WO2015127957A1 - Filling level sensor and method for determining a filling level - Google Patents

Abstract

The invention relates to a filling level sensor (1) comprising a longitudinally extending optical waveguide arrangement (2) having a light input (10) arranged at a first end (3) of the optical waveguide arrangement (2) and a light output (20) arranged at a second end (4) of the optical waveguide arrangement (2), wherein a sensor area (5) between the light input (10) and the light output (20) is configured in such a manner that the intensity of a light signal (S) on the way from the light input (10) to the light output (20) is changed on the basis of a fluid (F) at least partially surrounding the sensor area (5), wherein the optical waveguide arrangement (2) has, between the light input (10) and the light output (20), a longitudinally extending carrier (6) which enables a first signal path (S1) for the light signal (S), and the sensor area (5) of the optical waveguide arrangement (2) is in the form of longitudinally extending toothing, wherein the toothing has intermediate spaces (7) which can be entered by the fluid (F), wherein a second signal path (S2) is produced via the forms of the toothing and via the fluid (F) which has entered the intermediate spaces (7), which second signal path runs parallel to the first signal path (S1) at least in sections.

Description

description

Level sensor and method for determining a level

The invention relates to a fill level sensor comprising a longitudinally extending optical waveguide arrangement with a light input arranged at a first end of the optical waveguide arrangement and a light exit arranged at a second end of the optical waveguide arrangement, wherein a sensor area between the light entrance and the light exit is designed such that a light signal is changed in its intensity on the way from the light input to the light output as a function of a fluid surrounding the sensor region at least partially.

Furthermore, the invention relates to a method for determining the level of a fluid in a container, wherein by means of a signal generator generates a light signal and a light input of a longitudinally extending optical fiber array is supplied, wherein the light signal guided in the optical fiber assembly and along a sensor area on the way to a light output in response to a sensor region at least partially surrounding fluid is changed in intensity.

Level measurement using level sensors, especially for liquids in closed containers, is a constant problem for level sensor designers, especially in the case of reactive or pressurized fluids. Previously known approaches such. Sight glasses, floats, radioactivity, ultrasound, have the following disadvantages:

- There is always a risk of breakage / leakage in sightglasses, in floats there is an increased level of wear, in the case of radioactive radiation there is a burden on the personnel and there is an increased requirement for the approval procedure,

 With radar / ultrasound the effort is high or an electrical energy input into an explosive liquid is dangerous.

From the published patent application DE 199 29 279 AI a method and a device for level measurement in a closed container is known. A disadvantage of the known method is, if in a container with a level sensor once a liquid with a first refractive index is to be measured and on the other a liquid with a second refractive index to be measured, this can not be done without a recalibration. For example, such a container is available for gasoline from different manufacturers, it being known that different manufacturers color their gasolines differently colored.

It is therefore the object of the present invention to provide a level sensor which exhibits an invariance against a refractive index change of the liquid to be measured. The object is achieved for the level sensor mentioned above in that the optical waveguide arrangement has a longitudinally extending support between the light entrance and the light exit, which enables a first signal path for the light signal and the sensor area of the light guide arrangement is designed as a longitudinally extending toothing wherein the toothing has at least one intermediate space into which the fluid can penetrate, wherein a second signal path is formed by means of formations of the toothing and via the fluid which has penetrated into the at least one intermediate space. The additional second signal path preferably runs parallel to the first signal path, at least in sections parallel to the first signal path. It does not mean "parallel" mandatory geometrically parallel, but rather in the sense of a parallel connection of the two signal paths to understand.

A measuring principle to be applied to the level sensor is based on a measurement of the intensity attenuation of a

Light beam or a light signal over the length of a suitably designed component, for example in the form of a comb. The comb would then consist of transparent material, with a support of the comb having a significantly poorer conductivity for the light than the tines of the comb.

Due to the design of the level sensor selected in this way, two possible paths result for the light fed in at the upper end of the level sensor: firstly through the carrier of the comb and secondly through the tines and their filled intermediate spaces of the comb.

In the event that no fluid surrounds the level sensor, attenuation for a transition of light between the prongs of the comb is relatively large due to the large differences in the indices of calculation, so that only one light pipe can pass over the support of the comb. The light intensity which has arrived at a light output of the filling level sensor corresponds to an empty container state in a "dry case".

