EP4143553A1 - Device and method for ascertaining the thermal conductivity of a fluid - Google Patents
Device and method for ascertaining the thermal conductivity of a fluidInfo
- Publication number
- EP4143553A1 EP4143553A1 EP21723172.9A EP21723172A EP4143553A1 EP 4143553 A1 EP4143553 A1 EP 4143553A1 EP 21723172 A EP21723172 A EP 21723172A EP 4143553 A1 EP4143553 A1 EP 4143553A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- conductor
- fluid
- voltage
- thermal conductivity
- bridge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000012530 fluid Substances 0.000 title claims abstract description 209
- 238000000034 method Methods 0.000 title claims abstract description 49
- 239000004020 conductor Substances 0.000 claims abstract description 261
- 238000001514 detection method Methods 0.000 claims abstract description 26
- 239000000203 mixture Substances 0.000 claims description 75
- 238000005406 washing Methods 0.000 claims description 69
- 230000008014 freezing Effects 0.000 claims description 44
- 238000007710 freezing Methods 0.000 claims description 44
- 238000011156 evaluation Methods 0.000 claims description 42
- 230000003287 optical effect Effects 0.000 claims description 12
- 230000001360 synchronised effect Effects 0.000 claims description 7
- 238000005259 measurement Methods 0.000 claims description 5
- 239000007788 liquid Substances 0.000 description 66
- 230000008859 change Effects 0.000 description 32
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 25
- 239000004202 carbamide Substances 0.000 description 25
- 239000007789 gas Substances 0.000 description 21
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 15
- 230000002528 anti-freeze Effects 0.000 description 10
- 230000008901 benefit Effects 0.000 description 9
- 238000004140 cleaning Methods 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- 238000012545 processing Methods 0.000 description 7
- 230000006378 damage Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 230000000875 corresponding effect Effects 0.000 description 5
- 238000013461 design Methods 0.000 description 5
- 239000000446 fuel Substances 0.000 description 5
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 4
- 108010053481 Antifreeze Proteins Proteins 0.000 description 3
- 210000001742 aqueous humor Anatomy 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 230000002706 hydrostatic effect Effects 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 229910000679 solder Inorganic materials 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 238000010257 thawing Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000004922 lacquer Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000009659 non-destructive testing Methods 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
- G01N27/18—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by changes in the thermal conductivity of a surrounding material to be tested
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/18—Investigating or analyzing materials by the use of thermal means by investigating thermal conductivity
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/0007—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm for discrete indicating and measuring
Definitions
- the present invention relates to a device and a method for determining a property, in particular a thermal conductivity, of a fluid, in particular a fluid mixture formed from a plurality of fluids, which is in particular a washing liquid or an aqueous fuel solution for exhaust gas aftertreatment for a vehicle, as well as a fluid container and a vehicle.
- Optical sensors e.g. cameras, LIDAR, radar, etc., which are required for driver assistance systems and / or a system for autonomous driving, are increasingly being installed in vehicles.
- Optical sensors e.g. cameras, LIDAR, radar, etc.
- washing systems which have hitherto been mainly used in vehicles to clean a window and / or a light source, have no way of monitoring the washing liquid, so that at low temperatures the problem often arises that a fluid mixture consisting of water and at least one antifreeze liquid is mixed and used as a washing liquid, in a fluid container, in a line to a spray nozzle or on a window freezes due to an insufficient proportion of the anti-freeze liquid. As a result, cleaning is not feasible or visibility is even deteriorated.
- an aqueous urea solution (also known as AdBlue (registered trademark)) is used in modern diesel vehicles for exhaust gas aftertreatment (selective catalytic reduction (SCR)) in order to reduce the nitrogen oxides (NOx) emitted.
- SCR selective catalytic reduction
- the proportion of urea in the aqueous The standard urea solution, for example in the delivery state, is 32.5%, with a range between 31.8% and 33.3% being permissible for use in the vehicle. Since urea is gradually decomposed by UV radiation, the urea concentration may change over time in a container in which the aqueous urea solution is stored for the purpose of refilling and which is exposed to sunlight.
- water can evaporate from the container or a fluid container in the vehicle, so that the urea concentration also changes over time.
- a check of the required urea concentration can be carried out by means of a refractometer, which, however, is complex and therefore impractical when operating the diesel vehicle.
- a property, in particular the thermal conductivity, of a fluid, in particular a fluid mixture, which is used, for example, as a scrubbing liquid or for exhaust gas aftertreatment is determined in order to draw a conclusion about the composition or a degree of contamination thereof.
- a device for determining the property of the fluid or the fluid mixture has an electrical conductor arrangement which is designed such that it can be brought into contact at least partially or essentially completely or completely with the fluid.
- the conductor arrangement is designed as a voltage divider and has two elements.
- a series circuit consisting of, for example, a voltage divider, in particular to understand passive, electrical two-pole terminals, through which an electrical voltage is divided.
- the device according to the invention has a measuring bridge with two voltage dividers connected in parallel, each of which has two elements.
- One of the voltage dividers is formed by the above-mentioned conductor arrangement.
- the device also has a control unit for applying an alternating voltage to the measuring bridge and a voltage detection unit for detecting a bridge voltage.
- the device has an evaluation unit which is configured in such a way that it determines the property, in particular the thermal conductivity, of the fluid by evaluating the bridge voltage using the 3-omega method.
- the device determines whether the fluid has a predetermined property, i.e. for example the predetermined thermal conductivity, so that, for example, freezing is reliably prevented at a temperature corresponding to the predetermined thermal conductivity.
