Apparatus and method for capacitive fill level measurement

Abstract

The invention relates to a device (3) for capacitive fill level measurement on an outer wall of a fluid container (2) filled with at least one first fluid (14), comprising:-at least one first capacitor (7a) and a second capacitor (7b), which are arranged parallel to one another along a longitudinal direction (L) of the capacitors (7a, 7b) and can be placed on the outer wall of the fluid container (2), -a detection device (13) which is designed to apply a voltage to the capacitors (7a, 7b) in a time-shifted manner and to detect the charge of each capacitor (7a, 7b) in order to determine the capacitance of each capacitor (7a, 7b) by metering, the detection device (13) being further designed to compare the capacitance of the capacitors (7a, 7b) detected by metering with one another, and determining a filling level (F) of the fluid container (2) on the basis of the comparison, taking into account a positioning specification with respect to the fluid container.

Description

Technical Field

[0001] The present invention relates to a device for capacitively measuring the filling level on the outer wall of a fluid container filled with at least one first fluid. The present invention also relates to a system comprising the device and the fluid container. The present invention also relates to a method for capacitively measuring the filling level of a fluid container filled with at least one first fluid. Background Art

[0002] In the chemical industry, glass or plastic containers are widely used for storage or chemical reactions. To detect the filling level in the container, simple numerical scales printed on the container wall are usually sufficient for manual reading (in the manner of a measuring cup). For various reasons (such as cost or avoiding contact with the medium), the use of measuring equipment instruments to detect the filling level is often abandoned.

[0003] In addition, different liquids are often stored in the container, thus forming an interface layer (such as water and oil). For differentiating between and / or separately detecting the filling levels of the two fluids, simple non-contact instruments are not feasible.

[0004] Many containers are not fixed, so a measuring device that does not require a permanent line connection is needed to detect the filling level. Battery-powered and wireless solutions would be advantageous.

[0005] WO 2023 / 036423 A1 discloses a capacitive reading device for a pointer instrument. Summary of the Invention

[0006] The object of the present invention is to provide a device and related method for capacitively measuring the filling level that can be implemented with low cost and minimal invasiveness.

[0007] This object is achieved by the device for capacitively measuring the filling level on the outer wall of a fluid container filled with at least one first fluid according to claim 1. This object is also achieved by the system according to claim 8. This object is also achieved by the method for capacitively measuring the filling level of a fluid container filled with at least one first fluid according to claim 9. Advantageous improvements are described in the dependent claims.

[0008] According to the present invention, there is provided a device for capacitively measuring the filling level on the outer wall of a fluid container filled with at least one first fluid, comprising:

[0009] - at least one first capacitor and a second capacitor, which are arranged parallel to each other along the longitudinal direction of the capacitor and can be placed on the outer wall of the fluid container,

[0010] - A detection device, which is configured to preferably apply a voltage to the capacitors in a time-staggered manner and detect the charge on each capacitor, in order to determine the capacitance of each capacitor by metering.

[0011] The detection device is further configured to compare the capacitances of the capacitors detected by metering with each other, and based on this comparison, determine the filling level of the fluid container taking into account the positioning instructions regarding the fluid container.

[0012] The device according to the invention can be simply arranged on the outer wall of the fluid container. The capacitors are arranged parallel to each other in the longitudinal direction. In other words, the capacitors are arranged in a parallel and staggered manner with respect to each other.

[0013] The detection device of the device according to the invention is configured to preferably apply a voltage to the capacitors in a time-staggered manner. Depending on the dielectric constant of the fluid located in the fluid container, a specific charge is formed in each capacitor. This charge is measured by the detection device. The detection device derives the capacitance of each capacitor from the measured charge and the applied voltage. The voltage can be applied simultaneously to multiple or all of the capacitors. However, it is also possible to advantageously apply the voltage to the capacitors in a time-staggered and / or successive manner in order to prevent or at least reduce the mutual parasitic effects on the subsequently determined capacitances.

