DE102021130596A1 - Autonomous fill level sensor with a float, method for measuring a fill level and arrangement - Google Patents

Abstract

The invention relates to an autonomous fill level sensor (10) for measuring a fill level in a container (28), with a float (12), the float (12) having means for detecting a fill level (40). a particularly flexible and simple measurement of the filling level can be made possible. The invention also relates to a method for measuring a filling level with an autonomous filling level sensor (10) and an arrangement.

Description

The invention relates to a self-sufficient filling level sensor with a float according to claim 1. The invention also relates to a method for measuring a filling level with such a self-sufficient filling level sensor according to patent claim 8 and an arrangement of a filling level sensor in a container according to patent claim 15.

Level sensors for determining and/or monitoring a level in a container are known in various configurations from the prior art. Self-sufficient level sensors or self-sufficient field devices are also known from the prior art. They are characterized by simplified assembly without attaching a communication or supply line

Filling level sensors—also autonomous filling level sensors—are usually fixed to a wall area of a container with various structures, for example by screwing into the container, screwing on or clamping onto the container. There are also level sensors with a float, such as in the DE 10 2005 036 846 B4 However, fixed structures are also provided here on the outside of the container and the actual measurement is carried out by a device connected to the container.

The underlying object of the invention is to provide a filling level sensor, a method for measuring a filling level and an arrangement which enable a particularly flexible and simple measurement of the filling level.

The object is achieved according to the invention with the features of the independent claims. Further advantages and practical embodiments are described in connection with the dependent claims.

An autonomous filling level sensor according to the invention for measuring a filling level in a container has a float. The float has means for detecting a fill level. The fill level sensor is used in particular to detect a liquid level in a container.

A self-sufficient level sensor is characterized in that it has no wired energy supply and no wired communication line to another unit.

The level sensor is in particular a field device. In process automation technology, field devices are often used that are used to record and/or influence process variables. "Field" refers to the area outside of control rooms. In particular, such field devices are connected to higher-level units, for example control systems or control units. These higher-level units are used for process control, process visualization and/or process monitoring.

The autonomous level sensor according to the invention has a float. A float is a body that has such a buoyant force that it floats on the surface of a liquid. In particular, the float is a hollow body. A buoyant body and in particular a bladder filled with a gas, preferably air, can be arranged in this.

The float has means for determining a filling level. That is to say that it is already possible to detect the filling level using only the float. There are no further separate aids, which are arranged on the container, for example, are required.

A filling level sensor according to the invention, which has only one float, is particularly compact and simple and can be used in a variety of ways. It is not necessary to install further attachments on a container. The float can simply be placed in the container and the measurement can be started. The filling sand sensor can be moved freely within the container. Above all, a filling level sensor according to the invention is suitable for determining filling levels in mobile containers, such as in IBC containers (International Bulk Containers), which are transported frequently and on which the attachment of external structures is disruptive and expensive.

For the self-sufficiency of the filling level sensor, the float has in particular a transmission device for the wireless transmission of measured data or measured values and/or an energy store for its own energy supply. The transmission device can preferably be a radio module for narrowband radio technology (LoRa, Sigfox, LTE-M, NB-IOT), which transmits the measurement data or measurement values to a cloud, i.e. to a server on the World Wide Web. The energy store is designed in particular as a battery or accumulator and can also include an energy harvesting module. In particular, the float also has an evaluation and control unit.

To measure the fill level, the float has as a means of measuring the fill level in particular special a sensor unit in the form of a motion detector. The movement detector can be used to determine the fill level of the path that the liquid surface or the float travels when a container is being filled and also when it is emptied, and the fill level can be determined therefrom.

The float is preferably hollow on the inside and forms a housing within which all components, such as the energy supply, the transmission unit, the sensor unit and other components are arranged. The float forms the outer shell of the level sensor.