- it can be determined, for example, whether a fluid used for exhaust gas aftertreatment has a required flarea content.
- a signal can be output via a corresponding means, such as a display and / or a loudspeaker.
- the first element of the conductor arrangement is preferably a first conductor which, at least in the current-carrying state, has a resistance that is different from that of the second element.
- the second element of the conductor arrangement can be a second conductor which, in a currentless state, has the same resistance value as the first conductor.
- the two conductors are preferably designed so that the first conductor is in a live state is more heated than the second conductor. As a result, a resistance value of the first conductor can be different from that of the second conductor and the measuring bridge can be detuned, so that a bridge voltage can be detected.
- the second element can be a fixed resistor used in place of the second conductor.
- a fixed resistance is to be understood, for example, as a resistance that essentially does not change its resistance value even when the current is flowing through it and is therefore to be regarded as essentially constant under any conditions.
- the two resistors of the other voltage divider are preferably designed in such a way that their resistance value can be set or changed.
- the two adjustable resistors are preferably designed as digital potentiometers. In the current-carrying state, the first conductor heats up and therefore changes its resistance value, so that the first conductor and the fixed resistor have a different resistance value in the current-carrying state.
- the resistance value of the first conductor is preferably greater than that of the fixed resistor. However, the resistance value of the first conductor can also be smaller than that of the fixed resistor.
- the evaluation unit is preferably configured in such a way that it compares the two adjustable resistors before an alternating voltage is applied to the measuring bridge. This configuration offers the advantage that requirements with regard to manufacturing accuracy, which is required, for example, so that the first and second conductors have the same resistance value in a de-energized state, is reduced. In addition, the accuracy of the detection is increased because the measuring bridge is reliably calibrated by the evaluation unit before the start of a determination of the thermal conductivity.
- the fluid can be a fluid mixture which is formed from two fluids, of which a thermal conductivity is preferably known in each case.
- the evaluation unit can be configured in such a way that it determines a concentration or a mixing ratio as the property of the fluid mixture by comparing the thermal conductivity of the fluid mixture with the thermal conductivity of the two fluids from which the fluid mixture is mixed. Accordingly, a mixing ratio of the mixed fluid is accurate determinable.
- at least one of the two fluids can also be a fluid mixture, provided that the thermal conductivity thereof is known.
- the determination of a mixing ratio offers the advantage that the composition of the fluid mixture can be indicated to a user in an easily understandable manner.
- a freezing point of the two fluids from which the fluid mixture is formed can also be known.
- the evaluation unit is configured, for example, in such a way that it determines a freezing point as the property of the fluid mixture using the concentration of the fluid mixture.
- a freezing point of the fluid mixture can be precisely determined, so that a user can better judge whether the fluid mixture is suitable for a certain temperature.
- the fluid can be a fluid mixture which is preferably formed from two fluids, of which a thermal conductivity and a freezing point can be known.
- the evaluation unit can be configured in such a way that it determines a freezing point as the property of the fluid mixture by comparing the thermal conductivity with a characteristic curve, in particular in the form of a straight line.
- the straight line is obtained by a linear interpolation in which the thermal conductivity and the freezing point of the fluids are each used as a support point.
- the values of the thermal conductivity of the two fluids are each plotted on an x-axis of a Cartesian coordinate system and the values of the freezing points of the two fluids are plotted on a y-axis of the Cartesian coordinate system.
- the determined value of the thermal conductivity of the fluid mixture, which is formed from the two fluids, is then also plotted on the x-axis and the associated value of the freezing point of the thermal conductivity can consequently be determined as the y-axis value of the straight line at this point.
- This linear interpolation allows the freezing point to be determined in a simple manner and a user can assess precisely whether the fluid mixture is suitable for a specific temperature.
- a cross-sectional area of the first conductor is preferably smaller than that of the second conductor.
- the ratio between the cross-sectional areas of the first conductor and the second conductor can be in the range of 3 to 5 and preferably 4.
- the ratio of the cross-sectional areas of the first conductor and the second conductor can also be in the range from 2 to 6. This design of the first and the second conductor ensures sufficient heating of the first conductor, so that good accuracy of detection of the change in resistance is made possible.
- the alternating voltage is preferably sinusoidal.
- the applied alternating voltage can be generated in a simple manner and is suitable for processing in the 3-omega method.
- a current intensity of a current flowing through the conductor arrangement is advantageously in the range from 150 mA to 250 mA and is preferably 200 mA.
- the current intensity can also be in the range from 100 mA to 300 mA.
- the first and the second conductor can be arranged adjacent to one another. For example, they can overlap and / or overlap one another.
- the two conductors are preferably arranged on a common holding arrangement.
- the first and the second conductor are preferably arranged on a common circuit board or holding arrangement.
- the first conductor and the second conductor can be designed in a meandering manner.
- a space-saving conductor arrangement is achieved by a meandering arrangement of one conductor or both conductors on the board.
- a standard circuit board eg an FR4 circuit board
- a conductor is designed in a meandering shape, it has, for example, at least two legs at a parallel spacing and / or adjacent to one another, which are connected via a connecting section. A plurality of such legs are preferably provided, which are arranged next to one another and are connected via connecting sections.
- the first conductor for example, can be arranged on the holding arrangement between the legs of the second conductor. These two legs of the second conductor, between which the first conductor is arranged, can in this case have a greater distance from one another than the other legs.