[0014] The detection device is also designed to compare the measured capacitances of two capacitors. For example, if the detection device determines that both capacitors have the expected capacitance for the medium air, it can be assumed that the filling level in the fluid container is very low and does not reach the first capacitor. However, if the capacitances of both capacitors are significantly larger, it can be assumed that the filling level in the fluid container is high and reaches above both capacitors. If the capacitances of the two capacitors are different from each other within the measurement accuracy, it can be assumed that the filling level in the fluid container reaches the height of the first capacitor.

[0015] In order for the device according to the invention to be able to indicate the absolute filling level, positioning instructions must be provided to the detection device. It defines the height at which the device is arranged on the fluid container. It thus represents the so-called offset, which is zero in the simplest case. The detection device identifies the spacing between the capacitors. In combination with the positioning instructions, it can thereby precisely calculate the filling level of the fluid container.

[0016] The detection device can be directly arranged in the vicinity of the space of the capacitors, especially within a common housing. However, the components of the detection device that compare the capacitances and determine the filling level can also be arranged at a location remote from the capacitors, for example, in a cloud-based computing environment.

[0017] The device according to the invention has the advantage that it does not require movable mechanical parts to measure the filling level. In addition, only readily available standard components can be used. Additionally, the device does not enter the fluid container, which can be particularly problematic for handling chemically reactive fluids. The measurement of the filling level is not limited to a single fluid in the fluid container. Instead, up to N different fluids can be detected using N capacitors.

[0018] Obviously, the invention is not limited to two capacitors. Instead, the device can include three or more, a large number of capacitors. The applicable principle is: the more capacitors, the higher the spatial resolution. Therefore, using a large number of capacitors can indicate the filling level more precisely.

[0019] Preferably, the device has a shielding plate for electromagnetic shielding of the capacitors, especially from each other. The device according to the invention is arranged to detect the capacitance change caused by the different dielectric constants of different fluids within the fluid container. A suitable design for this is to shield the capacitors with a suitable shielding plate to prevent unwanted electromagnetic effects. In particular, the capacitors can be electromagnetic shielded relative to each other to prevent or at least minimize the distortion of the measurement results.

[0020] The detection device can include a capacitance-to-digital converter, which preferably has a measurement resolution of at least 24 bits.

[0021] In addition, the detection device can include a multiplexer, which has at least two voltage output terminals, and each voltage output terminal is conductively connected to a capacitor (more precisely: each voltage output terminal is connected to the electrode of the capacitor). In the case of three or more capacitors, the multiplexer can correspondingly have more voltage output terminals.

[0022] Preferably, the potential of the unpowered voltage output terminal of the multiplexer corresponds to the potential of the shielding plate. In this way, the currently unpowered capacitor can serve as an additional shield for the capacitor that is currently used to determine the capacitance and is supplied with voltage.

[0023] A printed circuit board (English: Printed Circuit Board, abbreviated: PCB) can be used as a carrier element for the electrodes / capacitors. Additionally, the carrier element can also be a flexible printed film, such as a polyimide or PU film.

[0024] In a preferred improvement of the present invention, the device includes at least one first, second, and third capacitor, which are arranged parallel to each other along the longitudinal direction of the capacitor. Here, the second capacitor is arranged between the first and third capacitors in the longitudinal direction. Here, the voltage output terminal of the multiplexer is conductively connected to the first and third capacitors, while the other voltage output terminal of the multiplexer is conductively connected to the second capacitor. The basic idea is that the voltage output terminal of the multiplexer can be connected to multiple capacitors. Thereby, a higher filling level resolution can be achieved without using a multiplexer with so many voltage output terminals. More information in this regard is disclosed by the description of the embodiments.

[0025] The above object is also achieved by a system, which includes a fluid container filled with one or more fluids and a device designed as described above. The device is arranged on the outer wall of the fluid container, and the longitudinal direction of the capacitor of the device is oriented along the direction of the filling level to be measured of the fluid container. In other words, the device is oriented vertically on the fluid container and fixed there by an appropriate means (such as pasting, clamping, etc.).

