DE3629966A1 - SENSOR - Google Patents

Description

The invention relates to a sensor for converting a physical quantity in an electrical starting material, with a light source, from which a bundle of light rays into a first surface, preferably a first front end surface a light-guiding body is coupled, the Light rays at an interface of the body depending totally reflected or from the physical size the body and the totally reflected Light rays on a second surface, preferably one of the second end face opposite first end face  fall, and with a plurality of photosensitive Elements for capturing one of the bundles after Total reflection or decoupling of the angular range.

Such a sensor is from Patents abstracts of Japan, June 21, 1980, Vol. 4/87.

The known sensor is used to measure the concentration of Lead accumulator battery electrolytes. He has one Light source on, from which a diverging beam through a diaphragm on an oblique side surface of a prismatic, light-guiding body falls. A lower, elongated one Interface of the body borders on the one to be measured Electrolytes. The light rays of the divergent Rays falling on the lower interface are there, depending on their angle of incidence and the density of the electrolyte either totally reflected or but decoupled from the body into the electrolyte. The totally reflected light rays fall on another, also inclined interface of the prismatic body, on which there is a gate of photosensitive elements located. Depending on how big the density of the measured Is electrolyte, the boundary between the shifts still totally reflected and the decoupled light rays of the bundle on the lower interface with the electrolyte and thus also the corresponding boundary line that on the Gate of light-sensitive elements covered by totally reflected Rays of light. Because even when rays of light be coupled out, a partial beam at the lower interface is reflected, results from the length of the gate seen the photosensitive elements, an intensity curve, that of a relatively low signal value  suddenly to a relatively high signal value increases. The known sensor now measures the amplitude of the rays of light falling through the various elements of the gate and pulls the respective position of the jump-like Signal rise on the gate as a measure of the density of the Electrolytes.

However, the known sensor has the disadvantage that it is very high precision must be adjusted, because with the only one Total reflection of the light rays in the prismatic Body already slight misalignments of the incident Bundle of light rays to falsify the Lead measurement result. In addition, the known sensor has the Disadvantage that a measurement of the density of the electrolyte practically only in a punctiform manner, namely in one in the Practice very small length section of the interface in which the transition from total reflection to decoupling varies so that the measurement result is only characteristic of the state of the electrolyte in a container, e.g. B. one Total battery is when the electrolyte is in the battery has the same density uniformly. This is in practice, however, not always the case, because at an easier one, e.g. B. warmer electrolyte in the top Accumulate accumulator while heavier parts are below discontinue, but on the other hand with accumulators, the movements subject, as is the case for example in motor vehicles the case is also due to the movement of the accumulators spatial density fluctuations occur to a considerable extent can. The known sensor cannot measure the acid density between the plates of a battery, and also installation in pipes is difficult. Another disadvantage of  known sensor is that it is systematic for only one only measurement task, namely the measurement of the density of the the medium adjacent to the prismatic body is suitable. Finally, the known sensor has the disadvantage that the measurement result is in analog form because the respective Signal intensity on the individual elements of the gate is detected. The measurement result is therefore sensitive to All kinds of drift phenomena, for example signs of aging of the optical elements involved.

Numerous sensors are also known which are based on opto- electronically using the refractive properties of a light guide physical quantities in electrical Convert output signals, these sensors work but also all with analog measurement generation, only with known sensors for detecting fill levels it is known to exceed a particular one Display limit value as digital yes / no signal, is a continuous digital level measurement however, this is also not possible.

The invention is based on the object, one To further develop sensors of the type mentioned in the introduction, that it is suitable for a variety of measuring tasks and The problem with the adjustment is that local Do not make disturbances in the vicinity of the sensor noticeable and finally, above all, a continuous digital display of the respective output signal is possible.

This object is achieved in that the Body is designed as an elongated light guide, in the light rays are totally reflected several times, that the photosensitive elements at an axial distance of  an end face are arranged and an impact surface for a bundle of light rays emerging from the end face form, and that the elements to an evaluation circuit are connected to a counter that measures the number of the bundle illuminated or alternatively the non-illuminated Outputs elements as an output signal in digital form. Below is just the count of the illuminated elements considered in more detail. Should be the number of unlit elements the total number must be counted and evaluated of all elements.

The object underlying the invention is thus complete solved. When using an elongated light guide with multiple total reflection become one Adjustment problems avoided because the length of the Seen light guide uniform light beam conditions anyway train, also in the area of the Any existing discontinuities in this way averaged. By guiding the light rays in the light guide can solve numerous different measuring tasks will. For example, like the one described at the beginning known sensor the refractive index and thus also the density of a medium surrounding the light guide is independent from its physical state are measured, there are continuous level measurements possible and there can also have geometric sizes, especially lengths be measured this way. This list limits however, the scope of the invention is by no means limited.  