- the first conductor is then preferably also designed with two or more legs which are connected via one or more connecting sections. These legs can be arranged next to one another, preferably with a parallel spacing. At least one or both conductors are advantageously arranged as compactly as possible.
- the first and / or the second conductor can be designed as wires.
- a wire is, for example, a metallic conductor with a round or angular or flat or square or profiled cross-section which, apart from its fastening section (s) or if it is not arranged or fastened on a substrate or in a holder, is completely covered by the fluid mixture is surrounded.
- the conductors designed as wire can be dimensionally stable, as a helix, as a loop, in a meander shape or in some other way wound or curved or shaped or arranged. It has been shown in tests that the use of wires as the first and / or second conductor significantly improves detection accuracy, in particular in comparison to the configuration in the form of conductor tracks.
- the conductor designed as wires or the conductor designed as a wire can / can be pretensioned by means of at least one elastic element in order to compensate for a change in length that occurs due to heating in the current-carrying state or a change in length of the holding arrangement due to a change in temperature.
- the elastic element can preferably be designed as a spring element.
- elevations between the two conductors / wires or the conductor / wire can be formed on the circuit board or the holding arrangement. These elevations can be cylindrical or cuboid. The elevations preferably extend up to a height which extends beyond a plane in which the conductors / wires are arranged. The elevations can also be formed in that the conductor / wire is arranged in a groove or a groove section, so that regions outside the groove section extend beyond a plane in which the conductor / wire is arranged. Since the freezing point of an aqueous urea solution is around -11 ° C, it can happen on cold winter days that the aqueous urea solution freezes.
- a heating element can therefore be arranged in a fluid container in order to heat the aqueous urea solution.
- a washing liquid can also freeze if the proportion of antifreeze is too low.
- the elevations ensure that a frozen section or portion of the aqueous urea solution or the washing liquid is limited or interrupted in the area of the circuit board or the holding arrangement. As a result, this section or portion can be thawed more easily and the thermal conductivity can be determined more quickly.
- the surveys ensure that there is contact between the Wires / conductors and frozen parts / bodies is prevented in order to prevent damage to the conductors / wires.
- the device according to the invention which has wires, can therefore also be used in an environment that is exposed to low temperatures, such as in a vehicle.
- the elevations can be arranged in such a way that they prevent contact between the first and second conductors or between individual meanders or sections of the conductors, so that a short circuit can be reliably prevented.
- At least one conductor section or several conductor sections of the conductors / wires can be contacted with the fluid.
- the conductor (s) and / or the conductor section (s) extends over a housing side of a housing that is open to the fluid or an open arrangement side of the holding arrangement. From the housing side / arrangement side, in turn, one or more elevations or protrusions (s) extend over the conductor (s) and / or the conductor section (s) in order to protect them from mechanical forces, such as ice contact.
- the circuit board or the holding arrangement can be protected with a cover or a lid, which can be designed in such a way that the fluid, the thermal conductivity of which is to be determined, can pass in order to communicate with the first and / or the second conductor in To get in touch.
- the cover or the lid can be designed with slots or holes for this purpose.
- the first conductor and the second conductor can be made of the same material. In this way, a simple production of the first and the second conductor can be achieved and a different material properties of the two conductors need not be taken into account.
- the first conductor and the second conductor can be covered or comprised with an insulation layer.
- a lacquer or solder mask can be provided as an inexpensive insulation layer. In this way, an extremely compact arrangement of the conductors is achieved, since a short circuit between adjacent meanders or helical turns of the conductor arrangement is reliably prevented.
- one of the fluids is water and the other of the fluids is an anti-freeze liquid or ethanol. Because of the freezing point range of such a fluid mixture, this composition of the fluid mixture is particularly suitable for use in a vehicle as a washing liquid.
- one of the fluids is urea and the other of the fluids is water.
- This composition is particularly suitable for use in exhaust aftertreatment in a diesel vehicle.
- control circuit is preferably formed inexpensively and simply from two transistor booster stages.
- the direct voltage used in an on-board electrical system of a vehicle can be converted into alternating voltage, preferably into a sinusoidal alternating voltage.
- the evaluation unit can be configured in such a way that it uses a software-implemented synchronous rectifier, also as a software-implemented lock rectifier, to transmit a signal component of the bridge voltage that has the single and / or multiple frequency, preferably three times the frequency, of the AC voltage.
- a software-implemented synchronous rectifier also as a software-implemented lock rectifier
- filters With a software-implemented synchronous rectifier this can The input signal, ie the bridge voltage, can be digitized by an A / D converter, preferably by an A / D converter of the evaluation unit.
- a table is preferably stored in the evaluation unit in which normalized amplitude values of the signal component to be filtered, ie the amplitude values of a sinusoidal voltage with the single or multiple frequency of the voltage applied to the measuring bridge, are stored.
- the digitized values of the input signal can then be multiplied, in particular correlated, with the values from the table.
- a sliding sum is then preferably formed over a multiple of the length of the table, ie over a multiple of the period duration of the signal component. The sliding sum can then be used as a measure of the amplitude of the signal component to be filtered in the input signal, ie in the bridge voltage.
- a fluid container or liquid container according to the invention has the device for determining the thermal conductivity of a fluid or fluid mixture.
- the thermal conductivity of a fluid or fluid mixture stored in the fluid container e.g. a washing liquid or a liquid for exhaust gas aftertreatment, can be determined. In this way it can be reliably determined whether the fluid mixture can be used for an intended application.
