Abstract:
In a device for measuring the filling level, thermoelements ( 20 ) are used which are disposed on a sheet-shaped support ( 25 ). The thermoelements ( 20 ) consist of two different materials and are disposed in two rows ( 71, 72 ) placed side by side. Two adjacent thermoelements ( 20 ) of said rows ( 71, 72 ) have a common junction point ( 23 ) that is heated. Both rows ( 71, 72 ) of thermoelements also have two additional junction points that are cold. A first group of thermoelements ( 20 ) is disposed with their supports ( 25 ) in the interior of the container and operate as measuring detectors. A second group of thermoelements ( 20 ) serves as reference sensors since they regulate the heat flow impinging upon the junctions points ( 23 ) relative to a defined reference voltage.

Description:
BACKGROUND OF THE INVENTION 
     A method for manufacturing a device where a set of thermoelements, comprised of two junction points between two different materials, are connected in series and function as measuring sensors. The measurement is based on the physical effect that the thermoelectric voltage of a thermoelement changes as a function of which materials, such as gas or liquid, the junction points come into thermal contact with. One junction point in the thermoelements is heated by an electric heat conductor with heating current being controlled when doing so. Therefore, this junction point is referred to as “hot junction point”. The other junction point is not heated and is therefore referred to as “cold junction point”. 
     In a known method (DE 40 30 401 B1) metals or semiconductors are vapor-deposited first onto foils and out of these stamped parts are cut which, by means of adhesives at the backside, are placed onto a sheet-shaped support. Subsequently, by screen printing narrow metallic conductive cement strips are applied so that thermoelements result. For a space-saving configuration L-shaped stamped parts are cut out of the foil strips and these are glued in mirror-symmetrical arrangement and with height staggering in two rows onto a support and then the ends of L-shaped legs are printed with a metallic conductive cement with lines such that serially connected thermoelements result. The manufacture of this known device is expensive and has a high failure liability. The manufacture of the stamped parts and their arrangement on the common support are cumbersome and errors are hardly avoidable. During stamping a relatively high amount of waste results which prevents an economic manufacture of the device. Alloys, such as nickel-chromium or constantan, important for the thermoelectric voltage, cannot be deposited onto the foil strip because they decompose during this process. 
     In another method (DE 4 34 646 A1) a stamped part in the form of a strip has also been cut out of a plastic foil which is then coated with a semi-conductor material by means of chemical, physical, or mechanical methods. On this strip a metallic conductive application layer was applied by screen printing at certain locations. This was supposed to result in large surface area connections of the thus resulting thermoelements. The thermoelements are series-connected. Onto the backside of the support a heating conductor in meander shape was printed by means of a metallic conductive cement. Because the heating current changes by a change of the surrounding temperature in the same direction, a reference sensor has been positioned on the heating conductor which controls the heating current by means of a compensation circuit. In this case, it was also not possible to use interesting alloys such as nickel-chromium or constantan neither during manufacture of the strips nor for printing of the strips. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to develop a method for a reliable manufacture of a space-saving device with high measuring precision for measuring the filling level in a container or for measuring gas by means of thermoelements. This is achieved according to the invention by the features to be explained in the following. 
     The invention has firstly recognized that the very interesting alloys for configuring thermoelements, chrome-nickel, on the one hand, and constantan, on the other hand, can be applied by sputtering onto a support. When sputtering, a high-energy plasma is directed onto a target where metals are impacted and are applied onto the desired carrier by means of a magnetic field. The invention uses in this connection masks where the shape of the resulting fields for the alloy for forming the thermoelements are very precisely formed by cutouts. The different masks are placed successively in a defined position so that during sputtering the different L-shaped and I-shaped fields in both rows have an extremely precise position relative to one another. On the backside of the support successively a fourth and fifth mask, either provided with a narrow or a wide slot, are provided for applying by sputtering of the desired materials, in particular, silver, a common heating conductor and its return line. The heating conductor can then be positioned precisely in the longitudinal center of the junction points between the two double rows provided on the front side of the carrier and in this way generates the common hot junction point. 
     In a similar way, at least one reference sensor is manufactured on a sheet-shaped support, respectively, an entire set of reference sensors. One can correct the undesirable temperature effect on the heating conductor also in other ways. 
     The invention also relates to a device produced according to the method according to the invention wherein the set of measuring sensors has correlated therewith a group of reference sensors. 