Another important advantage of the invention is that the Angular range of the bundle emerging from the light guide, in other words the so-called "acceptance cone" in digital Form is measured by the number of one certain value of physical size illuminated elements is counted and displayed. Any signs of aging or other drift phenomena have an effect so it does not interfere with the measurement result because the evaluation circuit for each individual photosensitive element only makes a yes / no decision, so that when appropriate set trigger level for the respective element without Significance is how great the intensity of each incident Light beam is or how the conversion factor from incident light beam to emitted voltage in the Element itself changed due to signs of aging Has.

Overall, the invention thus provides a universally applicable robust, reliable and against signs of aging insensitive sensor available.

In a preferred embodiment of the invention photosensitive elements at an axial distance from the second end face arranged.

This measure results in a particularly simple structure of the Light guide, for example in the case of a cylindrical one The light beam guides the beam into one radial end face coupled and the acceptance cone from the opposite radial end face emerging radiation is measured.  

In another embodiment of the invention second end face designed as a reactor and the photosensitive Elements are at an axial distance from the arranged first end face.

This measure has the advantage that with the acceptance of a somewhat more complicated construction of the sensor from only one single side must be accessible, at the same time the light is coupled into the sensor and used to measure the Acceptance cone is coupled out again. So designed The sensor is therefore particularly suitable for measuring tasks difficult to access places, for example to measure the Density or level of a liquid in one closed container.

In a variant of this embodiment, the Light guide divided into two axially spaced sections and the bundle is in the first face of the first axial section coupled, while the photosensitive Elements at an axial distance from the first End face of the second section are arranged.

Another variant serving similar purposes provides that the first end face in two axially spaced stages is formed and that the bundle in the front stage is coupled in while the photosensitive elements spaced axially from the rear step are.

These two variants have the common advantage that a spatial separation of the light source for what is to be irradiated Bundle of photosensitive elements for the  Measurement of the acceptance cone is possible because of these two Operations in axially spaced positions of the light guide occur.

In another embodiment of the invention Impact surface inclined to the axis of the light guide.

This measure has the advantage that when the acceptance cone is varied due to the inclination of the impact surface an enlargement of the area in which the edge of the Acceptance cone fluctuates.

In a preferred embodiment of this variant, the The impact surface is also curved in the specified manner, around any nonlinearities that may exist of the sensor to compensate.

In a first application example of the invention physical quantity the density of a surrounding the light guide Medium and the light guide is only with its second Front face optically coupled to the medium.

In a variant of this, the light guide can also only be used its outer surface can be optically coupled to the medium.

These measures have the advantage that the sensor is constructive to the respective spatial conditions of the measuring location can be optimally adjusted.

The light guide can both with its second end face as well as with its outer surface optically to the medium be coupled, reducing the sensitivity of the system can be increased.  

According to the invention, the medium can make a liquid more variable Density, but it can also be gases of variable pressure be measured because the density of the gas with its pressure varies.

In another area of application of the invention The physical quantity is a level of a sensor Liquid. In this case, the light guide is submerged part of its axial length into the liquid and the optical refractive index of the light guide decreases from its lower end upwards. More generally, is the physical size the location of a boundary layer between two Media, e.g. B. also between liquids with different Refractive indices.

This measure has the advantage that continuous level measurements are possible with digital measurement value generation, because the opening angle of the acceptance cone of each lowest refractive index is determined, that in the described Gradients of the refractive index over the axial Length of the light guide is just the one who is on the Surface of the surrounding liquid. With others Words, the opening angle of the acceptance cone is one maximum size with minimum fill level continuously smaller up to a maximum fill level, this variation of the acceptance cone in the manner described digital measured value is transformed.

In a further development of this variant, the light guide according to the invention axially juxtaposed sections different optical refractive index.  

This measure has the advantage that the light guide is easier can be made because for the sections on existing materials can be used.

In a further variant of this embodiment the light guide dimensioned so that the product of its half Thickness and tangent of the critical angle of total reflection of the light guide material lying outside the measuring liquid much smaller to the surrounding medium, is preferably ¹ / ₃ to ¼₀ the length of the light guide.

This measure has the advantage that at extremely low Levels a large jump in signal when the Level just exceeds or falls below a level that the product of half the thickness of the light guide and the tangent of the specified limit angle corresponds. Up to this The level of the level is namely the opening angle of the Acceptance cone a very large value, the critical angle Light guide / surrounding medium outside the liquid (in general: air), while when exceeded this height the opening angle abruptly on a very much lower value that decreases the critical angle of the light guide material / Liquid corresponds. This signal jump is in the light guide materials under discussion here much larger than the jumps in terms of sections their refractive index graded light guide, such as this was described in the previous section. The very large signal jump can therefore advantageously be used as a "reserve display" used to signal the user of the sensor that the level is at a very low lower Limit has dropped.  

In embodiments of the invention, the light guide is made made of glass or plastic, e.g. B. polymethyl acrylate (PMMA).

This measure also has the advantage that known materials with also known reproducible properties can be used.

In other variants of the invention, the light guide a translucent tube with a reference medium is filled, the chemical composition of which of the measuring medium surrounding the tube at a predetermined Value corresponds to the physical quantity.

This measure, known per se from DE-PS 34 02 374, has the advantage that the properties of the reference medium and the surrounding measuring medium with variations in the ambient conditions alike change so that too Drift phenomena can be excluded.

