SENSOR LINE, MEASURING ARRANGEMENT AND METHOD FOR DETECTING AN AMBIENT VARIABLE

Abstract

A sensor line, a measuring arrangement and a method detect a change in an ambient variable. The sensor line serves for detecting a change in an ambient variable, in particular the temperature. The sensor line has a first optical waveguide, a second optical waveguide and also a material that changes its transparency depending on the value of the ambient variable. The material is positioned between the first optical waveguide and the second optical waveguide in such a way that light from the first optical waveguide is able to be coupled into the second optical waveguide in an event of a change in the transparency.

Claims

1. A sensor line for detecting a change in an ambient variable, the sensor line comprising: a first optical waveguide; a second optical waveguide; and a material having a light transmissivity varying in dependence on a value of the ambient variable, said material being positioned between said first optical waveguide and said second optical waveguide such that light is able to be coupled radially from said first optical waveguide into said second optical waveguide depending on the value of the ambient variable.

2. The sensor line according to claim 1, wherein said material is configured in such a way that the light transmissivity changes abruptly.

3. The sensor line according to claim 1, wherein said material is selected in such a way that the light transmissivity of said material changes in a temperature-dependent manner.

4. The sensor line according to claim 3, wherein said material has a transparent plastic into which thermo chromatic pigments are introduced.

5. The sensor line according to claim 1, wherein said material is selected in such a way that said material changes transparency at a transition temperature of between 40 C. and 90 C.

6. The sensor line according to claim 4, wherein a proportion of said thermo chromatic pigments relative to a mass of said material has a value of between 1% by weight and 10% by weight.

7. The sensor line according to claim 1, further comprising a common sheathing enclosing said first optical waveguide and said second optical waveguide and configured to be reflective.

8. The sensor line according to claim 7, wherein said common sheathing is formed by a metal film.

9. The sensor line according to claim 1, wherein at least said first optical waveguide has a sheath composed of said material.

10. The sensor line according to claim 1, wherein said first optical waveguide and said second optical waveguide are twisted together.

11. The sensor line according to claim 1, wherein at least one of said first and second optical waveguides has an optical fiber and a cladding, wherein a part of said optical fiber is free of said cladding, wherein said material adjoins said part which is free of said cladding.

12. The sensor line according to claim 11, wherein said part of said optical fiber of said first optical waveguide and said part of said optical fiber of said second optical waveguide which are free of said cladding are directed toward one another.

13. The sensor line according to claim 1, wherein said first optical waveguide and said second optical waveguide are embedded into said material.

14. The sensor line according to claim 1, further comprising an outer protective sheath.

15. The sensor line according to claim 1, wherein the sensor line is integrated into a cable to be monitored.

16. The sensor line according to claim 15, wherein the cable is configured as a charging cable for charging a rechargeable battery of an electrically driven vehicle.

17. A measuring configuration for detecting an ambient variable, comprising: a sensor line containing a first optical waveguide, a second optical waveguide and a material having a light transmissivity varying in dependence on a value of the ambient variable, said material is positioned between said first optical waveguide and said second optical waveguide such that light is able to be coupled from said first optical waveguide into said second optical waveguide depending on the value of the ambient variable; a feed-in unit for feeding the light into said first optical waveguide; at least one receiving unit for receiving the light from said second optical waveguide; and an evaluation unit configured for evaluating the light received by said receiving unit and outputting a signal depending on a received value.

18. The measuring configuration according to claim 17, wherein said feed-in unit is configured to feed the light into said first optical waveguide at both ends.

19. The measuring configuration according to claim 17, wherein said receiving unit is configured for receiving the light from said second optical waveguide on both ends.

20. The measuring configuration according to claim 19, wherein the measuring configuration is configured for localizing a position of a local defect, namely a hot spot, and has recourse to calculated or stored location-dependent intensity profiles for the light fed in and for received light or is configured for detecting the received light on both of said ends and deduces the position of the local defect on a basis of an intensity received at said ends of said second optical waveguide.

21. The measuring configuration according to claim 17, wherein said evaluation unit is configured in such a way that said evaluation unit outputs a signal when a predefined limit value of a received intensity is exceeded.

22. The measuring configuration according to claim 17, further comprising a control device configured in such a way that a charging current or a cooling power is controlled depending on the signal.

