DE4434646A1 - Measuring system for electronic measuring of filling level of liquid esp. in vehicle fuel tank - Google Patents

Abstract

The measuring system has a group of thermocouple elements (30) as sensors which respectively have at least two connecting points between two different materials fitted on the front of a carrier, where high ohmic electrically conducting material (40) of the material of the thermocouple consists of a continuous strip (34) located on the electrically insulating carrier (27). The low ohmic electrically conducting material (45) forms a contact layer on the strip (34), disposed by intermediate spaces (31) in sections (46). The sections are connected full surface with the high ohmic electrical conducting material and complete the strips to the thermocouple elements, which essentially run in the longitudinal direction of the strip. The intermediate spaces between the sections are small compared to the length (44) of the sections. The heating conductors (26) are arranged in the end region (33) of each section and essentially run laterally across the strip (34).

Description

The invention relates to a device for electronically measuring the Level of a liquid in a container, especially in the Fuel tank of a vehicle, according to the preamble of claim 1.

The device works according to the following principle: immerses a heated thermocouple into a liquid, the level of which is measured should, because of the lower heat transfer resistance in the Liquid gives off more heat to the environment than in gaseous Me dium. This reduces the thermal voltage in the liquid. To this In this way it can be determined from the signal of the thermal voltage whether a certain thermocouple immersed in the liquid or not and so the Level can be determined.

In a known device of this type (DE-PS 40 30 401) Sensor thermocouples for both parallel and series connection constructed as individual elements by using a semiconductor as high-resistance electrically conductive material vapor-coated film strips cut or punched and with the help of an adhesive on the backing  be placed on the foil. Then, by screen printing from narrow Metal conductive adhesive sheets as a low-resistance electrically conductive material complete the thermocouple on the ends of the vapor-coated film tiert, wherein the combination of metal-semiconductor-metal is formed. It So always alternate low and high impedance conductors that only on egg ner relatively small point in contact. The ent the necessary temperature difference is due to a thermal voltage generates a heating conductor under one of the legs of the thermocouple tes runs. To maintain optimal and even thermal tension conditions in such a device, it is necessary the interface between semiconductor and metal exactly over the heating conductor. When using a large number of thermocouples per Tank sensors can practically no longer be processed manually, but only with the help of a machine. With simultaneous application all thermocouples as defined in claim 8 of said patent Die cuts have to be made for this Form of a comb, in series connection that of a meander, whereby in the latter case, the heating conductor also expediently alternates. Special tools are used to punch these shapes out of the strips necessary, the production of which is expensive. The Stan continues to fall zen also a relatively high waste especially from the material that in its manufacture by evaporating the semiconductor in a high vacuum is expensive.

Furthermore, the sensors described are only then completely correct work satisfactorily as long as the ambient temperature is only changes slightly or temperature influences from the outside z. B. by thermi shielding can be reduced to a minimum. However, it is the one set with strongly fluctuating ambient temperatures (e.g. -40 ° C... + 80 ° C), such shielding measures fail or become too expensive he. There are two main reasons for this measurement method  additional measurement errors, which, if they act in the same direction, 15 to 20 per make up a cent of the measured value of the thermal voltage.

The first mistake is that the proportionality factor is between the thermal voltage and the temperature difference between the two materials, which form the thermocouple itself is also temperature-dependent. I.e. for example, with an assumed constant temperature difference of 50 ° C at temperatures at the sensor of z. B. + 30 ° C and + 80 ° C usually a higher thermal voltage measured than at -40 ° C and + 10 ° C, although there is the same temperature difference.

Another error occurs when, as in claim 14 DE-PS 40 30 401 the heating current is kept constant. As with metallic Heating conductors (PTC behavior) the electrical resistance with the tempera heating increases, the heating output does not remain constant, but simply increases if the temperature increases. This increases the thermal voltage additionally at high ambient temperatures. One uses heating conductors with a negative temperature coefficient (NTC), the heating output drops with increasing temperature.

For the electronic signal processing of the measured values is the known Vor direction equipped with a module that has an integrated switch has a circle (IC component) and designed according to customer requirements will (ASIC). The block is according to claim 21 of DE-PS 40 30 401 placed on the support for the sensors. In this regard, it has in the Practice has shown that such a localization with respect to the Accessibility of the part is unfavorable for possible repairs, or egg ne increases the cost of the sensor, because the block has an immediate Unit forms with it.

It is therefore an object of the invention to be a device of the beginning  to improve the written type in terms of its structure, that the disadvantages described above compared to the prior art can be overcome. Specifically, this means an easier one To achieve structure of the device, the less expensive Her position but also an improved measurement accuracy in a large loading range of the ambient temperature.

This object is achieved in that the high-resistance electrically conductive hige material from a continuous, on the carrier Strip exists and the low-resistance electrically conductive material the strip is an overlay divided into sections by spaces layer forms. The sections are electrically conductive with the high-resistance capable material fully connected and complement the stripes Thermocouples that run essentially in the longitudinal direction of the strip. The gaps between the sections are small compared to the Ab cut length. The heating conductors are in the end area of the individual sections arranged and extend substantially in the transverse direction of the strip.

The high-resistance electrically conductive material is preferably a half conductor, while the low-resistance electrically conductive material from egg a metal conductive adhesive is formed.

The measures according to the invention have the following meaning in detail to. The semiconductor material, which is in the form of a strip on the carrier sits, forms a high-resistance continuous line connection between the individual thermocouples over the entire carrier. The metal leader adhesive creates a partially interrupted low-resistance line connection on the high-resistance conductor and is in full contact with it Connection. At the same time, he also completes it as the one for the generation of a thermal voltage required the second material Strips for a complete set of thermocouples. Because the edition  layer of the metal conductive adhesive according to the invention in the longitudinal direction of the strip has an extent that is large compared to the gaps, and can also be designed according to claim 4, consist in Comparison with the known device also be less demanding regarding the positional tolerance of the portions of the overlay in relation to the heating conductor.

The material forming the first material of the thermocouple can be evaporated on a separate film from the carrier and with the support layer from the second material and be so layered fabrics are attached to the carrier. The semiconductor ma material can also be applied directly in paste form using a screen printing process applied the carrier and then complete with the metal conductive adhesive be done.

