DE102010024058A1 - Device for determining filling level of container, has sound sensor attached to container, where sound sensor is connected to evaluation unit, and evaluation unit is arranged for determining helmholtz frequency of sound waves - Google Patents

Abstract

The device has a sound sensor (10) attached to a container (2), where the sound sensor is connected to an evaluation unit (16). The evaluation unit is arranged for determining the Helmholtz frequency of the sound waves that are received by the sound sensor. The change in frequency is determined by the evaluation unit, where the frequency is generated during filling process of a container. Independent claims are also included for the following: (1) a method for determining filling level of a container; and (2) a sewage system for a vehicle, particularly an airplane.

Description

TECHNICAL AREA

The invention relates to a device for detecting the level of a container, a method for detecting the level of a container and a dirty water system for a vehicle with at least one device for detecting the level of a container.

BACKGROUND OF THE INVENTION

The prior art has a wealth of different devices and methods for detecting levels in containers. Accurate knowledge of the level of a container is particularly important in vehicles in order to have security of sufficient quantities of supplies and existing holding capacity of waste water containers, so that the safe operation of the vehicle is not compromised.

In sewage systems and in particular black water systems in commercial aircraft, which can only absorb a limited amount of dirty water and consequently overfilling must be prevented, levels in the prior art via a pressure measurement on a container bottom, a capacitance measurement between individual measuring points or capacitive over a example in the Container laminated metal foil detected. Especially with dirty water tanks there is the disadvantage that sensors for detecting a level by contact with the liquid absorbed in the container can pollute or corrode. Although this is not the case with laminated films or measuring points, these precautions significantly increase the production costs and thus the manufacturing costs of the container.

DE 4 227 516 C2 and US 5,305,792 A show a dirty water system in an aircraft, which is equipped with a sensor for detecting the level of a dirty water tank.

SUMMARY OF THE INVENTION

The object of the invention is to reduce or eliminate one or more of the abovementioned disadvantages.

In particular, should be regarded as an object of the invention to propose a device for detecting the level of a container that can reliably detect the level in a container in the simplest and most cost-effective manner while being reliably protected from contamination and corrosion.

Preferably, the device according to the invention is also suitable for being retrofitted as simply as possible into already existing containers.

The object is achieved by a device having the features of independent claim 1. Advantageous further developments can be taken from the subclaims.

According to a first aspect, the device has at least one sound pickup and at least one evaluation unit connected to the sound pickup. The evaluation unit is set up to analyze the sound waves recorded by the sound sensor, wherein the analysis comprises the determination of at least one Helmholtz frequency.

For this connection, it is assumed that the free gas volume in the container, which contains no liquid to be absorbed and is located above the absorbed liquid, can be regarded as a Helmholtz resonator. This is characterized by a gas-filled cavity with a narrow opening to the outside, wherein the gas volume can vibrate due to the compressibility of the gas within the gas volume. The elasticity of the free gas volume in combination with the inert mass of the gas in the opening creates a mechanical mass-spring system with a pronounced self-resonance. Such a phenomenon can be observed, for example, in beverage bottles with a bottle neck having an opening. When blowing over the opening, a vibration is generated in the bottle, which creates a perceptible sound under favorable conditions. The characteristic frequency of this vibration is a Helmholtz frequency and depends on several factors, in particular the size of the free gas volume and the geometric dimensions of the inlet area to the free gas volume. From knowledge of the Helmholtz frequency, its size can be determined with known flow behavior at the opening to the free gas volume, so that from knowledge of the total size of the container and thus of the recordable volume can be determined how much liquid the container has already taken.

By analogy with this, in a container to be filled with a medium through an inlet opening, by a preceding or succeeding gas flow at the inlet opening, an open line to an inlet opening or at a flow edge disposed inside the container, an excitation could take place leads to a Helmholtz resonance. This can be used to determine the current level.

In a dimensionally stable container, a pressure equalization is required when flowing in a medium, which can be performed by an independent outflow or controlled discharge of gas from the free volume of gas through a pressure equalization port. With appropriate design of this pressure compensation opening could also be a suggestion of a Helmholtz resonance done, which can be used to determine the level.

Since a Helmholtz resonance can be excited both from the inlet opening and the pressure equalization opening, which in each case depend on the geometric boundary conditions at the inlet opening and the pressure equalization opening, two different Helmholtz frequencies could arise in such a case. The evaluation unit should preferably be set up to determine two different Helmholtz frequencies, which can each be used by the characteristic properties of the two opening areas for independent calculation of the free gas volume. This allows a plausibility check or averaging, which can prevent or at least reduce the risk of an incorrectly determined free gas volume.

