EP2870436A1

EP2870436A1 - Filling level measurement

Info

Publication number: EP2870436A1
Application number: EP13733260.7A
Authority: EP
Inventors: Franz Gerhard BOSBACH; Stefan Laue; Gerhard Lindner; Frank OBERMAIR; Joachim Schullerer
Original assignee: KSB AG
Current assignee: KSB SE and Co KGaA
Priority date: 2012-07-06
Filing date: 2013-06-26
Publication date: 2015-05-13
Also published as: DE102012211848A1; US20150192452A1; DE102012211848B4; KR20150028280A; CN104685326A; CN104685326B; WO2014005896A1

Abstract

The invention relates to an apparatus and a method for determining the filling level of a liquid in a container (4). The apparatus comprises at least one element (1, 2) which transmits and/or receives acoustic signals. The acoustic signals propagate along a surface of a solid (3). The solid (3) is arranged in such a manner that at least one part of a surface of the solid (3) can be wetted by the liquid. The solid (3) has, at different container heights, regions (5) which reflect the acoustic signals.

Description

description

level measurement

The invention relates to a device and a method for determining the level of a liquid in a container with at least one element that sends and / or receives acoustic signals.

Such devices are used for example in wastewater lifting systems. Lifting systems discharge waste water, which accumulates below the backflow level, backflow-proof. They are used to extract faecal wastewater from basements in residential buildings.

In conventional lifting systems, the level measurement and control takes place by means of a float switch. In this case, a measuring method with moving mechanical components is used. These are prone to contamination, such as occur in waste water from lifting equipment.

DE 10 2007 008 692 A1 describes a container of a lifting system in which sensors for detecting the liquid level are mounted at different container heights on the outside of the wall. This measuring device is firmly connected to the container. Thus, a flexible use of the device excludes for a variety of containers. A disadvantage of this system is the high number of sensors.

In DE 199 13 530 A1, a lifting system is described with a collecting container made of plastic. The collecting tank flows at irregular intervals a Fluids to. A pump pumps the liquid out of the container into a sewer system. For measuring the liquid level in the container is an element which is arranged at the top of the container. The element emits radar waves which are reflected by the surface of the liquid. The reflected waves are in turn received by the element. From the running time of the waves, the level is determined. The pump is switched on or off depending on the level. Methods for level detection with radar waves are expensive.

Furthermore, devices for level measurement are known in which an element is attached to the top of the container that transmits ultrasonic signals. These acoustic signals are reflected from the liquid surface and detected by the element. Ultrasonic level measurement is a non-contact process that operates on the runtime principle. Again, there is a risk of erroneous measurements of the liquid level due to floating foam, which reflects the ultrasonic waves.

The object of the invention is to provide a device for level measurement, which is insensitive to contamination and provides reliable measurements even when foam formation. In addition, the device should be inexpensive to manufacture and be characterized by reliability and a long service life.

This object is achieved in that propagate the acoustic signals along a surface of a solid, which is arranged so that at least a portion of a surface of the solid is wetted by the liquid and the solid body in different container heights has areas that reflect acoustic signals ,

According to the invention, surface acoustic waves are used for level determination, abbreviated AOW (English: SAW for surface acoustic waves). The acoustic signals propagate on the surface of a solid. The solid may optionally consist of a composite material. Preferably, however, it is formed from a single material, and it proves to be particularly advantageous to use a solid body of a metal. The solid body can have different geometric shapes, for example cuboidal or cylindrical. In a preferred embodiment of the invention is a hollow body, in particular, a hollow cylinder, ie a tube, proves to be advantageous. In a variant of the invention, the hollow body is closed with a bottom. Thus, it is prevented that liquid penetrates into the hollow body. The elements that generate and / or detect the surface acoustic waves are mounted on the inside. Thus, the acoustic signals propagate on the inner, dry surface of the tube and are reflected by areas that the tube has on its inside. The measuring tube dips into the liquid, whereby only the outside is wetted. Surprisingly, it has been found that below the liquid level the surface acoustic waves are more strongly attenuated, although they spread on the dry inside of the tube. The prerequisite is that the wall thickness of the pipe is not too large.