[0026] The object is also achieved by a detection system, which includes a plurality of devices as described above, these devices are connected to one or more upper evaluation units, and preferably these devices are arranged in a pipeline, and the outer wall of the fluid container is preferably made of plastic or glass.

[0027] The above object is also achieved by a method for capacitively measuring the filling level of a fluid container filled with at least one first fluid, the method including the following steps:

[0028] -a) Arranging the device on the outer wall of the fluid container, the device having at least one first capacitor and a second capacitor, these capacitors being arranged parallel to each other along the longitudinal direction of the capacitor, and the device also having a detection device;

[0029] -b) Applying a voltage to the capacitor preferably in a time-staggered manner by a detection unit;

[0030] -c) Detecting, by the detection unit, the charge generated by the applied voltage for each capacitor;

[0031] -d) Determining, by the detection unit, the capacitance of each capacitor by metering based on the applied voltage and the detected charge;

[0032] -e) Comparing the capacitances of the capacitors detected by metering to thereby determine the filling level of the fluid container.

[0033] The detection device may include a capacitance-to-digital converter, which preferably has a measurement resolution of at least 24 bits, and detects the charge generated by the applied voltage on each capacitor, and determines the capacitance of each capacitor by metering.

[0034] The detection device may further include a multiplexer, which has at least two voltage output terminals, and each voltage output terminal is conductively connected to a capacitor, and a voltage is applied to each capacitor through the voltage output terminal.

[0035] Preferably, the device includes at least a first, a second, and a third capacitor, which are arranged parallel to each other along the longitudinal direction of the capacitor, wherein the second capacitor is arranged between the first capacitor and the third capacitor along the longitudinal direction, and wherein the first voltage output terminal of the multiplexer is conductively connected to the first and third capacitors, and wherein the second voltage output terminal of the multiplexer is conductively connected to the second capacitor, wherein a voltage is applied to the first and third capacitors through the first voltage output terminal of the multiplexer, and wherein a voltage is applied to the second capacitor through the second voltage output terminal of the multiplexer. Description of the Drawings

[0036] The features, characteristics, and advantages of the present invention and their implementation become clearer in conjunction with the following description of the embodiments, and the embodiments are described in detail with reference to the drawings. The drawings show:

[0037] Figure 1 A schematic diagram showing a system having a device and a fluid container;

[0038] Figure 2 A schematic diagram showing the measurement of capacitance by the device according to the present invention;

[0039] Figure 3 A circuit diagram showing a part of the device according to the present invention;

[0040] Figure 4 A perspective view showing an embodiment of the device according to the present invention;

[0041] Figure 5 A side view showing the device according to the present invention;

[0042] Figure 6 A perspective view showing an embodiment of the device according to the present invention;

[0043] Figure 7 A diagram showing an aspect of the method according to the present invention;

[0044] Figure 8 A circuit diagram showing a part of another device according to the present invention;

[0045] Figure 9Shows an aspect of the device according to the present invention;

[0046] Figure 10 Shows a side view of the device according to the present invention; and

[0047] Figure 11 Shows a graph of measurements performed by the device according to the present invention. Detailed Description

[0048] Figure 1 Shows a side view of system 1 according to the present invention. System 1 includes a fluid container 2, a device 3, and a detection device 13 (see Figure 3 ). The fluid container 2 is made of glass in this example and can be filled with a fluid such as water or oil. The filling level F of the fluid container is measured vertically upward from the lower edge (bottom) of the fluid container 2 in Figure 1 .

[0049] Figure 1 Only a part of the device 3 is shown in Figure 1 . This part includes four power supply electrodes 4a, 4b, 4c, 4d, a sensor electrode 5, an electromagnetic shielding plate 6 arranged on the right side of the sensor electrode 5 in Figure 1 , and another shielding plate 8 arranged on the left side of the power supply electrodes 4a, 4b, 4c, 4d. The shielding plates 6, 8 can be made of aluminum, for example, and can have the same electric potential.