When the container is filled, the fluid collects on the bottom of the container and begins to wet the comb or the level sensor. As soon as the interspaces between the tines are wetted, it is additionally possible for the light beam or the light signal to take a path with less attenuation to the carrier via the wetted tines and their interstices (phase boundaries fixed - liquid - fixed, results in a smaller one) Refractive index difference). The second signal path created in the wetted case increases the light intensity at the lower end of the filling level sensor.

This increase is measurable and represents a measure of the minimum level of the actual level. Therefore, it is a particular embodiment of the invention that on the support a plurality of teeth, teeth or prongs are arranged as a toothing and the material of the carrier in comparison to the material of the toothing has a higher attenuation for the light signal.

Advantageously, the teeth, teeth or prongs are designed like a hammer. For an optimized transition of the light signal from one tooth, tooth or tines over the gap to the other tooth, tooth or prongs, it is advantageous if the hammer-shaped teeth, teeth or prongs are formed integrally with the carrier, and an array of protruding Stems form, each of the stems having a base in the region of the carrier and a head at the opposite end of the stem to the carrier.

The abovementioned embodiment variant is further optimized if a head has a first end face and a second end face, wherein the heads are arranged such that the second end face of a head in each case faces the first face of a head following in the longitudinal direction of the light guide arrangement a transition is formed for the light signal.

Furthermore, it is advantageous if the first and second

End face each form two facing wetting surfaces for the fluid, wherein the end faces are designed such that a drainage of the fluid is favored. Accordingly, the wetting surfaces of the teeth, tines or tines may be designed, for example, convex or conical or coated with Teflon or hydrophobin, whereby a drainage of the fluid from the wetting surfaces due to the surface tension is forced, which prevents incorrect measurements. In order to avoid scattering effects, the surface of the toothing can be coated with an opaque layer or an inwardly reflecting layer except for the wetting surfaces, preferably the respective end faces, teeth, teeth or prongs. The first and the last face in the overall structure should preferably also be coated with an opaque layer. Increased absorption or increased attenuation for the light signal in the carrier can be achieved by introducing bubbles into the carrier material. A roughening of the surface or a laser treatment of the carrier material leads to a higher attenuation for the light signal.

Bonding the teeth, teeth or prongs of a transparent material with an opaque carrier leads to a similar effect.

Spatial pitching of teeth, serrations or tines on the carrier would increase measurement confidence (a top view would then look like a star or a cross, for example). In this case, each quantization step is characterized by several simultaneous wetting processes. A slight axial offset of the tines of this arrangement, however, would further improve the resolution. Therefore, it is a special design, if a further longitudinally extending second toothing is arranged on the carrier, preferably a further third toothing, preferably a fourth toothing.

In order to be able to make a statement about the filling level in an exemplary cylinder or an elliptical tank, it is advantageous if the teeth, serrations or prongs on the carrier are not distributed in the same height but rather in a volume equivalent distributed on the carrier. In this way, with an increase in the filling level in relation to the volume which does not increase linearly therewith, a tank contents information can be obtained directly by the measurement without having to carry out a scaling or adaptation in an evaluation unit. For a horizontal cylinder in which the level sensor is arranged perpendicular to the axis of symmetry of the cylinder, a distribution would be made from the first end across the middle to the second end of the level sensor according to the non-linear volume function. In this case, the distances of the teeth are to be chosen to the center smaller than the distances of the teeth, which are arranged more to the ends. It is also advantageous if a further longitudinally extending second toothing is arranged on the carrier, which has an axial offset from the first toothing.

A further embodiment variant provides that the

Light output is divided into a first output and a second output, wherein the first output is connected to the second end of the second end towards hammer-shaped tooth, tine or prong and the second output at the second end of the longitudinally extending Trä - ger is arranged. On the one hand, it is possible to couple the two signal paths at the lower end of the optical waveguide arrangement and to determine the optical intensity via an optical sum output, but it is also possible to provide two optical outputs and to forward the detected two intensities to an evaluation unit, for example via two optical fibers ,

The initially stated object is also achieved by the method mentioned in the fact that the light signal in the light guide assembly between the light input and the

Light output via a longitudinally extending support, which allows a first signal path for the light signal and configured over the sensor region of the light guide assembly as a longitudinally extending toothing, wherein the toothing has spaces in which the fluid penetrates, wherein on the formations of the toothing and a second signal path is formed via the fluid which has penetrated into the intermediate spaces, which signal is at least partially parallel. Lel to the first signal path, depending on the level in the container more or less gaps are filled ge and thus the intensity of the light signal at the light output of the additional parallel second signal path is influenced accordingly, the intensity change is measured and the measured value to the level is closed. With this method, in contrast to an analog measuring method, a differential signal change or a sudden signal change is obtained, which has the advantage that this measuring method is invariant with respect to refractive index changes of different liquids.

