Apparatus for monitoring cell voltage

Abstract

The invention relates to a device for monitoring the cell voltage of single cells (3) of a fuel cell stack (1) formed by membrane electrode assemblies (4) and bipolar plates (6), which device has a measuring device (7) for each single cell (3), which measuring device comprises an optical signal generator (9) which can be driven by the measuring device. The device according to the invention is characterized in that the measuring device (7) is constructed on a flexible circuit board which is connected to the frame (5) of a frame-type membrane electrode assembly (4, 5) or is constructed as a part of the frame.

Description

Technical Field

[0001] The present invention relates to a device for monitoring the cell voltage of a single cell formed by a membrane electrode assembly and bipolar plates in a fuel cell stack, according to the type defined in detail in the preamble of claim 1. Background Technology

[0002] Monitoring the cell voltage of individual cells in a fuel cell stack is known in principle from existing technologies. This is often referred to or abbreviated as Cell Voltage Measurement (CVM). In fuel cell stacks, such as those used in vehicles, this CVM is relatively complex, expensive, and requires significant structural space. Furthermore, for reliable measurement, typically 200 to 400 individual cell contacts must be measured for each fuel cell stack and brought out if necessary. Additionally, the entire structure is located in a high-voltage environment and must be implemented accordingly for safety, such as in terms of insulation resistance, dielectric strength, creep, and creepage distances. Moreover, this structure is typically arranged within a housing around the fuel cell stack. Special explosion-proof protection is required because hydrogen can accumulate here due to permeation and leakage. Furthermore, the entire structure is located in an environment with high requirements for electrochemical corrosion.

[0003] To overcome this problem, DE 10 2007 015 735 A1 now proposes an optical cell voltage monitoring device for fuel cell stacks. In a measuring device fixed between the bipolar plates of a single cell, optical devices are arranged to generate optical signals of the voltage to be measured. These optical signals are then received in the form of optocouplers by sensors or detectors associated with the corresponding signal sources, thereby transmitting the measured value of the single cell voltage detected within the fuel cell stack to the external environment of the fuel cell stack. Here, high-resolution detectors can be used, and the number of detectors can be reduced by using reflectors.

[0004] This structure remains relatively expensive and complex, especially due to its arrangement between and connection to the bipolar plates. Furthermore, a high-resolution detector is required for signal processing, which is both prone to failure and complex and expensive. Summary of the Invention

[0005] The present invention now aims to provide an improved device for monitoring cell voltage according to the preamble of claim 1, which advantageously improves upon the prior art.

[0006] According to the invention, this objective is achieved by a device having the features of claim 1, and particularly the feature portion of claim 1. Advantageous designs and improvements of the device according to the invention are derived from the dependent claims.

[0007] Similar to that described in the prior art at the beginning, the device according to the invention specifies that each single cell is equipped with a measuring device having an optical signal generator. Now, according to the invention, the measuring device is constructed on a flexible circuit board, which is connected to or constructed as part of the frame of a framed membrane electrode assembly, i.e., a so-called MEFA (Membrane Electrode Framed Assembly). In modern fuel cell stacks, the MEFA plays a very decisive role. This structure is completed during the fabrication of the electrodes, the catalytically coated membrane, and the gas permeation layer, and then, for example, equipped with its own seals, is subsequently inserted as an MEFA between two bipolar plates when the fuel cell stack is stacked. Alternatively, the seals are connected to the bipolar plates accordingly or, in principle, also inserted during stacking. Nevertheless, the flexible circuit board is extremely simple and effective in the frame region and can also form part of the frame. Such a circuit board can include various functionalities, and in the structure according to the invention, at least includes a measuring device having an optical signal generator that can be driven / controlled by it.

[0008] Therefore, the structure is extremely simple and highly efficient in assembly. Here, the flexible circuit board requires almost no structural space occupied by other components within the fuel cell stack, allowing the device for monitoring the cell voltage of a single cell to be constructed approximately neutral to the structural space. Furthermore, by using an optical signal generator, as is known in principle from the prior art, that works in conjunction with an optical sensor in the form of at least one optocoupler, the requirements for electrical safety and explosion protection can be met without difficulty.