[0050] The power supply electrodes 4a, 4b, 4c, 4d and the sensor electrode 5 together form four capacitors 7a, 7b, 7c, 7d represented by a dashed box in Figure 1 . These electrodes 4a, 4b, 4c, 4d, 5 are arranged along the longitudinal axis L, for example, on a flexible printed film or a circuit board, which is not shown in Figure 1 for clarity (see Figure 9 ).

[0051] Figure 1 The part of the device 3 shown in is arranged on the outer wall (i.e., the outside of the fluid container 2) of the fluid container 2 in a suitable manner (adhesive, clamping device, etc.). Among them, the part of the device 3 is arranged such that the longitudinal axis L of the power supply electrodes 4a, 4b, 4c, 4d and / or the sensor electrode 5 matches the direction of the filling level F.

[0052] Voltages are applied to the power supply electrodes 4a, 4b, 4c, 4d in a time-staggered manner, which is the responsibility of the detection device 13 of the device 3 shown in Figure 3 . Figure 2 Is shown in cross-sectional view by way of example Figure 1Of the four capacitors 7a, 7b, 7c, 7d in [reference], the capacitor 7a formed by the power supply electrode 4a and the sensor electrode 5 is also shown, as well as the electric field E generated by the applied voltage. A part of this electric field E extends through the wall of the fluid container 2 (cross-sectional view) and is affected by the dielectric constant of the fluid in the fluid container 2.

[0053] The voltage is provided by Figure 3 the detection device 13 of the device 3 shown in [reference]. Figure 3 A circuit diagram of the detection device 13 of the device 3 is shown. On the left side, three capacitors 7a, 7b, 7c are shown. The power supply electrodes 4a, 4b, 4c of the capacitors 7a, 7b, 7c are each connected to the voltage output terminals 9a, 9b, 9c of the multiplexer 10. The multiplexer 10 is arranged to apply voltages to the voltage output terminals 9a, 9b, 9c in a time-staggered manner. The voltage is received at the voltage output terminal 11 ("EXC") of the capacitance-to-digital converter 12 from the capacitance in the detection device 13. The capacitance-to-digital converter 12 can be, for example, the AD7745 from Analog Devices. It is capable of detecting capacitances in the range of 0 to 8 pF with a resolution of 24 bits. The capacitance is measured through the input terminal 14 ("CIN(+)") connected to the sensor electrode 5. The internal structure of the capacitance-to-digital converter 12 is not the subject of the present invention and will not be further described.

[0054] For example, a 3-to-8 line decoder 74xx238 from Texas Instruments can be used as the multiplexer 10. The multiplexer 10 sets the voltage output terminals 9a, 9b, 9c to which no voltage is applied to the same potential as that of the shielding plate 6. Thus, all the power supply electrodes 4a, 4b, 4c, 4d to which no voltage is applied serve as shields for the power supply electrodes 4a, 4b, 4c, 4d to which voltage is applied. Regarding this, see Figure 4 [reference], which shows eight power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, the sensor electrode 5, and the shielding plate 6 arranged on the fluid container 2. In Figure 4 [reference], only the power supply electrode 4c is applied with voltage. At the time point shown in Figure 4 [reference], only the capacitor 7c formed by this power supply electrode 4c and the sensor electrode 5 is used for capacitance measurement.

[0055] Figure 5Shows how the capacitance measured by the detection device 13 can be correlated with the filling level F in the fluid container 2. The detection device 13 sequentially applies a voltage to the first three capacitors 7a, 7b, 7c (from bottom to top) and measures the capacitance of each capacitor 7a, 7b, 7c. This is mainly affected by the dielectric constant of the fluid 14 in the fluid container 2. As the transition is made to the fourth capacitor 7d, there is no longer any fluid 14 in the fluid container 2, which affects the electric field generated by the capacitor 7d and the finally measured capacitance. By comparing the capacitance measured on the fourth capacitor 7d with the capacitance measured on the third capacitor 7c, the filling level F in the fluid container 2 can be inferred. The spacing between the capacitors 7a, 7b, 7c, 7d from each other determines the resolution of the filling level that can be determined.