From the manufacturing point of view, it is evident that this in itself known application of a generally a few millimeters wide with the Semiconductors vaporized film strip or the semiconductor in paste form by screen printing directly onto the carrier over its entire length complicated, quickly executable process, in which no Ab case arises and its excellent application for this reason from before is part. Completion with the metal conductive adhesive creates is also highlighted in claim 8, except for the verb cables to the evaluation device no additional contacts rungen be provided within the meaning of claim 26, immediately a Rei circuit of all thermocouples.

Semiconductor material and metal conductive adhesive can be used in each of the sections the overlay by an equivalent circuit diagram of parallel electrical resistances of different sizes are described, the greater current flow through the smaller resistance of the metal  Conductive adhesive. Therefore, the voltage drop in this Ab cut low. In the spaces between the sections is the elek electric current forced its path through the high-resistance material take, depending on the specific resistance and the layer thickness the voltage drop can be significantly greater than in the sections the overlay and with the size of the space grows. Soon but are near the gaps under the sections of the Overlay layer arranged the heating conductors, which are sufficient for a sufficiently large Ensure temperature difference to create thermal voltage. Will now the spaces between the sections of the overlay are too small, he says also warms the unheated area, which is supposed to stay cold te, and the resulting thermal voltage is reduced. Because overall the measured voltage resulting from the resulting thermal voltage and span waste, should be as large as possible, and in terms of their Depends on the size of the distance between the sections of the edition stratified by the two opposite tendencies described is drawn, one can be at a certain distance size voltage maximum according to claim 3 as a criterion of an optima Look at the distance between the sections of the overlay.

The special imprint contour of the section provided according to claim 5 te of the overlay and the corresponding arrangement of the heating conductors provides the largest possible heated connection point and thus larger Safe thermal voltage, but avoids the undesirable temperature right along the support of the thermocouples. The sections of the ed layer of the metal conductive adhesive, for example an H or T Have shape and the heat conductor in the area of one leg of the H or the crossbar of the T may be arranged.

Materials such as silicon and germani are suitable as semiconductor materials um, tellurium, gallium arsenide etc., which are only in a layer thickness of we  few micrometers. According to An saying 6 for the overlay of the second material a material ge chooses who has only a slight inclination with the semiconductor material in enter into metallic terminations, as these often differ in terms of the resulting thermal voltage and the specific electrical resistance stand, which in turn determines the voltage drop, by unfavorable egg mark properties. It has been found that in particular a Paa Tellurium as a semiconductor material with nickel in the metal conductive adhesive has very favorable properties in this respect.

It is from the material economics and manufacturing point of view forth advantageous in the area of the connection points of all thermo oils elements arranged heating conductor as parts of a common heating conductor to design, which is guided in a meandering shape on the back of the carrier (Claim 7) and is generated by printing a metal conductive adhesive.

So that there is always a defined thermal voltage in the thermocouples it is important to keep the heating capacity of the heating conductor constant and, if necessary, to adapt to the respective environmental conditions. For the Power supplies can be constant current or constant voltage sources Find use (claims 9 and 12).

As described above, there are essentially two types of measurement of measurement errors. The easiest way to measure accuracy increase, is to use a constant current source according to claim 10, the choice of materials for the heating conductors and the thermocouples chend to meet the temperature coefficient mentioned such that the two measuring errors just compensate each other.

However, this will only be possible in a few cases, as a rule whose criteria are more important when choosing materials. It is therefore  expedient, the heating output depending on the ambient temperature suitable to change. Electrical resistors with de defined temperature behavior, such as thermistor (NTC resistors) or PTC thermistor (PTC resistors). These are used depending on the type of Deten power source according to claims 11 or 18 in the heating conductor circuit switched. The largely temperature-independent metal resistor stand serves to adapt or linearize the NTC (or PTC) Temperature characteristic to that of the thermocouples, i.e. for fine adjustment of compensation.

Claims 13 to 16 relate to the detailed design of the Measured value or signal processing of the temperature sensors, which according to The main claim is thermocouples, but also, as in claims 21 and 22 is executed, thermistor (NTC resistors), PTC thermistor (PTC- Resistors) or measuring wires with defined temperature-dependent behavior electrical resistance. According to claim 13 in the circuit in series with the thermocouples for level measurement solution an impedance converter for the input-side adaptation of the in the Ther measuring elements for measuring the level of the measuring thermo voltage on an egg connected to a reference voltage source, also in series downstream operational amplifier, which is connected as an inverter. That in the operational amplifier by comparing the signal of the measuring thermo Voltage of the thermocouples for level measurement with the voltage of the Reference voltage source formed voltage output signal is then processed analog (claim 14) or digital (claim 16). On Proverb 15 relates to an appropriate measure that the display of the sub a certain minimum fill level (reserve) is permitted.

The components provided according to claims 13 to 16 can be in are close to the sensors or are advantageously after Claim 17 partially or completely integrated into the evaluation device.  

To maintain the required heating conductor power are excluded the measures already described according to claims 10, 11 and 18 given the possibilities according to claims 19 (or 20), according to which one (or more reference thermocouples) are provided, the one Deliver signal, which after an appropriate transformation over a controller provided for the change of the current strength in the heating conductor circuit in the desired sense.

The same function can also, as set out in claim 23, by ei with the reference temperature sensors - such as the thermocouples (An Proverbs 19, 20), the temperature-dependent resistors (claim 21) or the measuring wires (claim 22) - coupled microcontroller will.

Finally, it is possible to determine the characteristics of the dependency Thermal voltage of the thermocouples fixed in the ambient temperature Memory of a microcontroller (EPROM) to capture and according to the measured ambient temperature the measured values of the thermal voltages of the Correct thermocouples without changing the heat conductor output is (claim 24).

Further measures and advantages of the invention result from the so far not mentioned claims, the following description and the Drawings. The invention is directed to all of them new features and combinations of features, even if they are not should be expressly put forward in the claims.