In a further variant of the invention, the light guide light-emitting elements after irradiation emit secondary light by means of a primary light.

This measure has the advantage that instead of a diffuse one Light radiation into the light guide also radiation is possible by means of a parallel bundle, in which case the diffuse light rays required for the invention can be represented by the secondary light. For example happen that the primary light on  Impurities (color centers) in the light guide that diffuse reflective interfaces that the primary light hits, be provided or that the light guide with luminescence centers is provided, which in turn generate secondary light.

This embodiment is particularly for a third Suitable scope of the invention, in which the physical Size is a length. In this case, that the optical refractive index of the light guide in axial direction from an end face of the light guide increases that the bundle of light rays in the radial direction at a distance of length from the end face on the side Light guide meets and that the photosensitive elements are arranged at an axial distance from the end face.

This embodiment of the invention, thus also makes use of the central idea of the invention, the variation of the acceptance cone in a digital way capture has the advantage that a length is non-contact can be measured because, depending on the refractive index of the luminescent light guide area on which the radial Measuring beam falls, at the front end a beam emerges, the acceptance cone of the refractive index of the depends on the light guide area.

In this embodiment of the invention, too, as well as this above for the scope the level measurement was described, either an optical fiber with continuously varying refractive index or but a stepped light guide with different sections Refractive index can be used.  

Finally, there is another embodiment of the invention preferred, in which the light source on a pulse generator is connected and the evaluation circuit a difference generator has inputs whose measurement values are switched on or switched off light source can be supplied.

This measure has the advantage that measurements in the Impulse pauses measured and thus external light influences can be compensated.

Further advantages result from the description and the attached drawing.

It is understood that the above and the features explained below not only in each specified combination but also in other combinations or can be used alone without the frame to leave the present invention.

Embodiments of the invention are in the drawing are shown and are described in the following description explained in more detail. Show it:

Figure 1 is a schematic representation of an optical fiber for explaining the present invention.

FIG. 2 shows a beam path as it occurs in the light guide according to FIG. 1;

Fig. 3 shows a first embodiment of a planar Lichtmeßanordnung for use in the sensor of the invention;

FIG. 4 shows a variant of the exemplary embodiment according to FIG. 3 with a linear light measuring arrangement;

Fig. 5 shows a first variant of an inventive sensor for measuring the density of a medium;

Fig. 6 shows a second variant thereof;

Fig. 7 shows a third variant thereof;

Fig. 8 shows a fourth variant of this;

Fig. 9a and 9b, an embodiment of an inventive sensor for measuring a level with associated characteristic of the refractive index over the length of the optical fiber used;

FIG. 10 shows a variant of the exemplary embodiment according to FIG. 9a with a stepped light guide;

FIG. 11a to 11c is a detailed view of the sensor of FIG 9a or Fig 10 to illustrate an inventive possible reserve indicator..;

FIG. 12 is an embodiment of a sensor of the invention for measuring a length;

Fig. 13 shows a first variant of a configuration according to the invention a light guide for use in one of the sensors according to Figures 5 to 11.

Fig. 14 shows a second variant thereof;

FIG. 15 is a third variant of this, however, for use in one of the sensors of Figures 5 to 12.

16 is a highly schematic circuit diagram for explaining the connection of a sensor of the invention.

Fig. 17 shows a further variant, similar to FIG. 1, to increase the measurement sensitivity of a sensor according to the invention.

In Fig. 1, 1 designates a light source from which a diverging ray beam 2 off and enters an adjacent upper end surface 3 of a cylindrical light guide 10. The point-shaped light source 1 with the diverging beam 2 is only to be understood here as an example, it will be explained further below that parallel beams can also be used, from which diverging secondary light in the interior of the light guide is derived.

In Fig. 1, 11 shows a first, axially directed light beam which passes through the light guide 10 without further deflection or obstruction. With 12 a , 12 b , a second light beam is identified, which strikes a lateral surface 19 of the light guide 10 so flat that it is totally reflected. The light beam 12 a , 12 b thus continues its path through the light guide 10 in the axial direction. 13 a , 13 b , on the other hand, denotes a third light beam which strikes the lateral surface 19 at such a steep angle that it is coupled out of the light guide 10 .

As a result, this means that after several reflection processes in the light guide 10 only light rays 11 or 12 a , 12 b are guided, which are either strictly axially directed or so flat that they are totally reflected on the lateral surface 19 . This creates a so-called "acceptance cone" 14 , which is used to denote the shape of a diverging bundle 17 of light rays emerging from a lower end face 16 .

An impact surface 15 is defined at an axial distance h from the lower end face 16 . Denoting the opening angle of acceptance cone 14 b, so resulting in the impingement 15 at a circular lower end surface 16 is a circular light surface with a peripheral annular region of the radial width x, the β from the angle and depends on the axial distance h.

If, as a result of a change in the refraction conditions in the light guide 10 or in the surrounding medium, the critical angle of the total reflection changes, the angle β and thus the dimension x also change .

