DE102014003270A1 - Capacitive measuring device for determining the filling level - Google Patents

Abstract

The invention relates to a capacitive measuring device 1 for determining the filling level of a filler 6 in a container 5, with a capacitive measuring sensor 2 with electrode elements 3, 3-1, 3-2, 4, wherein the electrode elements 3, 3-1, 3-2 , 4 are covered at different levels to varying degrees by the filler 6, resulting in different capacitances on the measuring sensor 2, wherein at least two electrode elements 3, 3-1, 3-2, 4 are provided, which in the vertical direction at least over a substantial Part of the filling level extend, wherein at least one electrode element forming a capacitance 4 at least in the region of the level to be measured with a dielectric layer 15, 22, 24-1, 24-2 provided, in particular coated, is.

Description

The invention relates to a capacitive measuring device for determining the filling level of a filler in a container, with a capacitive measuring sensor with electrode elements, wherein the electrode elements are covered at different levels to varying degrees by the filler, resulting in different capacitances on the measuring sensor, wherein at least two electrode elements provided are that extend in the vertical direction at least over a substantial part of the level height.

It is known to measure levels with capacitive electronic components. It is exploited that the filler whose level is to be measured, a different dielectric constant than air, which replaces the filler.

The DE 10 2005 053 330 A1 shows a capacitive measuring device, in which one electrode is designed as a rod and the other as a container wall. The electrode is insulated with a carbon layer.

From the DE 197 54 093 C2 shows a capacitive measuring device, which includes electrode elements with a triangular basic shape. Depending on the level, the electrode elements are covered differently from the filler. In order to be able to calculate a fill level or a fill level from the measurement signals obtained from the electrodes, the measuring device has to be calibrated, for which purpose filler has to be filled into the container due to unpredictable edge effects.

There is therefore a need for a capacitive measuring device that can be calibrated without filler in the container.

This object is achieved by a measuring device with the features of claim 1. Advantageous developments emerge from the subclaims.

As the core of the invention is considered that at least two or more capacitive electrode elements are arranged in the container, at least one of which is provided with a dielectric layer. Depending on the cross-sectional shape, the type of coating can be designed differently. The coated electrode element accordingly comprises a conductor part and a layer part. In a rectangular basic shape, for example, the conductor part and the layer part may also have a rectangular basic shape. In a circular basic shape, the conductor part and the layer part may be circular.

If an electrode element is used in the context of the invention, then such an electrode element comprises a metallic electrode, a counter electrode (eg a ground) and an intervening dielectric. One of the electrode elements must have a coating whose coating thickness is not equal to zero. In general, the two electrode elements are each provided with a coating, in which case the coating thicknesses of the two electrode elements are different. A measuring device with two electrode elements, of which an electrode element is carried out without a coating, but falls within the scope of the invention.

The electrode elements must extend with constant cross sections over the range of the level to be measured in order to ensure constant measuring conditions.

In this case, the word "coating" does not restrict the position of the dielectric layer, in particular it does not have to be arranged on the outside of the electrode element.

Through the dielectric layer, the calibration of the measuring device can be simplified so that it takes place in air and without filling the container. This becomes possible due to the electrode arrangement and geometry changed due to the dielectric layer.

The filler whose level is measured can be both a liquid and a bulk material. This depends on the location of the capacitive measuring device. The capacitive measuring device is preferably a measuring device for detecting the fill level of motor vehicle fuel or an oil level of a motor vehicle. The container may thus be a tank or an oil pan. For bulk material, the container is a bulk material container.

The electrode elements extend in the vertical direction at least between two boundary levels. This can be the minimum level and the maximum level. Especially in motor vehicles, the tank is usually not driven to the last drop empty or filled to overflow. Then the limit levels are levels above the minimum and below the maximum level. An exact level indication outside the limit levels is then not possible, only qualitative statements can be made, namely that the lower limit level falls below or the upper limit level is exceeded. The limit levels always deviate from the minimum and / or maximum level if this is an operating condition is reached, which is out of the ordinary in any way or in which there are already malfunctions.

Preferably, the electrode elements are elongated and aligned substantially parallel in the longitudinal direction. Due to the parallel orientation, the evaluation formula simplifies the calculation of the filling level, since the filler uniformly distributes the electrode elements, i. H. applied to the same extent. Although a change in the filling level by the height ☐h always applies at least to all the electrode elements with the same change in height, in the case of non-parallel conductors, this causes different changes in the applied length. Then, the exact position of the electrode elements would have to be known to each other. Therefore, a parallel alignment of the longitudinal axes of the electrode elements is advantageous.

Advantageously, at least one electrode element may be without a dielectric layer. This simplifies the manufacture of the electrode elements. It is only preferred that the electrode elements are coated differently. This implies that an electrode element is not coated at all. The differences may be in a different height of the dielectric layer and / or a different dielectric constant. However, the most cost-effective production is when one of the electrode elements simply consists of a conductor part and has no layer part.