23. A method for detecting an ambient variable, which comprises the steps of: providing a sensor line having a first optical waveguide, a second optical waveguide and a material with a light transmissivity varying in dependence on a value of the ambient variable; feeding light into the first optical waveguide and, when a predefined value of the ambient variable is exceeded, the material changes transparency and the light is thus coupled into the second optical waveguide; and receiving and evaluating an intensity of the light coupled in the second optical waveguide.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0050] FIG. 1 is a diagrammatic, cross-sectional view of a sensor line in accordance with a first variant of the invention;

[0051] FIG. 2 is a cross-sectional view of the sensor line in accordance with a second variant of the invention;

[0052] FIGS. 3A-3C are sectional views of the sensor line of a third variant in simplified basic illustrations for elucidating a coupling of light from a first optical waveguide into a second optical waveguide;

[0053] FIG. 4A is a simplified circuitry illustration of a measuring arrangement;

[0054] FIG. 4B is a circuit illustration similar to FIG. 4A supplemented by intensity profiles for illustrating the localization of a hot spot;

[0055] FIG. 5 is a simplified illustration of a charging system for charging a motor vehicle; and

[0056] FIG. 6 is a graph showing a profile of the light coupled into the second optical waveguide as a function of a temperature loading.

DETAILED DESCRIPTION OF THE INVENTION

[0057] In the figures, identically acting parts are illustrated with the same reference signs.

[0058] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a sensor line 2 for detecting an ambient variable which has a first optical waveguide 4a and also a second optical waveguide 4b. The first optical waveguide 4a has a sheath 6 composed of a material M that changes its transparency depending on the value of the ambient variable. The first optical waveguide 4a is preferably realized as an optical fiber, in particular as a so-called lateral light fiber, such that the light L fed into the first optical waveguide 4a can be emitted radially. By virtue of the sheath 6, the light is reflected at the interface layer between the lateral light fiber and the sheath, such that light can propagate in the longitudinal direction of the optical waveguide 4a as long as the sheath is not transparent.

[0059] The second optical waveguide 4b is preferably likewise configured as an optical fiber. In this case, it is configured in such a way that light L can penetrate radially from outside.

[0060] The fibers are polymer fibers (POF), in particular. They are configured for example as commercially available PU fibers.

[0061] The two optical waveguides 4a, 4b are furthermore surrounded by a common sheathing 8, which is configured such that it is reflective in the direction of the optical waveguides 4a, 4b. Preferably, the sheathing 8 itself is configured as a metal film or contains a metal layer on its inner side. Preferably, the sheathing 8 has a reflectance of up to more than 90% for light L emerging from the first optical waveguide 4a.

[0062] The sensor line is preferably used for monitoring the temperature, in particular of a cable. The ambient variable is the temperature. In the event of a predefined temperature value (the so-called transition temperature) being exceeded, the material M changes its transparency from nontransparent to transparent. This enables the light from the first optical waveguide 4a to be coupled into the second optical waveguide 4b. The change in transparency is made possible by so-called thermochromic pigments P that are admixed with the material M during the production thereof. By virtue of the reflective sheathing 8, a high proportion of the light L is coupled into the second optical waveguide 4b.

[0063] In addition, the sensor line 2 is preferably configured for determining and localizing locally occurring changes in temperature (so-called Hot Spots). This Hot-Spot detection is made possible on account of the thermochromic pigments P, which can change their transparency locally, for example. Analogously thereto, the light L is coupled into the second optical waveguide 4b in particular locally at this transparent location of the sensor line 2.

[0064] In the case of the configuration in accordance with FIG. 2, the second optical waveguide 4b is also surrounded by a sheath 6 composed of the material M. The two optical waveguides 4a, 4b are preferably configured identically, in particular as lateral light fibers. The advantage of this configuration is the reduced susceptibility of the second optical waveguide 4b to interference vis--vis light L not coupled in from the first optical waveguide 4a. On account of the sheath 6 around the second optical waveguide 4b, light L is coupled into the latter only after the exceedance of the transition temperature and the associated change in the transparency of the material M. As in the case of the variant in FIG. 1, too, a common sheathing 8 is arranged. The latter is additionally surrounded by an outer protective sheath 12. The latter is preferably implemented in all variants.

[0065] FIGS. 3A-3C illustrate the cross sections of a third configuration variant for elucidating the coupling of the light L from the first optical waveguide 4a into the second optical waveguide 4b. This variant differs from those from FIG. 1 and FIG. 2 to the effect that the first optical waveguide 4a and the second optical waveguide 4b contain an optical fiber F, in particular a polymer optical fiber F, and a cladding 10, wherein a part 11 of the fiber F is free of cladding 10. Both optical waveguides 4a, 4b are arranged alongside one another. In addition, the material M adjoins at least the part 11 that is free of cladding 10. In the case of the preferred configuration in FIGS. 3A to 3C, the two optical waveguides 4a, 4b are embedded in the material M, that is to say are in each case completely surrounded by the latter.