In the drawing The invention is below in several exemplary embodiments shown. Show it:

Fig. 1 shows schematically, an application of the tung Vorrich invention,

Fig. 2 shows in perspective, partly in ger outbreak, the meter shown for the device of Fig. 1 with recognizable therein Thermoelementträ,

Fig. Greatly enlarged, cross-sectional view of sensors by a film having top and bottom-side coating for illustrating a first process step for producing the inventive Sen 3,

Fig. 4 schematically shows a part of the front of the thermocouple carrier with inventively embodied sensors and heating conductors on its rear side,

Fig. 5 diagrammatically the front of a further thermocouple carrier with inventively embodied sensors and a mäanderför mig extending heat conductor, and its return line on the back of the wearer,

Fig. 6, greatly enlarged, shows a longitudinal section through the carrier element thermocouples in Fig. 5 in the direction of the arrows VI-VI with additional representation of the top and bottom cover sheets provided with metal cladding,

Fig. 7 also in high magnification, a further longitudinal section through the thermocouple carrier shown in Fig. 5 or in Fig. 4 taken along the center line of the sensors with a representation of the preferred We ges of the electric current and the contacts on the first and last thermocouple,

Fig. 8 shows schematically the dependence of the thermal voltage of the ver various factors contributing to the determination of the optimum size of the gaps between the portions of the plating layer of the metal conductive adhesive,

Fig. 9 is an electrical circuit of is connected to a constant voltage source Heizleitungszweiges the invention Before direction with correction for the effect of ambient temperature on the heating power,

Fig. 10 is an electric circuit of a constant current source in closed Heizleitungszweiges the invention Before direction with correction for the effect of ambient temperature on the heating power,

Fig. 11 is an electric circuit of the apparatus of the invention showing the measured value evaluation and reference thermocouple,

Fig. 12 is a circuit diagram of the device according to the invention, showing the measured value evaluation and Error correction using a microcontroller

Fig. 13 is a circuit diagram of a part of the inventive apparatus showing the measured value evaluation and maintenance of a constant Heizleiterleistung using a Micro Control coupler,

Fig. 14 shows a part of the electrical circuit of the inventive device for parallel evaluation of the voltage of the thermocouples,

Fig. 15 evaluation a part of FIG. 11 corresponding electrical circuit of the device according to the invention, showing the measured value and correction heating power, but using Meßdrähten with a defined temperature-dependent behavior of the electrical resistance,

Fig. 16 shows a part of the Fig. 11 corresponding electrical circuit of the device according to the invention showing the measurement value evaluation and heating power correction, but using temperature-dependent resistors.

As can be seen in FIG. 1, the device according to the invention is suitable for determining the respective filling contents of a container 11 , preferably the fuel tank of a vehicle. The tank can also have an irregular shape for better use of space in the vehicle. The device includes a measuring device 12 in the container interior 19 , which forwards the signals via a connecting line 18 to an evaluation device 13 , where they are processed and lines 18 'control a display device 14 via the connecting lines. The measuring device 12 is immersed in the liquid 15 in the container 11 , the fill level 16 of which can be determined by the device 10 . This is done by an electronic measurement of the height of the liquid level 17 in the container 11th

The measuring device 12 includes, as can be seen from Fig. 2, a dip tube 22 which is arranged in the area of the level 16 to be measured in the container interior 19 Be. Inside 25 of immersion tube 22 is the actual sensor 20 , which consists of a carrier 27 with a bevy of specially designed sensors 30 . To minimize the influence of the vehicle movement, which can lead to uncontrolled wave movements of the liquid level 17 in the container 11 , a diaphragm with a narrowed opening 23 in the dip tube 22 is provided. Through the opening 23 there is a slowed flow 24 of the liquid into the dip tube 22 ; and in this way, for example, the brief changes in height of the liquid level 17 in the container 11 in the dip tube 22 caused by braking or acceleration movements of the vehicle become almost ineffective.

An embodiment of the invention is explained in more detail in FIG. 4. A semiconductor material 40 , which is applied in the form of a strip 34 on the carrier front side 28 , forms a high-resistance, continuous line connection between the individual thermocouples 30 . By means of egg nes conductive adhesive 45 on the high-resistance semiconductor layer 40 is interrupted in places, and thus divided into sections 46 , low-resistance line connection is generated, which, in contrast to the conventional thermocouples, is in full contact with the semiconductor layer 40 . The metal conductive adhesive 45 , as the second material required for the generation of a thermal voltage ΔU (ΔT), completes the strip 34 for a complete family of the thermocouples 30 . Despite the full-surface connection of the semiconductor layer 40 and the metal conductive adhesive layer 45 , a thermal voltage .DELTA.U (.DELTA.T) can arise due to the different specific electrical resistances of the two materials 40 , 45 of the thermocouples 30 , which is not compensated for by a short-circuit current. The sections 46 of the support layer of the metal conductive adhesive 45 have an extension 44 in the longitudinal direction of the strip 34 which is large compared to the gaps 31 , and the width 43 of the sections 46 extends almost over the entire width 21 of the strip 34 .

Fig. 3 illustrates a first stage of the process for producing the sensors 30. It is characterized in that the semiconductor material 40 is applied as a layer on a plastic film 41 separated from the carrier 27 , for example by chemical or physical deposition from the gas phase (CVD, PVD) or by spraying or screen printing. On the underside of the film 41 there is an adhesive layer 39 , which simplifies subsequent attachment to the carrier 27 . The plastic film 41 coated with the semiconductor material 40 and provided with the adhesive layer 39 forms a uniform sheet-like structure 42 which can be regarded as a preliminary product for the production of the sensors 30 . From this fabric 42 , strips 34 are then cut in further process steps, onto which the metal conductive adhesive layer 45 is applied by screen printing and which are then fastened to the carrier 27 . The material of the carrier 27 is a sheet-shaped plastic. A flexible film should also be used for this, as for the fabric 42 . The semiconductor material 40 can also be brought directly onto the carrier 27 in the manner described above.

By electrically insulated, but thermally in contact, elec trical heat conductors 26 , each in the one end region 33 of the sections 46 of the metal conductive adhesive layer 45 on the back of the carrier 29 in the transverse direction to the strip 34 , which is used to create the thermal voltage ΔU (ΔT) indispensable temperature difference ΔT between the unheated end 32 and the heated end 33 of each Thermoelemen tes 30 generated. In FIG. 4, a liquid level is assumed 16 bit 17 causes the liquid level above the height region of the two sensors shown bottom 30. The result of this is that with these and the sensors 30 , which are arranged even deeper, and which are immersed in the liquid 15 , the heat generated by the heating conductor 26 is dissipated better than with the sensors 30 located above the liquid level 17 . Because of the larger temperature difference ΔT occurring in the latter between the cold end regions 32 of the measuring thermocouples 30 and the end regions 33 of the sections 46 of the metal conductive adhesive layer 45 , a greater thermal voltage ΔU (ΔT) than in the ones below it arises under the Level 16 lying sensors 30 .