In general, for a Helmholtz excitation, a flow of a compressible medium, in particular a gas required, whose flow direction and velocity undergoes a change by a change in cross section and is thereby vibrated, resulting in an excitation of the total free gas volume. The medium to be filled into the container can furthermore have any state of aggregation, as long as it can be ensured that a gas flow prevails before, during or after filling, which causes a detectable Helmholtz resonance, at least for a short time.

This would be the case, for example, with dirty water tanks in commercial aircraft, which have a negative pressure relative to the dirty water collecting devices and induce through a switching valve or the like an air flow into the container, which leads to the discharge of dirty water into the container. The initial air flow can reach a speed of up to 150-200 m / s in modern sewage systems, which is clearly sufficient for the excitation of a Helmholtz vibration. It should be noted here that in such an air flow within a supply line to an inlet opening of the dirty water tank, the entire supply line for excitation of the Helmholtz vibration leads and therefore the entire air-flow section of the supply line can be considered as a "bottleneck".

The evaluation unit is to be understood as an electronic device which preferably has an A / D converter which is capable of generating digital data which can be processed from analog signals of the sound transducer. These can be analyzed and processed with suitable algorithms and processing methods to achieve the desired effect according to the invention.

According to an advantageous embodiment of the device according to the invention, the analysis unit is adapted to detect a change in a Helmholtz frequency, which occurs between two successive filling operations of the container or during the duration of a single filling operation, if it can be ensured that an initial or continuous gas flow leads to an excitation of the gas volume. As a result, it is not necessarily necessary to determine the exact size of the free gas volume, but it can already be pointed out an increase in the Helmholtz frequency to an imminent and expected full filling of the container, such as by reaching or exceeding a predetermined Helmholtz frequency.

In an advantageous embodiment of the device according to the invention, the sound pickup is designed as a structure-borne sound pickup, which can be arranged on an outer side of the container to be filled. As a result, no special devices, receptacles or fasteners need to be created within the container that can secure the transducer within or above the free volume of gas. This further protects the transducer from contamination or corrosion.

In an advantageous embodiment of the device according to the invention, the analysis unit is set up to detect a frequency spectrum that is registered by the sound pickup. With the help of a filter clearly perceptible, d. H. detected sufficient amplitude sound waves with one or more discrete frequencies within the frequency spectrum and used to calculate the free gas volume. The analysis could be done with methods or filters based on Fourier transforms or wavelet analyzes.

According to an advantageous embodiment of the invention, an additional, separate excitation arrangement could be provided, which is set up to carry out a Helmholtz excitation within the free gas volume. This exciter arrangement could be realized by a sound transducer, the noise in the form of sound waves in the free gas volume or in an opening near Area, such as at the inlet opening or at a pressure equalization opening, initiates.

As an alternative or in addition to such an excitation arrangement, it would also be possible to use a blowing device which introduces a short air pulse into the free volume of gas via an interfering edge in order to cause the resulting Helmholtz oscillation.

Equally, an interfering edge could be provided which could be arranged in the region of the inlet opening if it can be assumed that not only pure liquid but also a gas volume can flow into the container. With a suitably designed interfering edge, the effect of exciting a Helmholtz resonance could be enhanced to allow for an accurate determination of the free gas volume.

According to an advantageous development of the invention, alternatively or additionally, an interfering edge could be arranged on an air outlet opening of the container in order to cause escaping air to excite a Helmholtz vibration.

The object is further achieved by a method for determining the filling state of a container, which essentially comprises the steps listed below.

After opening an inlet opening for causing a gas flow in an inlet region and a resulting Helmholtz resonance within the free gas volume, the sound waves present within the free gas volume are detected. Subsequently, a Helmholtz frequency is determined from the detected sound waves and used to determine the free gas volume in the container.

The object is further achieved by a dirty water system for a vehicle having a vacuum under a container having a closable inlet opening through which dirty water can be sucked into the container. When opening the inlet opening the dirty water pipe is subjected to a negative pressure in front of the container, so that dirty water flows through the dirty water pipe to the container. Initially, however, there may be a flow of gas present in the dirty water line into the container, through which a Helmholtz resonance can take place with sufficient flow velocity, which can be registered by the sound pickup and used to determine the Helmholtz frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and applications of the present invention will become apparent from the following description of the embodiments and the figures. All described and / or illustrated features alone and in any combination, the subject matter of the invention, regardless of their composition in the individual claims or their relationships. In the figures, the same reference numerals for identical or similar objects.

1 shows a dirty water system, which is equipped with a device according to the invention.

2 shows a method according to the invention.

