DE2034344A1 - Device for measuring physical quantities by measuring the intensity of a bundle of light rays - Google Patents

Description

PATENT LAWYERS Dr. phil. G. NICKEL · DR.-ING. J. DORNER

β MONKS 15 LANDWEHRSTR. 35 POST BOX 10 *

TEL. (OB !!> 555719

Munich, July 5th, 1970 Attorney file number: 144 - Pat. 3

-üipl.-Chem. Helmut Ulrich, 8 Munich-Allach, Waldhornstr.

Device for measuring physical quantities by measurement the intensity of a light beam.

The invention relates to measuring devices "in which the Intensity of a light beam is measured, on which a physical variable to be examined acts.

Known devices of this type are smoke density meters or 'i'rübungsmesser, in which in a light beam path between a light source and an intensity meter, a light beam influencing, in particular absorbing Medium is introduced. In general, the light emitted by a light source is bundled and then passed freely over a measuring section to at the other end of the measuring section for the intensity measurement to be caught.

In the known facilities, however, it turns out to be Disadvantage that the light supplied to the measuring section and

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also the light which is again derived from the measuring section outside the measuring section is subject to the influence of the free environment, so that the light intensity measurement is falsified can be. In the known devices, a measuring section cannot be provided in a confined area either, see above that in these cases the known advantages of this measuring principle cannot be exploited.

^ UfgaDe are dissolved, measured by means of measuring the intensity of a light beam, a ^v ielzahl physical quantities under almost any conditions or be able to determine - by the invention which is to.

This requirement should also be used under extreme conditions, for example in an environment at risk of explosion, in the smallest of spaces, for example with dimensions of fractions of a millimeter and at high temperatures, for example 1000 C, met can be.

The solution to the problem is achieved in that a light source opposite the free environment optically essentially closed light guide and from "a light intensity meter one opposite the free environment optically essentially closed light conductors are led to a light beam transitiona control station, in which the passage of the light rays from the light feed line to the light discharge line depends on the one to be measured Size is controllable.

The light beam transition control station can according to the invention have many shapes. In particular, it can have two opposing end faces of two light guides contain, which under the action of the variable to be measured towards each other or away from each other or in a certain Displacement position can be moved against each other.

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If the light feed and the light discharge are from one and the same light guide, for example a fiber light guide, formed so can be in the beam transition control station opposite a diffuse or a smooth reflector can be provided on an end face of this light guide, which under the action executes movements corresponding to the size to be measured with respect to the end face of the light guide, as previously with regard to of the two light guide end faces mentioned.

Another embodiment of the invention provides in which Light beam transfer control station by changing the conditions for the reflection of light rays at a phase boundary between the material of a light pipe section and its surroundings, depending on the size to be measured, a change in intensity at the output of the light conductor to generate, which is then displayed or registered.

Appropriate configurations of the invention and special applications otherwise form the subject matter of the attached claims. In the following the invention is carried out by the Description of a number of exemplary embodiments with reference to the accompanying drawings. Show it:

Figure 1 is a simplified representation of a

in / direction according to the invention 'block symbols,

FIG. 2 shows a configuration different from that of FIG Device according to the invention, '

FIG. 3 shows a device which is again designed differently,

Figures 4a to 4c are schematic representations of various Embodiments of the beam transition control station,

Figures 5a and 5b further embodiments of the beam transition control station,

FIGS. 6a and 6b again show other beam transfer control stations with an elastic light * pipe section,

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Figures 7a to 7i embodiments of the S-traiiienüber-

corridor control station with a fiber optic, section of certain surface curvature,

Figures 8a to 8c depictions showing the use of . explain the device according to the invention as a balance,

I ¹ IgUr 9 a section through a device according to the invention that can be used as a pressure measuring probe,

Figures 10a and 10b other embodiments of a Pressure measuring probe,

■ fc'igur 11 a device according to the invention as a printing ' knife,

• ^ igur 12 a device according to the invention as a level indicator,

FIG. 13 shows a device according to the invention as a detector to determine the height of a liquid interface,

FIG. 14 shows a device according to the invention as a vibration indicator or frequency detector,

■ fc'igur 15 a device according to the invention as Refractive index meter,

FIG. 16 shows a device according to the invention as a temperature detector and

^r igur 17 a device according to the invention as

Solidification front detector for transparent melts.