[0056] Wherein each power supply electrode 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j must be connected to the voltage output terminals 9a, 9b, 9c of the multiplexer 10. The number of electrode numbers can also be equal to the number of electrodes that can be switched for measurement. In the case of using an 8-to-1 multiplexer 10, one of the eight power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h can be activated for measurement respectively. If these eight electrodes are simply arranged parallel to each other, the filling level can only be measured within the measurement area where these eight electrodes are arranged.

[0057] If the filling level of the entire container is to be detected with a resolution of 1% of the measurement range, then 100 power supply electrodes must be arranged linearly according to the above scheme. Therefore, a 100-to-1 multiplexer 10 is required, which is complex in terms of current circuit technology. Figure 6 The shown embodiment provides a solution to this. Each voltage output terminal 9a, 9b, 9c of the multiplexer 10 is connected to two or more power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l. In the case of multiple uses, the capacitance measurement range of the detection device 13 is designed such that the signal output reaches 100% only when the fluid has reached all the power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l corresponding to the respective voltage outputs 9a, 9b, 9c, and the signal output reaches 50% when the fluid reaches half of the corresponding power supply electrodes.

[0058] In this way, a large number of power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l can be set with relatively few voltage output terminals of the multiplexer 10, thereby enabling a high spatial resolution.

[0059] Figure 7Shows another illustrative example. Device 3 here has 16 power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l, 4m, 4n, 4o, 4p and sensor electrodes 5. The multiplexer 10 here has four voltage output terminals 9.1, 9.2, 9.3, 9.4 (similar to the voltage output terminals 9a, 9b, 9c in the previous figures), and each voltage output terminal is respectively connected to four of the power supply electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l, 4m, 4n, 4o, 4p. For example, the first voltage output terminal 9.1 is connected to the first power supply electrode 4a, the fifth power supply electrode 4e, the ninth power supply electrode 4i, and the thirteenth power supply electrode 4m. Therefore, the spacing between the power supply electrodes 4a, 4e, 4i, 4m connected to the voltage output terminal is four power supply electrodes respectively. For the other voltage output terminals 9.2, 9.3, 9.4, this design similarly applies.

[0060] The height 14 of different filling levels of the fluid (water and oil) is shown on the right. The signal output levels of the capacitances measured respectively for the voltage output terminals 9.1, 9.2, 9.3, 9.4 are shown in the table list below. For the first column, the filling level of water reaches the second power supply electrode 4b and / or the second capacitor. The first power supply electrode 4a is connected to the first voltage output terminal 9.1, and the second power supply electrode 4b is connected to the second voltage output terminal 9.2. The signal output levels of the capacitances measured with respect to the corresponding voltage output terminals 9.1, 9.2 are 25% respectively because the filling level does not reach the remaining power supply electrodes connected to the two voltage output terminals 9.1, 9.2. The second, third, and fourth columns also show the corresponding signal output levels in a similar manner. For the fifth column, water reaches the ninth power supply electrode 4i. This results in a signal output level of 50% for the respective capacitances of the second, third, and fourth voltage output terminals 9.2, 9.3, 9.4, and a signal output level of 75% for the capacitance of the first voltage output terminal 9.1.

[0061] For the capacitances with respect to the second, third, and fourth voltage output terminals 9.2, 9.3, 9.4, the signal output level is further increased by 3% because oil only brings a relatively small increase in capacitance compared to water. Therefore, the detection device 13 can easily detect the height of the filling level of water and the height of the filling level of oil, and only requires a multiplexer 10 with four voltage output terminals for this purpose.

[0062] Figure 8 Shows another embodiment of the detection device 13 of device 3.