Accordingly, discrete measured values are used to determine the filling level, the number of which results from the number of intermediate spaces and thus a measured value is assigned to each intermediate space, as a result of which the filling level is calculated as a function of the spaces filled with fluid.

For the calculation are provided: d _s static optical attenuation

d _L Fluid-wetted optical damping

d _q optical cross-damping (stalk)

I ₀ input light intensity

I _L Fluid-side intensity

Ι _Ξ static intensity

 N number of levels total

 L level = number of fluid-covered

 Interim rooms

Based on simplified assumptions I _L , Ι _Ξ and finally the level L can be calculated.

N

(2)

Bei dieser Herleitung wurden alle Querdämpfungen bei untergetauchten Zähnen, Zacken oder Zinken vernachlässigt und des Weiteren wird angenommen, dass über „trockene" Zähne kein Licht angekoppelt wird. Aus Formel (3) ist zu ersehen, dass der erfindungsgemäßen Idee entsprechend d_L und d_s unter- schiedlich sein müssen, um einen Messeffekt zu erzielen. Dieser Unterschied wird als Sprung in einer Messwertkurve ermittelbar sein. (1)

(2)

In this derivation, all transverse losses in submerged teeth, teeth or prongs have been neglected, and it is further assumed that no light is coupled through "dry" teeth From formula (3) it can be seen that d _L and d _s correspond to the inventive idea This difference will be determinable as a jump in a measured value curve.

Formula (4) suggests to metrologically determine both Ι _Ξ and I _L. In principle, however, it is also possible to couple the static intensity Ι _Ξ and the fluid-side intensity I _L and to determine the total optical intensity via an optical sum output. The invention will be explained in more detail with reference to embodiments and a drawing. The drawings show in detail in a schematic representation:

1 shows a first embodiment of the invention

 Level sensor,

2 shows a second embodiment of the filling level sensor,

3 shows a detail of a section of the

 Level sensor,

4 shows a scheme for representing the concatenated optical attenuations (equivalent circuit diagram),

FIG. 1 shows a container with fill level sensor, FIG. 1 shows a further alternative embodiment of a fill level sensor with a plurality of teeth and FIG 7 shows a step-shaped measured value diagram.

According to FIG. 1, a fill level sensor 1 comprising a longitudinally extending optical waveguide arrangement 2 having a light input 10 arranged at a first end 3 of the light waveguide arrangement 2 and a light output 20 arranged at a second end 4 of the light waveguide arrangement 2 is shown. A sensor region 5 between the light input 10 and the light output 20 is designed as a toothing with a first tooth ZI to an eighth tooth Z8. The individual teeth

Z1, ..., Z8 are arranged on a support 6. The longitudinally extending support 6 enables a first signal path S 1 (see also FIG. 3) for the light signal S fed in via the signal input 10.

In contrast to the prior art, the sensor portion 5 of the light guide assembly 2 is designed as a longitudinally extending toothing, the toothing has spaces Z, in which a fluid F can penetrate, via the teeth Z1, ..., Z8 of the teeth and A second signal path S2 (see FIG. 3) arises via the fluid F which has penetrated into the interspaces Z, which extends at least in sections parallel to the first signal path S1. Compared with the material of the teeth Z1,..., Z8, the carrier 6 has a material which, in comparison with the material of the teeth Z1,..., Z8, has a higher attenuation for the light signal S (indicated by a gray hatching). , The teeth Z1,..., Z8 are integrally formed with the carrier 6, each tooth having a stem 7, each of the stems 7 having a base 7a in the region of the carrier 6 and a head 7b at the end opposite to the carrier 6 of the stem 7 has.