- the device for determining the thermal conductivity can be arranged in a partial area of the fluid container which is spatially separated from a main area of the fluid container but which can communicate fluidically with the main area.
- the device can partially or from a protruding bottom or wall section of the fluid container be completely surrounded and the bottom or wall section can have slots or holes, so that the fluid stored in the fluid container can be reliably brought into contact with the device for determining the property of the fluid.
- a freezing section can be limited in the area of the device for determining the thermal conductivity, and a time for thawing, for example by means of a heater arranged in the fluid container, can be reduced in this way.
- the risk of mechanical damage to the device for determining the thermal conductivity is reduced.
- the fluid container can have a sensor for detecting a fill level.
- This sensor can in particular be an ultrasonic sensor or a sensor for detecting the hydrostatic pressure in the fluid container.
- the fill level in the fluid container can also be determined.
- a means can be provided that emits an acoustic and / or visual warning, e.g. via a loudspeaker and / or a display, if the determined fill level is not sufficient for an intended application.
- the level in the fluid container can be determined and a warning can be issued if this is too low for an intended application.
- the device for determining the thermal conductivity of the fluid and the sensor for level measurement can be designed as a common module. In this way, an inexpensive and space-saving arrangement can be achieved.
- the fluid container can have a detection means which detects a filling and / or an emptying of the fluid container with / of liquids.
- a detection means which detects a filling and / or an emptying of the fluid container with / of liquids.
- a washing system according to the invention has the fluid container according to the preceding aspects.
- a property, in particular a thermal conductivity, of the fluid or fluid mixture can thus be determined so that freezing of the washing liquid can be reliably prevented.
- a device according to the invention for exhaust gas aftertreatment has a fluid container according to the preceding aspects.
- a property, in particular a thermal conductivity, of a fluid or fluid mixture that is used for exhaust gas aftertreatment can be determined so that exhaust gases emitted by a vehicle are reliably cleaned.
- a vehicle according to the invention has a washing system with a fluid container according to one of the preceding aspects, which is used for cleaning a vehicle component and / or an optical sensor and / or a light source and / or a window. Accordingly, the property, in particular the thermal conductivity, of a fluid or fluid mixture used as a washing liquid for the vehicle can be determined in order to reliably prevent it from freezing.
- the vehicle has a vehicle component, in particular an optical sensor and / or a light source and / or a pane, which is / are cleaned by the washing system. Accordingly, cleaning thereof is ensured even at low temperatures, since freezing of the washing liquid in the washing installation can be reliably prevented by using the device according to the invention for determining the properties of the fluid.
- the vehicle according to the invention has a device for exhaust gas aftertreatment with a fluid container according to one of the preceding aspects. Consequently, the property of a fluid or fluid mixture used for exhaust gas aftertreatment can be determined in order to determine the flarnea concentration in the fluid mixture therefrom. In this way, reliable exhaust gas cleaning can be carried out.
- a method for determining a property, in particular a thermal conductivity, of a fluid has the following steps: applying an alternating voltage to a measuring bridge; Detecting a bridge voltage; and determining a thermal conductivity as the property of the fluid mixture by evaluating the bridge tension using the 3-omega method.
- the method can be carried out when filling and / or emptying of a fluid container is detected according to one of the preceding aspects.
- the frequency of execution of the method can be reduced, so that a processing load on the evaluation unit is reduced.
- the method can be carried out when switching on and / or switching off an ignition of a vehicle.
- the frequency of execution of the method can also be reduced, so that a processing load on the evaluation unit is reduced.
- an initial step for balancing the measuring bridge can be carried out according to one aspect of the invention.
- the evaluation unit can then be designed to cause at least one of the two transistor booster stages to apply a direct voltage to the measuring bridge.
- the DC voltage has a value of 200 mV.
- the value of the direct voltage can also be between 100 mV and 500 mV.
- the bridge voltage is then recorded and the evaluation unit changes the resistances of the two adjustable resistors. A DC voltage is then again applied to the measuring bridge and the bridge voltage is recorded.
- This process is carried out until the bridge voltage, which is detected in response to the applied DC voltage, is essentially equal to a voltage of 0V.
- the measuring bridge can be adjusted reliably. This procedure is advantageously carried out when commissioning or starting a detection of the property in order to initially align the measuring bridge.
- the evaluation unit can be designed so that it filters out a signal component of the bridge voltage which corresponds to the single frequency of the alternating voltage applied to the measuring bridge.
- the amplitude of this signal component of the bridge voltage can be used as a measure for the detuning of the measuring bridge and the evaluation unit can be designed in such a way that it changes the resistance value of the adjustable resistors in such a way that the signal component of the bridge voltage, which corresponds to the simple frequency of the applied alternating voltage, in Is essentially 0V.
- This procedure offers the advantage that a detuning of the measuring bridge can be detected during a measuring operation. Accordingly, detunings of the measuring bridge that occur, for example, as a result of heating during operation, can be detected and the measuring bridge can then be adjusted.
- a reserve container with an anti-freeze liquid or with flarea can be provided. This can be fluidically connected to the fluid container. It would then be conceivable that the antifreeze liquid could be fed into the fluid container if necessary, e.g. via a controllable valve. This takes place, for example, if it is determined that there is too little antifreeze liquid or flare in the fluid container.