     In the known device (DE 44 34 646 A1) it was considered necessary to position the reference sensors independent of the measuring sensors in order for them not to come into contact with the liquid. If this was not done, their control effect would not have been possible. Therefore, in the known devices the reference sensor(s) have always been arranged external to the container whose filling level was to be measured. This not only requires a corresponding space expenditure but also entails circuit problems when connecting the measuring sensors and their heating conductor. The independent arrangement of the reference sensor(s) requires corresponding measures for their protection. This requires additional components which increase the space requirement. The separate attachment of the reference sensors increases also their failure liability. The manufacture and assembly of the known reference sensors and their protection are cumbersome and cost-intensive. 
     This is however also solved by the invention by the following measures according to which the reference sensors together with the measuring sensors are arranged in the container interior. Their interconnection is particularly simple. The container itself provides the protective function for the reference sensors arranged in its interior. The control effect of the reference sensors remains thus in effect because its junction points are brought into contact with a body having a constant thermal conductivity. This can be achieved in the form of a thermal insulation which protects the junction points of the reference sensors relative to the liquid. Such a body of constant thermal conductivity could also be a plastic body. The measuring sensors and reference sensors are insulated relative to the corresponding electric heat conductors. 
     Another possibility resides in that the reference sensors are arranged at the bottom of the container where there is always residual liquid present which ensures the constant thermal conductivity between the hot and cold junction points. Finally, it would also be conceivable to use for this purpose the upper area of the container where even for a full filling level no liquid will reach. In the latter case, the gas which is always present thereat provides the constant thermal conductivity. In these two last mentioned alternatives, corresponding bulges in the interior of the container are available for receiving the reference sensors in the container interior. 
     The simplest possibility for realizing the invention is however the aforementioned use of thermal insulation in the area of the reference sensors for which purpose different possibilities are provided. Some of them are mentioned in the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further measures and advantages of the invention result from the dependent claims, the following description, and the drawings. In the drawings, the invention is schematically illustrated in several embodiments. It is shown in: 
     FIG. 1 schematically an application situation of the inventive device in a fuel tank of the vehicle; 
     FIG. 2 schematically the construction principal of the measuring device, arranged in the fuel tank, of the first embodiment of the device according to the invention where the components of a measuring and control device are arranged on the same support; 
     FIG. 3 a circuit diagram of a first embodiment of the device illustrated in FIG. 2; 
     FIG. 4 on a greatly enlarged scale the plan view onto the thermoelements of the measuring sensor of a second embodiment of the device according to the invention where the reference sensors are positioned on a separate support; 
     FIGS. 5 and 6 in approximately natural size the upper partial piece and the two end pieces of two masks with which the first material for manufacturing the thermoelements of the measuring sensors illustrated in FIG. 4 are applied on the front side of a foil-shaped support which is not illustrated in detail; 
     FIG. 7 a corresponding partial piece of a third mask which serves for sputtering the other material for the thermoelements onto the measuring head of FIG. 4; 
     FIGS. 8 and 9 the corresponding masks for sputtering a material forming the heat conductor for current supply and for serving to heat the heat conductor of the hot junction points in the thermoelements of the measuring head of FIG. 4; 
     FIG. 10 a cross-section of the finished support receiving only the measuring heads according to FIG. 4 before being mounted in a fuel tank of a vehicle; 
     FIG. 11 the schematic plan view onto an envelope receiving the measuring device of FIG. 3; 
     FIG. 12 schematically, in analogy to FIG. 10, a cross-section of the envelope illustrated in FIG. 11 along the section line XII—XII which illustrates the interior configuration; 
     FIG. 13 in an illustration corresponding to FIG. 12 an alternative embodiment of the device of FIG. 3 according to the invention 
     FIG. 14 in a plan view corresponding to FIG. 11 a partial piece of an alternatively embodied envelope of the device of FIG. 3 according to the invention; 
     FIG. 15 in an illustration corresponding to FIG. 12 a cross-section of the device illustrated in FIG. 14 along the section line XV—XV indicated therein; and 
     FIG. 16 again a cross-section, in analogy to FIG. 15, of a further modified embodiment according to the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     As illustrated in FIG. 1, the device  10  according to the invention can serve for determining the respective filling level of a container  11 . It is comprised in the present case of a fuel tank  11  of the vehicle. Such a fuel tank has a complex spatial shape for the reason of optimal use of the available space in the vehicle. The device according to FIGS. 1 through 3 comprises in the container interior  19  a combined measuring device identified by  12  that is connected by connecting and control lines  18  with an electrical evaluation device  13  and a display  14 , for example, in the form of a display device. In the interior of the container a liquid  15  is present, for example, fuel, wherein as a function of the liquid consumption, a changing filling level  16  results. Above the liquid level  12  a gas  17  is present, for example, air, together with the vapors of the liquid  15 . The filling level  16  is determined by the electrical circuit illustrated in FIG. 3 wherein the measuring device  12  follows the general construction principle illustrated in FIG.  2 . 