According to the invention, the solid body is arranged such that at least part of a surface is wettable by the liquid. This may be the surface of the solid on which the AOW spreads and / or another surface that, for example, is opposite to it.

The solid has areas that reflect the surface waves. For this purpose, the solid body has suitable, in particular sharp-edged, geometry changes. The areas are preferably recesses which are introduced into the surface. In particular, elongated depressions that run approximately horizontally are suitable. In a particularly advantageous variant, cuts are milled into the surface and / or hammered in, with particular notches prove to be beneficial. It can also be a groove as a recess in the solid a be brought. The areas may also be formed as elevations of the surface of the solid.

In principle, it is also possible that the solid body is formed by a piece of the container wall. However, it proves to be particularly advantageous if the solid body is formed as an independent component which is arranged in the container. The solid at least partially immersed in the liquid and has in different container heights on reflective areas. For the part of the solid that does not dip into the liquid, the acoustic signals are reflected undisturbed at the notches. The reflected signals are detected by a detector formed either by the same element that generates the SAW or is formed as a discrete element.

In the part of the solid which dips into the liquid, the acoustic signals are strongly damped by the liquid. This is also referred to as "decoupling" of the signals, so that the signals reflected by the areas below the liquid level are greatly attenuated.

The reflected signals are analyzed or evaluated by a unit. The unit is set up in such a way that it determines the fill level from the wave pattern of the reflected signals. The wave pattern is a detection of the intensities of all reflected acoustic signals, depending on the transit times. Acoustic signals, which are reflected by reflections near the bottom of the container, have a longer transit time than acoustic signals from further above. The acoustic signals reflected at the areas are also called echoes.

Below the liquid level, the echoes are greatly attenuated. Based on a comparison with reference measurements carried out, for example, with a completely empty container, the unit can determine the filling level, since the signals of the reflection regions below the liquid level are greatly attenuated with respect to the reference values. In the method according to the invention, the following steps are carried out.

Generation of acoustic signals,

Propagation of the acoustic signals along a surface of a solid, at least partial reflection of signals at areas of the solid, which are arranged in different container heights,

Detection of the reflected signals,

Determination of the transit times of the reflected signals,

Determination of the signal strengths of the reflected signals,

Comparison with reference values,

- Determination of the level.

This is a procedure that is repeated at regular intervals. The solid body preferably has a longitudinal extent and is arranged vertically in the container. Decisive for the quality of the evaluation is also the location of the reflection areas. These can be arranged parallel to one another in the propagation direction of the acoustic signals. However, in such an arrangement, the reflected signals are superimposed. An evaluation of the wave pattern becomes more difficult. In a particularly advantageous embodiment of the invention, the reflective regions are arranged laterally offset relative to the propagation direction of the acoustic signals. This reduces the superpositions of the reflected signals. At least a part of the reflected signals reaches the detector without multiple reflections. This gives a wave pattern in which the individual echoes are well distinguishable.

The elements for generating the surface acoustic waves preferably consist of a piezoelectric substrate on which a comb electrode is applied as a transmitter. This forms an interdigital transducer (IDT = interdigital transducer), the so-called transmitter-interdigital transducer (transmitter IDT), which generates a surface wave on the piezoelectric substrate. The excitation frequency is chosen such that Lamb waves or surface waves are preferably generated in the transition region between Lamb and Rayleigh waves. In a variant of the invention, the elements are arranged on the surface of the solid. For this purpose, the piezolelektrer Subtrat is acoustically conductive connected to the solid. This can be done by an adhesive. The surface waves are transmitted from the piezoelectric substrate to the solid and propagate on a surface of the solid.

