of electromagnetic waves in vacuum to

Propagation speed in the medium. The complex refractive index is linked to permittivity and permeability. Here, the permittivity is a measure of the permeability of a material for electric fields and the permeability is a measure of the permeability of a material for magnetic fields. Permittivity and dielectric conductivity are synonymous terms. The relative permittivity, also called

Permittivitätszahl or referred to as the dielectric constant, describes the permittivity of a medium to the permittivity of the vacuum. Magnetic substances are classified by permeability as diamagnetic, paramagnetic or ferromagnetic substances.

Although in the following almost exclusively on the measurement of relative

Dielectric constant is taken, the device according to the invention can be used analogously to detect fill level with appropriate media via a permeability measurement.

Preferably, the sensor consists of an electrode which is arranged on an insulating material; Electrode and insulation material form a measuring cell.

An advantageous embodiment of the solution according to the invention provides that the sensor or the measuring cell is arranged on the inner wall of the container, on the outer wall of the container or in the medium. Likewise, the sensor or the measuring cell can be an integral part of the container wall. Since the microwaves are e.g. penetrate a plastic bag, the sensor or the measuring cell can be glued to the outer wall of a plastic container. It goes without saying that the device according to the invention is designed so that it extends either over the entire filling level of the container, or that it is shorter and covers only a portion of the maximum level, e.g. 0% -50% or 60% ... 100%. In addition, the device according to the invention can also be used as a limit switch.

The device according to the invention can also be referred to as a microwave resonator. Depending on the conditions prevailing at the interface with the medium, the device according to the invention is able to make statements regarding the electrical or magnetic properties or the changing electrical or magnetic properties of the medium. The self-excited system oscillates in the steady state on a defined oscillation frequency, which is located in the microwave range. The self-excited oscillating frequency of the self-excited system, that is the microwave resonator, depends on the refractive index at the interface with the medium, wherein the microwave resonator must be arranged with respect to the interface so that the

Oscillation frequency is influenced by the properties of the medium. Thus, the microwave resonator must be located in close proximity to the medium or in the medium. It goes without saying that the thickness of the wall can be greater if the medium has a high dielectric constant. Measured in the

In connection with the invention, the oscillation frequency or the frequency change due to the influence of the medium. For this purpose, a frequency counter is preferably used as the frequency detector.

An advantageous embodiment of the device according to the invention provides that the frequency band in which the self-excited system is oscillatable, is outside the natural frequency of the sensor. The natural frequency of the sensor is reflected by the geometric dimensions of the sensor or the transit time of the sensor

determined electromagnetic waves within the sensor. As a result, the self-excited system has a low quality; This is very beneficial for the self-excited system. In addition, the frequency deviating from the natural frequency prevents the sensor from acting as an antenna and absorbing or emitting large amounts of energy. Thus, interference is reduced. In the

Device according to the invention are preferably the following operating or

Vibration frequencies used: 2.4 GHz, 433 MHz, 866 MHz or 5.8 GHz. In general, at least any frequency in the frequency range between 300 MHz and at least 30 GHz can be used.

The device according to the invention may preferably, but not exclusively, be used for determining the filling level in small containers. In particular, small containers are understood to be containers having a longitudinal extent of less than or significantly less than 1 m. Determining a small level is very important in many applications. Important areas of application are medical technology and the pharmaceutical industry. In the pharmaceutical industry shows up in

Increasingly, the trend is that the production of drugs via biotechnology processes takes place in small batches. Since the solution according to the invention can be produced very inexpensively, it is also in disposable containers, in particular in disposable bags, such as infusion bags, Abstoffbeuteln or

Process containers preferably used. By disposing of the container one-time use sterilization can be saved for further use. There the device according to the invention or the measuring cell or the sensor - as already mentioned - also easily adapted from the outside to the container, for example, can be glued, a repeated use of different containers is not excluded. Also, a recycling is easily possible.