The apparatus of Figure 1 includes a light beam transition control station 1, via a light feed line 2 with a light source 3 and a light lead, 4 with a Light intensity meter 5 is connected. To the light beam transfer control station 1, the variable M to be measured acts in the manner indicated in FIG. 1 and influences the control station 1 in such a way that they are each different depending on the instantaneous value of the quantity to be measured allows a large amount of light to pass from the light feed line 2 into the light output line 4.

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In the embodiment according to Figure 2, the light supply · line and the light dissipation in one and the same light guide channel 6. The end of the light guide channel 6 is with the light source 3 and with the light intensity meter 5 over a beam splitting device 7 in connection, which at the embodiment shown is formed by a semi-transparent mirror. The light supply and the Light dissipation to or from the light guide channel 6 can, however also take place in such a way that the light beam of the light source at an angle on the end face of the light pipe 6 is projected, while the light emerging from the light pipe 6 to the light intensity meter is also projected is derived at a certain angle.

.Figur 3 shows that the light feed line and the light discharge can also be formed by individual fiber groups of a fiber light line 8 , whereby the individual groups can either run in an orderly or arbitrarily distributed manner in the light line strand and only form a branch at the end of the light line in the form shown, so that one group of fibers is led to the light source 3, while the other group of fibers leads to the light intensity meter 5.

The following drawing figures serve to explain the Structure and mode of operation of the Sirahlen transition control

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station 1. The measured value-dependent control of the light-beam transition from the light feed line to the light discharge line can take place in that two opposing light guide end faces y and 10 are moved towards or away from one another depending on the measured value. After a certain percentage of through the light feed line 2 up to the end face 9 light rays are not axially parallel but along a refracted one The line that the light pipe runs through is the intensity of the light that can be discharged via the light conductor 4 from the

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Distance between the end faces 9 and 10 and thus from the Value of the variable to be measured, which determines this distance.

Figure 4b shows one form of the beam transition control station, in which the end faces 9 and 10 are not towards one another and from one another are movable away, but can be offset from one another in the transverse direction depending on the size to be measured, see above that in turn, depending on the offset position, a certain amount of light from the light feed line 2 for light discharge 4 and thus arrives at the light intensity meter.

Instead of the light guide end faces according to FIG. 4a, which can be moved towards and away from each other, the end faces 9 ¹ and 10 'can also be arranged fixedly in a common plane, as shown in FIG movable away from them. The amount of light passing from the light guide 2 to the light guide 4 increases the closer the reflector 11 is to the end faces 9 'and 10 ·. However, this only applies up to a certain minimum distance. If this minimum distance is still not reached, the reflector 11 covers the end faces 9 '

| and 10 ', as it were, and it takes place in this approach area a very steep drop in the amount of light coming from the light pipe 2 to the light pipe 4. This appearance can can be used to create a second measuring range in measuring devices of this type.

If the light feed line and the light discharge line run in one and the same light guide channel, as shown for example in Figure 2, the light beam ^{transition control station can contain a reflector 12 or 13 opposite the single end face 9 lg} , which is again perpendicular to the end face depending on the measured value or is movable parallel to the end face

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and thus influences the light return in the light guide channel 6.

Referring to Figures 6a and 6b, the beam transition control station can also be constructed in such a way that a light guide section H made of elastic material between the light feed line 2 and the light output line 4 is connected. The light pipe section 14 consists, for example, of an elastic, crystal-clear rubber, which, when compressive forces occur between the light guide parts 2 and 4, the one shown in Figure 6a, takes on a barrel shape, which makes the surface of the Light guide section 14 curves so strongly that for certain Light rays exceeded the critical angle of total reflection so that these light rays no longer reach the light guide 4- but exit into the free environment. So is the amount of light reaching the light conductor 4 depends on the degree of compression of the light conductor section 14 and can can be used as a measure of the size of the stowage force. Corresponding applies to the arrangement shown in pigur 6b, in which the light guide section 14 is displaced Light guides 2 and 4 is distorted and thereby receives a surface curvature at which for certain light rays again the critical angle of total reflection is exceeded.