In a practical embodiment of a level sensor according to the invention, the float has a gas reservoir, a compressor and an expandable bladder. The gas holder, the compressor and the expandable bladder are functionally connected. In particular, air is stored in the gas reservoir. The gas from the gas reservoir can be fed into the bladder as needed. The bubble is stretchable and expands depending on the amount of gas fed. Bubbles with a volume in the range of 200 cm ³ are considered to be particularly suitable. A compressor is provided for transferring the gas from the bladder into the gas storage device, which compressor transfers the gas into the gas storage device in compressed form. The gas in the gas reservoir has a higher pressure and a higher density than in the bladder. Depending on how much gas is in the bubble, the buoyancy of the swimmer can be varied. By transferring the gas from the bladder to the gas reservoir, the buoyancy of the swimmer is reduced and the swimmer can be made to sink. The swimmer himself is designed in such a way that he can dive down. If gas from the gas reservoir is fed into the bladder, the buoyancy is increased and the swimmer rises to the surface of the liquid. In particular, the weight of the sensor and the maximum volume of the expandable bubble are matched to one another in such a way that the sensor can emerge up to the surface of a liquid, depending on the density of the filling material. Overall, it is made possible for the swimmer to be able to measure the distance from the liquid surface to the bottom of the container independently of the current level of the liquid surface. The filling level sensor can then also be introduced into already filled containers and then determine the filling level. Further details on this are described below in connection with the method.

In particular, the float is spherical. The spherical shape has the advantage that as little as possible gets caught on the float and that the float can't jam inside the container.

In particular, the float is made of plastic. Thus, the float is inexpensive and light. In particular, the float can also be used in aggressive media, such as in alkalis or acids.

In order for the level sensor according to the invention to function as reliably as possible, the float is in particular balanced in such a way that the transmission unit is arranged in an upper area within the float when the float is in the floating state. In the upper area of the float means in particular in the upper half of the float, in particular in the area which lies above the liquid surface. In particular, the weight distribution within the float is chosen so that the float orients itself so that the transmission unit is located at the top. In order to correspondingly tare the float, the energy store can be arranged in the other half, for example, in which the transmission unit is not arranged. It is also conceivable to arrange additional weight inside the float. The space for the propagation of the bubble is at least predominantly provided for the area in which the transmission unit is also arranged. Due to the transmission unit being arranged above, outside the water surface, a weakening of the transmission quality through absorption of the radio waves in the liquid is avoided as far as possible, thus maximizing the range.

If it should be necessary, a repeater for signal transmission can be arranged in particular on the outside of the container.

In a further embodiment, the transmission unit is designed in such a way that it is deactivated in the submerged state. Since radio transmission is not possible or only possible with difficulty in many liquid media, the level sensor is particularly energy-saving. The deactivation can be done by a sensor or by a valve to control the air bubble.

In a further practical embodiment of the filling level sensor according to the invention, the movement detector is an inertial measurement unit (IMU). Such a measuring unit has a number of inertial sensors, such as acceleration sensors and yaw rate sensors, which are spatially distributed. In particular, the IMU has three acceleration sensors (translation sensors) oriented perpendicularly to one another for detecting the translational movement and three yaw rates oriented perpendicularly to one another sensors (gyroscopic sensors) for detecting rotating movements. The IMU is in particular the measuring unit of an inertial navigation system (Inertial Navigation System, INS), with the INS being used to determine the lift velocity. The distance covered by the swimmer can be determined from the buoyancy rate and the time.

In particular, the filling level sensor additionally has a sensor unit for detecting the temperature and/or a sensor unit for detecting the density of the filling material. The area of application of the fill level sensor can thus be expanded.

The invention also relates to a method for measuring a filling level with an autonomous filling level sensor as described above. The fill level can be measured particularly easily due to the self-sufficiency of the fill level sensor. In particular, the float swims at the level of the surface of the filling material or the liquid and detects the distance covered with the movement detector. The current fill level can then be determined from this.

In order to also measure the fill level of a container that is already filled, i.e. without the fill level sensor having already been inserted into the empty container, the level of the liquid can be specifically "traversed". In this case, the float is first caused to sink by emptying a gas (in particular air)-filled bladder within the float. Emptying ends when the motion detector no longer detects the float sinking any further. The float is then assumed to have reached the bottom of the tank. After the descent, an ascent process is initiated by filling the bladder with gas until no further ascent is detected by the motion detector. During the surfacing process, the movement detector is used to determine the buoyancy speed of the swimmer and from this the distance covered.