[0009] According to a highly suitable improvement of the device according to the invention, the measuring device can be electrically connected to two adjacent bipolar plates via a flexible conductor and / or, particularly preferably, via spring contacts. This connection, achieved through a flexible conductor forming a conductor loop between the flexible circuit board with the measuring device and the bipolar plates, is correspondingly simple and allows for the inevitable lengthening of the fuel cell stack during operation (which can be due to pressure and / or temperature variations). A similar situation is allowed by using spring contacts between the measuring device or the flexible circuit board equipped with the measuring device and adjacent bipolar plates. Furthermore, the variant with spring contacts is particularly simple in assembly because there is no need to specifically focus on the contact engagement of the measuring device, which is automatically established when the components of the fuel cell stack are stacked, whereas with the use of flexible conductors, the measuring device must be connected, for example, by brazing.

[0010] Here, the measuring device itself can be constructed in a known manner. According to a particularly suitable design of the device according to the invention, the measuring device includes a boost chopper in each case. This boost chopper can then correspondingly increase the relatively low voltage of a single battery cell to effectively drive an optical signal generator, which may, for example, include one or more LEDs. Here, power is supplied by the respective battery cell itself, thus eliminating the need for additional measures regarding the connection of this structure.

[0011] Here, in each individual cell, the cell voltage, which serves as a physical input parameter for the measuring device, is between 0 and typically 1.23V. The cell voltage, typically higher than 0.6V, can be correspondingly increased, for example, to a voltage level of 2.4V to 4V, by a corresponding boost chopper (preferably constructed as part of an integrated circuit) and an oscillating circuit acting as a beat or frequency generator. This boost chopper, acting as a DC / DC boost chopper, drives the LEDs of the optical signal generator, particularly multi-color LEDs or multiple LEDs with different brightness, color, blink frequency, etc., all of which can be used, for example, to receive the voltage of the monitored individual cell non-contactly via a CCD or CIS sensor and to perform corresponding evaluations for controlling the fuel cell stack.

[0012] Here, according to a highly advantageous improvement of the device according to the invention, the optical signal generator is constructed in such a way that it can be driven by the measuring device in different states, wherein the drivability preferably includes four different states. The first state of these states (and ideally the normal state) can be that the optical signal generator remains off. That is, if the optical signal is not activated, the cell operates within a preset theoretical range. If problems such as low voltage (commonly referred to as Low Cell), high voltage (High Cell), or more seriously, cell reversal occur, the optical signal generator is activated accordingly by the measuring device. In operation, the typical voltage for Low Cell is less than 600mV for a single cell, and the voltage for High Cell is greater than about 825mV. Cell reversal occurs when a single cell provides a voltage of -10mV to -800mV, mostly about -600mV.

[0013] Therefore, the activated optical signal generator reveals problems related to the corresponding single cell and thus, in fact, to the fuel cell stack comprising the single cell. Ideally, the difference can also be discerned through at least two distinct states of the optical signal generator in the on state, thus revealing whether the single cell is functioning correctly (i.e., the optical signal generator is off), whether the optical signal generator is turned on due to the cell providing excessively high or low voltage, or whether the optical signal generator is turned on because the single cell has the opposite polarity (this is often referred to as Cell Reversal). Here, Cell Reversal is the most important state to indicate, followed by Low Cell. Excessively high voltage (often referred to as High Cell) is the least dangerous state.

[0014] Therefore, the simplest approach is to simply indicate that there is a problem, regardless of what the problem is, and then to differentiate the problem into Cell Reversal and other problems, thus reducing High Cell and Low Cell to the same state, or, more preferably, to explicitly indicate all three states when it is easily implemented in terms of cost and structural space.

[0015] Here, to illustrate the various states, different known feasible methods can be used. For example, in the case of one or more monochromatic light sources in an optical signal generator, different flashing frequencies can be used to distinguish the states. However, it is particularly preferable to use different colors.

[0016] According to a highly suitable design of the device according to the invention, it can be specified that the optical signal generator of each measuring device is formed by a light-emitting diode (LED), which can emit at least two, preferably three, colors of light. That is, the LED can be configured in particular as a so-called multi-color LED. Thus, depending on the state, the multi-color LED can remain off, corresponding to the normal state of a single cell, or it can emit a first color, such as white, corresponding to a lower voltage of the single cell, or it can emit, for example, red, corresponding to a reversal of the polarity of the single cell. Optionally, for example, blue can indicate that the voltage of the single cell is too high.