While a certain relative movement of light guide paths was used for the measurement in the forms of the beam transition control station described above, FIGS. 7a to 7i show embodiments in which the geometric shape of a light guide section of the beam transition control station remains unchanged. In a curved light guide section 15 between the light feed line 2 and the light discharge line 4, a certain weakening of the light flux reaching the light discharge line 4 occurs due to the fact that some light. _t , are no longer totally reflected in the area of the curvature

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but emerge into the free environment. If a liquid level 16 is now raised in such a way that it is the light guide section 15 reached in the manner shown, the ratio of the refractive indices in that of the Liquid wetted area of the surface of the light guide section 15 changed so much that no total reflection more occurs, so that the luminous flux exiting via the light conductor 4 depends on the degree of wetting of the curved Light guide section 15 is weakened, of course the liquid level 16 is only mentioned here as an example. An elimination of total internal reflection in the curved one Light guide section 15 can also be locally limited by condensation droplets or by contact with a solid, which will be discussed further below. ·

Run light inlet and light dissipation in one and the same light conduit 6, it may be carried on the curved light pipe section 15 also connect an ßeflexionseinrichtung 17, which in the ^A usführungsform of FIG shape 7b of a cone has, while in the embodiment of Figure 7c for this purpose final mirror coating is provided.

Other embodiments of a light guide section with increased surface curvature are shown in FIGS. 7c to 71. The embodiment according to FIG. 7d contains a light guide section 18 in the form of a multi-thread screw in the radiation access control station, so that a multiple or multi-stage attenuation of the light ^{flux reaching the light discharge lc} 4 occurs when, for example, the liquid level 16 wets the individual G-lengths of the screw 18 .

According to - ^ igur 7e, the beam transition control station can also

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a hook-shaped curved light guide section 19 or contain a compressed section 20 according to Figure 7f, in which the surface curvature is such that the contact of the light guide with a substance from opposite the Standard conditions deviating refractive index leads to an at least partial elimination of total reflection. Figure 7g Fig. 10 shows an embodiment in which the light guide portion of increased surface curvature has the shape of a Constriction 21 has.

As an area of increased surface curvature, there is also a To understand light guide section, the surface of which is formed in cross section by a broken line. An example of this is shown in FIG. 7h, in which the light guide formed, for example, by a glass rod 6 is ground to the shape of a cone at the end 22 located in the light beam transition control station.

The embodiment of the control station shown in FIG. 7i is characterized by a light guide section 19 'more variable Curvature, the curvature values are chosen so that a certain shape of the characteristic of the light intensity can achieve smesser reaching luminous flux. For example, a linearization of the characteristic or also a certain curvature in a selected range of characteristics be achieved.

Figure 8a shows an embodiment of the invention for use as a highly sensitive balance in which a rod light line 6 through a glass cut 23 into an evacuable Vessel 24 is guided and carries a support for a weighing pan 26 near its end. The end face of the light pipe 6 is opposite a small mirror 27, which is also passed through the ground glass 23 on a mirror Retaining wire 28 is adjustably attached .. The rash of the light intensity meter 5 meter is of

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the deflection of the Idchtleitungsstabes 6 according to the Load on the weighing pan 26 dependent. Of course, the scales can also be set up so that under the load of the weighing pan 26 a relative movement between two opposing light guide end faces of the light feed line or the light dissipation takes place, as FIGS. 8b and 8c show.

Another embodiment of the invention is used as a pressure measuring probe, whose aging in a housing 29, Pressure-sensitive membrane 30 of the end face 31 of a fiber light line 32 is opposite. The fibers of the light guide 32 form a light feed fiber group 33 and a light discharge fiber group 34 Side, the membrane 30 is designed as a reflector or mirrored and causes pressure-dependent deflection a variable transition from LiclrjT from the light feed line 33 for light derivation 34 in accordance with the considerations made in connection with FIG. 4c. It is here pointed out that the pressure measuring probe according to Figure 9 can be built extremely small and thus for medical Investigations are particularly suitable for which an • Introduction the probe into narrow channels or vessels is necessary.

The pressure measuring probe according to ^ igur 10a corresponds in its rear Structure of the device shown in FIG. % r front that However, the beam transition control station forming part includes a mirror coating 35 at the front end Light guide section 36 which is exposed in a region 37 opposite an elastically deformable casing 38. Addicted of the pressure acting on the casing 38 the sheath is deformed in such a way that it attaches itself to the exposed area 37 of the light guide section to a variable extent in each case 36 and in this area accordingly

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eliminates the total reflection, so that the light dissipation 54 removable calibrated quantity fluctuates depending on the measured value.

While in the embodiment according to FIG. 10a an interspace is shown between the sheath 38 and the area 37 of the light guide section 56, the sheath 58 can also present the light guide section with an elastic, rough or profiled surface which is increasingly smoothed by the external pressure and thus has a contact surface with the Liehtleitungsabschnitts that becomes larger or smaller as a function of the measured value.