Further applications can be found in the chemical process engineering and in the

Food industry. From DE 10 2012 104 075 A1 from 09.05.2012 a sensor has become known which is so sensitive that it can be used in connection with the invention. The corresponding disclosure content of DE 10 2012 104 075 A1 (not prepublished) is attributable to the disclosure content of the present invention.

An advantageous embodiment of the device according to the invention suggests that the evaluation unit calculates the level absolutely or relative to the maximum height of the level of the container according to the following formulas: h = [DK _mess - DK _ATM ] / [DK _M - DK _ATM ]

respectively.

H = [DK _meas - 1] / [DK _M - 1] ^* 100%

Here, DK _meas characterizes the relative permittivity measured with the sensor, DK _ATM the relative permittivity of the gas phase in the area above the surface of the medium, DK _M the relative permittivity of the medium, h the determined height of the level and H the maximum height of the level in the medium Container.

According to an advantageous development of the device according to the invention, it is provided that the relative permittivity of the medium is predetermined. This is easily possible in many applications, since the composition of the medium is well known and constant. Alternatively, it is possible to provide a first reference sensor. This is preferably designed analogously as the sensor according to the invention for level measurement. The first reference sensor is at least temporarily arranged so that it interacts with the medium in the container over the entire longitudinal extent of the electrode. The frequency detector, which is assigned to the electrode of the sensor (this solution is suitable for cost reasons), or even a separate frequency detector measures the frequency of the first reference sensor. The evaluation unit determines on the basis of the relative dielectric constant measured by the sensor and the predetermined or determined by the first reference sensor relative

Dielectric constant of the medium, the level or the predetermined limit of the Medium in the container. In this connection, it should be mentioned once again that the solution according to the invention also reacts to the magnetic property of the medium.

According to an advantageous embodiment of the device according to the invention, it is proposed that the relative permittivity of the medium in the gas phase is predetermined. Since it is in many cases air, the default is simple. Alternatively, a second reference sensor is provided, which preferably corresponds to the sensor or the first reference sensor in terms of its construction and its function. The second reference sensor is oriented essentially perpendicular to the electrode of the sensor and arranged in a region of the container in which the influencing of the electromagnetic waves coupled to the electrode of the second reference sensor is at least temporarily constant by the medium in the gas phase. In any case, the second reference sensor must be arranged so that the influence of the medium on the measured values of the second

Reference sensor is excluded. The evaluation unit determines or monitors the fill level or the predetermined limit level of the medium in the container on the basis of the predetermined or determined relative dielectric constants.

A preferred solution aims to detect a separating layer occurring in a container and to determine its thickness. In this case, in the container next to the medium whose level is to be monitored, and the medium in the gas phase another medium, which is arranged in the separating layer. Typical examples are an oily substance above a water surface, or a deposit at the bottom of the container. In this context is a third

Reference sensor provided, which is also based again on the same measurement principle as the sensors described above. However, the linear expansion of the third reference sensor is different from the linear expansion of the sensor. The third reference sensor is aligned substantially parallel to the sensor. The

Linear expansion of the third reference sensor is dimensioned such that the upper end region is always above the maximum height of the separating layer. The end region of the sensor facing the bottom of the container and the end region of the third reference sensor facing the bottom of the container are at least approximately at the same height. The evaluation unit also determines the thickness of the separating layer based on the relative dielectric constants in addition to the fill level of the medium in the container.

The evaluation is carried out by means of the evaluation unit preferably according to the following formulas: h = [[L + L / G -2 (l + DK _mess + DK ₃ )] / [L / G-DK _mess -DK ₃ -l] - DK ₃ ] / [DK _M - 1] * 100% t = [L + L / G -2 (l + DK _meas + DK ₃ )] / [L / G-DK _mess -DK ₃ -l] * 100%

Characterized:

DK _measures the relative permittivity measured with the sensor,

DK ₃ the relative dielectric constant measured with the third reference sensor, L: the longitudinal expansion of the third reference sensor,

G: the length of the sensor,

t: the thickness of the release layer. According to an advantageous development of the device according to the invention, all sensors have a defined length extension. In the event that the maximum filling level of the medium in the container is a multiple of the longitudinal extent of the electrode or of the sensor, a plurality of sensors are arranged in series with one another over the filling level on or in the container.