[0066] The cladding 10 ensures the best possible light guiding in the longitudinal direction of the respective optical waveguide 4a, 4b. A radial emergence of light L is prevented by the cladding. Light L can therefore emerge only in the cladding-free parts 11. In this case, the cladding-free part 11 extends in particular only over less than half of the circumference, and in the exemplary embodiment for instance over one quarter or one fifth of the circumference. In the longitudinal direction, the cladding-free part 11 preferably extends over the entire length of the respective optical waveguide 4a, 4b.

[0067] Preferablyas illustratedthe two cladding-free parts 11 of the two optical waveguides 4a, 4b are directed toward one another and are therefore situated opposite one another. This thereby realizes a short path section for coupling the light L from the first optical waveguide 4a into the second optical waveguide 4b.

[0068] This coupling-in of the light L is schematically illustrated in the three illustrations of FIGS. 3A-3C. FIG. 3A shows the sensor line 2 in the quiescent state. Neither the first optical waveguide 4a nor the second optical waveguide 4b is guiding light L. In FIG. 3B, light L is fed into the first optical waveguide 4a. However, the value of the temperature in the region of the sensor line 2 is below the transition temperature. The material M is nontransparent in this state and thus replaces the cladding 10 at the cladding-free part 11. Consequently, light L from the first optical waveguide 4a is not coupled into the second optical waveguide 4b.

[0069] The behavior of the sensor line when the transition temperature is exceeded is illustrated in FIG. 3C. When the transition temperature is exceeded, the material M changes its transparency from nontransparent to transparent and enables the light L from the first optical waveguide 4a to be coupled into the second optical waveguide 4b.

[0070] FIG. 4A shows a simplified circuitry illustration of a measuring arrangement 14. The measuring arrangement includes a feed-in unit 16 for feeding light L into the first optical waveguide 4a, a receiving unit 18 for receiving the light coupled in from the second optical waveguide 4b, and an evaluation unit 20 for evaluating the light received by the receiving unit and for outputting a signal S.

[0071] The feed-in unit 16 is configured in such a way that it is connected to the first optical waveguide 4a at both ends, that is to say that light L is fed in at both ends of the optical waveguide 4a during operation. Analogously thereto, the receiving unit 18 is configured in such a way that it is positioned at both ends of the second optical waveguide 4b, that is to say that light L which emerges at the two ends is detected at both ends. For this purpose, by way of example, a respective photodiode is arranged at both ends. The advantage of this configuration is that the sensitivity of the sensor line 2 is increased. The feeding of light into the first optical waveguide 4a at both ends preferably ensures a uniform illumination of the first optical waveguide 4a. This feeding-in of the light on both sides is based on the consideration thatindependently of the position within the sensor line 2an intensity of the light L that is as uniform as possible is ensured when the light L is coupled into the second optical waveguide 4b.

[0072] Alternatively, the measuring arrangement 14 is configured in such a way that the feed-in unit 16 feeds light L into the first optical waveguide 4a on one side and the second optical waveguide 4b has the receiving unit 18 at both ends. Such a configuration is illustrated in FIG. 4B.

[0073] FIG. 4B additionally also illustrates an intensity profile for the intensity IS of the light coupled into the first optical waveguide 4a and an intensity profile for the intensity IE of the light coupled into the second optical waveguide 4b.

[0074] A localization of a Hot Spot X0 is made possible in particular with such a measuring arrangement 14. Light is coupled into the second optical waveguide 4b only at the position of the Hot Spot X0.

[0075] Owing to the damping, the intensity IS of the light fed into the first optical waveguide 4a decreases continuously, in particular linearly, as is illustrated in the upper intensity profile. At the location of the Hot Spot X0, a defined proportion of the intensity IS existing at this position is coupled into the second optical waveguide 4b. This coupled-in intensity IE propagates in the second optical waveguide 4b to both ends and in the process is likewise damped linearly, for example. At the two opposite ends, usually different intensities IEL (left-hand side) and IER (right-hand side) are then detected.