The construction of the pressure measuring probe according to FIG. 10a can also be implemented using a single optical fiber 59, which is covered or siliconized up to near the front end by a reflective intermediate layer 40 and has a mirror coating 41 at its front end. The elastic sheathing 38 touches the exposed area of the optical fiber 59 in the length between the intermediate layer 40 and the mirror coating 41, depending on the magnitude of the applied pressure. JJie pressure measuring probe of Figure * 10b can be carried out as the devices of Figures 9 and 10a ₁ whereby extremely difficult measuring points can also be investigated in the art, both now in medicine as an even smaller dimensions ·

boll the device according to the invention for measuring the pressure in a container designated by 42 in FIG the beam transition control station can be except for a curved light line section terminating a light line 6 19 'contain a pressure-sensitive bellows 45, which a liquid volume 44 depending on the

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ORIGINAL INSPECTED

■ in the container 42 effective pressure against the light guide section 91 'so that the mode of operation described in connection with FIGS. 7a and 7i is achieved.

An interface 45 between two located in a container 46, different liquid volumes 47 and 48

can be scanned according to * igur 12 in that the light intensity meter 5 is connected to threshold value indicators 49 or 50, from which the device 49 emits a signal as soon as the level of the liquid 48 reaches the light guide section 19 'and thus a certain weakening of the luminous flux from the Light guide 6 brings about, while the threshold value indicator 50 responds when the interface between the liquids 47 and 48 reaches the light guide section 19 ¹ .

Another possibility for measuring the liquid level in a container 51 is indicated in FIG. Here the light supply line, the light discharge line and the beam transition control station are essentially formed by a liquid-filled, transparent tube 52 which stands in the container 51. The I ¹ IUssigkeitsfüllung of the tube 52 is preferably the same type as ¹ i ¹ lüssigkeit which is to be filled into the container 51st If liquid now reaches the container 51 via an inlet 53, the total reflection is eliminated at the areas of the tube 52 wetted with liquid from the outside and only the luminous flux determined by the cone i> 4 'reaches the light intensity meter 5, which points to the Contains the end of the tube 52 placed collecting reflector 55. The rise of the liquid in the container 51 thus has the effect as if a perforated diaphragm corresponding to the cross section of the tube 52 were displaced in accordance with the movement of the liquid level with respect to the light source 56 located at the lower end of the tube 52

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and controls the amount of light that the light intensity meter controls 5 reached.

According to FIG. 14, the invention can also be used for selective frequency measurement or as a vibration detector. In this embodiment, the control station has the form of a liquid volume 57 connected between light feed line 2 and light discharge line 4, which is exposed to the shocks or vibrations to be determined or measured. As soon as waves form on the surface of the liquid volume 57, the total reflection in these areas is at least partially eliminated and the light that would otherwise be due to the total reflection. and optionally an additional metal coating 58 is guided from the light supply line 2 to the light dissipation 4, now occurs in the manner indicated by the surface of the liquid volume 57 from # Upon the occurrence of standing waves occurs in the Lichtab- '■■ _ line 4 a defined weakening of the Luminous flux, so that the arrangement responds selectively to certain frequencies.

The device according to the invention can also be designed as a refractive index meter and in this case has a TJ-shaped tube 59 according to FIG . A light source 3 is inserted into one leg, while the Meflorgan of the light intensity meter b is inserted into the other leg. In addition, the legs of the U-Eohres 59 have nooit liquid supply lines and drainage lines 60 'or. 61, According to the considerations made in connection with FIG. 7a, the conditions for total reflection in the bend of the U-tube 59 depend on the ratio of the refractive numbers of the substance in the U-tube and the substance in the surrounding tree * Is the

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If the refractive index is known in the area, then the attenuation is known of the luminous flux reaching the light intensity meter 5 on the refractive index of the substance introduced via the feed line 60.

FIG. 16 shows an embodiment of the invention which is used as a selective temperature meter. The front end of a probe 63 is inserted into a heated space 62 and contains a light guide 64, the end face of which is opposite a small reflector 66 held on a casing 65. Between the end face of the light guide 64 and the reflector 66 there is a disk 67 made of a material which melts at a certain temperature and changes from the solid, opaque state of aggregation to the liquid, transparent state of aggregation. So while below a certain temperature the light introduced from the light source via the light guide 64 at the pane 6? is absorbed, the light passes above a certain temperature through the melt of the disc 67 to the reflector 66 and throws it back into the light pipe 64 in order to then reach the light intensity meter and there generate a signal which indicates the temperature above the melting point of the component 67 temperature in the room 62 reports.