FIG. 2 shows the relationships explained for FIG. 1 again for the quantification of the effect that occurs. A fourth light beam 18 is now guided in the light guide 10 , the section 18 a of which strikes the lateral surface 19 just under the critical angle a _T of total reflection. Expressed in graphic terms, this means that all light rays incident in the hatched area in FIG. 2 are totally reflected, while all rays incident more steeply than light beam 18 are coupled out of light guide 10 . The light beam 18 is now (just) still totally reflected in its section 18 a and a reflected section 18 b strikes the lower end face 16 . Provided that the light beam section 18 b occurs outside the total reflection area of the refraction conditions prevailing on the lower end face 16 , a section 18 c of the light beam 18 is coupled out of the lower end face 16 , namely at an angle β which is just the opening angle β of the acceptance cone 14 in Fig. 1 corresponds.

If n _{i denotes} the refractive index of the light guide 10 , n _a the refractive index of the medium surrounding the light guide 10 in the region of its lateral surface 19 and n _st the refractive index of the medium surrounding the light guide 10 on the lower end face 16 , it can be shown that that the following applies to the opening angle β of the acceptance cone 14 :

It goes without saying that n _{i is} greater than n _a and n _st . In the event that the refraction ratios on the lateral surface 19 and on the end surface 16 are the same, ie n _a = n _st , the formula given is simplified accordingly.

It can thus be seen that the width x to be seen in FIG. 1 over the opening angle b and the distance h is a direct measure of the refraction ratio of the light guide 10 to the medium surrounding it.

According to the invention, the width x is now output in digitized form as a measured value.

Fig. 3 shows a this embodiment of the invention, can be seen at the turn of the optical fiber 10 from which a light beam in the shape of the acceptance cone 14 emerges below. In addition, an acceptance cone 14 a is shown in broken lines, which is intended to symbolize a second measured value.

Below the light guide 10 , a flat detector array 22 can be seen at an axial distance in the imaginary impact surface, which can be designed, for example, as a charge shift semiconductor component (CCD). The detector array 22 consists of a multiplicity of detector elements 23 distributed in an area, which can be individually controlled and read out. A symbolized data line 24 leads to an evaluation circuit 25 , which essentially contains a digital counter.

In the illustrated example the case of the solid line drawn acceptance cone 14, hatched in Fig. 3 8 detector elements are illuminated, so that after counting of these elements of the same is a digital value "8" is output via the data line 24 in the evaluation circuit 25 at the output. Almost any resolution of the measurement result can be achieved by a corresponding number of detector elements 23 and, if this should be of practical importance, a limit value can be specified by setting a certain trigger threshold for only partially illuminated detector elements 23 , from which a detector element 23 is illuminated or counted unlit. Any gray transitions in the edge area of the acceptance cone 14 can also be precisely defined in this way.

It is seen from Fig. 3 without further ado that illuminated at a magnification of the acceptance cone 14 in a cone 14 a (shown in dashed lines) has a correspondingly larger number of detector elements 23 and hence also a correspondingly larger digital value appears at the output of the evaluation circuit 25th

FIG. 4 shows a variant in which the distance x from FIG. 1 is not determined by an area measurement as in FIG. 3 but only by a measurement along a straight line. For this purpose, a linear detector array 26 is provided, for example a linear diode gate or the like. It can be seen from Fig. 4 that in the case of the solid acceptance cone 14 four detector elements 23 are illuminated, which in turn have been hatched in Fig. 4, while when the acceptance cone is opened to a value 14 a in the illustrated example six detector elements are illuminated. In this case too, the number of illuminated detector elements is counted and output in the form of a digital value at the output of the evaluation circuit 25 .

Figs. 5 to 8 show four embodiments in which the sensor of the invention is for measuring the density of a surrounding medium, in particular a liquid, is used.

Fig. 5 shows an embodiment in which a light guide 29 is surrounded in the area of its outer surface 19 by a mirror 30 , so that light can only emerge from the lower end face 16 . The light switch 26 passes through a bore in a wall 31 of a liquid container. The detector array 22 is located on an opposite wall 32 of the container, spaced apart from the lower end face 16 , the data line 24 of which is led through the wall 32 to the outside. The light guide 29 is surrounded by a measuring liquid 33 , the density of which is to be measured. The mirroring can be made of metal or a transparent cladding with a lower refractive index than the light guide itself.

The bundle of rays 2 entering the light guide 29 at the upper end (not shown ) now passes through the light guide 29 in the axial direction, no light rays emerging from the outer surface 19 as a result of the mirroring 30 . This is only the case on the lower end face 16 and, because of the optical mechanism already explained, light emerges from the end face 16 only in the acceptance cone 14 , which is measured in the manner described by means of the detector array 22 .

Since the refraction ratios on the lower end face 16 change depending on the density of the measuring liquid 33 , the opening angle of the acceptance cone 14 in the arrangement according to FIG. 5 is a direct measure of the density of the measuring liquid 33 .