[0017] Alternative designs may specify that the optical signal generator of each measuring device has at least two light-emitting diodes (LEDs). Here, the two or preferably three LEDs of the optical signal generator can emit the same color, but this requires evaluation by two different optical sensors. Alternatively, according to a particularly suitable improvement of the device according to the invention, the LEDs can also emit different colors. In this case, a single optical sensor is essentially sufficient if the optical sensor has a corresponding electronic evaluation device that can distinguish the different colors of light produced when using multicolor LEDs in the optical signal generator, for example, by performing Fourier analysis on the received signal.

[0018] That is, different light colors can also be produced simply and effectively by using multiple separately constructed LEDs, depending on the requirements. This may be a simpler and more cost-effective variant than using more complex multicolor diodes, but it requires structural space for multiple light-emitting diodes. Therefore, depending on the situation, this or other variants may be advantageous.

[0019] Despite these two variations, the final result is light that preferably indicates different problems with the corresponding individual cells by using different colors in the on / off state. It is now feasible to use appropriate optical sensors to scan / query, individually or in the manner shown in the prior art described at the beginning, via mirrors and high-resolution sensors at each individual optical signal generator of multiple measuring devices. However, in practice, it often doesn't matter which individual cell in the fuel cell stack is causing the corresponding problem, because a response involving the entire fuel cell stack is usually necessary, or, for example, the entire fuel cell stack must be disconnected to avoid further damage, since disconnecting individual cells is not practically possible.

[0020] Therefore, a highly suitable and cost-effective improvement to the device according to the invention specifies that the signals of all optical signal generators in the fuel cell stack are connected to at least one optical sensor via at least one optical conductor. Thus, a particularly suitable design of the invention can specify the use of an optical conductor. Currently, in principle, each individual light-emitting diode or each light source of a single optical signal generator can have its own optical conductor that directs light toward a common optical sensor or toward a small number of optical sensors. However, a particularly simple and efficient structure is the use of at least one strip-shaped optical conductor, specifically in such a way that, according to an advantageous design of the device according to the invention, the optical signal generator couples / injects its light into one of the longitudinal sides of the strip-shaped optical conductor, and at least one optical sensor is arranged at at least one end of the strip-shaped optical conductor.

[0021] For example, a single optical conductor, extending along the stacking direction of the fuel cell stack, where the optical signal generator of each measuring device adjusts the light for activation, can be sufficient to simultaneously drive all signal generators using a single optical sensor. Thus, through such an optical conductor, problems within the fuel cell stack can be identified by this single optical sensor. If the response is to shut down the fuel cell stack, this is perfectly sufficient and allows for a significant reduction in the cost currently used for single-cell voltage monitoring.

[0022] According to a highly suitable improvement to this concept, an electronic evaluation device can be assigned to the optical sensor, and this device is configured to distinguish colors. When red light appears at a corresponding level, it can be filtered out, for example, by performing a Fourier analysis on the data received by the optical sensor. Thus, it is also possible to detect, through a single sensor on multiple individual cells and, if necessary, through multiple active optical signal generators, whether one or all of the individual cells have a "Low Cell" or "High Cell" problem, or whether one or more of them have a polarity reversal problem.

[0023] This functionality is achieved not only when there is only one multicolor LED capable of producing different colors, but also when multiple LEDs of different colors are used (both of which direct their light into the same photoconductor).

[0024] An alternative design for a variant having at least two separate LEDs, preferably with different light colors, may further specify the presence of at least two strip-shaped light conductors, for example, arranged in parallel, while the individual LEDs of the optical signal generator are similarly arranged side-by-side and staggered transversely in the stacking direction. Thus, through two or three light conductors extending along the battery stack, the light from one LED can be purposefully directed to a region at one end of the battery stack. Subsequently, through sensors on each light conductor, the presence of one LED or the other LED can be detected, without complex software analysis, of one or the other state, i.e., the presence of at least one Low Cell, High Cell, or at least one cell with its polarity reversed.

[0025] Depending on the number of individual cells and the length of the fuel cell stack, it may be advantageous, and feasible, for the design variant of the strip-shaped light conductor described above, to arrange optical sensors at each end of the fuel cell stack, i.e., at both ends of the light conductor, thereby improving reliability in cases where light output is low in the region of the optical sensors. Attached Figure Description

[0026] Other advantageous designs of the device according to the invention are also derived from the embodiments shown in detail with reference to the accompanying drawings.