It is particularly advantageous in this context if the sensors are available with the same length extension as a band or as a piece goods. Preferably predetermined breaking points are then provided between the individual sensors, so that the number of sensors can be tuned by suitable separation to be measured or monitored maximum filling level of the medium in the container.

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

1 shows a schematic representation of a first embodiment of the measuring arrangement according to the invention for level measurement in a container,

2: a schematic representation of a second embodiment of the

Measuring device according to the invention for level measurement in a container,

3 shows a schematic representation of a third embodiment of the measuring arrangement according to the invention for level measurement in a container,

4: a schematic representation of a fourth embodiment of the

Fig. 5a: the measuring arrangement shown in Fig. 4 with sensor electronics and

Evaluation electronics in a first embodiment,

5b: the measuring arrangement shown in Fig. 4 with sensor electronics and

Evaluation electronics in a second embodiment, 6a-6d: different configurations of a preferably used measuring arrangement according to the invention,

Fig. 7a-Fig. 7c: different variants of the measuring arrangement according to the invention,

Fig. 8a, Fig. 8b: further advantageous embodiments of the invention

Device and

Fig. 9: a schematic representation of the solution according to the invention, which is used to control a pump and

With reference to the schematic representation shown in FIG. 1 of a first reduced to the essential arrangement of a device according to the invention for

Level measurement in a container 2, the measuring principle of the solution according to the invention is explained in more detail. The container 2 is partially filled with a medium 3. Of the

Sensor 1 is attached to the container 2 from outside and placed substantially parallel to the longitudinal axis of the container 2. The level h of the medium 3 in the container 2 can be given as an absolute measure or as a percentage with respect to the maximum filling height H possible in the container 2.

According to the invention, the knowledge is exploited that a microwave resonator 1 positioned on a container with a simple elongate electrode 4 outputs the linear mean value of the relative dielectric constant of the adjacent media (3, 14) in the form of a frequency. The sensor 1 according to the invention forms the mean value of the adjacent media in the form that, for example, a medium 3 adjacent to the sensor 1 with a relative permittivity DK _M of 4 and a medium 14 adjoining the sensor 1 with a relative of 75% Dielectric constant DK _A ™ of 1 (air) gives a measured dielectric constant DK _MESS of DK _MESS = 0.25 ^* 4 + 0.75 ^* 1 = 1.75, or the relative permittivity DK _MESS of 1.75 results

frequency to be assigned. The arrangement shown in FIG. 1 can be used if the dielectric constant DK _{M of} the medium 3 and the dielectric constant DK _A TM of the gas phase 14 are known. This can be assumed in many applications in the food, pharmaceutical and chemical industries.

The medium 3 changes in composition during one

Monitoring process or is the composition of the medium 3 per se not As is known, the solution shown in FIG. 2 lends itself. In addition to the sensor 1, the actual level sensor, a reference sensor 6 is provided, which is arranged on / in the container 2, that it at least temporarily over its entire

Longitudinal extent interacts with the medium 3 located in the container 2. Since the frequency of the oscillatory system in interaction with the medium 3 adjusts itself to a frequency which allows an unambiguous assignment to the dielectric constant DK _{M of} the medium 3, the dielectric constant DK _{M of} the medium 3 can be determined via the reference sensor 6. The formula for determining the level h of the medium 3 in the container 2 is as follows: h ^* DK _M + (1-h) ^* DK _ATM = DK _meas (1)

This yields: h = [DK _meas - DK _A TM] / [DK _M - DK _A TM] (2)

In the simple case that the gas in the gas space 14 is air, the dielectric constant DKATM = 1 ■ The equation can then be rewritten as follows: h = [DK _MESS - DKATM] / [DK _M - DKATM] (3) or normalized to the maximum level H in the container 2

H = [DK _meas - 1] / [DK _M - 1] ^* 100% (4)

FIG. 3 shows a preferred measuring arrangement when the dielectric constant DK _A TM of the medium in the gas phase 14 fluctuates or is unknown. In addition to the sensor 1 and the first reference sensor 6, a second reference sensor 7 is then provided, which is arranged so that it interacts at least temporarily only with the gas phase 14. Based on the self-adjusting frequency, the dielectric constant DK _A TM of the gas phase 14 can also be determined unambiguously here. The level h or H can be calculated using one of the previously mentioned formulas.