     Instead of the combined measuring device  12  according to FIGS. 1 through 3, it is also possible to arrange a measuring device part  66  for measuring sensors according to FIG. 4 and 10 in this way which has correlated therewith an analog measuring device part, which will be explained in more detail in the following, for reference sensors with analog construction. This other measuring device part, in contrast to the first embodiment of FIGS. 1 through 3, can then also be arranged external to the tank inasmuch as it is ensured that the temperature difference between the measuring medium and the other measuring device part is limited and, for example, does not surpass ±20° C. In the measuring device  12  as well as in the measuring device part  66  a plurality of thermoelements  20  are used whose configuration will be explained with the aid of FIG.  4 . 
     The thermoelements  20 , as can be seen in FIG. 4, can be arranged in two rows  71 ,  72  and are comprised of two different materials  21 ,  22  which however match one another within the rows  71 ,  72 . In the present case, one material  21  can be a nickel-chrome alloy while the other material  22  is, for example, constantan. These materials  21 ,  22  are applied onto the front side  26  of a sheet-shaped support  25  which is advantageously embodied as a foil. The material of the foil may be a polyamide or polyether ether ketone (PEK). The materials  21 ,  22  are applied by sputtering which has been found to be especially suitable for the selected special configuration. For this purpose, the masks which are shown in FIGS. 5 through 7 are used. The first mask  67  of FIG. 5 serves for applying the first material  21 . It contains two rows of L-shaped cutouts  70 ,  70 ′ which after sputtering generate two mirror-symmetrically arranged L-shaped fields  73 ,  73 ′ of the material  21  on the support foil  25 . These fields  73 ,  73 ′ are facing one another with their long L-legs  74 ,  74 ′ but are spaced apart from one another by a spacing  76  which is sufficient for insulation purposes. Accordingly, the two correlated short L-legs  75 ,  75 ′ are positioned respectively in the two outer border areas of the thermoelement rows  71 ,  72 . The mask  67  has, of course, also a cutout for the first terminal tab  77  to be formed of the two future thermoelement rows  71 ,  72 . The two end faces  79 ,  79 ′ of the long L-legs  74 ,  74 ′ are laterally displaced relative to one another by a certain amount in the two rows  71 ,  72 . 
     The aforementioned first material  21  is supplied by a second mask  68  according to FIG. 6 also onto the front side  26  of the support foil  25  and generates after sputtering the second terminal tab  78  shown in FIG.  4 . Only thereafter the third mask  69  illustrated in FIG. 7 is used which has two rows of I-shaped cutouts  80 ,  80 ′. These then generate the I-shaped fields  83 ,  83 ′, illustrated in FIG. 4, in the two rows  71 , 72 . The two I-shaped fields  83 ,  83 ′ are exactly aligned with respect to the length as well as with respect to their width and position with the aforementioned L-shaped fields  73 ,  73 ′. 
     The two inwardly oriented end area is  82 ,  82 ′ of the I-shaped fields  83 ,  83 ′ overlap with the long legs  74 ,  74 ′ of the respective L-shaped fields  73 ,  73 ′ located in the respectively oppositely positioned rows  72 ,  71 . These overlaps are positioned, for example, on the line  84  indicated in a dash-dotted line in FIG. 4, approximately in the longitudinal center between the two thermoelement rows  71 ,  72  to be formed. The two outwardly oriented end areas  81 ,  81 ′ of the two I-shaped fields  83 ,  83 ′, in turn, overlap with the ends of the two short L-shaped legs  75 ,  75 ′ of the respective neighboring L-shaped fields  73 ′,  73 . These outer overlaps of  81 ,  75  or  81 ′,  75 ′ are located in the edge areas of the two rows  71 ,  72 . 