[0027] in:

[0028] Figure 1 A schematic diagram of a fuel cell stack is shown;

[0029] Figure 2 A portion of a fuel cell stack having the device according to the invention is shown;

[0030] Figure 3 It shows the relationship with Figure 1 Similar figures, which have particularly advantageous designs of the device according to the invention;

[0031] Figure 4 The illustration shows a possible design of the device according to the invention, with reference to a portion of the device and fuel cell stack of the first possible embodiment;

[0032] Figure 5 The illustration shows a possible design of the device according to the invention, with reference to a portion of the device and fuel cell stack of the second possible embodiment;

[0033] Figure 6A partial illustration of the device and fuel cell stack according to a third possible embodiment is shown, illustrating a possible design of the device according to the invention; and

[0034] Figure 7 A partial illustration of the device and fuel cell stack according to a fourth possible embodiment is shown, illustrating a possible design of the device according to the invention. Detailed Implementation

[0035] exist Figure 1 The diagram illustrates a fuel cell stack, indicated by 1, in a very generalized manner. Here, between two end plates, each indicated by 2, there are multiple individual cells, indicated by 3, where not all individual cells are shown, and not all shown individual cells are labeled. This structure of fuel cell stack 1 is known to those skilled in the art. The fuel cell stack 1 shown here is a cryogenic fuel cell with PEM individual cells, i.e., cells with a catalytically coated proton conduction membrane.

[0036] exist Figure 2 The diagram shows a portion of the fuel cell stack in an enlarged view. The central single cell 3 shown here (only the upper part is shown) includes a so-called membrane electrode assembly 4, which comprises a catalytically coated membrane on one hand and a gas diffusion layer and electrodes on the other. Here, the membrane electrode assembly is bonded to a frame 5. This structure is also called a frame-type membrane electrode assembly or membrane electrode frame assembly (MEFA). Here, MEFAs 4 and 5 may be equipped with their own seals, which are not shown here. Thus, this structure is also called SMEFA. Alternatively, the seals may be installed during stacking or arranged in bipolar plates 6 arranged adjacent to MEFAs 4 and 5 respectively. Figure 2 The illustration shows two of the bipolar plates 6. Each bipolar plate has a flow field (not shown) on one side for distributing hydrogen-containing gas to two adjacent single cells, and a flow field (not shown) on the other side for distributing oxygen-containing gas to two adjacent single cells. Typically, a flow field for cooling the medium is arranged between the bipolar plates, within the bipolar plates 6. All of these are known to those skilled in the art of fuel cells. The bipolar plates 6 can be made not only of metal, but also of plastic equipped with conductive fillers or of a conductively coated plastic material. All of these are not of paramount importance to the present invention and will not be described in detail here.

[0037] A flexible circuit board (not shown) connected to or part of frame 5 is constructed here, carrying a measuring device (represented by 7), shown here on frame 5. Measuring device 7 includes various components, such as a boost chopper and a means for detecting the voltage of the single cell 3, and is connected to the frame 5 of the single cell. Preferably, the measuring device 7, arranged on the flexible circuit board connected to or formed by frame 5, makes electrical contact with two bipolar plates 6 adjacent to the measuring device via flexible electrical contacts 8, specifically with the positive surface of the corresponding bipolar plate 6 on one side and the negative surface of the corresponding bipolar plate 6 on the other side. Thus, the voltage of the single cell 3 associated with the measuring device in fuel cell stack 1 can be monitored by measuring device 7.

[0038] Now, it is important for the operation of fuel cell stack 1 to distinguish different states in terms of voltage. This includes the normal state, the state with a decreased cell voltage (referred to as "Low Cell"), the state with a increased voltage (referred to as "High Cell"), and the state in which the polarity of a single cell 3 is reversed. This state is often referred to as "Cell Reversal." Now, what is crucial for driving fuel cell stack 1 is whether all the single cells 3 of the fuel cell stack are operating normally, or whether one or more of the single cells are in one of the aforementioned dangerous states, where the Low Cell and High Cell states are not as dangerous as the Cell Reversal state.