In Fig. 7, the contact 38 of the connecting line 36 at one of the heated points 33 of the first thermocouple 30 on the carrier 27 with the metal conductive adhesive layer 45 and the contact 37 of the connection line 35 to one of the unheated points in the end region 32 of last thermocouple 30 shown on the carrier 27 with the semiconductor layer 40 . The connecting lines 35 , 36 lead to the evaluation device 13 . All thermocouples 30 are thus connected in series. The contacts at the contacts 37 , 38 of the connecting lines 35 , 36 can be tapped from the electrical voltage resulting from the sum of the individual thermal voltages ΔU (ΔT) of all thermocouples 30 , both those below the liquid level 17 with low thermal voltage ΔU (ΔT) and those above the liquid level 17 with a higher thermal voltage ΔU (ΔT) minus the resistance-related voltage drop in the conductors, and thus represents a measure of the fill level 16 of the liquid 15 in the container 11 .

Fig. 7 illustrates the main path 52 of the electric current through the formed from the family of the thermocouples 30 probe 20th The electrical current preferably flows through the sections 46 of the low-resistance metal conductive adhesive support layer 45 , in which there is only a very slight drop in the electrical voltage. Where the metal conductive adhesive layer 45 is interrupted by gaps 31 , the current path 52 runs through the high-resistance semiconductor material 40 , which causes a higher voltage drop per path unit flowed through. The large extent 44 of the sections 46 of the metal conductive adhesive 45 in the longitudinal direction of the strip relative to the interstices 31 ensures that the voltage drop in the interstices 31 remains relatively small.

The exact definition of the size Δ1 of the spaces 31 between the sections 46 from the metal conductive adhesive layer 45 represents, as already mentioned, an optimization problem which is illustrated by FIG. 8. In the diagram, the voltage difference ΔU is plotted against the size Δ1 of the interstices 31 . There are two opposing dependencies: the dependency ΔU (ΔT) of the thermal voltage on the temperature difference between the warm and cold end regions 32 , 33 of the sensors 30 and the dependency ΔU (R) of the voltage drop due to the ohmic resistance R in the semiconductor layer 40 in the spaces 31 with the size Δ1. With increasing size Δ1 of the inter mediate spaces 31 up to a certain value, the temperature difference ΔT, and thus the resulting thermal voltage ΔU (ΔT), increases because the cold end regions 32 of the sensors 30 are less affected by the heat conduction from the heating conductor 26 of the adjacent thermocouple 30 to be influenced. If this value is exceeded, however, an enlargement of the interstices 31 no longer has an effect on the thermal voltage ΔU (ΔT). At the same time, according to Ohm's law and the law of resistance, the voltage drop ΔU (R) increases steadily with increasing distance variable Δl. The optimal distance length Δ1 _opt is reached when the voltage ΔU measured between the heated end region 33 and the unheated end region 32 of the sensors 30 has a maximum value ΔU _max .

Fig. 5 and Fig. 6 show a further embodiment of the invention. The sections 46 of the support layer of the metal conductive adhesive 45 have an H contour here, and a single heating conductor 26 common to all the thermocouples 30 is guided in a meandering shape on the back of the carrier 29 and is arranged in the region of one leg of the H. The crossbar of the H represents a tapered area 54 of the sections 46 of the metal conductive adhesive support layer 45 , while the legs of the H form non-tapered areas 55 . With this design, the advantages already mentioned occur. The heating conductor return line 47 is formed with a relatively large width 48 , whereby it is achieved that it heats up less than the conductor lines 26th The heat conductor 26 and its return line 47 are also produced with a metal conductive adhesive by strip-shaped or web-shaped printing on the back of the carrier 29 . In FIG. 6, a sheath of the thermocouple carrier 27, not shown in FIG. 5, is also visible through outer, fuel- and temperature-resistant and fuel-tight, provided with a metal liner 53 cover films 50 , 51 , the metal layer 53 being conductive with the electrical system -Mass 49 is connected.

FIGS. 9 and 10 show two possibilities of electrical circuits of the circuits for the heat conductors 26 of the thermocouples 30, with which the heating power is changed geän suitable depending on the ambient temperature. In FIG. 9, the circuit of the heating conductors 26 is fed by a constant voltage source 56 and in FIG. 10 by a constant current source 57 . In series with the constant voltage source 56 are an elec trical resistor 58 with a defined temperature behavior, such as a thermistor (NTC resistor) or a PTC resistor (PTC resistor), and a parallel connected metal film resistor 59 . The constant current source 57 has an electrical resistor 58 with a defined temperature behavior, such as a thermistor (NTC resistor) or a PTC resistor (PTC resistor), and a metal film resistor 59 connected in parallel.

Now, as described at the beginning, with constant heating voltage ( Fig. 9) and with metallic heating conductors 26 (PTC behavior), the fact that the electrical resistance of the heating conductor 26 increases with the ambient temperature, so a decreasing heating power and thereby likewise falling thermal voltage .DELTA.U (.DELTA.T) prevents a decreasing portion of the voltage from dropping across resistors 58 , 59 connected in series with constant voltage source 56 . The electrical resistance 58 with the defined temperature behavior must be an NTC resistance. If heat conductor 26 with negative temperature coefficient (NTC) is used, the upstream electrical resistor 58 with the defined temperature behavior must be a PTC resistor.

Occurs with constant heating current ( Fig. 10) and with metallic Heizlei tern 26 (PTC behavior), the fact that the electrical resistance of the heating conductor 26 increases with the ambient temperature, then an increasing heating power and thereby also increasing thermal voltage ΔU (ΔT) thereby prevents an increasing proportion of the current from flowing through the branch parallel to the constant current source 57 , which in this case must contain an NTC resistor. If heating conductor 26 with a negative temperature coefficient (NTC) is used, the electrical resistor 58 with the defined temperature behavior in the parallel branch must be a PTC resistor.