It goes without saying that instead of a measuring liquid 33 , a gas can also be enclosed between the walls 31, 32 , the density of which changes with the gas pressure, so that a gas pressure measurement is possible in this way.

Fig. 5 can be modified in the following manner: In place of the elements 22 occurs, a light source, and the elements 22 are arranged at an axial distance from the unshown upper end face of the light guide 29 above it.

FIG. 6 shows a further exemplary embodiment for density measurement, in which a light guide 34 is guided through two openings in alignment in the walls 31, 32 of the container for the measuring liquid 33 . In the area of the passages, reflectors 30, 30 a are attached to the outer surface 19 , while the outer surface 19 is washed around by the measuring liquid 33 .

In this embodiment, the beam of rays in the form of the acceptance cone 14 emerges from the light guide 34 outside the container and strikes the detector array 22 arranged at an axial distance for the measurement value processing already described.

In the exemplary embodiment according to FIG. 6, the refraction conditions in the area of the lateral surface 19 of the light guide 34 thus determine the measurement, but the result corresponds to the measured value that of the arrangement according to FIG. 5.

Fig. 7 shows a further variant, in which a light guide 35 is divided into two axially offset sections 35 a , 35 b . The upper section 35 a is provided with an upper end face 3 a , into which the beam 2 is coupled. Below the lower end face of the upper section 35 a there is either a flat detector array with an opening aligned with the light guide 35 or laterally two separate detector arrays 22 a , 22 b , as shown in FIG. 7, with a corresponding free space between them leave open, through which the beam 2 ', which has emerged from the lower portion 35 a below, can pass through.

The lower section 35 b penetrates a bore in the wall 31 of the container for the measuring liquids 33 . Apart from a reflective coating 30 in the area of the passage through the wall 31 , the lower section 35 b is non-reflective in the area of its lateral surface 19 and borders directly on the measuring liquid 33 . However, the lower end face 16 is provided with a mirror 36 or another suitable reflector. This means that a light beam 37 guided in the lower section 35 b is directed upwards again after striking the mirror 36 , so that a beam in the form of the acceptance cone 14 emerges at an upper end face 3 b of the lower section 35 b . The opening angle of the acceptance cone 14 is again measured in the manner described by the detector array 22 a , 22 b .

A light guide 40 , which in turn passes through the upper wall 31 of the container for the measuring liquid 33 , is formed in the area of this throughput as a lower section with a larger diameter, to which an upper section 40 a with a smaller diameter adjoins. The lower section 40 b thereby has an annular end face 41 b , while the upper section 40 a has a circular end face 41 a . In this end face 41 a, the beam hits 2 and passes into the lower portion 40 b, by the downwards of the sensor of FIG. 8 as well as that of FIG. 7 is formed. The light reflected from the lower end of the light guide 40 at its mirror (not shown in FIG. 8) now exits through the annular end face 41 b of the lower section 40 b and reaches the detector array 22 a , 22 b , which in turn is designed in accordance with FIG. 7 is.

With a further group of exemplary embodiments of the invention, as shown in FIGS. 9 to 11, the level of a liquid can be measured with a sensor of the type according to the invention.

Fig. 9a shows for this purpose an elongated optical fiber 50 that emerges over a part of its axial length in the measurement liquid 33, which is in turn contained in the container with the walls 31, 32. The light guide 50 is in turn provided on its lower end face 16 with a mirror 36 , so that the measuring arrangement itself corresponds to that as was shown in the formula for FIGS. 7 or 8 for the case of density measurement.

A special feature of the arrangement according to FIG. 9a is that the refractive index n of the light guide 50 varies over its axial length z . The course of the refractive index n over the axial length z is shown in FIG. 9b and it can be seen that the refractive index n has its highest value at approximately 1.6 at the lower end and its lowest value at approximately 1.4 at the upper end.

It was already explained at the beginning in the basic explanations of the mechanism of action of the sensors according to the invention in FIGS. 1 and 2 that the opening angle β of the acceptance cone 14 is smaller, the lower the refractive index of the light guide material. Illustrated in a clear manner, this means that with a low refractive index of the light guide material, more and more light beams are coupled out of the light guide and only the very flat, ie, almost parallel to the light guide axis, light beams are guided in the light guide. In the event that the refractive index varies over the length of the light guide, this means that the area of the light guide which limits and thus defines the acceptance cone has the lowest refractive index.

In the case of the exemplary embodiment in FIGS . 9a and 9b, however, in relation to the surrounding measuring liquid 33 , this is always the area of the light guide 50 which adjoins the surface of the liquid 33 , ie defines a fill level 51 .

If, in the illustration in FIG. 9a, the fill level 51 drops from an upper maximum value to a lower minimum value, this means that an acceptance cone emerging at the not shown upper end of the light guide 50 increases its opening angle β with decreasing fill level 51 , so that to FIGS. 3 and 4 described manner is possible, a digital level measurement.

In the case of the light guide 50 with the refractive index gradient according to FIG. 9b, this characteristic can be generated by setting the degree of polymerization over the length, for example in the case of a plastic light guide. A change in the refractive index via selective pressure, radiation or the like is also conceivable.