The head 7b of each tooth Z1,..., Z8 has in each case a first end face 8 and a second end face 9, wherein the heads 7b are arranged such that in each case the second face Front side 9 of a head 7b facing the first end face 8 of a following in the longitudinal direction of the light guide assembly 2 head 7b, whereby a transition for the light signal S is formed (see FIG 3).

According to FIG. 2, an alternative embodiment of the fill level sensor from FIG. 1 is shown. As a significant difference, the light guide arrangement 2 according to FIG. 2 has a first output 21 for the light signal S, which has passed the second signal path S2 and a second output 22 for the light signal S

Light signal S, which has gone the first signal path Sl on. The first output 21 is connected to the second end face 9 of the first tooth ZI and the second output 22 is arranged at the second end of the longitudinally extending support 6.

FIG. 3 shows a detailed representation of the level sensors 1 previously described in FIG. 1 and FIG. 2. Shown is a section of the level sensor 1 with respect to the teeth Z1, Z2, Z3 with the respective gaps Z. A fluid F is up to a fill level L, which reaches into the middle of the second tooth Z2. With this level L, the gap Z between the first tooth ZI and the second tooth Z2 is completely wetted. Between the first tooth ZI and the second tooth Z2 now phase boundaries set solid-liquid-solid. Since the fluid F has a higher calculation index than air, the light signal S can split from its first signal path Sl and search for a second signal path S2 via the second tooth Z2 via the liquid fluid F in the first tooth ZI. If none of the teeth Z1,..., Z3 wetted, then the light signal S could reach the light output 20 only via the first signal path S1 and would accordingly have a lower intensity than if the light signal S were across the first signal path S1 and the second signal path S2 to the light output 20 passes. In phase boundaries, the ratio of the indices of calculation of the material of the teeth to the fluid is important. Similar calculation indices result in a significantly better liquid-filled gap. transition for the light, as in a transition with the phase boundaries fixed-gaseous-fixed, prevail at which very different indices of calculation. This increase in the additional intensity of the light signal S via the second signal path S2 can be measured and thus represents a measure of the minimum height of the actual fill level L. For an approximate calculation, the equivalent circuit shown in FIG. 4 is used for the optical attenuation in the different signal paths. I ₀ is an input light intensity which initially strikes the static attenuation d _{s of} the carrier 6. The static damping d _{s of} the carrier 6 continues through the respective damping boxes d _s to the output l _s for the static intensity I _s . The static intensity I _s corresponds to the light intensity which arrives at the light output 20 solely because the light signal S has traveled its way through the carrier 6. d _q is in this case the first optical transverse damping, ie the light signal S finds its way through, for example, the second tooth Z2. Then it encounters a fluid-wetted optical attenuation d _L. Depending on how many interdental spaces are wetted, the number of d _L boxes for the fluid-wetted optical attenuation d _{L increases here} . At the end of the row of teeth, ie at the first tooth ZI, one then obtains a fluid-side intensity I _L. If the two intensities I _L and I _s combined, one obtains an increase in the static intensity I _s , which is measurable, and thus represents a measure of the minimum height of the actual liquid level.

5 shows a container 40 in which a fluid F is enclosed. In the container 40 gas-tight filling level sensor 1 is installed. About an optical flameproof

Connection are integrated in the container 40 of the light input 10 and the light output 20. A signal generator 41 generates the light signal S and supplies it to the light input 10. On the Light output 20, the resulting light is returned to an evaluation unit 42 and assigned to a measuring stage.

The evaluation unit 42 mentioned in FIG. 5 picks up the measurement curve shown in FIG. 7, depending on the fill level L. The measured curve is represented by the filling level L as intensity I. There are steps for the interdental spaces Z between the first ZI and the second tooth Z2, between the second tooth Z2 and the third tooth Z3, between the third tooth Z3 and the fourth tooth Z4, between the fourth tooth Z4 and the fifth tooth Z5 , between the sixth tooth Z6 and the seventh tooth Z7. Starting from the static intensity Ι _Ξ , which corresponds to the light intensity through the carrier 6, a jump in intensity can be recorded at a first stage, namely when the fluid F is between the first tooth ZI and the second tooth Z2. The intensity jumps each time higher as the level L increases and so fills the interdental spaces between the remaining teeth.