Particularly preferably, the electrode elements may be formed as capacitor plates. The shape as plates is easy to prepare and storable. Advantageously, the electrode elements may consist of rectangular and adjacent capacitor plates.

With particular advantage, the electrode elements can be the same length and / or the same width and / or the same height. The length is measured in the longitudinal direction, the width and height can be determined on a front page. Instead of a same width and height, a substantially identical cross section may be required, since a width and height is only defined for rectangular cross sections and no longer for circular or elliptical cross sections. Instead, equivalent conditions have to be fulfilled: equal radii, etc. Only the same length must be the electrode elements.

Conversely, in the described embodiment of the electrode elements, it is very easy to make them of the same length, since they require no specific length ratios. This makes it possible, in particular, to produce the electrodes by the meter. As a result, the adaptation to different container geometries can be extremely simplified, since the electrodes are easily cut to length and do not have to follow elaborate calibration measurements.

The dielectric layer of the electrode element can preferably occupy at least one third of the cross-sectional area of the electrode element.

Furthermore, the at least one coated electrode element may be coated on at least half of the cross-sectional area. Accordingly, a third or half of the material of the coated electrode element is formed by the dielectric or the dielectric layer.

With particular advantage, the electrode elements can be arranged in chambers of a housing. As a result, the electrode elements are easy to manufacture, transportable and mountable. For example. For example, two conductor parts can each be inserted into one chamber and the remainder filled with a dielectric or different dielectrics. The conductor parts may have any cross-sections, the cross-section of an electrode element is determined by the cross-sectional shape of the chambers and is preferably rectangular. Also a cutting is then very easy to perform. For this purpose, the housing also marks z. B. in the form of notches. A significant advantage is that, as described above, a calibration is only required with air, which greatly simplifies the calibration.

In the following the invention will be explained in more detail by means of embodiments in drawing figures. Showing:

1 a capacitive measuring device,

2 a highly schematic representation of one half of a capacitive liquid sensor with two electrode elements, suitable for the mathematical derivation of the formula;

3 two electrode elements in a first embodiment,

3a , b two electrode elements according to 3 with modified cross-sections,

4 a circuit diagram of the measuring arrangement.

1 shows a capacitive measuring device 1 with a capacitive measuring sensor 2 comprising two electrode elements 3 and 4 , The electrode elements 3 and 4 are in a container 5 arranged. The container may be a tank or other container for holding a liquid or a bulk material. Generally speaking, there is a filler 6 with a level inside the container 5 , The fill level can also be referred to as fill level. The measuring sensor 2 can on a lid 7 of the container 5 be attached. The embodiment of the electrode elements 3 and 4 is in the 2 to 4 shown in more detail. Out 1 but can already be seen that the electrode elements 3 and 4 are elongated and reach into the interior of the container. The longitudinal axes of the electrode elements 3 and 4 are arranged parallel to each other. Furthermore, they are preferably also parallel to the container wall or the longitudinal axis of the container 5 arranged. This applies to all configurations of the electrode elements 3 and 4 ,

The electrode elements range from a lower limit level 8th to an upper limit level 9 , which in this case are not the minimum or maximum level. Is the container 5 the tank or the oil pan of a motor vehicle, so levels are below the lower limit level 8th or above the upper limit level 9 critical for the operation of the motor vehicle. In one case, the motor vehicle stops, in the other case, the tank overflows or it can come at high outside temperatures to an expansion of the fuel, then the filler 6 is. To leave the room, the tank must never be filled to the brim.

This in 2 illustrated embodiment shows half of a sensor with electrode elements 3 . 4 in a perspective partial view. The electrode elements 3 . 4 each comprise two chambers 10 . 11 in a housing 12 are arranged with rectangular cross-section.

The electrode element 3 has an uncoated ladder part 13 on, the electrode element 4 whereas a ladder part 14 and a coating (layer part 15 ). The two electrode elements 3 . 4 thus form two different capacities.

The cross sections, ie the heights and widths of the two chambers 10 . 11 the two electrode elements 3 . 4 are essentially the same, but the chamber 11 of the electrode element 4 in the embodiment about halfway with the substrate forming a layer part 15 is filled.

The housing 12 and in particular the ladder parts 13 . 14 opposite housing sections are connected to ground.

3 shows a further embodiment, the ladder parts 13 . 14 the two electrode elements 3 . 4 are arranged in the middle of the chambers, ie insulated from the outer sides forming the mass, in the case of the electrode element 3 are in turn coatings 15 provided, so that in turn different capacities C1 and C2 form.

As in the 3a . 3b can be seen, the chambers 10 . 11 have different cross sections, z. In 3a be elliptical and in 3b circular. The ladder parts 13 . 14 according to 3 are flat, the ladder parts 13 . 14 in 3b however, they have a round cross-section, ie they are rod-shaped or wire-shaped.