     FIG. 10 shows a cross-section of a finished measuring device part  66  from which the further process for mounting can be taken. As can be seen therein, on the backside  27  of the foil  25  a heat conductor  28  is applied which extends approximately in the longitudinal center of the foil  25  and aligned with the line  84  shown in FIG.  4 . Accordingly, the overlaps of  79 ,  82 ′ and  79 ′,  82  taking place in the longitudinal center between the two rows  71 ,  72  provide the necessary decisive hot junction point  23  for the thermoelements  20 . Accordingly, the two outer overlaps  81 ,  75  and  81 ′,  75 ′ are the corresponding cold junction points  24 ,  24 ′ in the oppositely positioned border areas of the double rows  71 ,  72 . 
     The heat conductor  28  can be applied by the sputtering method onto the foil backside  27  for which purpose the masks  85 ,  86  shown in FIGS. 8 and 9 are used. The material for the heat conductor is advantageously silver. For the actual heat conductor  28  the mask  85  has a narrow slot  88  whose size corresponds to the strength of the heating current and the desired temperature increase of the hot junction point  23 . At the end of the slot  88 , widened terminal areas are provided whose incidental heating is undesirable. For completion of the heating circuit the second mask  86  for application of a neighboring silver conductor is used for which purpose a widened slot  87  with junction point at the ends is provided. Accordingly, the current return  89  for the heat conductor  28  is generated, which is illustrated in FIG.  10  and which in the operating situation is not to be heated by the heating current. 
     The thus produced pre-product is then coated on all sides with the plasma polymer layer  90 , according to FIG.  10 . This layer  90  is also applied by means of the sputtering method. It forms an excellent barrier layer relative to diffusion of foreign atoms into the foil. Modified silicone-hydrocarbon layers are suitable as plasma polymers. 
     As has been mentioned above, FIGS. 2 and 3 show an embodiment modified relative to the measuring device part  66  of FIGS. 4 and 10 where the thermoelements  20  are divided into two branches  34 ,  44  having different functions relative to one another which in the following generate two measuring sensors  43  and reference sensors  33  combined in a common measuring device  12 . In FIGS. 2 and 3 the thermoelements  20  are illustrated conventionally; however, expediently, the same thermoelement configuration as that of the double rows  71 ,  72  illustrated in FIG. 4 will be used. The measuring sensors  34  as well as the reference sensors  33  are heated at their hot junction points  23  by a suitable extension of the same electrical heating conductor  28 . Not only the configuration and the number of the two sensors  33 ,  43  are identical but, expediently, also its arrangement pattern  34 ,  44  shown in FIG. 3 on the, preferably common, support foil  25 . 
     The measuring sensors  34 ,  44 , as illustrated in FIG. 2, are arranged at different but defined levels in the container interior  19  as required for the desired measuring-technologically determination of the filling level  16 . This configuration also is mirrored in the arrangement of the reference sensors  33 , even though the thermoelements  20  in the reference branch  44  are not to respond to differences of the filling level of the tank, which will be explained in more detail in the following. This symmetrical configuration of the sensors  33 ,  43  on both sides makes possible, as a result of their pattern identity, an especially simple and quick manufacture of both branches  34 ,  44 . 
     Even though it is possible to then also apply the aforementioned plasma polymer layer  90 , explained in connection with FIG. 10, onto the combined measuring device  12  as a protection, FIG. 12 shows an alternative which relates back to the embodiment of FIGS. 2 and 3. Here, an envelope  50  is provided which also prevents a direct contact of the sensors  33 ,  34  with the respective possibly aggressive media. In order to prevent reliably diffusion of liquid molecules into the interior  51  of the envelope, the envelope is comprised of a very thin metal foil  50  which, however, basically remains thermally transparent, particularly in the area of the measuring sensors  43 . For this reason, the metal foil  50  has a minimal thickness of, for example, the 3 to 8 μm. Accordingly, the respective measuring sensors  43  with their cold junction points  24  can feel the different thermal conductivity of the liquid  15  and the gas  17 . The metal foil  50  acts also as a vapor lock and is soldered at the seam  54  illustrated in FIG.  12 . The metal foil  50 , as illustrated in FIG. 3 by reference numeral  65 , is connected to ground potential and serves additionally for shielding electromagnetic fields. Between the metal foil  50  and the support foil  25 , supporting the diverse thermoelements  20  and lines, covering foils  52 ,  53  are provided which serve for electrically isolating the metallic foil  25  relative to the thermoelements  20 . The metal foil  50  is comprised preferably of copper or copper alloys, such as CuZn or CuNi (constantan). 