- FIG. 1 schematically shows a circuit diagram of a device for determining a property of a fluid mixture which is used in a fluid container of a washing system for a vehicle;
- FIG. 2 shows a conductor arrangement according to an embodiment of the present invention with a first conductor and a second conductor which are applied to a circuit board;
- FIG. 3 shows a flow chart of a method for determining a thermal conductivity of a fluid when the first and second conductors are used
- FIG. 4 is a diagram schematically showing a straight line for determining a freezing point of a fluid mixture
- FIG. 5 schematically shows a circuit diagram of a device for determining a thermal conductivity which is used in a fluid container of a device for exhaust gas aftertreatment for a vehicle;
- FIG. 6 and 7 show a measuring bridge with a conductor arrangement in which the first and second conductors are designed as wires;
- FIGS. 8 and 9 show a measuring bridge with a conductor arrangement in which a first conductor designed as a wire and a fixed resistor are connected in series;
- FIG. 10 shows a flow chart of a method for determining a thermal conductivity of a fluid when the fixed resistor is used
- FIG. 11 shows an embodiment of a holding arrangement for holding a conductor designed as a wire
- Figure 12 is a schematic block diagram of a software implemented synchronous rectifier.
- a device 1 for determining a property, in particular a thermal conductivity, of a fluid the fluid is particularly a fluid mixture that is mixed from water and ethanol, which is the basis for most commercially available antifreeze liquids, and is used as a washing liquid for a washing system 50 of a vehicle 70 for cleaning an optical sensor, a window and a / or a light source is used.
- the wax liquid is stored in a fluid container 30 for this purpose.
- the washing liquid is to be understood as a fluid mixture in the following description.
- the device 1 according to the present embodiment is designed for use in a vehicle 70.
- a thermal conductivity of the washing liquid is used as a measure of the mixing ratio of water to ethanol.
- Water has a thermal conductivity of 0.556 [W / (m * K)] and ethanol has a thermal conductivity of 0.173 [W / (m * K)].
- a washing liquid mixed from water and ethanol accordingly has a thermal conductivity that lies between these two values, so that a conclusion about the mixing ratio of the washing liquid is possible by comparing the determined thermal conductivity with a predetermined thermal conductivity. If it is necessary, for example, that a minimum proportion of ethanol is present in the washing liquid in order to reliably prevent freezing, then the value of the determined thermal conductivity must be less than or equal to the specified thermal conductivity.
- the specified thermal conductivity is specified beforehand by a manufacturer of the device 1, the washing system 50 or the vehicle 70.
- the specified thermal conductivity can also be adjusted accordingly based on different influences, e.g. date, location, weather forecast, etc.
- the device 1 for determining the thermal conductivity of a fluid mixture formed from a plurality of fluids has for this purpose an electrical conductor arrangement 2, a measuring bridge 4, a control unit 6, a voltage detection unit 8 and an evaluation unit 10.
- the electrical conductor arrangement 2 is designed in such a way that it can at least partially be brought into contact with the washing liquid.
- the electrical conductor arrangement 2 shown in FIGS. 1 and 2 is brought into contact with the fluid mixture by being completely immersed in the washing liquid that is stored in the fluid container 30 of the washing system 50 so that it is completely surrounded by the fluid mixture.
- the electrical conductor arrangement 2 has a first conductor 21 and a second conductor 22 connected in series.
- the first conductor 21 and the second conductor 22 have the same resistance value in a currentless state.
- the two conductors 21, 22 are designed in such a way that the first conductor 21 is more heated than the second conductor 22 in a current-carrying state.
- the conductor arrangement 2 shown in FIG. 2 is used, in which the two conductors 21, 22 are arranged in the form of conductor tracks on a circuit board 26 in a meandering manner.
- the two conductors 21 and 22, as shown in FIG. 2 have several legs 23 and connecting sections 24 between these legs 23.
- the first conductor 21 is also arranged in a meandering shape between two legs 23 of the second conductor 22.
- the arrangement of the two conductors 21 and 22 is not limited to the arrangement shown, and the two conductors 21 and 22 can, for example, also be arranged in a meandering manner only in sections.
- only one of the two conductors 21, 22, preferably the second conductor 22, can be arranged in a meandering manner.
- the two conductors 21, 22 in the form of conductor tracks on the circuit board 26, e.g. on an FR4 circuit board, by a known printing process, an inexpensive and robust conductor arrangement 2 can be obtained.
- the meandering arrangement of the two conductors 21, 22 offers the advantage of a space-saving arrangement of the conductor arrangement 2 in the fluid container 30.
- a cross-sectional area of the first conductor 21 is smaller than that of the second conductor 22. Accordingly, the second conductor 22 must be longer than the first conductor 21 by a factor by which the cross-sectional area of the second conductor 22 is is greater than that of the first conductor 21 so that the first conductor 21 and the second conductor 22 have the same resistance value in the de-energized state.
- the cross section of the second conductor 22 is larger by a factor of 4, so that the first conductor 21 must have four times the length in order to have the same resistance value.
- the factor is not limited to a factor of 4 and can range from 3 to 5. Such a design of the two cross-sectional areas ensures sufficient detection accuracy in the event of a change in resistance described below in the current-carrying state.
- the two conductors 21, 22 are implemented by conductor tracks made of copper. However, another material such as nickel can be used.
- the two conductors 21, 22 are preferably made from the same material, so that an influence of a different material in the dimensioning and the change in resistance described later in the current-carrying state does not have to be taken into account.
- the production of the electrical conductor arrangement 2 is simplified.