As already explained above, the swim bladder is emptied in particular by means of a compressor. The compressor compresses the gas expanded in the bladder and transfers it to a gas reservoir.

In a further practical embodiment of the method according to the invention, the geometry of the container is taken into account to determine the filling level. The geometry includes in particular the base area and the progression of the cross-sectional area of the container over the height of the container. The float can thus be placed in different containers. It is possible for the geometric data to be entered and the filling level can then be determined on the basis of the data entered. The input can be made in particular via a mobile device or the higher-level unit, which each communicate with an evaluation unit.

Alternatively, the geometry of the container can already be stored in a database. This is particularly useful for standardized containers, such as IBC containers. The user can, for example, select the appropriate container from a list or, in a particularly simple embodiment, the data of the standardized container is stored and the filling level sensor is only suitable for measuring a filling level in such containers.

After the end of the surfacing process, i.e. when the float has reached the surface of the filling material, the determined values are transmitted to a higher-level unit. In particular, the transmission only takes place if the transmission unit is arranged outside the liquid. In particular, the at least one buoyancy speed or a distance already evaluated therefrom or a filling level are transmitted as values. The evaluation can already take place on the part of the swimmer or in the superordinate unit.

The method is particularly energy-saving if the level sensor is deactivated after a measurement. After the level sensor has risen to the surface of the liquid and transmitted the measured data, the level sensor switches to a deactivated state in which little power is consumed. Activation can take place either on demand or after a certain period of time. In particular, activation is event-based, i.e. in the event of a fill level change.

In a further practical embodiment of the method according to the invention, the surfacing process is checked for different buoyancy speeds. If different buoyancy rates are detected, layers of different filling materials with different densities can be inferred from this, since the buoyancy rate depends on the density of the filling material.

Furthermore, the invention also relates to an arrangement of a level sensor as described above in a container. The float is freely movable in the container. That is, the float is not directly or indirectly connected to the tank.

• 1 einen Füllstandsensor in einer schematischen Darstellung im Querschnitt,
• 2 die Anordnung eines Füllstandsensors in einem Behälter in einer abgesenkten Position in einer schematischen Darstellung,
• 3 die Anordnung gemäß 2 mit einer aufgetauchten Position des Füllstandsensors in einer schematischen Darstellung, und
• 4 ein Ablaufdiagramm eines Verfahrens zur Messung des Füllstandes.

Further practical embodiments and advantages are explained below in connection with the figures. Show it:

• 1 a level sensor in a schematic representation in cross section,
• 2 the arrangement of a level sensor in a container in a lowered position in a schematic representation,
• 3 the arrangement according to 2 with a surfaced position of the level sensor in a schematic representation, and
• 4 a flow chart of a method for measuring the fill level.

In 1 a self-sufficient level sensor 10 is shown schematically. The level sensor 10 is shown in cross section with a view of the level sensor 10 from above.

The level sensor 10 has a float 12, which is designed as a hollow body and surrounds several components. In the present case, the float 12 is made of plastic and is spherical.

In the float 12 is an energy store 14 in the form of a battery, a combined transmission unit 16 and evaluation unit 18 and a means for level measurement 40 - here a sensor unit 20 in the form of a movement detector - arranged. The movement detector 20 is an IMU with a number of acceleration and yaw rate sensors. The evaluation unit 18 is also used to determine a speed from the acceleration data from the sensors.

Furthermore, an expandable bladder 22 is arranged in the float 12, which can be filled with gas (air) as required and can increase or decrease its volume according to the double arrow. A compressor 24 and a gas reservoir 26 are connected to the bladder 22. The compressor 24 can extract gas from the bladder 22 and supply it to the gas reservoir 26 in compressed form. Furthermore, gas can be filled into the bladder 22 from the gas reservoir 26 . The gas in the gas reservoir 26 has a higher density and a higher pressure than in the bladder 22.

The following is related to the 3 until 5 the functioning of the filling level sensor 10 is explained.

In the 3 and 4 a container 28 - here a standardized IBC container - is shown. The container 28 is surrounded by a frame 30 and has a lid 32 . A liquid 34 is arranged in the container 28 .