Claims

claims 1. fill level sensor (1) comprising a longitudinally extending optical waveguide arrangement (2) with a light input (10) arranged at a first end (3) of the light waveguide arrangement (2) and a light output disposed at a second end (4) of the light waveguide arrangement (2) 20), wherein a sensor area (5) between the light input (10) and the light output (20) is configured such that a light signal (S) on the way from the light input (10) to the light output (20) in response to a sensor region (5) at least partially surrounding Fluid (F) is changed in intensity, The light guide arrangement (2) can be arranged between the light input (10) and the light output (20).  a longitudinally extending carrier (6), which enables a first signal path (Sl) for the light signal (S) and  the sensor region (5) of the optical waveguide arrangement (2) is configured as a longitudinally extending toothing, wherein the toothing preferably has a gap (7) into which the fluid (F) can penetrate, wherein the teeth are formed by toothed formations Interspace (7) penetrated fluid (F) a second signal path (S2) is formed. 2. level sensor (1) according to claim 1, wherein on the carrier (6) a plurality of teeth, teeth or prongs (Z1, ..., Z8) are arranged as a toothing and the material of the carrier (6) compared to the material of the toothing has a higher attenuation for the light signal (S). 3. fill level sensor (1) according to claim 2, wherein the teeth, teeth or prongs (Z1, ..., Z8) are designed hammer-shaped. 4. Level sensor (1) according to claim 3, wherein the hammer-shaped teeth, teeth or prongs (Z1, ..., Z8) are integrally formed with the carrier (6), and an arrangement of protruding form the stems (7), wherein each of the stems (7) has a base (7a) in the region of the support (6) and a head (7b) at the end of the stem (7) opposite the support (6). 5. level sensor (1) according to claim 4, wherein a head (7) each have a first end face (8) and a second end face (9), wherein the heads (7) are arranged such that in each case the second end face (9). a head (7) of the first end face (8) of a longitudinal direction of the light guide assembly (2) following head (7) facing, whereby a transition for the light signal (S) is formed. 6. level sensor (1) according to claim 5, wherein the first and second end face (8,9) each have two opposing Form wetting surfaces for the fluid (F), wherein the end faces (8,9) are designed such that a drainage of the fluid (F) is favored. 7. level sensor (1) according to one of claims 1 to 6, wherein a further longitudinally extending second toothing (32) on the carrier (6) is arranged, preferably a further third toothing (33), preferably a fourth toothing (34). 8. level sensor (1) according to one of claims 1 to 6, wherein a further longitudinally extending second toothing (32) is arranged on the carrier, which has an axial offset from the first toothing (31). 9. Filling level sensor (1) according to one of claims 5 to 8, wherein the light output (20) is divided into a first output (21) and a second output (22), wherein the first output (21) on the second end face (9 ) of the hammer-shaped tooth, tine or prong (Z8) arranged towards the second end, and the second exit (22) is arranged at the second end of the longitudinally extending support (6). 10. A method for determining the level (L) of a fluid (F) in a container (40), wherein by means of a signal generator (41) generates a light signal (S) and a light input (10) assigned to a long-extending optical fiber assembly (2) leads, wherein the light signal (S) in the light guide assembly (2) and along a sensor region (5) on the way to a light output (20) in response to a sensor region (5) at least partially surrounding fluid (F) in his Intensity is changed, in that the light signal (S) in the optical waveguide arrangement (2) lies between the Light input (10) and the light output (20) via  a longitudinally extending carrier (6), which enables a first signal path (Sl) for the light signal (S) and via  the sensor region (5) of the optical waveguide arrangement (2) is designed as a longitudinally extending toothing, wherein the toothing has intermediate spaces (Z) into which the fluid (F) penetrates, wherein the toothed formations and the spaces (Z ) penetrated fluid (F), a second signal path (S2) is formed, which extends at least partially parallel to the first signal path (Sl), wherein  Depending on the level (L) in the container (40) more or less spaces (Z) are filled and thus the Intensity of the light signal (S) at the light output (20) due to the additional second signal path (S2) is influenced, wherein the intensity change is measured and is closed by the measured value on the level (L). 11. The method according to claim 10, wherein for the determination of the filling level (L) discrete measured values (M1,..., M7) are used which result from the number of spaces (Z) and thus a measured value (M1,. .., M7) is assigned, whereby the level (L) is calculated as a function of filled with fluid (F) spaces (Z).