[0039] Now, the measuring device 7 can detect these states. Unlike conventionally constructed devices for monitoring the voltage of individual cells 3 in the fuel cell stack 1, the measuring device 7, integrated into the frame 5 in the manner described herein, has the advantage that it is directly mounted during cell manufacturing rather than being installed afterward and requiring separate electrical contact. To reliably provide a signal even within hazardous areas related to explosion protection due to possible hydrogen leakage from the fuel cell stack 1, the measuring device 7 has an optical signal generator 9. This optical signal generator 9 can, in particular, indicate the aforementioned states of the voltage of the individual cell 3, for example, remaining off when the voltage is normal and illuminating in one of the other states in the simplest case.

[0040] Therefore, the detection and evaluation of the signal from the optical signal generator can, in principle, be achieved using methods known from existing technologies, such as a series of detectors or redirecting the light to a high-resolution detector. All of these are conceivable in principle, but the required structural space and cost are relatively high. Especially in vehicle applications, this is often sufficient if at least one of the individual cells 3 of the fuel cell stack 1 is known to have a corresponding problem. In this case, a response must be made by disconnecting the entire fuel cell stack 1 or by correspondingly altering its medium supply, although there are doubts.

[0041] Now, in Figure 3 In the diagram, with Figure 1 Similarly, a simplest variation of this structure is illustrated with reference to the fuel cell stack 1. Each of the individual cells 3 shown has a measuring device 7, which includes an optical signal generator 9. A light conductor 10 extends along the entire fuel cell stack 1 in the stacking direction s. Specifically, the optical signal generator 9 of all measuring devices 7 of all individual cells 3 laterally couples its light to the longitudinal side of the light conductor 10, which is configured with a cross-sectional shape, for example, a square or strip-shaped light conductor. Now, an optical sensor 11 is arranged at at least one end side, or optionally at both end sides, specifically preferably in the region on the end side facing the end plate 2 of the fuel cell stack 1 or ending in the region of the end plate. In principle, one optical sensor 11 is sufficient. However, when the number of individual cells 3 is relatively high and the length of the fuel cell stack 1 in the stacking direction s is large, it is advantageous to simultaneously provide another optional optical sensor 11 in the region of the second end plate 2, so as to obtain reliable results in the case where only one individual cell 3 generates a signal through the optical signal generator 9 of its measuring device 7, which is relatively far from only one optical sensor 11 along the stacking direction s and therefore cannot be reliably detected by the optical sensor.

[0042] As explained above, it is now advantageous to know whether the LowCell problem, HighCell problem, and / or Cell Reversal problem have been identified by the optical sensor 11. In principle, different approaches exist for this, which are described below. Figures 4 to 7 The diagrams in the document illustrate and explain accordingly. Here, partial views of one of the end plates 2 and three individual cells 3 and their measuring devices 7 are shown respectively.

[0043] exist Figure 4In the illustrated configuration, each measuring device in measuring apparatus 7 has a light-emitting diode (LED) 12 as an optical signal generator 9. The LED 12 is configured as a multi-color LED capable of displaying different colors. When the voltage of the corresponding single cell 3 is normal, the LED remains off. In a Low Cell, the LED emits a first color, such as yellow; in a High Cell, it emits a second color, such as blue; and during cell polarity reversal, i.e., Cell Reversal, it emits a third color, such as red. The emitted light, collected by the light conductor 10 and guided to the region of the sensor 11 by one or optionally two optical sensors 11 arranged at the two end plates 2, is then evaluated by an electronic evaluation device 13. In this electronic evaluation device 13, in particular, Fourier analysis can be performed to analyze the different colors of light detected by the sensor 11. If the light is only monochromatic, for example, present as yellow light, one or more Low Cell problems can be reported by the electronic evaluation device 13. If the light only includes red light, one or more Cell Reversal problems can be reported accordingly. If the light contains only blue light, one or more High Cell problems can be reported. If the light contains all three colors, then a Low Cell problem and a Cell Reversal problem can also be reported accordingly. In terms of hardware, this requires a multi-color LED 12, and in terms of software, a corresponding evaluation is needed in an electronic evaluation device 13.

[0044] Instead of different light colors, or in principle as a supplement, different flashing frequencies or flashing sequences, i.e., sequences of defined flashing patterns, can also be used so that different states of at least one single cell 3 in the fuel cell stack 1 can be detected by at least one optical sensor 11.