The largely temperature-independent metal resistor 58 is used in both cases ( FIGS. 9 and 10) to adapt or linearize the NTC or PTC temperature characteristic to that of the thermocouples 30 , that is, for fine adjustment of the compensation.

Fig. 11 shows a circuit which automatically corrects errors due to temperature effects and long-term changes due to the aging of the resistances of the grid lines 26 occur. Such aging errors are particularly present when 26 materials are used for the heating conductor, which are printed or vapor-deposited using the screen printing method. If the electrical resistance of the heating track 26 changes due to aging effects, then the heating power and thus also the thermal voltage ΔU (ΔT) changes. The extensive temperature dependency and resistance of the circuit to errors caused by a change in the heating conductor resistance is achieved by a control device 60 . In this case, by regulating the heating current, the thermal voltage ΔU (ΔT) is kept constant at one or more reference thermocouples 61 connected in series. The reference thermocouples 61 must have the same physical properties as the measurement thermocouples 30 . It is necessary that the same heating current flows through both the heating line 26 of the measuring thermocouples 30 and that of the reference thermocouples 61 . The thermocouples sharp, consisting of a plurality of measurement thermocouples 30 connected in series, provide the measurement thermal voltage 62 , which is further evaluated. All thermocouples 30 , 61 are heated.

Since the electrical resistance of many series-connected thermal elements 30 is highly resistive in general, is to adapt the abutment 30 prior thermocouples at the entrance of the downstream Ver stärkers 63 an impedance converter 64 is provided. The amplifier 63 compares the measurement thermal voltage 62 with the voltage of a reference source 65 . The reference voltage source 65 is set once so that the output voltage 66 of the operational amplifier 63 is zero if none of the thermocouples 30 are immersed in the liquid 15 . Since in this case the thermal voltage 62 is greater than in the case of immersion of the thermo elements 30 in the liquid 15 , the display voltage must be reversed. This is caused by the Operationsver 63 switched as an inverter.

Its output voltage 66 is now processed further. For an analog display 14 ', which can be spatially separated from the evaluation electronics 13 , it is useful to convert the measuring voltage 66 in the module 67 into a proportional display current. This display current flows through the analog display instrument 14 '. Any existing resistances in the supply line do not falsify the display. With the help of in a current divider circuit to the display instrument 14 'connected in parallel th adjustment resistor 68 , the display of the fill level 16 can be "fully" adjusted for the display. If only some of the thermocouples 30 dip into the liquid 15 , the voltage 66 will rise compared to the voltage at the "empty" limit (zero volts) and will reach a maximum at the "full" limit. As a result of the conversion of this voltage 66 into current values, there is a linear relationship between the fill level 16 and the display in the display instrument 14 '. To operate the display instrument 14 ', it is necessary to connect its second connection depending on the design of the voltage-current converter 67 to the supply voltage 69 or to the reference ground.

If a digital evaluation 14 '' of the fill level 16 is provided, the output voltage 66 proportional to the fill level 16 is digitized in an analog-to-digital converter 70 , evaluated in the evaluation circuit 71 and shown in the digital display 72 . In the evaluation circuit 71 , a conversion from liters to gallons, cubic meters, etc. or a consideration of the irregularities in the geometric shape of the container 11 can take place. Also digital threshold monitoring, e.g. B. to monitor a certain minimum level of level 16 , can be made.

If a purely analog display 14 'of the level 16 of the liquid 15 in the container 11 is provided, with the aid of an analog reserve display evaluation 14 ''' the drop below a certain liquid level 17 is displayed. A reference voltage 73 is compared with the voltage 66 in a threshold switch 74 . If the voltage 66 falls below a value determined by the reference voltage source 73 , the reserve indicator 75 lights up.

The circuit for correcting the temperature influences and the aging effects of the heating conductor 26 has the following structure:
The reference thermocouples 61 generate a reference thermo voltage 76 . The reference thermocouples 61 are connected to the evaluation electronics via an impedance converter 77 . The thermal voltage 76 of the reference elements 61 is now compared in the operational amplifier 78 with a voltage from a reference voltage source 79 . The operational amplifier 78 has no output voltage if the voltage of the reference voltage source 79 and the reference thermal voltage 76 are the same. In this case, the heating current for all thermocouples 30 , 61 is not readjusted via the heating current control device 60 . It's the right size. But changes the reference thermal voltage 76 because z. B. has changed the power of the heating conductor 26 by temperature changes, the heating current is readjusted until the reference thermal voltage 76 is the same as the voltage of the reference voltage source 79 . The reference thermal voltage 76 is thereby kept constant. In this process, the current for the heat conductor 26 of the measuring thermocouples 30 is set so that it assumes the correct value for the respective ambient temperature. As a result, the voltage 62 of the measuring thermocouples 30 is always kept constant, regardless of the ambient temperature. An unstabilized heating voltage source 80 is located in the heating conductor circuit. If measuring thermocouples 30 are now immersed in the liquid 15 , the measuring thermoelectric voltage 62 can drop as before, since this itself is not regulated. The heating current for the thermocouples 30 can be adjusted by changing the voltage of the reference voltage source 79 .

The number of measuring thermocouples 30 or the number of reference thermal elements 61 may, but need not, be identical to one another. Only one reference thermocouple 61 is shown in FIG. 10. It is only essential that the physical behavior of the individual measuring thermocouples 30 and the individual reference thermocouples 61 is identical. If there are still small deviations in behavior or if the control circuit shows temperature drift behavior, if extreme measuring accuracies are required, an additional correction of the thermal voltage 62 can be made via a resistance compensation 58 , 59 , as explained above in the explanation of FIGS. 9 and 10, be made. The described regulation of the electric current of the heating conductor 26 only works if the reference thermocouple 61 either constantly immerses in the liquid 15 to be measured, or it is ensured that the reference thermocouple 61 never immerses in the liquid 15 .