     In the present case, the thermoelements  20  of the entire set of measuring sensors  43  in the branch  44  as well as the entire set of the reference sensors  33  in the branch  34  are switched in series, respectively. The corresponding two terminals  45 ,  46  or  35 ,  36 , according to FIG. 2, are guided out of the enclosing metal foil  50 , taking into account electrical isolation, wherein, according to the circuit shown in FIG. 3, one terminal  35 ,  45  can be connected to ground potential, respectively. It is also possible to employ a different circuit. Instead of the serial connection, it is also possible to employ a parallel connection of the respective thermoelements  20  in order to perform an evaluation of the thermoelectric current because in this case the thermoelectric voltage would be constant. 
     The hot junction points  23  of the measuring sensors  43  which are maintained by the electrical heating line  28  at higher temperatures, as well as the cold junction points  24  are in thermal contact with the respective environment external to the envelope  50 . As a result of the already mentioned different thermal conductivities of the two media  15 ,  17 , the junction points  23 ,  24  reach a different temperature level corresponding to the respective different height level of the liquid level  29 . The subset  47  of the measuring sensors  43  shown in FIG. 2, which is located at the level of the liquid  15 , reaches as a result of the good thermal conductivity in this area a lower temperature than that of the residual set  48  above the liquid level  29  because the medium  17  that is present therein and is a gas dissipates the generated heat badly. When different filling levels  16  are present, this results in a different measured voltage at the terminal  46  of FIG. 3 which is determined in the following measuring circuit  40  of the evaluation device  13 . 
     In the measuring circuit, a reference voltage source  41  is provided relative to the ground potential which acts onto the input of an operational amplifier  42 . The measured voltage U meas  at  46  is supplied via an impedance converter  49  to the other output operational amplifier  42  and provides an output signal at the output line  60 . The output signal can then be guided via an analog digital converter to an evaluation circuit which controls, for example, a digital filling level indicator. Another possibility resides in that the output signal  60  is supplied via a voltage current converter to an analog display  14  according to FIG.  1 . The output signal  60  depends on the filling level  16  which can be read by the aforementioned circuit means in the display or the analog indicator  14 . With a suitable threshold switch the output signal can also be used for controlling a suitable reserve display for the filling level  16 . 
     The invention ensures that the reference sensors  33  are not affected by the different measuring level  16  between the two media  15 ,  17 , but that instead, despite their parallel position relative to the measuring sensors in the container interior  19 , they always have the same thermal conductivity at their junction points  23 ,  24 . For this purpose, generally speaking, a thermal insulation is employed which expediently covers the entire branch  34  of the reference sensors  33 . This is explained in connection with FIGS. 11 to  16  in different embodiments. 
     In FIGS. 11 and 12 the insulation is in the form of a continuous airbag  55  which is seated on the outer side of the metal foil  50 . It covers the entire field, indicated in FIG. 11 by dash-dotted lines, with the branch  34  of the reference sensors  33 . The field which is illustrated analogously in FIG. 11 with the branch  44  of the measuring sensors  43  is, of course, free thereof. 
     In the schematic of FIG. 13 the thermal insulation is in the form of a foam layer  56  which in this case is also applied on the outer side of the metal foil  50 . In the alternative illustrated in FIG. 16, the two cover foils  52 ,  53  are used as supports for the foamed material layer  56  on both sides. Accordingly, the foamed material  56  is thus positioned in the interior  51  of the envelope  50 . 
     In the last embodiment of FIGS. 14 and 15, air chambers  57  are used for thermal insulation which can be correlated individually to the reference sensors  33 . These air chambers  57  in this case are also on the outer side of the metal foil  50 . The air chambers  57  can also be arranged at the inner side of the metal foil  50 . Further alternatives could reside also in that such thermal insulation means are, for example, integrated directly in the cover foils  52 ,  53  in that it is formed at the locations or zones of the reference sensors  33  of an especially great thickness. 
     As illustrated in FIG. 3, the reference sensors  33  are provided for controlling the heat current flowing within the heating circuit  30  which is supplied from a voltage source  37  within the heating circuit  30 . The branch  34  provides the “sensing member” of the control circuit  62  whose control member  38  is arranged in the heating circuit  30  and serves for adjusting the heating current. The thermoelectric reference voltage U ref  present at the terminal  36  is connected via impedance converter  59  to the input of an operational amplifier  58  whose other input is connected to an adjustable, but fixed reference voltage source  39 . The output signal at the output line  61  of the operational amplifier  58  controls the control member  38  in the heating circuit  30 . When as a result of temperature effects or aging effects the electrical resistance of the heating conductor  28  is changed or as a result of fluctuations of the supply voltage, the heating current is corrected by the control circuit  62 . 