A measuring arrangement which is suitable in particular for level measurement in the presence of a separating layer 9 is shown in FIG. 4. The third reference sensor 8 is preferably formed analogously to the sensor 1 or the first reference sensor 6 or the second reference sensor 7. The linear expansion L of the active part of the third reference sensor 8 differs from the linear expansion G of the active part of the sensor 1. In particular, the longitudinal extent L of the third reference sensor 8 is such that the upper end region 24 always lies above the maximum height of the separating layer 9 in the container 2. The third reference sensor 8 is aligned substantially parallel to the sensor 1 - in the case shown, both are parallel to

Longitudinal axis of the container 2. The bottom 25 of the container 3 facing end portion 27 of the sensor 1 and the bottom 25 of the container 3 facing end portion 26 of the third reference sensor 8 are at least approximately at the same height. The sensor and transmitter is not shown separately in Fig. 4 determined on the basis of the measured and / or predetermined relative dielectric constants _M DK, DK _A TM, DK _measuring the thickness t of the release layer 9. In the formulas below DK _T denotes the dielectric constant of the medium in the separation layer 9 and DK _3, the measured from the third reference sensor 8 dielectric constant. h ^* DK _M + (1-ht) ^* DKATM ⁺ t ^* DKj = DK _meas (5)

such as

h * DK _M + (Lht) ^* DK _A TM + t * DK _T = DK ₃ (6)

The level (H) can be calculated according to the following formula:

H = [[L + L / G -2 (1 + DK _mess + DK ₃ )] / [L / G-DK _mess -DK ₃ -1] - DK ₃ ] / [DK _M - 1] ^* 100% ( 7) with £ _h = ε ₀ ^* DK _M

For the thickness t or T of the separating layer 9 follows:

T = [L + L / G -2 (1 + DK _me ss + DK ₃ )] / [L / G-DK _me ss-DK ₃ -1] ^* 100% (8) with ε _τ = ε ₀ ^* ( 1 + DK _mess + DK ₃ - L / G) In the case described, the separating layer 9 is above the first reference sensor 6 and below the upper end portion 24 of the third reference sensor 8. The lower end portions 25, 26 of the sensor 1 and the third reference sensor eighth not at a height, so the dielectric constant DK _A TM of the gas phase 14 must be taken into account. For this purpose, as already described above, a second reference sensor 7 can be used. From DE 10 2012 104 075 A1 from 09.05.2012, a sensor has become known which is so sensitive that it can be used to determine the dielectric constant of the separating layer 9 (here an indirect measurement of the foam thickness and density). The corresponding content of DE 10 2012 104 075 A1 (not

pre-published) is attributable to the disclosure of the present invention.

In principle, it is of course possible in connection with the invention, all known dielectric constants of the medium and the gas phase possibly also the

Separating layer, not to measure, but to specify the transmitter. Because the Dielectric constant DK _{M of} a medium 3, especially in water but also in other common media, is temperature dependent, should improve the

Measuring accuracy at least one temperature sensor (not shown) may be provided. This makes it possible to computationally compensate for the temperature effect.

FIGS. 5a and 5b show the measuring arrangement shown in FIG

Frequency detector 1 1, sensor electronics 12 and evaluation or evaluation unit 28 shown in two different embodiments. In FIG. 5a, each sensor or each reference sensor 1, 6, 8 is assigned a respective sensor electronics 12. In Fig. 5a are thus three oscillatory systems. These are from the first one

oscillatory system 1, 12, the second oscillatory system 6, 12 and the third schiwngfähigen system 7, 12. This solution is quite possible, since the component costs for the required electronics are relatively low. In order to save energy, the individual sensors 1 and reference sensors 6, 7, 8 alternately from the

Evaluation electronics 28 controlled.