In principle, as can be seen from FIGS. 15 and 16, for measuring the fill level 16 of the liquid 15 in the container 11 and for correspondingly correcting the measured values, other sensors 81 , 82 , 83 can also be used instead of the thermocouples 30 , 61 in FIG. 84 can be used. These can be heated electrical resistors, such as NTC or PTC resistors 81 , 82 or heating wires 83 , 84 , which use the temperature dependence of the electrical resistance for the measurement. The constant voltage sources 85 , 86 connected to the sensors 81 , 82 , 83 , 84 via series resistors cause a current flow, which in turn causes a voltage drop at the sensors 81 , 82 , 83 , 84 . The voltage drop is compared in operational amplifiers 63 , 78 with the voltages of reference voltage sources 65 , 79 . The output signal of the operational amplifier 63 is used for displaying 14 the measured value, the output signal of the operational amplifier 78 for controlling 60 the heating power of the heating conductor 26 .

As FIG. 12 shows, there is also the possibility of correcting the detected values of the measuring thermal voltage 62 with the aid of a microcontroller 90 as a function of the ambient temperature. The thermocouples 30 are heated with the aid of the heating conductor 26 . The energy source required for the heating is a constant current source or a constant voltage source 80 . It is necessary to keep either the heating current or the heating voltage constant. The total thermal voltage 62 will have a characteristic which is dependent on the ambient temperature. This voltage characteristic is detected and stored once in the non-volatile memory module (EPROM) 89 of the microcontroller 90 . The temperature-dependent thermal voltage 62 of the measurement is evaluated with the help of the microprocessor 87 , the measurement result is corrected in accordance with the ambient temperature of the thermocouples 30 and displayed in the analog or digital display element 14 . For this purpose, the ambient temperature is determined with the aid of a temperature sensor 91 and the measured values are digitized in the analog-digital converter 92 . These are now used to correct the measurement thermal voltage 62, which is also digitized in the analog-digital converter 92 . The temperature sensor 91 may have a voltage-dependent electrical resistance, for. B. an NTC resistor. A reference thermocouple 61 , heated on one side by the heating line 26 , as in FIG. 11, whose thermal voltage 76 is used for microprocessor-controlled correction of the display value of the fill level 16 , can also be used here.

Assuming a of the circuits of Fig. 11, 15, or 16 or a different sensor 82, 84, the current in the heating conductors 26 also using a micro may be controllers 90 readjusted so by means of a reference thermocouple 61, that the reference thermocouple voltage 76 and the reference current is kept constant. For this purpose, the Heizlei ter 26 of the measuring sensors 30 , 81 , 83 and the reference sensors 61 , 82 , 84 must be flowed through by the same current ( Fig. 13). The heating current source 80 is controlled by the microprocessor 87 by means of the control voltage 88 via the control device 60 .

The use of the circuits according to FIGS. 9 to 13 and 16 is, as shown in the drawings, both advantageous in the separate evaluation of the measurement thermal voltages 62 of the individual sensors 30 , 81 (parallel evaluation), and in the evaluation of the total voltage 62 of sensors 30 , 81 connected in series. In addition, it is also for sensors 20 designed differently than in FIGS . 4 to 6, for example for sensors according to DE-PS 40 30 401, applicable. For a parallel evaluation of the voltages of the measuring thermocouples 30 , which is particularly suitable for the use of a microcontroller 90 , the contacts 37 , 38 of the connecting lines 35 , 36 ( FIG. 7) are provided in each cold and warm end area 32 , 33 of the sensors 30 . Each measuring thermocouple 30 , as shown in FIG. 14, is electrically connected to an impedance converter 64 and an operational amplifier 63 connected to a reference voltage source 65 , the output signals 66 of which are queried by a multiplexer 93 , processed further in the evaluation device 13 and in the display device 14 ( FIG. 1) being represented.

Reference list

10 device
11 containers
12 measuring device
13 evaluation device
14 display device
14 ′ analog display element
14 ′ ′ elements of the digital evaluation and display
14 ′ ′ ′ reserve display elements
15 liquid in 11
16 level of 15
17 liquid level of 16
18 connecting line
18 ′ connecting line
19 interior of the container
20 sensors
21 width of 34
22 immersion tube
23 narrowed opening in 22
24 fluid flow
25 pipe interior
26 heating conductors
27 carriers
28 front of carrier
29 back of carrier
30 measuring thermocouple, sensor
31 spaces in 45
32 end range of 30 (cold), unheated places
33 end area of 30 and 46 (warm), heated connection points
34 strips
35 connecting line in 32
36 connecting line in 33
37 contacting 35 with 40
38 contacting 36 with 45
39 adhesive layer on 41
40 semiconductor material
41 plastic film
42 fabrics for the production of 30
43 latitude of 46
44 length of 46
45 metal conductive adhesive layer
46 section of 45
47 Heating conductor return line
48 width of 47
49 electrical system ground
50 top cover film
51 lower cover film
52 main route of electric current through 20
53 metal lamination
54 tapered area of 46
55 non-tapered area of 46
56 constant voltage source
57 constant current source
58 NTC or PTC resistor
59 Metal film resistor
60 control device, adjustable resistance
61 Reference thermocouple
62 Measuring thermal voltage
63 amplifiers (OPV)
64 impedance converters
65 Reference voltage source
66 amplified measuring voltage, output signal from 63
67 voltage-current converters
68 setting resistance
69 supply voltage
70 analog-digital converter (ADC)
71 digital evaluation circuit
72 digital level indicator
73 Reference voltage for reserve display
74 threshold switches
75 Reserve display
76 Reference thermal voltage
77 matching circuit (impedance converter)
78 operational amplifiers (OPV)
79 Reference voltage source
80 heating voltage source
81 NTC or PTC measuring sensor
82 NTC or PTC reference sensor
83 measuring wire
84 reference measuring wire
85 constant voltage source
86 constant voltage source
87 microprocessor from 90
88 control voltage
89 non-volatile memory (EPROM) from 90
90 microcontrollers
91 temperature sensor
92 analog-digital converter (ADC)
93 multiplexer (MUX)
94 series resistor for 85
95 series resistor for 86
Δ1 size of 31
Δ1 _opt optimal size of 31
ΔT temperature difference
ΔU voltage between 32 and 33
ΔU (R) voltage drop
ΔU (ΔT) thermal voltage
ΔU _max maximum voltage between 32 and 33
R ohmic resistance

Claims (26)