- first and second conductors 21, 22 are preferably covered with solder mask, so that a short circuit between the individual meanders of the first and second conductors 21, 22 due to the washing liquid present in between is avoided.
- the first conductor 21 is heated more than the second conductor 22 due to its smaller cross-sectional area. Consequently, a resistance value of the first conductor 21 increases more than the resistance value 22 of the second conductor. Since the conductor arrangement 2 is completely immersed in the fluid mixture, the strength of the heating of the first conductor 21 also depends on a thermal conductivity of the washing liquid. When the washing liquid has a high thermal conductivity, the first conductor 21 is heated less than when the washing liquid has a low thermal conductivity. A washing liquid with a high thermal conductivity thus cools the first conductor 21 better than a washing liquid with a low thermal conductivity. Accordingly, the magnitude of the change in resistance of the first conductor 21 can be used as a measure of the thermal conductivity of the washing liquid.
- a measuring bridge 4 which is designed, for example, as a Wheatstone measuring bridge, with two voltage dividers connected in parallel, one of the voltage dividers being used by the electrical conductor arrangement 2, i.e. consequently by the series connection of the first conductor 21 and the second conductor 22 is formed.
- the other voltage divider is formed by two resistors R1 and R2, each of which has the same resistance value.
- an alternating voltage is applied to the measuring bridge 4 by the control unit 6.
- the control unit 6 is formed in the present embodiment from two transistor booster stages 61, 62, so that a conversion of the direct voltage of the electrical system of the vehicle 70 into an alternating voltage is possible.
- the first transistor booster stage 61 applies a positive voltage
- the second transistor booster stage 62 alternately applies a negative voltage to the measuring bridge 4.
- the alternating voltage is in particular a sinusoidal alternating voltage, so that the 3-omega method described below can be carried out.
- the control unit 6 applies the alternating voltage to the measuring bridge 4, so that a current in the range of approximately 200 mA flows in the series circuit comprising the first and second conductors 21 and 22.
- the current strength is not limited to this value and can be in the range from 150 mA to 250 mA.
- the first conductor 21 is heated by a few Kelvin in the current-carrying state, as a result of which its resistance value increases, which in turn leads to a detuning of the measuring bridge 4.
- a bridge voltage Ub is present between the two voltage dividers, which voltage is detected by the voltage detection unit 8.
- the voltage detection unit 8 is in the present embodiment, as shown in FIG.
- the amplified voltage Uv thus corresponds to the bridge voltage Ub and processing of the amplified voltage Uv is to be understood as processing the bridge voltage Ub.
- the evaluation unit 10 is formed by a known microcontroller with RAM, ROM, CPU, I / O connections, A / D converter, etc.
- the evaluation unit 10 is configured in such a way that it determines the thermal conductivity of the fluid mixture by evaluating the bridge voltage Ub or the increased voltage Uv, which corresponds to the bridge voltage Ub, using the 3-omega method as the property of the fluid or fluid mixture.
- the 3-Omega method was first described by Jason Randall Foley in 1999 in "The 3-Omega method as a nondestructive testing technique for composite material characterization". The contents thereof are incorporated herein by reference.
- a metal wire in contact with a sample i.e. the first conductor 21, is used as both a heater and a thermometer.
- the ac voltage U0 is applied to the measuring bridge 4 by the control unit 6, so that the current I flows through the first conductor 21 at the same frequency. Consequently, a power that oscillates at twice the frequency is converted into heat in the first conductor 21, so that a temperature of the first conductor 21 and consequently also its resistance value changes at twice the frequency of the applied alternating voltage U0.
- the measuring bridge 4 is detuned and the bridge voltage Ub, which also oscillates at twice the frequency as the change in resistance, is generated.
- the resistance values of the two resistors 41, 42, which form the second voltage divider of the bridge circuit 4, as well as the resistance values of the first are designed in such a way that they have the same resistance value R in a currentless state.
- the second conductor 22 is designed in such a way that its resistance value essentially does not change in a current-carrying state. This has the advantage that the bridge voltage is proportional to the change in resistance AR2i of the first conductor 21 and can be expressed by the following equation:
- the bridge voltage Ub has a signal component which has three times the frequency of the alternating voltage applied to the measuring bridge 4.
- This so-called 3-omega-sign component is filtered in software.
- the evaluation unit 10 is therefore configured in such a way that it filters a signal component of the bridge voltage Ub which has a multiple frequency, preferably three times the frequency, of the AC voltage by means of a software-implemented synchronous rectifier or software-implemented lock-in amplifier shown in FIG. 12.
- the software-implemented synchronous rectifier uses a table 602 in which the amplitude values of the signal component with the multiple frequency, preferably three times the frequency, are stored in a standardized manner as a reference.
- the evaluation unit 10 then correlates the values of the bridge voltage Ub digitized by means of an A / D converter 604 of the evaluation unit 10 with the standardized amplitude values stored in the table 602 and forms a sliding sum over a multiple of the length of the table, ie over a multiple of the period of the signal component.
- the sum S can then be used as a measure of the component or the amplitude of the signal component in the bridge voltage Ub.
- the 3-omega signal component can be determined in a simple and inexpensive manner.
- the amplitude of the signal with three times the frequency of the bridge voltage is a direct measure of the thermal conductivity of the fluid.
- the determined thermal conductivity lies between the two values for the thermal conductivity of water and ethanol, so that it can be used as a measure for the mixing ratio.