Instead of a light guide 50 with a continuously varying refractive index n , a light guide 52 can also be used, as shown in FIG. 10, which is divided into a plurality of axially adjacent sections 53 . The sections 53 ₀, 53 ₁ ... 53 _n are designed so that their associated refractive indices n ₀, n ₁, n ₂ ... n _n decrease from bottom to top. The characteristic curve of FIG. 9b for the light guide 50 of FIG. 9a would therefore tend to be the same, but in a slightly stepped form.

The sections 53 can also be provided with a continuously varying refractive index n , so that a gradual measurement is possible through the grading of the sections 53 and a fine measurement within that section 53 is also possible through their axially varying refractive index n .

FIGS . 11 a to 11 c also show a phenomenon which occurs in the light guides 50 according to FIG. 9 a, 9 b or 52 according to FIG. 10 and is particularly advantageous for indicating small residual amounts of measuring liquid 33 . This is particularly advantageous, for example, for the fill level display in petrol tanks of motor vehicles if a "reserve display" is to be set up there as a particularly salient value in order to draw the driver's attention to the fact that the gasoline supply has dropped below a certain minimum quantity.

To explain this phenomenon in FIGS . 11a to 11c, reference is first made to FIG. 11c, where a light guide 59 of width d is shown with its longitudinal axis 64 . At the lower end of the light guide 59 , the two critical angles of the total reflection α _TL for the case of air surrounding the light guide 59 and α _TF for the case of the measuring liquid 33 surrounding the light guide 59 are shown.

In FIG. 11 a, 60 denotes a light beam entering from above, which is inclined so that it runs just under the critical angle α _TL for surrounding air and is thus totally reflected on the outer surface 19 of the light guide 59 surrounded by air. At the very low fill level 61 shown in FIG. 11 a, this means that - although a very small lower part of the light guide 59 is still surrounded by measuring liquid 33 - this light beam 60 is reflected upwards again via the mirror 36 and the lateral surface 19 and thus defines an acceptance cone at the upper end of the light guide 59 , the opening angle of which defines the limiting angle α _TL for surrounding air, ie is very large.

This reflection of light rays 60 with an inclination up to the critical angle α _TL for surrounding air is possible until the fill level 61 has reached a height 62 shown in FIG. 11a. The height 62 results from the intersection line of a cone 63 about the axis 64 of the light guide 59 , the outside angle of the cone 63 being exactly the same as the critical angle a _TL for surrounding air. If the fill level exceeds the height 62 , reflection of light rays 60 towards the upper end of the light guide 59 is no longer possible. Rather, the situation shown in FIG. 11c occurs that, at a higher fill level 65, the light beam 60 is coupled out into the measuring liquid 33 because the larger critical angle α _TF for surrounding liquid now defines the refraction conditions on the lateral surface 19 of the light guide 59 .

If one now considers the characteristic of the opening angle β of the acceptance cone as a function of the filling height F shown in FIG. 11b, it can be seen that up to the height 62 the opening angle β assumes the value β _L , which - as already explained above - from Limit angle α _TL is defined for surrounding air. If the fill level exceeds the height 62 , the value of the opening angle β suddenly drops to a value β ₀, which is defined by the critical angle a _TF for surrounding liquid.

If the light guide, as shown in FIG. 10 with 52, is stepped in its axial length, then, as shown in FIG. 11b at the upper edge, further steps β ₁ etc. can follow, but these further steps are much smaller than that lower level from b _L to β ₀ because such large jumps in limit values α _T no longer occur.

The very large signal jump from b _L to β ₀ can therefore be used to activate a reserve display. The point of use of this reserve indicator can be determined, as can easily be seen from FIG. 11a, by dimensioning the thickness d of the light guide 59 in relation to the critical angle α _TL for surrounding air.

A third area of application of sensors according to the invention is in the measurement of geometric variables, in particular a length y , as is shown in FIG. 12 using an example.

A light guide 70 is divided in the axial direction into sections 71 , one of which is denoted by 71 _n in FIG. 12. The sections 71 consist of luminescent material and one of the luminescent elements is designated 72 in the section 71 _n . Sections 71 each have different refractive indices and the refractive index of section 71 _n is designated n _n . The value of the refractive index increases from section to section in Fig. 12 from right to left.

A narrow bundle of rays or a light beam 73 , which is directed radially toward the light guide 70 , strikes a side surface 74 of the light guide 70 . As a result, luminescence is excited in each of the sections 71 and the secondary light emitted thereby from the luminescence element 72 propagates in the axial direction of the light guide 70 . The secondary light directed to the left in FIG. 12 arrives at the end of the light guide 70 on a radial end face 75 and exits there again in the form of an acceptance cone 14 , so that, in the manner already described, a measurement of the opening angle β _{n of} the acceptance cone 14 by means of a Detector arrays 22 is possible.

Because the refractive index n of the sections 71 increases toward the end face 75 , the opening angle of the acceptance cone 14 is determined by the section 71 itself acted upon by the light beam 73 , because the sections 71 lying further forward in the beam direction towards the end face 75 always have a larger acceptance cone Allow 14 , but do not take advantage of this because there is no suitable "steep" beam.