For the investigation of certain crystallization or solidification processes it is sometimes important to determine the position of a bristling front The device according to FIG. 17 is used for this purpose and contains a number of staggered side by side arranged light guides 68, which in each case in certain Altitudes within a container 69 end. The colder is filled with a substance, which in the solidified state is opaque, but at the end faces, the power

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lines 68 generates a diffuse reflection. In the molten state, however, the substance in the container 69 is transparent, so that the light supplied via the light lines 68 leaves the end faces of the light lines and is not reflected to the new display device 70. It should be mentioned here that in FIG. 17 the devices for supplying the light from a light source to the light guides 68 have been omitted to simplify the illustration.

The output-side ends of the light pipe 68 are in a Row arranged side by side along a scale division of the display device 70, so that the end faces of the individual. Light lines are exposed on a scale. Depending on the position of the solidification front 71 inside the container 69, so those end faces of light lines on the display device 70, which belong to light guides in the solidified part of the material located in the container 69 end up.

Finally, it should be pointed out that the individual forms of the beam transition control status _f given above, for example in accordance with FIGS.

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Claims (1)

Claims ; Device for measuring physical quantities by measuring the intensity of one of the relevant to measuring size influenced light beam, characterized in that from a light source (3) one opposite the free environment optically essentially closed light supply line (2 or 6 or Ö) and from a light intensity meter (5) one opposite the free environment optically essentially closed light conduction (4 or 6 or B) to a light beam transition control station (1) are guided, in which the passage of the light rays from the light feed line to the light discharge line is dependent is controllable by the size to be measured. 2. Device according to claim 1, characterized in that for the light feed and the light dissipation Separate light guide channels (2, 4 and 6) are provided are. 3. Device according to claim 1, characterized in that for the light feed and the light dissipation at least one common light guide channel (6) is provided, on which the light source (3) and the light intensity meter (5) end facing a beam splitting (7) takes place. 4. Device according to one of claims 1 to 3 »characterized in that the light feed line (2 or 6 or 8) and / or the light emission (4 or 6 or Ö) from a fiber light line or a rod light line is or are formed. - 16 - 109883/1000 5. device according to one of claims 1 to 4, characterized in that the control station (1) has two opposing end faces (9, Io) of each connected to the light supply and discharge or these forming light guides (2, 4) which can be moved against one another under the action of the variable to be measured are (Figures 4a and 4b). 6. Device according to claim 5> characterized in that that the end faces (9> 10) can be moved towards or away from one another (FIG. 4a). 7. Device according to claim 5, characterized in that the end faces (9, 10) are mutually opposite in the transverse direction are displaceable (Figure 4b). - 8. Device according to one of claims 1 to 4, characterized in that the control station (1) contains a diffuse or smooth reflector (11 or 12 or 13), which of the end surface or the end surfaces (9 ¹ , 10 ¹ or . 9 ¹¹ ) of one or more light conduits or light conduits (2, 4 or 6) connected to or forming the light supply and discharge line and is movable with respect to this end face or these end faces under the influence of the variable to be measured (Figures 4c to 5b). 9. Device according to claim 8, characterized in that the reflector (11 or 12) on the end surface or the end surfaces (9 ^f , 10 'or 9 ¹¹ ) can be moved towards or away from it or inwardly (Figures 4c and 5a). - 17 - 109883/1000 10. Set up after. Claim ö, characterized in that that the reflector (13) can be displaced in the transverse direction with respect to the band surface or the end surfaces (9 ″) is (Figure 5b). 11. Device according to one of claims 1 to 4, characterized in that the control station (1) has a light guide section (14 or 15 or 16 or Lö or 19 or 19 'or 20 or 21 or 22 or 37 or 57), in which, under the influence of the variable to be measured, different conditions for the reflection of light rays at a phase boundary between the material of the light guide section and its surroundings can be generated. 12. Device according to claim 11, characterized dadurcri, that the light guide section depending on the size to be measured in different ways or in different degrees with a gas, a liquid or a pesticide comes into contact (Figures 7a to 7i and 10a to 15). 13 · Device according to claim 11, characterized in that that the light guide section (14) is elastic and that in the light guide section below the effect of the variable to be measured, a region of increased surface curvature can be generated in which The critical angle of total reflection is exceeded at least for a certain proportion of the light rays (Figures 6a and 6b). H. Device according to claim 11 or 12, dadurcii characterized in that the light guiding portion is an area has increased surface curvature (Figures 7a to 7i) - 1d - 109883/1000 15. Device according to claim 14, characterized in that the area of increased surface curvature is formed by a bend in the light guide section (15 or 19 ¹ ). 