1. Device ( 10 ) for electronically measuring the fill level ( 16 ) of a liquid ( 15 ) in a container ( 11 ), in particular in the fuel tank of a vehicle,
with a host of thermocouples as sensors ( 30 ), each having at least two connection points between two different materials, on the front ( 28 ) of an electrically isolating, the sheet-shaped carrier ( 27 ) attached and with this at different, defined height are arranged inside the container ( 19 ),
one material of the thermocouples ( 30 ) consisting of a layer of a high-resistance electrically conductive material ( 40 ) and the other material consisting of a low-resistance electrically conductive material ( 45 ),
further arranged on the back ( 29 ) of the carrier ( 27 ) are electrical heating conductors ( 26 ) in the region of connection points of all thermocouples ( 30 ),
and finally an evaluation device ( 13 ) is connected to the thermocouples ( 30 ), which acts as an indicator ( 14 ) of the fill level ( 16 ),
characterized,
that the high-resistance electrically conductive material ( 40 ) consists of a continuous strip ( 34 ) located on the carrier ( 27 ),
the low-resistance, electrically conductive material ( 45 ) on the strip ( 34 ) forms a support layer which is divided into sections ( 46 ) by spaces ( 31 ),
the sections ( 46 ) are fully connected to the high-resistance electrically conductive material ( 40 ) and complete the strip ( 34 ) to form thermocouples ( 30 ) which run essentially in the longitudinal direction of the strip ( 34 ),
the gaps ( 31 ) between the sections ( 46 ) are small compared to the length ( 44 ) of the sections ( 46 ),
and the heating conductors ( 26 ) are arranged in the end region ( 33 ) of the individual sections ( 46 ) and run essentially in the transverse direction of the strip ( 34 ). 2. Device according to claim 1, characterized in that the high-ohmic electrically conductive material ( 40 ) is a semiconductor and the never-ohmic electrically conductive material ( 45 ) is a metal conductive adhesive. 3. Apparatus according to claim 1 or 2, characterized in that the size (Δ1 _opt ) of the spaces ( 31 ) between the sections ( 46 ) of the metal conductive adhesive ( 45 ) is set such that the between the heated connection points ( 33 ) and the unheated points ( 32 ) measured voltage (ΔU) of each of the thermocouples ( 30 ) has a _maximum value (ΔU _max ) ( Fig. 8). 4. Device according to one of claims 1 to 3, characterized in that the width ( 43 ) of the sections ( 46 ) of the metal conductive adhesive ( 45 ) extends over a substantial part of the width ( 49 ) of the strip ( 34 ) ( Fig. 4). 5. Device according to one of claims 1 to 4, characterized in that sections ( 46 ) of the metal conductive adhesive ( 45 ) are provided in their contours with a neck-like taper ( 54 ), the heating conductor ( 26 ) in the non-tapered area ( 55 ) of the sections ( 46 ) are arranged ( FIG. 5). 6. Device according to one of claims 1 to 5, characterized in that the metal conductive adhesive ( 45 ) consists of a material which forms with the semiconductor material ( 40 ) only a few or no inter-metallic phases. 7. Device according to one of claims 1 to 6, characterized in that in the end region ( 33 ) of the individual sections ( 46 ) of all thermocouples ( 30 ) arranged heating conductors ( 26 ) represent parts of a single common heating conductor ( 26 ) which is meandering on the back of the carrier ( 29 ) is guided ( Fig. 5). 8. Device according to one of claims 1 to 7, characterized in that one of the heated connection points ( 33 ) of the first thermocouple ( 30 ) on the carrier ( 27 ) and a non-heated point ( 32 ) of the last thermocouple ( 30 ) the carrier ( 27 ) with the lines ( 35 , 36 ) to the evaluation device ( 13 ) are contacted, and so all thermocouples ( 30 ) are connected in series ( Fig. 7). 9. The device according to one or more of claims 1 to 8, characterized in that the heating conductor ( 26 ) is fed by a constant current source ( 57 ). 10. The device according to claim 9, characterized in that the material of the heating conductor ( 26 ) has such a temperature coefficient of specific electrical resistance and the thermocouples ( 30 ) such a temperature coefficient of the proportionality factor of thermal voltage (ΔU (ΔT)) and temperature difference (ΔT ) between the two materials ( 40 , 45 ) of the thermocouples ( 30 ), which due to an increase or decrease in the ambient temperature caused by the change in the heating power of the heating conductor ( 26 ) and the change in the same temperature difference (ΔT) between the Compensate for both materials ( 40 , 45 ) of the thermocouples ( 30 ) resulting thermal voltage (ΔU (ΔT)) when the ambient temperature rises or falls. 11. The device according to claim 9, characterized in that the constant current source Kon ( 57 ) an electrical resistor ( 58 ) with a defined temperature behavior, such as a thermistor (NTC resistor) or a PTC resistor (PTC resistor), and a metal film resistor ( 59 ) are connected in parallel ( FIG. 10). 12. The device according to one or more of claims 1 to 8, characterized in that the heating conductor ( 26 ) by a constant voltage source ( 56 ) is fed. 13. The device according to one or more of claims 1 to 12, characterized in that electrically in series with the Thermoelemen th ( 30 ) for level measurement, an impedance converter ( 64 ) for the input adjustment term in the thermocouples ( 64 ) for level measurement Measuring thermal voltage ( 62 ) to a reference voltage source ( 65 ) connected, also in series downstream operation amplifier ( 63 ), which is connected as an inverter and which sen by comparing the signal of the measuring thermal voltage ( 62 ) of the thermocouples for level measurement with Voltage of the reference voltage source ( 65 ) formed voltage output signal ( 66 ) in the evaluation device ( 13 ) is further processed ( Fig. 11). 14. The apparatus according to claim 13, characterized in that in the evaluation device ( 13 ) for analog evaluation and display of the filling level ( 16 ) with the operational amplifier ( 63 ) in series switched voltage-current converter ( 67 ), which Voltage output signal ( 66 ) of the operational amplifier ( 63 ) converted into a proportional display current, and also a display instrument ( 14 ') are located, in which a setting resistor ( 68 ) is connected in parallel in a current divider circuit, and depending on the design of the voltage current -Converters ( 67 ) to the supply voltage ( 69 ) or to the reference ground is ruled out ( Fig. 11). 