3 shows an aircraft having a dirty water system, which is equipped with a device according to the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

1 shows a dirty water tank 2 that has an inlet opening 4 has, over the dirty water in the container 2 can get. For detecting the level of dirty water 6 According to the invention, the size of the free gas volume 8th above the dirty water 6 in the container 2 determined. For this purpose, a sound pickup 10 used, the exemplary on the outside, as close as possible to the container 2 is arranged and thereby can absorb structure-borne sound. The sound pickup 10 could be designed as a ceramic Schallaufnehmer. The arrangement of the sound pickup 10 but may not necessarily be on a top of the container 2 take place, also side surfaces or a bottom of the container 10 would be eligible for the arrangement.

In the container 2 There is a negative pressure relative to its environment, as is common, for example, in a dirty water system of an aircraft. The vacuum may be achieved either by means such as a vacuum pump, such as a centrifugal compressor, or by a lower ambient pressure level, for example, when the invention is used in an aircraft.

By opening a valve 12 a vacuum connected to the inlet opening dirty water line is subjected to the negative pressure, resulting in a suction effect, through the dirty water in the inlet opening 4 is sucked in. Subsequently, the dirty water collects in the container 2 ,

By the arrangement of the inlet opening 4 at an upper side of the container 2 is assumed that the inlet opening 4 not permanently in direct contact with dirty water, but at least in the region of the inlet opening 4 Air or other gas is present, which immediately after opening the valve 12 is accelerated by the suction effect and into the container 2 flows. Due to the discontinuous cross section in the area of the inlet opening 4 For example, the incoming gas can be vibrated and a Helmholtz resonance in the free gas volume 8th induce with the help of the sound pickup 10 can be detected. Furthermore, here is an additional interfering edge 14 shown, which serves to increase the reliability of a vibration excitation of the gas.

In the realization of the device according to the invention in an aircraft, there especially in a dirty water system, the Störkante could 14 already be realized by a flush valve (also called "flush valve") of the toilet, which is located on a the container 2 opposite end of a line to the inlet opening 4 located. The interfering edge preferably has a sharp geometric boundary or other discontinuity to force a local change in the flow behavior of the incoming gas and to increase the noise bandwidth so as to cause resonant vibration.

wobei c die Schallgeschwindigkeit, S die Querschnittsfläche der betrachteten Öffnung („Resonatorhalsöffnungsquerschnitt”), beispielsweise der Einlauföffnung 4, V das freie Gasvolumen und L die effektive Länge effektive Länge des schwingungserregten Gasvolumens (”Resonatorhalslänge”), analog zu einer Länge eines Flaschenhalses. Die Querschnittsfläche S kann durch Messen bestimmt werden, während die effektive Länge L durch experimentelle Versuche ermittelt werden könnte, bei bekanntem freiem Gasvolumen V. Die obige Gleichung ist über Korrekturfaktoren und dergleichen an die real vorliegenden Bedingungen anzupassen, etwa durch die Form

wobei der Ausdruck 2ΔL auch als Mündungskorrektur bezeichnet wird.With the sound pickup 10 is an analysis unit 16 connected, for example via a data line 18 and a data input 20 , The analysis unit 16 is adapted to detect detected sound waves with a filter algorithm 22 to filter so that a Helmholtz frequency can be identified. With the aid of this Helmholtz frequency and knowledge of the respective opening-near region, such as a resonator neck length, a free gas volume can in principle be determined according to the following equation:

where c is the speed of sound, S is the cross-sectional area of the considered opening ("resonator neck opening cross-section"), for example the inlet opening 4 , V the free gas volume and L the effective length effective length of the vibration excited gas volume ("resonator neck length"), analogous to a length of a bottleneck. The cross-sectional area S can be determined by measuring, while the effective length L could be determined by experimental tests, with known free gas volume V. The above equation is to be adjusted via correction factors and the like to the actual conditions, such as the shape

where the term 2ΔL is also referred to as the orifice correction.

At a data output 24 Then, the determined volume in the form of data or signals to other systems or the like can be sent.

The analysis unit 16 does not necessarily have to be designed as a separate unit, but it could for example also be integrated in a control or regulating device belonging to a dirty water system or the like and, for example, the valve 12 controls. Irrelevant, whether the analysis unit 16 is a separate unit or not, can be at a status input 26 a status of the valve 12 be captured, so that the analysis unit 16 Only then does sound undergo an analysis as soon as the valve 12 is open and dirty water in the container 2 flows.

The valve 12 can also be via any connection 28 be connected to a control or regulating device, which is not taken into account in the present presentation.