It should be noted that, of course, other cross sections which are suitable for forming different capacitances with different dielectrics are within the scope of the invention. It is basically also possible within the scope of the invention that the ladder parts 13 and 14 different cross sections, but have coatings with the same thickness.

4 shows a schematic representation of the measuring arrangement. The electrode element 3 is about the capacity 25 and the electrode element 4 about the capacity 26 shown. The capacity 27 is a coupling capacity that is either offset or disabled by a switching arrangement. The of the electrode elements 3 and 4 removed signals are in the controller 28 processed.

The control device 28 can on the container 5 arranged, but it can also be kept away in a central control system.

bx

– effektive Breite der Elektrode

a

– Sensor-Länge

le

– Eintauchtiefe; Flüssigkeitspegel

vx

– Distanz Elektrode – Profil (Masse)

dx

– Substratdicke

εrs

– rel. Permitivität des Substrats

εr

– rel. Permitivität der Flüssigkeit

ε0

– Permititvität des Vakuums (8,85 pF/m)

dabei gilt folgende Randbedingung: C1 > C10 C2 > C20 für C1 = 0;
C2 = 0 ist
Fuel (C1, C2) = 0;
Sonderfall für X11 = 0
d ≔ dx v ≔ vxThe following is a calculation example given, which is not exhaustive, but can also be modified. In this case, a linear sensor is used in the sense of the invention, the following being valid for the calculation:

bx

- effective width of the electrode

a

- Sensor length

le

- immersion depth; liquid level

vx

- Distance electrode - profile (mass)

dx

- Substrate thickness

εrs

- rel. Permittivity of the substrate

.epsilon..sub.R

- rel. Permittivity of the liquid

ε0

Permitivity of the vacuum (8.85 pF / m)

the following boundary conditions apply: C1> C10 C2> C20 for C1 = 0;
C2 = 0
Fuel (C1, C2) = 0;
Special case for X11 = 0
d ≔ dx v ≔ vx

C10 and C20 are capacitances of the two electrodes for le = 0, d. H. immersed and without liquid

LIST OF REFERENCE NUMBERS

1

measuring device

2

measuring sensor

3

electrode element

4

electrode element

5

container

6

filler

10

chamber

11

chamber

12

casing

15

dielectric layer

19

width

20

width

21

length

22

dielectric layer

24

dielectric layer

29

width

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 102005053330 A1 [0003]
• DE 19754093 C2 [0004]

Claims (13)

Capacitive measuring device ( 1 ) for determining the fill level of a filler ( 6 ) in a container ( 5 ), with a capacitive measuring sensor ( 2 ) with electrode elements ( 3 . 3-1 . 3-2 . 4 ), wherein the electrode elements ( 3 . 3-1 . 3-2 . 4 ) at different levels to varying degrees of filler ( 6 ), whereby different capacities at the measuring sensor ( 2 ), wherein at least two electrode elements ( 3 . 3-1 . 3-2 . 4 ) are provided, which extend in the vertical direction at least over a substantial part of the level height, characterized in that at least one capacitive electrode element ( 4 ) at least in the region of the level to be measured with a dielectric layer ( 15 . 22 . 24-1 . 24-2 ), in particular coated, is. Measuring device according to claim 1, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) are elongated and aligned in the longitudinal direction substantially parallel. Measuring device according to claim 1 or 2, characterized in that at least one electrode element ( 3 . 3-1 . 3-2 ) has no dielectric layer. Measuring device according to claim 3, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) are formed as capacitor plates. Measuring device according to one of the preceding claims, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) consist of rectangular and contiguous capacitor plates. Measuring device according to one of the preceding claims, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) have the same length (21). Measuring device according to one of the preceding claims, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) the same width ( 19 . 20 . 29 ) exhibit. Measuring device according to one of the preceding claims, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) have a constant cross-section over the entire level to be measured. Measuring device according to one of the preceding claims, characterized in that the dielectric layer ( 15 . 22 . 24-1 . 24-2 ) of the electrode element ( 3 . 4 ) at least one third of the cross-sectional area of the electrode element ( 3 . 4 ). Measuring device according to one of the preceding claims, characterized in that the dielectric layer ( 15 . 22 . 24-1 . 24-2 ) of the electrode element ( 3 . 4 ) at least half of the cross-sectional area of the electrode element ( 3 . 4 ). Measuring device according to one of the preceding claims, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) in chambers ( 10 . 11 ) of a housing ( 12 ) are arranged. Measuring device according to one of the preceding claims, characterized in that the electrode elements ( 3 . 3-1 . 3-2 . 4 ) are arranged side by side along two longitudinal edges. Measuring device according to one of the preceding claims, characterized in that the longitudinal axis of the dielectric layer ( 15 . 22 . 24-1 . 24-2 ) substantially parallel to the longitudinal axis of the electrode elements ( 3 . 3-1 . 3-2 . 4 ) is arranged.

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