In the embodiment shown in FIG. 5b, a plurality of sensors 1, 6, 8 are connected via a changeover switch 10 with only one sensor electronics 12 and a frequency detector 11. The switching of the switch 10 is controlled by the evaluation / evaluation unit 28. In this embodiment, there is only one oscillatory system. Depending on the position of the switch 10, the oscillatable system consists of one of the following three configurations: the sensor 1, the switch 10 and the sensor electronics 12, or the first reference sensor 6, the switch 10 and the sensor electronics 12, or the third reference sensor 8 , the switch 10 and the sensor electronics 12th

FIGS. 6a-6d show different embodiments of a preferably used measuring arrangement according to the invention, which are configured as adhesive devices 16 or as stickers. Each sticker 16 is provided with at least two sensors 1, 6 and at least one connector 15. The

Measuring arrangements can be made very compact. If a correspondingly high operating frequency is selected, the sensors shown can also be implemented in MEMS technology. The adhesive arrangements 16 shown can moreover be integrated without problems in, for example, a disposable plastic bag (medical technology) or in a mini-bioburper container. The measurement can also be made here through the non-conductive and non-magnetic wall. FIGS. 7a-7c show further different variants of FIG

see measuring arrangement according to the invention. Each of the sensors 1 shown in FIG. 7 a has a defined length G. In the event that the maximum filling level H of the medium 3 in the container 2 is a multiple of the longitudinal extent G of the electrode 4 and the sensor 1, several sensors 1 are arranged in series over the maximum filling height H or arranged in the container 2 ,

It is considered to be particularly advantageous in conjunction with the solution according to the invention if the sensors are present in the meter 19, and it is possible, by appropriately shortening the sensor 1, 8 to the desired or required maximum

Adjust fill level H of the container 2. For this, however, a calibration of the sensor 1, 8 must be done. To perform a correct measurement, the

Evaluation unit 28, 29, the respective length of the sensor 1, 6, 7, 8 be known, and / or it must be known for the purpose of adjustment at the time of measurement, at least the current level. To ensure higher measurement accuracy, the sensor 1, 8 should be placed at two measurement points, e.g. the measuring points "minimum level" and "maximum level

In addition, a learning phase can be provided, in which the outer band limits of a sensor are determined.The level is then distributed evenly or according to container shape from 0% to 100% in the measured range During this training phase, it is necessary, at least once the minimum and the maximum level to be measured, is referred to in deisem

Related to the already cited non-prepublished German patent application of the applicant. By a two-point adjustment can also on the first reference sensor 6 for

Measurement of the dielectric constant DK _{M of} the medium 3 are omitted (see Fig. 1). As previously stated, it is alternatively possible that the operating personnel

Dielectric constant DK _{M of} the medium used 3 of the evaluation unit 28 pretends. However, this requires that the dielectric constant DK _{M of} the medium 3 is constant within the desired measurement accuracy during the measurement.

In practice, the length of a given sensor 1 hardly with the

Linear expansion of a container 2 or an arrangement at which the level is to be determined or monitored to match. For a larger container 2, it may be sufficient to measure the level h only in a certain limit range. A corresponding application example is visualized in FIG. 9. The arrangement shown is a gate circuit for fixing the upper one

Turn-off point 21 and the lower turn-on 22 of a pump 20th Another elegant method is shown in Fig. 8b. The meter goods 19 has predetermined breaking points 18, which are characterized for example by imprints. The operating personnel selects the predetermined breaking point 18, which is suitable for the installation, for shortening the sensor 1, 8 and communicates this to the evaluation electronics 29. In the evaluation 29 of the frequency detector 1 1, the sensor electronics 12 and the evaluation are included. This solution is more comfortable than the reduction shown in Fig. 8a by means of a cutting tool to the required length and the message about the jeweile length to the evaluation unit 28. In addition, can be prevented by the reduction in predetermined sections that the reduction is too low and the Sensor 1 does not work due to the non-attainment of the required minimum length. A cut below the necessary minimum length irreversibly damages the sensor. The reason for this is the following: The frequency detector 1 1 within the evaluation unit 29 has a lower detection threshold, above which Verändeurngen be detected at a connected sensor 19. In order to ensure a safe measurement above this detection threshold, a minimum length of the sensor 19 is provided, which ensures that a sufficient interaction between the microwaves and the electrical or mangetic properties of the adjacent medium or the adjacent media is guaranteed. This detection threshold is dependent on the circuit complexity that is operated in the sensor electronics 12 and the frequency detector 1 1.