16. The device according to claim 14, characterized in that the area of increased surface curvature of a multi-thread helical shape (1 <3) of the light guide section is formed (Figure 7d). 17 · Device according to claim 14, characterized in that the light guide section (.19 *) has a has a certain length of variable curvature (Figure 7i) lo. Device according to one of Claims 1 to 4 for use as a refractive index meter for liquids, characterized by a U-shape (59) each with the light feed line and the light line forming or attached to them connected legs, which have fluid connections (CO, 61) and with one connecting the legs Bend in which, depending on the refractive index of the liquid passed through the U-tube, to different degrees the total reflection is eliminated (Figure 15). 19. Device according to one of Claims 1 to 4 for use as a temperature detector, characterized in that that the control station on the one hand from an end face of the or a light guide (64) and on the other hand from a Reflector (66) contains limited space, which of a melting at a certain temperature and thereby transparent solid (67) which becomes cloudy or opaque in the solidified state is fulfilled (FIG. 16). - 19 _r
109883 / 100C 20. Device according to one of claims 1 to 4, for use as a solidification front detector for transparent melts, characterized in that the control station has several in the possible migration range of the solidification front (71) contains staggered, in the melt »immersed light guide end faces, of which from individual light guide paths (68) to separate the Position of the display devices reporting the solidification front (70) lead (Figure 17). 21. Device in particular according to claim 20, characterized in that a display instrument with Pointerless scale (70) is provided, which along a scale graduation output end faces of a plurality of Light lines (68), which correspond to the to be displayed Size can be selectively acted upon with light. 22. Device according to one of claims 5 ″ to 10 for use as a balance, characterized in that an the light guide (6) leading to an end face or a support (25) for a weighing pan (26) on the reflector is arranged (Figures 8a to 8c). 23 device according to claim 8 or 9 for supplying, Application as a pressure measuring probe, characterized in that a pressure membrane (30) is arranged at the end of a fiber light line (32, 33 »34), the end face of which faces the light line Side is designed as a reflector (Figure 9). 24. Device according to claim 23, characterized in that that individual fiber groups (33 »34) each form the light feed and the light discharge, where the number and / or the distribution of the individual fibers of each group accordingly a desired display characteristic are selected. - 20 - 109883 / 1Q00 25. Device according to claim 11 for use as Pressure or force meter, characterized in that an elastic solid (3 ^) under the action of the to be measured Pressure or the force to be measured in different ways or to different degrees to the surface of the Light guide section (36 or 39) can be pressed in such a way that in this area at least partially the total reflection is eliminated in the light guide. 26. The device according to claim 25, characterized in that the light guide section of one opposite the elastic solid exposed length of a length in the remaining area with an optically final Coating (40) and formed at one end ″ with a mirror coating (41), individual optical fiber (39) is. 27. Device according to claim 11 for use as a vibration or vibration meter, characterized in that that the light guide section is connected between the light feed line (2) and the light discharge line (4) Liquid volume (57) which is arranged in a container serving as a vibration transmitter and whose surface can be changed by waves in such a way that at least partially total reflection on the surface is eliminated (Figure 14) 28. Device according to claim 12 for use as a liquid level meter, characterized in that "the Light guide section has the shape of a tube (52), which is in a cylinder vessel (51) that can be filled with liquid, the filling level of which can be determined and that the Tube also at least over the entire height swept over by the level of the liquid in the cylinder vessel Liquid, in particular the same liquid as the cylinder vessel, is filled (Figure 13) - 21 - 109883/1000 29. Device according to one of claims 14 to 17 or 2ö, characterized in that the light intensity meter is connected to threshold indicators (49, 50) (Figure 12). 30. Device according to one of claims 14 to 17 for use as a force or pressure gauge, characterized in that that under the effect of the force to be measured or the pressure to be measured, a liquid level (44) is relative can be moved to the area of increased surface curvature of the light guide section (19 ') (FIG. 11). 31. Device according to claim 30 _9, characterized in that a bellows (43) exposed to the pressure to be measured serves to raise or lower a liquid volume (44) with respect to the said light guide section (19 ') (Figure 11). - 22 - Blank page