     This symmetrical configuration of the measuring and reference sensors  43 ,  33  results in new surprising effects. When the container  11  is empty, the measured voltage U meas  at  46  in FIG. 3 will always be identical to the reference voltage at  36 . As a result of manufacturing tolerances, the individual thermoelements  20  can have different thermoelectric voltages for the same temperature. For a sufficiently large number of thermoelements  20  in the two branches  34 ,  44 , the different thermoelectric voltages will compensate one another. Measuring errors can result as a function of the surrounding temperature but they are completely compensated by the device according to the invention for the following reason. 
     Even when the temperature difference ΔT between the cold and the hot junction points  24 ,  23  remains constant, an increase of the surrounding temperature results in an increase of the thermoelectric voltage in the thermoelements  20 . For an increase of the surrounding temperature the thermoelectric voltage of the individual elements  20  increases in the reference branch  34  and in the measuring branch  44  by the same amount. Due to the control circuit, the heating current in the heating circuit  30  is controlled so long until the reference voltage U ref  at  36  will have the original value. Thus, the heating current in the heating circuit  30  drops and, moreover, the measured voltage U meas  will drop to the original value. This control functions even when, for example, only one thermoelement  20  in the two branches  34 ,  44  is exposed to a higher surrounding temperature. 
     When using the device  10  in a fuel tank  11 , great temperature differences between the liquid  15  and the gas  17  arranged above can occur, for example, when filling in that heat of the summer where cold fuel  15  is filled into the hot tank  11 . It can be determined by theoretical calculations of the full and the empty tank  11  as well as experimentally that the obtained measured voltage U meas  in the measuring branch  44  is independent of the surrounding temperature when the reference branch  34  which serves for controlling the heating current in the heating circuit  30  has the same configuration as the measuring circuit  44 . The temperature effects occurring in both branches  34 ,  44  do not cause a measuring error. This also holds true for any desired filling level  16  in the container  11 . Even when horizontal temperature layers are present within the container  11 , the resulting measuring errors in the two branches  34 ,  44  are compensated. 
     When the support foils  25  provided with the thermoelements  20  are mounted vertically in the tank  11 , the vertical electrical field component of an impinging electromagnetic wave results in a voltage induction in the longitudinal direction of the foil. Such a potential will occur however in the measuring branch  44  as well as in the reference branch  43  and, accordingly, will overlay the wanted signals U meas  and U therm . Low-frequency noise fields effect low-frequency noise voltages which can be filtered only with difficulty. Since however in the device  10  according to the invention the direction and the amount of the induced voltages in both branches  44 ,  34  is identical, respectively, these effects are also basically canceled out. The device according to the invention accordingly has as a result of its symmetrical configuration a high stability with respect to its electromagnetic compatibility (EMV). 
     The symmetrical configuration of the two branches  44 ,  34  with separate electronic device has the advantage that, as a result of the large number of thermoelements  20 , the reference voltage U ref  is so large that it can be transmitted without noise. By means of symmetrically twisted electrical lines for the reference voltage U ref  and the measured voltage U meas , the noise voltages can be minimized. With regard to high-frequency considerations, both lines are provided with identical loads and behave identically in the case of noise fields with respect to the induction of noise voltages. The induced noise voltages are identical with respect to their amount and phase and thus effect no display errors in the display  14 . 
     As has been mentioned before, in FIGS. 4 and 10 only one measuring device part  66  is shown which in connection with the last described embodiment  12  comprises measuring sensors identified by  43 . This measuring device part  66  is thus within the container interior  19  of FIG. 1. A corresponding further measuring device part which comprises at least one single reference sensor is provided on a separate support, for example, a further foil. This further support can then be arranged also externally to the container interior  19  and is thus never in contact with the liquid medium  15  of FIG.  1 . More beneficial is also in this connection a plurality of thermoelements as reference sensors  33  which then should have expediently the configuration illustrated in FIG.  4 . When these reference sensors  33  of the other measuring device part also are immersed in the liquid entirely or partially, then the thermal insulation  56  already described will also be used here. With respect to the configuration of FIG. 10, thermal insulation would be provided at locations identified therein with  56  and illustrated in dash-dotted lines. 