The measuring arrangement can also be designed such that two sensors 1

are provided with different longitudinal extent, which project from above into the container 2 or are immersed temporarily. From this, the immersion depth can be calculated in the medium 3 and be deduced the level h of the medium 3 in the container. The dielectric constant of the medium 3 can be predetermined or detected by another sensor.

LIST OF REFERENCE NUMBERS

1 sensor

2 containers

3 medium

4 electrode

5 insulation material

6 first reference sensor / sensor for the determination of DK _M

7 second reference sensor / sensor for determining DK,

8 third reference sensor / sensor for the determination of DK ₃

9 separating layer

10 switches

1 1 frequency detector

12 sensor electronics

13 interface

14 gas phase

15 connectors

16 adhesive arrangement

17 compact reference sensor

18 predetermined breaking point

19 B a ndwa re / Mete rwa re

20 pump

21 upper switch-off limit

22 lower switch-on limit

23 measuring cell

24 upper end area

25 bottom of the container

26 lower end portion of the third reference sensor

27 lower end of the sensor

28 evaluation electronics / evaluation unit

Frequency detector / sensor and evaluation electronics / evaluation unit

Claims

claims

1 . Device for determining or monitoring the filling level (h, H) or a predetermined limit level of a medium (3) in a container (2),

- with a self-excited system consisting of

a vibration generating unit for generating electro-magnetic waves within a predetermined frequency band,

- At least one sensor (1) with an electrode (4) under a

predetermined angle to the longitudinal axis of the container (2) is arranged, wherein the electrode (4) is acted upon by the electromagnetic waves, wherein the at least one sensor (1) with respect to the medium (3) is arranged such that the phase position of the at Surface of the medium (3) reflects electromagnetic waves under the influence of the medium (3) changes, and

a feedback circuit which feeds back the electromagnetic waves to the at least one sensor (1), whereby the frequency of the

self-excited system is determined,

with an evaluation unit (28, 29) based on the detected frequency of the respective level dependent relative dielectric constant (DK _MESS ) and / or the

Determined permeability of the medium (3) and determined on the basis of the determined relative permittivity (DK _MESS ) or the permeability of the medium (3) the level (h) or reaching the predetermined level of the medium (3) in the container (2).

2. Apparatus according to claim 1,

wherein the sensor (1) consists of an electrode (4) which is arranged on an insulating material (5), and

wherein the electrode (4) and the insulating material (5) form a measuring cell (23).

3. Apparatus according to claim 1 or 2,

wherein the sensor (1) or the measuring cell (23) is arranged on the inner wall of the container (2), on the outer wall of the container (2) or in the medium (3).

4. Apparatus according to claim 1, 2 or 3,

wherein the evaluation unit (28, 29) the level (H, h) absolute or relative to the maximum height of the level of the container (2) calculated according to the following formulas: h - [DK _MESS - DK _ATM ] / [DK _M - DK _ATM ] respectively.

H = [DK _meas - 1] / [DK _M - 1] * 100% with DK _measures the relative permittivity measured with the sensor (1), with DK _ATM the relative permittivity of the gas phase (14) in the area above the surface (13 ) of the medium (3) and DK _M the relative permittivity of the medium (3).