15. The apparatus according to claim 13, characterized in that in the evaluation device ( 13 ) for analog evaluation and display ( 14 ''') falling below a certain level ( 16 ) with the operational amplifier ( 63 ) connected in series to a reference voltage Source ( 73 ) connected threshold switch ( 74 ), by which by comparing the voltage output signal ( 66 ) of the operational amplifier ( 63 ) with the voltage of the reference voltage source ( 73 ) formed output signal when the level falls below a certain level ( 16 ), the reserve display ( 75 ) is turned on ( Fig. 11). 16. The apparatus according to claim 13, characterized in that in the evaluation device ( 13 ) for digital evaluation and display ( 14 '') of the fill level ( 16 ) with the operational amplifier ( 63 ) in series connected analog-to-digital converter ( 70 ) and a digital evaluation circuit ( 71 ) digital display ( 72 ) are located ( Fig. 11). 17. The device according to one or more of claims 13 to 16, characterized in that the impedance converter ( 64 ), reference voltage source ( 65 ) and operational amplifier ( 63 ) are integrated in the evaluation device ( 13 ). 18. The device according to one or more of claims 12 to 17, characterized in that in series with the constant voltage source ( 56 ) for the heating conductor ( 26 ), an electrical resistor ( 58 ) with a defined temperature behavior, such as a thermistor (NTC- Resistor) or a PTC thermistor (PTC resistor), and a parallel-connected metal layer resistor ( 59 ) are connected ( Fig. 9). 19. The device according to one or more of claims 12 to 17, characterized in that by the common heat conductor ( 26 ) in addition to the thermocouples ( 30 ) for level measurement, a reference thermocouple ( 61 ) with the same physical properties as the thermocouples ( 30 ) is heated for level measurement, and in the circuit in series with the reference thermocouple ( 61 ) an impedance converter ( 77 ) for the input-side adaptation of the resulting in the reference thermocouple ( 61 ) resulting reference thermoelectric voltage ( 76 ) to a connected to a reference voltage source ( 79 ), also is connected in series downstream operational amplifier ( 78 ), the output signal formed by comparing the signal of the reference thermal voltage ( 76 ) of the reference thermocouple ( 61 ) with the voltage of the reference voltage source ( 79 ) to a change caused by a variable resistance arranged in the heating circuit ( 60 ) Current in Heating conductor (26), performs on the basis of the changing temperature difference (.DELTA.T) of the thermocouples (30, 61), the thermal voltage (76) of the reference thermocouple (61) is changed until the of the thermal voltage (76) of the reference thermocouple (61) formed signal and the voltage of the reference voltage source ( 79 ) in the operational amplifier ( 78 ) have the same size ( Fig. 11). 20. The apparatus according to claim 19, characterized in that in addition to the thermocouples ( 30 ) for level measurement instead of a reference thermocouple ( 61 ) several series-connected reference thermocouples ( 61 ) are heated by the common heating conductor ( 26 ). 21. The apparatus of claim 19 or 20, characterized in that instead of the thermocouples ( 30 ) for level measurement and the reference thermocouples ( 61 ) each thermistor (NTC resistors) or PTC thermistor (PTC resistors) ( 81 , 82 ) by the common heating conductor ( 26 ) are heated, the temperature-dependent voltage drop across the hot or cold conductors ( 81 , 82 ), caused by the current flowing due to constant voltage sources ( 85 , 86 ) connected via series resistors ( 94 , 95 ) , in the operational amplifiers ( 63 , 78 ) connected in series with the reference voltages ( 65 , 79 ) is compared ( FIG. 16). 22. The apparatus according to claim 19 or 20, characterized in that instead of the thermocouples ( 30 ) for the level measurement and the Re ferenzthermoelemente ( 61 ) each measuring wires ( 83 , 84 ) with a defined temperature-dependent behavior of their electrical resistance through the common heat conductor ( 26 ) are heated, the temperature-dependent voltage drop across the measuring wires ( 83 , 84 ), caused by the current flowing due to series resistors ( 94 , 95 ) connected NEN constant voltage sources ( 85 , 86 ) in the series after switched operational amplifiers ( 63 , 78 ) with the reference voltages ( 65 , 79 ) is compared ( Fig. 15). 23. Device according to one of claims 19 to 22, characterized in that instead of the impedance converter ( 64 , 77 ) and the operational amplifier ( 63 , 78 ), a microcontroller ( 90 ) with an analog-to-digital converter ( 92 ) is connected , on the input side with the lines ( 35 , 36 ) of the sensors ( 30 , 81 , 83 ) for level measurement with a reference sensor ( 61 , 82 , 84 ) and on the output side with an analog or digital display element ( 14 ) and with an im Heizstromkreis angeordne th adjustable resistor ( 60 ) for changing the current in the heating conductor ( 26 ) is coupled, which keeps the voltage in the reference sensor ( 61 , 82 , 84 ) constant ( Fig. 13). 24. The device according to claim 9 or 12, characterized in that the evaluation device ( 13 ) is a microcontroller ( 90 ) consisting of an analog-digital converter ( 92 ) and a microprocessor ( 87 ) with a construction stone ( 89 ) for a non-volatile memory in which the characteristic of the dependence of the thermal voltage (ΔU (ΔT)) of the thermocouples ( 30 ) on the ambient temperature is stored, the microcontroller ( 90 ) on the input side except with the lines ( 35 , 36 ) of the thermocouples ( 30 ) also with a temperature sensor ( 91 ), which detects the ambient temperature, and on the output side is coupled to an analog or digital display element ( 14 ) and the measuring thermo-voltage ( 62 ) of the thermocouples ( 30 ) digitized in the analog-digital converter ( 92 ) by the signal from the temperature sensor ( 91 ) in the microprocessor ( 87 ), which is also digitized in the analog-digital converter ( 92 ), in accordance with the characteristic of the dependence of the thermospan voltage (ΔU (ΔT)) of the thermocouples ( 30 ) is corrected by the ambient temperature ( FIG. 12). 25. The device according to claim 24, characterized in that the temperature sensor ( 91 ) for the ambient temperature is a heated temperature-dependent resistor. 26. Device according to one of claims 13 to 21, characterized in that with a parallel evaluation of the voltage of the thermo elements ( 30 ) or the hot or cold conductor ( 81 ) with the operational amplifiers ( 63 ) in series a multiplexer ( 93 ) is switched, the output signal of which is further processed in the evaluation device ( 13 ) ( FIG. 14).