The echoes are detected by an element that serves as a detector. This detector also comprises a piezoelectric substrate with a comb electrode. It acts as a receiver interdigital transducer (receiver IDT) and converts the received surface acoustic waves into electrical signals. In a variant of the invention, the detector is likewise fastened directly on the solid body, for example by means of an adhesive.

In an alternative embodiment of the invention, at least one of the elements is arranged on the surface of a head part. This head part can be acoustically coupled to the solid body. The coupling can be realized by a greased or glued Schlifasstassung. The head part can be connected to different solids. Thus, for example, a plurality of measuring tubes with different lengths can be coupled to the head part, so that only once a transmitting or receiving electronics is necessary. With a headboard thus different measuring lengths can be realized. In a particularly favorable variant, the unit is set up via the wave pattern of the echoes to detect the type of the connected measuring tube, in the manner of a bar code.

Instead of a separate AOW transmitter and receiver, a common electroacoustic converter can also be used, which is switched alternately as transmitter and receiver in multiplex mode. Further features and advantages of the invention will become apparent from the description of embodiments with reference to drawings and from the drawings themselves.

It shows

1 shows a section through a measuring tube for level measurement,

2 shows a wave diagram of a measurement, FIG. 3 shows a lifting system with a fill level measuring device,

Fig. 4 shows an arrangement of the reflective areas.

FIG. 1 shows a device for determining the level of a liquid. A first element 1 serves as a transmitter and generates acoustic signals. A second element 2 serves as a detector and receives reflected acoustic signals. Both elements 1, 2 comprise a piezoelectric substrate in each of which a comb electrode is inserted. They form an interdigital transducer (IDT = interdigital transducer) for the conversion of electrical signals into acoustic signals at the transmitter or for the conversion of acoustic signals into electrical signals at the receiver.

The elements 1, 2 are mounted on a solid body 3. The solid 3 is designed as a cylindrical hollow body whose bottom is closed and which is open at the top and thus forms a measuring tube. The measuring tube is arranged in a container 4, which is shown in Fig. 3. The measuring tube is made of aluminum and is aligned vertically in the container 4.

On the inside of the measuring tube areas 5 are arranged, which reflect the acoustic signals. The areas 5 are notches, which are milled into the measuring tube. The regions 5 are arranged in parallel one above the other so that in the variant illustrated in FIG. 1 multiple reflections occur which interfere with one another. In FIG. 1, by way of example, five reflective regions 5 are shown, two of which are above the liquid level and three below the liquid level. The echoes of the upper two areas show a high signal strength. The echoes of the lower three areas show only a small signal strength, since the acoustic waves are damped by the liquid on the outside of the tube. Although the AOW spreads on the inside of the measuring tube and the liquid wets the outside of the measuring tube, the damping is so clear that it can be used to determine the filling level.

Fig. 2 shows wave patterns of the reflected acoustic signals at different levels. The fill levels are indicated in centimeters in the top right corner next to the respective wave pattern. In the case of the wave patterns, the signal strengths are plotted as a function of the propagation times of the signals. Wave groups reflected from areas farther down the solid 3 have longer durations and are thus located further to the right in the diagrams. Wave groups, which are reflected by areas further up the solid 3, have shorter durations and are in the diagrams follow lent left.

The signal strength in the exemplary embodiment is given in mVpp since the detector converts the received acoustic signals into electrical signals which are recorded in millivolts from peak to peak.

The upper wave pattern with a level of 0 cm is used as a reference, since none of the reflected wave groups of liquid is attenuated. With a fluid level of 1 cm, the wave group is attenuated far right, so that their signal strength decreases. At a level of 2 cm, the two right-hand wave groups are damped, and at a level of 4 cm, the three right-hand wave groups are damped. By comparing the determined wave pattern with reference values, a unit 6 determines the fill level. The unit 6 is shown schematically in FIG. It may be a computer, a control device or a control device. The unit 6 is set up to detect the signal strength of the reflected signals as a function of the transit times and to determine the fill level by comparison with reference values. The more reflected wave groups are damped, the higher the level. The level can be calculated using the number of undamped and / or damped wave groups. In a particularly advantageous variant of the invention, the unit 6 is also used for controlling and / or regulating the filling level. Fig. 3 shows that the unit 6 is connected to a motor 7 of a pump located in the interior of the container 4. In the embodiment, an electric motor is used, which drives a centrifugal pump. The unit 6 switches the motor 7 on and off.