[0045] The structure can be modified as follows: the multi-color LED 12 can be completely omitted. Now, in principle with... Figure 4 The diagrams in the text are similar to the understanding. Figure 5The structure in the optical signal generator 9 is configured such that each component has two different light-emitting diodes 14 and 15. If necessary, this can be a more cost-effective variation than using multi-color LEDs, provided there is sufficient space in the existing structure. In this variation, the two different colored LEDs 14 and 15 couple their light into the photoconductor 10 in the same manner as described above. Subsequently, they are similarly detected by at least one sensor 11 and evaluated in the electronic evaluation device 13. Thus, including the "off" state, the two different LEDs 14 and 15 exemplarily shown here can exhibit a total of three states. This could be, for example, the normal function where both LEDs 14 and 15 are off, a High Cell or Low Cell problem where one of the LEDs, such as LED 14, is on, or a Cell Reversal problem where, for example, LED 15 is on. Of course, the structure can also be extended accordingly to have a third LED, so that in this structure, the High Cell state and the Low Cell state can also be distinguished from the signals arriving at at least one optical sensor 11.

[0046] In addition, Figure 6 The illustration shows another variation. Instead of arranging LEDs 14, 15 adjacent to each measuring device in the measuring device 7 as optical signal generators in the stacking direction, the LEDs 14, 15 can also be arranged laterally and staggered in the stacking direction. Specifically, for example, they can be arranged as follows: Figure 6 As shown in the diagram, LEDs 14 and 15 couple their light into two parallel extending light conductors 10 and 16. Here, the LEDs can be of different colors, but it is also possible to use only LEDs of the same color. In this case, in Figure 6 The diagram above shows LED 14, which is activated to indicate, for example, Low Cell or High Cell, by the optical signal generator 9. Figure 6 In the illustration, the LED 15 arranged below in the region of the second light conductor 16 indicates a Cell Reversal. Thus, the optical sensor 11 can directly indicate a Low Cell problem in a known manner without further evaluation of the light color and transmit it to the corresponding control device; correspondingly, one or more Cell Reversal problems are indicated by the optical sensor 17 at the end of the other light conductor 16.

[0047] Now, as explained in principle above, this in Figure 6The structure shown can also extend beyond the two LEDs 14 and 15 to include a third LED 18, and in this case, another light conductor 19 and another optical sensor 20 are correspondingly extended. This is in Figure 7 The corresponding diagram shows, Figure 7 In other respects, it is understood as... Figures 4 to 6 The diagram is similar. Thus, through this structure, one of the states of interest can be indicated respectively in each of the individual photoconductors 10, 16, and 19.

[0048] In general, the structure is extremely simple in all variations and can be implemented with very few optical sensors 11, 17, 20. These optical sensors only need to identify the presence of light and, if necessary, the color of light, and there are no high requirements for these optical sensors, such as high pixel resolution.

[0049] These structures are suitable in principle for any type of fuel cell stack 1, especially for PEM fuel cells. These structures are particularly suitable for vehicle applications of this type of fuel cell stack 1 because they meet both the constraints of structural space and the very high cost pressures of assembling and manufacturing the fuel cell stack 1.

[0050] The device for monitoring cell voltage in the feasible implementation variant described herein achieves this ideally.

Claims

1. A device for monitoring the cell voltage of a single cell (3) of a fuel cell stack (1), the single cell comprising a membrane electrode assembly (4) and a bipolar plate (6), the device having a measuring device (7) for each single cell (3), the measuring device comprising an optical signal generator (9) drivable by the measuring device, characterized in that, The measuring device (7) is constructed on a flexible circuit board connected to or constructed as part of the frame (5) of the frame-type membrane electrode assembly. The optical signal generator (9) of each measuring device (7) is formed by a light-emitting diode (12) configured to emit light in at least two colors.

2. The device according to claim 1, characterized in that, The measuring device (7) is electrically connected to two adjacent bipolar plates (6) via flexible conductor elements and / or spring contacts (8).

3. The device according to claim 1 or 2, characterized in that, The measuring device (7) includes a boost chopper.

4. The device according to claim 1 or 2, characterized in that, The optical signal generator (9) is configured such that the optical signal generator can be driven by the measuring device (7) in at least three different states.

5. The device according to claim 1 or 2, characterized in that, The optical signal generator (9) of all measuring devices (7) is connected to at least one optical sensor (11) via at least one optical conductor (10, 16, 19).

6. The device according to claim 5, characterized in that, An electronic evaluation device (13) is provided for evaluating data from the at least one optical sensor (11), the electronic evaluation device being configured to evaluate the detected signal in terms of whether a specific color and / or flashing frequency is present.

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