For completeness, it should be mentioned that the container 2 a pressure compensation opening 30 has, through which excess air can escape. Equally could be at this exhaust port 30 also a vacuum generator 32 be arranged, the container 2 always under negative pressure, as soon as dirty water in the container 2 should be filled or constant during the period of operation of the vehicle concerned. Should this be the case, it is necessary to inform the evaluation unit that a vacuum generator provides for the negative pressure, since the relevant gas volumes and the effective length L can change as a result of this operating state, for example through an additional, open valve.

It should also be mentioned at this point that a vibration excitation at the exhaust port 30 could lead to a Helmholtz resonance. It would also be possible for both the inlet opening 4 as well as the pressure equalization opening 30 induce a Helmholtz resonance and the transducer 16 Two different Helmholtz resonances can be detected and evaluated, for example by a Fourier transformation in which both resonant frequencies are visible as frequency peaks.

It should be noted that the device according to the invention is not limited to use in a vehicle, but can be used in any system and in any system in which at least for a short time an air flow into a container is to be expected.

In 2 an embodiment of a method according to the invention for detecting a level of a container is shown. On opening 34 a filling opening 4 Sound waves are within a free gas volume 8th of the container detected 36 , Subsequently, a Helmholtz frequency is determined from the detected sound waves 38 and determines the free gas volume in the container 40 , The determination can include a relative or absolute determination, ie it is either the absolute free gas volume 6 determined or a change in the free gas volume 6 based on a registered change of the determined Helmholtz frequency.

Finally shows 3 an airplane 42 That with a dirty water system 44 equipped, which is a container 2 with an inlet opening 4 includes. For the purpose of a particularly lightweight construction of the container 2 be made of a fiber composite, such as a CFRP or GRP, which may be additionally provided with an inner lining of a thin layer of stainless steel. By using a device according to the invention for detecting the level in such a container, the container 2 be designed exclusively against the background of ideal mechanical properties, as a sound pickup can be easily retrofitted and on an outside of the container 2 Could find space. The position of the container 2 is chosen only as an example. In addition to the position shown, it is also suitable for the type of installation of the container 2 in the form of a sewage tank as possible in the stern of the aircraft 42 so that it can be avoided that come out with the gas flow germs during the flight, for example, with fresh water fittings in contact.

In addition, it should be noted that "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. It should also be appreciated that features described with reference to any of the above embodiments may also be used in combination with other features of other embodiments described above. Reference signs in the claims are not to be considered as limiting.

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

• DE 4227516 C2 [0004]
• US 5305792 A [0004]

Claims (10)

Device for detecting the level of a container ( 2 ), comprising - at least one on the container ( 2 ) attachable sound sensor ( 10 ), - at least one with the sound sensor ( 10 ) associated evaluation unit ( 16 ), whereby the evaluation unit ( 16 ) is arranged to emit at least one Helmholtz frequency from the transducer ( 10 ) and to determine from the Helmholtz frequency a free gas volume in the container. Apparatus according to claim 1, wherein the evaluation unit ( 16 ) is adapted to determine a change in the Helmholtz frequency, which occurs between two successive filling operations of the container ( 2 ) entry. Apparatus according to claim 1, wherein the evaluation unit ( 16 ) is set up during the period of a single filling operation of the container ( 2 ) to determine a change in a Helmholtz frequency. Device according to one of the preceding claims, wherein the sound sensor ( 10 ) as an on an outside of the container ( 2 ) attachable structure-borne sound pickup is executed. Device according to one of the preceding claims, wherein the evaluation unit ( 16 ) is adapted to detect a sound frequency spectrum which is emitted by the sound sensor ( 10 ) and to determine at least one Helmholtz frequency from the detected frequency spectrum. Apparatus according to any one of the preceding claims, further comprising an additional exciter assembly for exciting a Helmholtz resonance. Device according to one of the preceding claims, further comprising at least one interfering edge for exciting a Helmholtz resonance in the free gas volume of the container ( 2 ) Method for determining the filling state of a container ( 2 ), comprising the steps: - opening a filling opening ( 4 ); - Detecting sound waves within a free gas volume ( 8th ) of the container ( 2 ); Determining at least one Helmholtz frequency from the detected sound waves and determining the free gas volume ( 8th ) in the container ( 2 ). Dirty water system for a vehicle, comprising: - at least one container ( 2 ) for receiving dirty water; At least one on the container ( 2 ) attachable sound sensor ( 10 ), - at least one with the sound sensor ( 10 ) associated evaluation unit ( 16 ), whereby the evaluation unit ( 16 ) is arranged to emit at least one Helmholtz frequency from the transducer ( 10 ) and to determine from the Helmholtz frequency a free gas volume in the container. Use of a dirty water system according to claim 9 in an aircraft.

Images