[0076] A receiver of the receiving unit 18 from which the Hot Spot X0 is at the smaller distance detects a higher intensity IEL of the light L. On account of this difference in the intensities IEL and IER at the two ends, the position of the Hot Spot X0 can be determined mathematically or else by comparison with characteristic values stored in a table, for example. In particular, an assignment of intensity ratios between IEL and IER to a position is carried out here. In the exemplary embodiment in FIG. 4B, the intensity IEL of the coupled-in light L at the left-hand receiver is higher than the intensity IER at the right-hand receiver. In this respect, a Hot Spot which occurs at the left-hand edge of the sensor line 2 is involved.

[0077] The received light L or a reception signal correlated with the intensity of the received light L is forwarded to the evaluation unit 20 for evaluation, where a signal S is output depending on the intensity of the light.

[0078] FIG. 5 illustrates a charging system for charging a motor vehicle 30 in a grossly simplified fashion. In this case, the sensor line 2 is integrated into a charging cable 24 for the thermal monitoring of the charging cable 24.

[0079] The charging system contains a charging column 26 having a charging device 28 for charging a battery (not illustrated in more specific detail here) of a motor vehicle 30 via the charging cable 24 with a charging current LS. For this purpose, the charging cable 24 has a charging connector 32 on one side.

[0080] The charging connector 32 preferably has a standardized plug connection. Besides the charging current line 29 carrying the charging current LS, the charging cable 24 fitted to the charging connector 32 also contains the sensor line 2. Preferably, the charging cable is realized in such a way that it comprises a parallel arrangement of charging current line 29 and sensor line 2. This configuration of the charging cable 24 as illustrated in FIG. 5 has the advantage that even locally occurring changes in an ambient variable are detected in a simple manner since the sensor line extends over the entire length of the charging current line 29.

[0081] The sensor line 2 is preferably used for monitoring the temperature of the charging cable 24. For this purpose, the evaluation unit 20 and the control device are integrated into the charging column 26, for example, as is illustrated in FIG. 5. This enables the charging current LS to be regulated in the event of imminent overheating of the charging cable 24 as a result of the flowing charging current LS. For this purpose, the evaluation unit 20, the control device 22 and the charging device 28 are interconnected with one another in such a way that the signal S output by the evaluation unit 20, depending on the intensity of the coupled-in light L, is detected in the control device 22. Afterward, a reduction closed-loop control for the charging current LS is carried out by the control device 22 on the basis of the signal S. This has the consequence that the charging current LS for charging the battery in the motor vehicle 30 is reduced in the charging device 28. This reduced charging current remains connected until the temperature loading within the charging cable 24 has decreased in such a way that the temperature-dictated outputting of the signal S on account of the lack of coupling of the light L into the second optical waveguide 4b of the sensor line 2 is extinguished. This takes place as soon as the temperature within the charging cable is below the transition temperature of the material M. The temperature monitoring is advantageously connected as set point-actual value closed-loop control. The controlled variable is the transition temperature of the material M or the light coupled into the second optical waveguide 4b.

[0082] Alternatively or supplementarily, the control device has a closed-loop control of a cooling power if the monitoring of temperature-regulated cables is involved. Specifically, a constant charging current LS is set and the cooling power is correspondingly controlled by closed-loop or open-loop control. By means of the cooling power, it is therefore ensured that the cable 2 does not exceed a predefined temperature.

[0083] A graphical elucidation of the principle for detecting the change in an ambient variable, said principle being utilized in the sensor line 2, is illustrated in a simplified fashion in FIG. 6.

[0084] In the graph there is a profile 34 of the intensity I of the light L coupled into the second optical waveguide 4b, and also a temperature profile 36 within the sensor line 2. The abscissa axis indicates the length X of the sensor line 2. The temperature T and respectively the intensity I of the coupled-in light L are plotted jointly on the ordinate axis 40. Furthermore, the transition temperature T1 of the material M is depicted as a dashed line.

[0085] If consideration is given to the temperature profile 36, upon the exceedance of the transition temperature 38 at a Hot Spot X0 the abrupt rise in the light intensity I within the second optical waveguide 4b can be discerned. This has the consequence that, as long as the temperature has a value above the transition temperature T1, light L is coupled into the second optical waveguide. Upon the undershooting of the transition temperature 40, the coupling of light L into the second optical waveguide 4b is extinguished abruptly.

[0086] In addition, the binary character of the sensor line 2 is discernible from the profile 34 of the intensity I in the second optical waveguide 4b. This character has the advantage that it enables a simple and reliable detection of light in the second optical waveguide 4b.