- the determined thermal conductivity can then be compared with a predetermined thermal conductivity in order to assess whether a mixing ratio of the washing liquid stored in the fluid container 30 is suitable for the intended use in the washing system 50 of the vehicle 70, so that freezing is reliably prevented. If it is necessary, for example, that a minimum proportion of ethanol is present in the washing liquid in order to reliably prevent freezing, then the value of the determined thermal conductivity must be less than or equal to the specified thermal conductivity.
- a suitable warning signal can be displayed to a driver of the vehicle 70 via a display and / or a loudspeaker of the vehicle so that he is prompted to change the mixing ratio of the washing liquid.
- the fluid container 30 has a sensor for level measurement.
- the sensor is an ultrasonic sensor for measuring the fill level or a sensor for measuring the hydrostatic pressure.
- the device 1 for determining the property of a fluid mixture formed from a plurality of fluids is used for the washer 50 of the vehicle 70, and a thermal conductivity thereof is determined as the property.
- the washing system 50 has the fluid container 30 for storing the washing liquid and a detection means can be provided which detects a filling and / or emptying of the washing fluid container 30 with / of liquids. If, for example, one of the fluids, ethanol or water, is filled into the washing fluid container 30, it can be assumed that a mixing ratio and consequently also the thermal conductivity of the washing liquid changes. Accordingly, a determination of the thermal conductivity can be started, for example on the basis of a detection of the filling of the fluid container 30 with a fluid, in order to determine whether the washing liquid continues to have a predetermined thermal conductivity. As a result, it is possible to reduce a frequency of detection of the thermal conductivity.
- the washing liquid is formed from the two fluids water and ethanol, each of which has a known thermal conductivity.
- the evaluation unit 10 can then also be configured such that it determines a concentration as the property of the fluid mixture by comparing the thermal conductivity of the fluid mixture with the thermal conductivity of the two fluids. This embodiment offers the advantage that a driver of the vehicle can easily understand the mixture ratio.
- the evaluation unit 10 can additionally be configured such that it determines a freezing point as the property of the fluid mixture using the concentration of the fluid mixture.
- the freezing point of the washing liquid can then be communicated to the driver by means of a suitable display, so that he can judge precisely whether a mixing ratio of the washing liquid needs to be changed so that it is reliably prevented from freezing.
- the evaluation unit 10 can do so be configured to determine a freezing point as the property of the fluid mixture by comparing the thermal conductivity with a straight line.
- the straight line is obtained by a linear interpolation in which the thermal conductivity and the freezing point of the fluids are each used as a support point.
- the values of the thermal conductivity of the two fluids are each plotted on the x-axis of a Cartesian coordinate system and the values of the freezing points of the two fluids are each plotted on the y-axis of the Cartesian coordinate system.
- the freezing point of the fluid mixture can then, as shown in FIG.
- the washing system 50 is built into the vehicle 70 and is used in particular to clean an optical sensor that is used for a driver assistance system and / or a system for autonomous driving.
- the washing system 50 can, however, also be used to clean a light source and / or a window of the vehicle 70.
- the washing system 50 has further components, such as, for example, lines, pumps, spray nozzles, wipers, etc., which are required for cleaning the optical sensor, the light source or the window.
- Steps S1 to S6 of a method 100 for determining the thermal conductivity of a fluid or fluid mixture are described below with reference to FIG. 3.
- the evaluation unit 10 is configured in such a way that it controls the other components of the device 1 for determining the thermal conductivity, so that the individual steps S1 to S6 of the method 100 are carried out.
- the evaluation unit 10 is able to communicate with other units and means, not shown, such as the detection means for detecting filling / emptying, which are installed in the vehicle 70 and are communicatively connected to one another via a vehicle bus, for example .
- the method 100 is in the form of software in RAM or ROM and is carried out by executing commands by the CPU and outputting and receiving signals at the I / O ports.
- step S1 it is checked whether an ignition of the vehicle 70 is switched on and / or off. If it is not detected that the ignition is switched on and / or off (No in S1), it is waited until a corresponding signal is received. If the ignition is switched on and / or off (Yes in S1), S2 is carried out.
- step S2 it is determined on the basis of a signal received from the detection means whether filling and / or emptying of the fluid container 30 with / from a liquid is detected. If it is not determined that filling and / or emptying has taken place (No in S2), processing goes back to the beginning of the method. If it is determined that filling and / or emptying has occurred, processing goes to step S3.
- the method 100 can also be carried out without steps S1 and S2, so that the method 100 begins directly with step S3.
- the method 100 is repeated at a predetermined interval.
- the method 100 can also have only one of the two steps S1 or S2.
- the order of the two steps S1 and S2 can also be changed.
- the evaluation unit 10 controls the control unit 6 in order to apply the alternating voltage to the measuring bridge 4 and the method 100 goes to step S4.
- the voltage detection unit 8 detects the bridge voltage Ub or an amplified voltage Uv corresponding to the bridge voltage Ub and the method 100 goes to S5.
- the evaluation unit 10 filters the signal component of the voltage Uv, which corresponds to three times the frequency of the voltage applied to the measuring bridge 4, and uses this to determine the thermal conductivity of the washing liquid.
- the concentration and / or the freezing point of the washing liquid is determined in the manner described above.
- the device 1, the method 100 for determining a thermal conductivity of a fluid or the fluid mixture and the fluid container 30 have been described for use in the washing system 50 for the vehicle 70. It should be noted that the device 1 and the method 100 are not limited to this and can be used in any area in which a thermal conductivity of a fluid is to be determined.