It can therefore be determined by measuring the opening angle b _n , on which of the sections 71 the light beam 73 has fallen. This means in other words that the opening angle β _n is a measure of the length y when y defined as the distance of the light beam 73 from the front end face 75 miles.

It is understood that in this way also by appropriate Expansion of the arrangement in the sensors level created can be where the position of an incident Light point can be measured in the plane.  

FIGS. 13 to 15 also show some variants of light guides as can be used for some of the exemplary embodiments according to FIGS. 5 to 12.

Fig. 13 shows the variant in which a light conductor 80 consisting essentially of a light-transmissive tube 81, such as a glass tube is filled with a reference media 82. The reference medium 82 is either of the same chemical type as the surrounding medium, for example the measuring liquid 33, or of a defined, different type in order to be able to eliminate disturbance variables in this way.

If, for example, the light guide 80 is used to measure the density of an acid, then this acid can be used as the reference medium 82 , the density of which corresponds to a specific reference value of the acid serving as the measuring liquid 33 . External influences, which then affect the measuring liquid and the reference medium equally, are then no longer included in the measurement result.

FIG. 14 shows a further variant in which a light guide 85 essentially consists of a translucent body 86 made of glass, plastic or the like. However, as shown in the left half of FIG. 14, a luminescent body 87 is arranged at the lower end of the light guide 85 , but, as the right half of FIG. 14 shows, a diffuse reflector 88 can also be arranged there.

The light guide 85 thus makes it possible to apply a parallel beam to the sensor, which at the lower end merges into a diffuse, secondary-emitted or reflected beam which emits light beams of different inclinations upwards again. Such an arrangement can, for example, be used advantageously in the exemplary embodiments of FIGS. 7 and 8.

FIG. 15 shows a variant in which a light guide 90 in turn consists of a translucent body 91 , in which either luminescent elements 92 or diffusion elements, for example color centers or the like, are introduced as a whole.

As the lower half of FIG. 15 shows, this is also possible with liquids, similar to the embodiments according to FIG. 13, in that a glass liquid 93 contains a reference liquid 94 of a predetermined chemical composition, in which suspended particles 95 are contained as a suspension.

In this way, secondary light can also be used in different ways as reflected or generated by secondary emission Light used to diffuse the light Boundaries of the light guide reflected or coupled out to become.

Fig. 16 shows a very schematic circuit diagram of a circuit arrangement for operating a sensor according to the invention.

A pulse generator 100 operates the light source 1 , which emits a clocked beam 2 on a light guide 102 . External light 103 also falls on the light guide 102 . The light guide 102 is connected via suitable detector and evaluation devices, as explained in FIGS. 3 and 4, to an amplifier 104 , which is further acted upon by the output of the pulse generator 100 .

The circuit arrangement according to FIG. 16 has the sense of correcting the influence of the external light 103 . For this purpose, the signal captured by the light guide 102 and originating solely from the external light 103 is determined and stored in the amplifier 104 during the pulse pauses of the pulse generator 100 . During a pulse of the pulse generator 100 , a measured value is again formed, which has arisen in the light guide 102 by the beam 2 of the light source 1 and the influence of the external light 103 and the previously determined measured value of the external light 103 alone is subtracted from this measured value. Since the external light 103 is generally a constant disturbance variable, the influence of the external light 13 can be compensated for in this way.

Finally, FIG. 17 shows a possibility of increasing the width x in FIG. 1 to increase the measuring accuracy by increasing the resolution.

A light guide 106 similar to that in FIG. 1 is located with its lower end at an axial distance from a striking surface 107 , which, however, is inclined to a longitudinal axis 108 of the light guide 106 . In this way, there is an increased width x 'when the bundle of light rays in the form of the acceptance cone 14 falls on the impingement surface 107 .

It is further shown in Fig. 17 with 107 a , 107 b that in addition to or instead of the inclination to the axis 108 , the impingement surface 107 can also be given a curved course in order to compensate or generate certain characteristics in this way, depending on that is desirable in the specific application.

Claims (21)