The pump is a check valve 8 downstream. On the container 4 of the lifting plant, a feed pipe 9 is connected, flows through the liquid in the container 4.

The designed as a measuring tube solid 3 detected according to the principle described above, the level. At a lower limit of the liquid level, the unit 6 stops the motor 7. At an upper limit of the liquid level, the unit 6 starts the motor 7, so that again liquid is pumped out.

Fig. 4 shows a variant in which the reflective regions are arranged offset. Instead of separate SAW transmitters and receivers, a common electroacoustic converter is used here as element 1, 2, which is switched alternately as transmitter and receiver in multiplex mode. The solid 3 is a plate of aluminum with a thickness of 1 mm. The plate can be rolled into a tube. The elements 1, 2 are arranged in this case on the inside of the tube. The IDT is glued to the solid and has a club-shaped radiation characteristic, which is shown as dashed lines and has an angle of approximately 30 °. The areas 5 are in relation to the propagation direction of the acoustic Signals arranged laterally offset from one another, so that the emitted wave group reaches each area 5 directly. This ensures that the echoes again run directly back to the IDT, without causing multiple reflections.

Claims

Level measurement

1 . Device for determining the level of a liquid in a container (4) having at least one element (1, 2) which transmits and / or receives acoustic signals, characterized in that the acoustic signals propagate along a surface of a solid (3), which is arranged so that at least part of a surface of the solid body (3) is wettable by the liquid and the solid body (3) in different container heights regions (5) which reflect the acoustic signals.

2. Device according to claim 1, characterized in that at least one of the elements (1, 2) with a unit (6) is in communication, which is adapted to detect the signal strength of the reflected signals as a function of the transit times and by comparison with Reference values to determine the level.

3. Apparatus according to claim 1 or 2, characterized in that the solid body (3) is designed as a component which is arranged in the interior of the container (4).

4. Apparatus according to claim 3, characterized in that the component is designed as a hollow body.

5. Apparatus according to claim 4, characterized in that the hollow body is closed by a bottom which prevents penetration of the liquid into the hollow body.

6. Device according to one of claims 1 to 5, characterized in that the regions (5) are formed as depressions in the surface of the solid body (3).

7. Device according to one of claims 1 to 5, characterized in that the regions (5) are formed as elevations of the surface of the solid body (3).

8. Device according to one of claims 1 to 7, characterized in that the regions (5) are arranged laterally offset from one another with respect to the propagation direction of the acoustic signals.

9. Device according to one of claims 1 to 8, characterized in that at least one of the elements (1, 2) on the surface of the solid body (3) is arranged.

10. Device according to one of claims 1 to 9, characterized in that at least one of the elements (1, 2) is arranged on the surface of a head part, which is acoustically coupled to the solid body (3).

1 1. Method for determining the level of a liquid in a container (4), in particular with a device according to one of claims 1 to 10, comprising the following steps:

Generation of acoustic signals,

Propagation of the signals along a surface of a solid (3), at least partial reflection of signals at regions (5) of the solid (3), which are arranged in different container heights,

Detection of the reflected signals.

12. The method according to claim 1 1, characterized in that the transit times of the reflected signals are determined.

13. The method of claim 1 1 or 12, characterized in that the signal strengths of the reflected signals are determined.

14. The method according to claim 12 and 13, characterized in that the signal strengths of the reflected signals are detected as a function of the transit times.

15. The method according to any one of claims 1 1 to 14, characterized in that the level is determined by a comparison with reference values.