To determine the fill level in the container 28, the fill level sensor 10 floats freely in the liquid 34 in the container 28. The float 12 is designed in such a way that it can both submerge (cf. 2 ) as well as in the liquid 34 and in particular on the liquid surface (cf. 3 ). Structures or attachments to the container 28 are not required.

The float 12 is balanced in such a way that the transmission unit 16 is arranged in the area of the float 12 which is arranged above the surface of the liquid 34 .

In 5 a flow chart of the method for determining the fill level is shown.

The filling level measurement is started with step S1. If there is no data regarding the current filling level or the filling level is not 0, in step S2 the float 12 is caused to submerge. For this purpose, gas is transferred from the bladder 22 into the gas reservoir 26 by means of the compressor 24 .

In step S3 it is queried whether the bottom of the container 28 has been reached, ie whether the movement detector 20 no longer detects any further sinking. If this is the case (J) (cf. 2 ), the measurement is started in step S4 and the surfacing process begins in step S5. To this end, gas is transferred from the gas reservoir 26 into the bladder 22 . The bubble 22 slowly expands and the float 12 moves toward the liquid surface. In step S6 it is queried whether the swimmer 12 has surfaced completely, ie whether no further upward movement is detected by means of the movement detector 20 .

If the float 12 has surfaced completely (cf. 3 ), the evaluation of the buoyancy rate determined by means of the movement detector 20 (or in the case of a filling material with several layers, the several buoyancy rates) takes place in step S7. The distance covered by the float 12 is determined from the buoyancy rate, and from this the fill level can be determined, taking into account the geometry of the container 28 .

The determined values are sent by the transmission unit 16 in step S8. After the data has been sent, the filling level sensor 10 switches to a deactivated state in step S9.

Reference List

10

autonomous level sensor

12

swimmer

14

energy storage

16

transmission unit

18

evaluation unit

20

Sensor unit, motion detector

22

bladder

24

compressor

26

energy storage

28

container

30

frame

32

Lid

34

liquid

40

Means for level measurement

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was 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.

Patent Literature Cited

• DE 102005036846 B4 [0003]

Claims (15)

Autonomous fill level sensor for measuring a fill level in a container (28), with a float (12), characterized in that the float (12) has means for detecting a fill level (40). Level sensor according to the preceding claim, characterized in that the float (12) has an energy store (14), a transmission unit (16) and/or a sensor unit (20) in the form of a movement detector. Level sensor according to one of the preceding claims, characterized in that the float (12) has a gas reservoir (26), a compressor (24) and an expandable bladder (22). Level sensor according to one of the preceding claims, characterized in that the float (12) is of spherical design. Level sensor according to one of the preceding claims, characterized in that the float (12) is tared such that the transmission unit (16) is arranged in the floating state of the float (12) in an upper region of the float (12). Level sensor according to one of the preceding claims, characterized in that the movement detector (20) is an inertial measuring unit. Level sensor according to one of the preceding claims, characterized in that the float (12) additionally has a sensor unit for detecting the temperature and/or a sensor unit for detecting the density of the filling material (34). Method for measuring a filling level with an autonomous filling level sensor (10) according to one of the above Claims 1 until 7 . Method according to the preceding claim, characterized in that the swimmer (12) is first caused to sink by emptying the gas-filled bladder (22) until the movement detector (20) no longer detects any further sinking, after which the swimmer is caused to emerge (12) by filling the bladder (22) with gas until no further surfacing of the swimmer (12) is detected by the motion detector (20), and during the surfacing the buoyancy rate of the swimmer (12) is determined and therefrom determined the level. Method according to the preceding claim, characterized in that the bladder (22) is emptied by means of a compressor (24). Method according to one of the preceding claims, characterized in that the fill level is determined taking into account the geometry of the container (28). Method according to one of the preceding claims, characterized in that after the swimmer (12) has finished surfacing, the determined values are transmitted to a superordinate unit. Method according to one of the preceding claims, characterized in that the filling level sensor (10) is deactivated after a filling level measurement. Method according to one of the preceding claims, characterized in that the surfacing process is checked for different buoyancy speeds. Arrangement of a filling level sensor (10) according to one of the above Claims 1 until 7 in a container (28), characterized in that the float (12) is freely movable in the container (28).

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