5. Device according to one or more of the preceding claims,

wherein the relative dielectric constant (DK _M ) of the medium (3) is predetermined, or wherein a first reference sensor (6) is provided which is designed in accordance with the sensor (1), wherein the first reference sensor (6) is arranged at least temporarily so in that it interacts with the medium (3) over the entire longitudinal extent of the electrode (4), the frequency detector measuring the frequency of the first reference sensor (6), and wherein the evaluation unit (28, 29) is measured from the sensor (1) Relative dielectric constant (DKmess) and the predetermined or from the first reference sensor (6) determined relative permittivity (DK _M ) of the medium (3) the level (h, H) or the predetermined level limit of the medium (3) in the container (2) certainly.

6. Device according to at least one of claims 1-5,

wherein the relative dielectric constant (DK _A ™) of the gas phase (14) medium (3) is predetermined, or

wherein a second reference sensor (7) is provided, which is designed in accordance with the sensor (1) and / or the first reference sensor (6), wherein the electrode of the second reference sensor (7) substantially perpendicular to the electrode (4) of

Sensor (1) is oriented and wherein the second reference sensor (7) in a region of the container (2) is arranged, in which the influence of the coupled to the electrode (4) of the second reference sensor (7) electromagnetic waves by the in the Gas phase (14) located medium (3) is at least temporarily constant, and wherein the evaluation unit (28, 29) based on the predetermined or determined relative

Dielectricity (DK _mesS, DK _M ) determines or monitors the level or the predetermined limit level of the medium (3) in the container (2).

7. Device according to one or more of the preceding claims,

wherein in the container (2) next to the medium (3) in the gas phase (14) and the medium (3) whose level (h, H) is monitored or determined, a second in one

Separating layer (9) arranged medium (3) is present,

wherein a third reference sensor (8) is provided, which is formed according to the sensor (1) or the first reference sensor (6) or the second reference sensor (7) is, wherein the longitudinal extent (L) of the third reference sensor (8) from the longitudinal extent (G) of the sensor (1) differs, wherein the longitudinal extent (L) of the third reference sensor (8) is dimensioned so that the upper end portion (24 ) is always above the maximum height of the separating layer (9), wherein the third reference sensor (8) is aligned substantially parallel to the sensor (1), wherein the bottom (25) of the container (3) facing end portion (27) of Sensor (1) and the bottom (25) of the container (3) facing the end region (26) of the third reference sensor (8) are at least approximately at the same height, and wherein the evaluation unit (28, 29) on the basis of the determined relative permittivity of the Thickness (t) of

Separation layer (9) determined.

8. Apparatus according to claim 7,

wherein the evaluation unit (28, 29) calculates the level (h) of the medium (3) in the container (2) according to the following formula: h = [[L + L / G -2 (1 + DK _mess + DK ₃ )] / [L / G-DK _mess -DK ₃ -l] - DK ₃ ] / [DK _M -1] * 100% and the thickness (t) of the separating layer (9) is calculated according to the following formula: t = [L + L / G -2 (l + DK _mess + DK ₃ )] / [L / G-DK _mess -DK ₃ - 1] * 100% with the following abbreviations:

DK _mess : the relative permittivity measured with the sensor (1),

DK ₃ : the relative permittivity measured with the third reference sensor (8), L: the longitudinal extent of the third reference sensor (8),

G: the length of the sensor (1).

9. Device according to one or more of the preceding claims,

wherein the sensor (1) has a defined longitudinal extent (G), and wherein in the event that the maximum filling level of the medium (3) in the container (2) is a multiple of the longitudinal extent (G) of the electrode (4) and the Sensor (1) is several

Sensors (1) in a row to each other over the maximum filling height distributed on or in the container (2) are arranged.

10. Device according to one or more of claims 1-9,

wherein a multiplicity of sensors (1) with the same length extension (G) are present as band goods (19), predetermined breaking points (18) being provided between the individual sensors (1), so that the number of sensors (1) can be separated by suitable separation to the measured or monitored maximum filling level of the medium (3) in the container (2) is tuned.

1 1. A device according to at least one of claims 1 -10,

wherein the frequency detector and the evaluation unit (28, 29) are assigned to a plurality of sensors (1) and / or reference sensors (6, 7, 8).