[0063] Figure 9Shows another embodiment of the power supply electrodes 4a, 4b, 4c and the sensor electrode 5. The circuit can be configured to have a relatively large length and thus be adjusted as needed to match the length of the corresponding fluid container (e.g., by cutting). In Figure 9 it is shown on the right side that the power supply electrodes 4a, 4b, 4c do not have to be arranged directly parallel to each other, but can also be arranged around the sensor electrode 5 in an alternating manner. What is important is that their axes k are arranged substantially parallel to each other.

[0064] Figure 10 Shows a side view of the first part of the device 3 according to the invention. In Figure 10 the visible power supply electrodes 4a, 4b, 4c, 4d (and the sensor electrode 5 obscured by the power supply electrodes 4a, 4b, 4c, 4d in Figure 10 ) are fixed to the outer wall of the fluid container 2 by means of an adhesive 15. It can also be seen that there are portions of the shielding plates 6, 8 provided in the longitudinal direction L in order to shield the capacitors from each other. The electrodes 4a, 4b, 4c, 4d and the shielding plates 6, 8 are arranged on a flexible film 16 and are made of copper or conductive ink. The thickness of the electrodes 4a, 4b, 4c, 4d, 5 is 25 micrometers. Above this (on the right side in Figure 10 ) there is a further shielding layer 17. The thickness of this shielding layer can be 35 micrometers.

[0065] Figure 11 Shows the measurement results obtained using 24 power supply electrodes (3×8 with an 8-to-1 multiplexer). The electrode size is 20 mm×10 mm and the spacing between the electrodes (in the direction of the longitudinal axis L) is 1 mm. The measurement range is 270 mm. After each measurement, the filling level in the fluid container is increased in steps of 5 mm.

[0066] The capacitance changes stepwise in steps of 33% of the signal output (since 3 electrodes are connected, i.e., 3 capacitors are connected in parallel). The x-axis shows the filling level in the fluid container and the y-axis shows the capacitance measured for eight power supply electrodes (and / or the capacitors formed by them). Above a filling level of 100 mm, the channel associated with the first power supply electrode (marked as K in Figure 11 ) measures approximately 1.7 pF (66% of the capacitance signal output). Above a filling level of 190 mm, this channel outputs completely at 2.6 pF (100%).

[0067] Although the present invention has been described and illustrated in detail by means of preferred embodiments, the present invention is not limited to the disclosed examples, and other variants can be derived therefrom by those skilled in the art without departing from the scope of protection of the present invention.

Claims

1. An apparatus (3) for capacitively measuring a filling level on an outer wall of a fluid container (2) filled with at least one first fluid (14), the apparatus comprising: - at least one first capacitor (7a) and a second capacitor (7b), the first capacitor and the second capacitor being arranged parallel to each other along a longitudinal direction (L) of the capacitors (7a, 7b), and the first capacitor and the second capacitor being capable of being placed on the outer wall of the fluid container (2), - a detection device (13) which is arranged to apply voltages to the capacitors (7a, 7b), preferably in a time - staggered manner, and to detect the charge on each capacitor (7a, 7b) in order to determine the capacitance of each capacitor (7a, 7b) by metering, wherein the detection device (13) is further arranged to compare the capacitances detected by metering of the capacitors (7a, 7b) with each other and to determine the filling level (F) of the fluid container (2) based on the comparison taking into account positioning instructions regarding the fluid container.

2. The apparatus (3) according to claim 1, the apparatus having shielding plates (6, 8, 17) for electromagnetic shielding of the capacitors (7a, 7b) from each other in particular.

3. The device (3) according to any one of the preceding claims, wherein, The detection device (13) includes a capacitance - to - digital converter (12) which preferably has a measurement resolution of at least 24 bits.

4. The device (3) according to any one of the preceding claims, wherein, The detection device (13) includes a multiplexer (10) which has at least two voltage output terminals (9a, 9b), each of the voltage output terminals being conductively connected to a capacitor (7a, 7b).