     The aforementioned chain arrangement of the thermoelements could also be used for gas quantity measurements. A preferred application in this context is the air quantity measurement for injection engines. For a certain engine output an internal combustion engine requires a certain mixture of air (oxygen) and fuel. For determining the intake air quantity in the injection motors an air quantity measuring device is used. 
     In conventional systems, inter alia, a mechanically operating air quantity measuring device is used. In this connection, the intake air stream moves a throttle flap against the restoring force of a spring. A potentiometer converts the angular position of the vacuum flap into a corresponding voltage value. 
     The same object can also be taken on by a thermoelement chain which is positioned in the intake pipe because cooling of the warm junction points of the heated thermoelements acts proportionally to the air flow. The stronger the flow of air, the more reduced is the thermoelectric voltage sum. Effects of the temperature of the intake air, supply voltage fluctuations, and aging effects can be completely compensated by a control of the heating current by means of thermally insulated reference thermoelements positioned in the air flow. 
     List of Reference Numerals 
       10  device 
       11  container, fuel tank 
       12  combined measuring device 
       13  evaluation device 
       14  display, analog display 
       15  liquid, first medium in  19   
       16  filling level in  19   
       17  gas, second medium in  19   
       18  connecting and control line 
       19  container interior of  11   
       20  thermoelement 
       21  first material of  20 =CiNi 
       22  second material=constantan 
       23  hot junction point between  21 ,  22   
       24 ,  24 ′ cold junction point between  21 ,  22   
       25  sheet-shaped support, support foil 
       26  front side of  25   
       27  backside of  25   
       28  electrical heat conduction, heat conductor 
       29  liquid level between  15 ,  17   
       30  heating circuit for  28   
       31  first terminal of  28   
       32  second terminal of  28   
       33  set of reference sensors 
       34  reference branch, field of  33   
       35  first terminal of  34   
       36  second terminal of  34   
       37  voltage source 
       38  control member of  62   
       39  reference voltage source in  62   
       40  measuring circuit 
       41  reference voltage source in  40   
       42  operational amplifier in  40   
       43  set of measuring sensors 
       44  measuring branch, field of  43   
       45  first terminal of  44   
       46  second terminal of  44   
       47  partial set of  43  in  15   
       48  residual set of  43  in  17   
       49  impedance converter 
       50  envelope, metal foil 
       51  envelope interior 
       52  first cover foil in  51   
       53  second cover foil in  51   
       54  sealed seam of  50 , soldering seam 
       55  thermal insulation, airbag (FIGS. 4,  5 ) 
       56  thermal insulation, foamed layer (FIGS. 10,  13 ,  16 ) 
       57  thermal insulation, air chamber (FIGS. 14,  15 ) 
       58  operational amplifier in  62   
       59  impedance converter in  62   
       60  output signal line in  40   
       61  output signal line in  62   
       62  control circuit 
       63  partial group of  33   
       64  remaining group of  33   
       65  ground potential for  50   
       66  measuring device part (FIG. 4) 
       67  first mask for  21  of  20  (FIG. 5) 
       68  second mask for  21  of  20  (FIG. 6) 
       69  third mask for  22  of  20  (FIG. 7) 
       70 ,  70 ′ L-shaped cutout in  67   
       71  first row of  20  (double row) 
       72  second row of  20  (double row) 
       73 ,  73 ′ L-shaped fields of  21  in  67  (FIG. 5) 
       74 ,  74 ′ long leg of  73 ,  73 ′ 
       75 ,  75 ′ short leg of  73 ,  73 ′ 
       76  spacing between  74 ,  74 ′ 
       77  first terminal tab of  21  on  25   
       78  second terminal tab of  21  on  25   
       79 ,  79 ′ end piece of  74 ,  74 ′ 
       80 ,  80 ′ I-shaped cutouts in  69  (FIG. 7) 
       81 ,  81 ′ outer end area of  83 ,  83 ′ 
       82 ,  82 ′ inner end area of  83 ,  83 ′ 
       83 ,  83 ′ I-shaped fields of  22   
       84  line, longitudinal center between  71 ,  72   
       85  first mask for  28  (FIG. 8) 
       86  second mask for  28  (FIG. 9) 
       87  wide slot in  86  (FIG. 9) 
       88  narrow slot in  85  for  28  (FIG. 8) 
       89  current return 
       90  plasma polymer layer (FIG. 10)