1. Sensor for converting a physical quantity into an electrical output signal, with a light source ( 1 ), from which a bundle ( 2 ) of light beams ( 11, 12, 13; 18; 37; 60; 73 ) in a first surface 74 , preferably a first front end face ( 3; 41 ) of a light-guiding body is coupled in, the light rays ( 11, 12, 13; 18; 37; 60; 73 ) being totally reflected at an interface ( 16, 19 ) of the body depending on the physical size or are coupled out of the body and the totally reflected light beams ( 12 b ; 18 b ; 37; 60 ) fall on a second surface ( 75 ), preferably a second rear end surface ( 16 ) opposite the first end surface ( 3; 41 ), and with a plurality of light-sensitive elements ( 23 ) for detecting an angular range β taken up by the bundle ( 2 ) after total reflection or decoupling, characterized in that the body as an elongated light guide ( 10; 29; 34; 35; 40; 50; 52; 59; 70; 80; 85; 90; 102; 106 ) is formed, in which light rays ( 12 b ; 18 b ; 37; 60 ) are totally totally reflected several times, that the light-sensitive elements ( 23 ) are arranged at an axial distance h from an end face ( 3; 16; 41 ) and a striking surface ( 15; 107 ) for a bundle ( 17 ) emerging from the end face ( 3; 16; 41 ) form light beams, and that the elements ( 23 ) are connected to an evaluation circuit ( 25 ) with a counter which measures the number of the Bundle ( 17 ) illuminated or alternatively the non-illuminated elements ( 23 ) as an output signal in digital form. 2. Sensor according to claim 1, characterized in that the light-sensitive elements ( 23 ) are arranged at an axial distance h from the second end face ( 16 ). 3. Sensor according to claim 1, characterized in that the second end face ( 16 ) is designed as a reflector and that the light-sensitive elements ( 23 ) are arranged at an axial distance h from the first end face ( 3 ). 4. Sensor according to claim 3, characterized in that the light guide ( 35 ) is divided into two axially spaced sections ( 35 a , 35 b) and that the bundle ( 2 ) in the first end face ( 3 a) of the first axial section ( 35 a) is coupled in, while the photosensitive elements are arranged at an axial distance from the first end face ( 3 b) of the second section ( 35 b) . 5. Sensor according to claim 3, characterized in that the first end face is formed in two axially spaced stages ( 41 a , 41 b) and that the bundle ( 2 ) is coupled into the front stage ( 41 a) while the photosensitive elements are arranged at an axial distance from the rear step ( 41 b) . 6. Sensor according to one of claims 1 to 5, characterized in that the impact surface ( 107 ) to the axis ( 108 ) of the light guide ( 106 ) is inclined. 7. Sensor according to one of claims 1 to 6, characterized in that the impact surface ( 107 a , 107 b) is curved in a predetermined manner. 8. Sensor according to one of claims 1 to 7, characterized in that the physical size of the refractive index and thus the density of a medium surrounding the light guide ( 29 ) and that the light guide ( 29 ) only with its second end face 16 optically to the medium is coupled. 9. Sensor according to one of claims 1 to 7, characterized in that the physical variable is the density of a medium surrounding the light guide ( 34; 35; 40 ) and that the light guide ( 34; 35; 40 ) only with its outer surface ( 19th ) is optically coupled to the medium. 10. Light guide according to claim 8 or 9, characterized in that the medium is a liquid ( 33 ) of variable density. 11. Sensor according to one of claims 8 or 9, characterized characterized in that the medium is a gas variable Pressure is. 12. Sensor according to one of claims 1 to 7, characterized in that the physical quantity is a fill level ( 51; 61, 65 ) of a medium, preferably a liquid ( 33 ), that the light guide ( 50; 52; 59 ) via a Part of its axial length is immersed in the medium and that the optical refractive index n of the light guide ( 50; 52; 59 ) decreases upwards from its lower end. 13. Sensor according to claim 12, characterized in that the light guide ( 52; 59 ) axially juxtaposed sections ( 53 ) with different optical refractive index n . 14. Sensor according to claim 12 or 13, characterized in that the light guide ( 59 ) is dimensioned such that the product of its half thickness d and the tangent of the critical angle a _{TL of} the total reflection of the light guide material lying outside the medium to the medium surrounding it is essential is smaller, preferably a third to a fortieth of the length of the light guide ( 59 ). 15. Sensor according to one of claims 1 to 14, characterized in that the light guide ( 10; 29; 34; 35; 40; 50; 52; 59 ) consists of glass or plastic. 16. Sensor according to one of claims 1 to 14, characterized in that the light guide ( 80 ) has a translucent tube ( 81 ) which is filled with a reference medium ( 82 ) whose chemical composition is that of the measuring medium surrounding the tube ( 81 ) corresponds to the physical quantity at a predetermined value. 17. Sensor according to one of claims 1 to 16, characterized in that the light guide ( 70; 85; 90 ) has light-emitting elements ( 72; 92; 95 ) which emit secondary light after irradiation by means of a primary light. 18. Sensor according to claim 17, characterized in that the physical variable y is a length that the optical refractive index n of the light guide (70) in the axial direction from one end face (75) decreases the light guide (70) indicates that the bundle of light rays ( 73 ) strikes the light guide ( 70 ) laterally in the radial direction at a distance of the length y from the end face ( 75 ) and that the light-sensitive elements are arranged at an axial distance from the end face ( 75 ). 19. Sensor according to claim 18, characterized in that the light guide ( 70 ) in the axial direction arranged side by side sections ( 71 ) with different optical refractive index n . 20. Sensor according to claim 18 or 19, characterized in that the light-emitting elements are luminescent elements ( 72 ). 21. Sensor according to one of claims 1 to 20, characterized in that the light source ( 1 ) is connected to a pulse generator ( 100 ) and that the evaluation circuit ( 25 ) has a difference former ( 104 ), the inputs of which are the measured values when the or switched off light source ( 1 ) can be fed.