5. The device (3) according to claim 2 and 4 or according to claims 2, 3 and 4, wherein, The potential of the un - energized voltage output terminals (9a, 9b) of the multiplexer (10) corresponds to the potential of the shielding plates (6, 8, 17).

6. The device (3) according to any one of the preceding claims, wherein, The capacitors (7a, 7b, 7c) are arranged on a circuit board or a flexible film.

7. The device (3) according to at least claim 4, the device comprising at least a first capacitor (7a), a second capacitor (7b) and a third capacitor (7c), the first capacitor, the second capacitor and the third capacitor being arranged parallel to each other along the longitudinal direction (L) of the capacitors (7a, 7b, 7c), wherein, The second capacitor (7b) is arranged between the first capacitor (7a) and the third capacitor (7c) along the longitudinal direction (L), and wherein the voltage output terminal (9a) of the multiplexer (10) is conductively connected to the first capacitor (7a) and the third capacitor (7c), and wherein the further voltage output terminal (9b) of the multiplexer (10) is conductively connected to the second capacitor (7b).

8. A system (1) comprising a fluid container (2) filled with one or more fluids and a device (3) according to any one of the preceding claims, the device being arranged on an outer wall of the fluid container (2), wherein, The longitudinal direction (L) of the capacitors (7a, 7b, 7c) of the apparatus (1) is oriented along the direction of the filling level (F) to be measured of the fluid container (2).

9. The system (1) according to claim 8, wherein, The outer wall of the fluid container (2) is made of plastic or glass.

10. A method for capacitively measuring the filling level (F) of a fluid container (2) filled with at least one first fluid, comprising: a) Place the device (3) on the outer wall of the fluid container (2), wherein the device (3) has at least a first capacitor (7a) and a second capacitor (7b), and the first capacitor and the second capacitor are arranged parallel to each other along the longitudinal direction (L) of the capacitors (7a, 7b), and the device further has a detection device (13). b) Apply voltage to the capacitors (7a, 7b) preferably in a time - staggered manner through the detection device (13). c) Detect the charge generated on each capacitor (7a, 7b) due to the applied voltage through the detection device (13). d) Determine the capacitance of each capacitor (7a, 7b) by metering through the detection device (13) based on the applied voltage and the detected charge. e) Compare the capacitances of the capacitors (7a, 7b) detected by metering to determine the filling level of the fluid container (2) from the comparison.

11. The method according to claim 10, wherein, The detection device (13) includes a capacitance - to - digital converter, which preferably has a measurement resolution of at least 24 bits, and the capacitance - to - digital converter detects the charge generated on each capacitor (7a, 7b) due to the applied voltage and determines the capacitance of each capacitor (7a, 7b) by metering.

12. The method according to claim 10 or 11, wherein, The detection device (13) includes a multiplexer (10), which has at least two voltage output terminals (9a, 9b), and the voltage output terminals are each conductively connected to the capacitors (7a, 7b), and the voltage is applied to each capacitor (7a, 7b) through the voltage output terminals.

13. The method according to claim 12, wherein, The device (3) includes at least a first capacitor, a second capacitor, and a third capacitor (7a, 7b, 7c), and the first capacitor, the second capacitor, and the third capacitor are arranged parallel to each other along the longitudinal direction (L) of the capacitors (7a, 7b, 7c), wherein the second capacitor (7b) is arranged between the first capacitor (7a) and the third capacitor (7c) along the longitudinal direction (L), and wherein the first voltage output terminal (9a) of the multiplexer (10) is conductively connected to the first capacitor (7a) and the third capacitor (7c), and wherein the second voltage output terminal (9b) of the multiplexer (10) is conductively connected to the second capacitor (7b), and wherein the voltage is applied to the first capacitor (7a) and the third capacitor (7c) through the first voltage output terminal (9a) of the multiplexer (10), and wherein the voltage is applied to the second capacitor (7b) through the second voltage output terminal (9b) of the multiplexer (10).

Images