- the washing system 50 according to the invention is not limited to an application in the vehicle 70 and can be used for surveillance cameras, weather sensors or other units in which freezing of a washing liquid is to be reliably prevented in order to ensure cleaning even at low temperatures.
- FIG. 5 schematically shows a circuit diagram of the device 1 for determining a thermal conductivity of a fluid or fluid mixture.
- the fluid mixture is in particular an aqueous fuel solution that is mixed from water and fuel and is used as a liquid for exhaust gas aftertreatment in a device 60 for exhaust gas aftertreatment in vehicle 70.
- the device 1 for determining a thermal conductivity of a fluid mixture is attached in or on a fluid container 40 of the device 60 for exhaust gas aftertreatment.
- a thermal conductivity of the aqueous fuel solution is used as a measure of the mixing ratio of fuel to water.
- An aqueous flare solution suitable for exhaust gas aftertreatment has a concentration of 32.5%, so that the aqueous flare solution has a thermal conductivity of 0.57 W / (m K). If the determined thermal conductivity deviates from the specified thermal conductivity, the aqueous flare solution does not the required urea concentration. As a result, it may be necessary to replace the aqueous urea solution stored in the fluid container 40 or to refill water or urea.
- FIGS. 6 and 7 show a measuring bridge 240 with a conductor arrangement 200 in which a first conductor 221 and a second conductor 222 are designed as wires.
- a wire is understood to be a metallic conductor with a round or angular cross-section, which is attached to a holding arrangement only at its two ends. The section in between is completely surrounded by the fluid mixture.
- the first conductor 221 has a multiple length, preferably four times the length, of the second conductor 222 and for this reason has a cross section that is smaller than the cross section by the ratio of the length of the first conductor 221 to the length of the second conductor 222 of the second conductor 222 is. Accordingly, the first conductor 221 and the second conductor 222 have the same resistance value in a currentless state.
- the first conductor 221 is attached to the conductor arrangement 200 in a meandering or loop-shaped manner. It should be noted that the cross-section of the two conductors 221 and 222 in FIG. 6 and FIG. 7 is drawn identically for reasons of drawing. The cross-section of the two conductors 221 and 222 is actually different from one another.
- the two conductors 221 and 222 are stretched over a recessed surface 202 of a holding arrangement 201 in a plane parallel to the recessed surface 202, so that they are completely surrounded and surrounded by the fluid or fluid mixture. In this way, the two conductors 221 and 222 can be brought into full contact with the fluid. In this way, a detection accuracy of the thermal conductivity can be further improved by the device according to the invention.
- the two conductors 221 and 222 are guided over openings 204 in order to form the individual meanders.
- elastic elements for example spring elements (not shown)
- the two conductors 221 and 222 or adjacent meanders or loops of the first conductor 221 can be prevented from touching one another, and a short circuit can thereby be reliably prevented.
- a change in length or shape of the holding arrangement 201 due to a change in temperature can also be compensated for.
- Block-shaped elevations 206 are arranged between the two conductors 221 and 222 and the meanders of the first conductor 221.
- the elevations 206 extend from the fourth recessed surface 202 to a plane which is also parallel to the recessed plane and spaced further apart from the recessed surface 202 than the plane in which the first and second conductors 221 and 222 are arranged. Accordingly, the elevations 206 likewise prevent the first and second conductors 221 and 222 and the meanders of the first conductor 221 from coming into contact. In addition, a larger section in the area of the conductor arrangement 200 is prevented by the elevations 206 from freezing.
- an aqueous urea solution for exhaust gas aftertreatment has a freezing point of -11 ° C and therefore it can happen on cold winter days that the aqueous urea solution freezes.
- the antifreeze content of a washing liquid can be too low, so that it can also freeze on cold winter days.
- a frozen section of the fluid mixture in the area of the conductor arrangement 200 can be thawed more quickly by a heater arranged in the fluid container 40 for the aqueous urea solution, so that a reliable determination of the thermal conductivity of the washing liquid or the aqueous urea solution is possible more quickly after the vehicle 70 has been started is.
- the two resistors 41 and 42 of the other branch of the measuring bridge 240 are designed as resistors with fixed resistance values.
- the resistance values of the two resistors 41 and 42 are selected so that the measuring bridge 240 is balanced in a currentless state.
- the two resistors 41 and 42 and the conductor arrangement 200 with the first and second conductors 221 and 222 can be arranged on a common arrangement, such as a common circuit board, or can be arranged spatially separated from one another and connected to one another via cables or lines.
- holes 208 are formed into which pins of a lid or a cover (not shown) for the conductor arrangement 200 can be inserted.
- screws can also be screwed into the holes in which a thread is formed in order to connect the cover to the holding arrangement 201.
- the cover can further prevent a larger area of the aqueous urea solution in the area of the two conductors 221 and 222 from freezing. So that the fluid mixture can continue to be brought into contact with the first and second conductors 221 and 222, the cover has slots or holes through which the fluid mixture can flow to the first and second conductors 221 and 222. In addition, the cover can reduce the risk of mechanical damage to the first and second conductors 221 and 222.
- a measuring bridge 340 according to a further embodiment of the present invention is shown in FIGS. 8 and 9.
- one of the voltage dividers is formed by a conductor arrangement 300 according to another embodiment.
- a first conductor 321 in the form of a wire, which is attached to a holding arrangement 301, and a fixed resistor 322 are connected in series.
- the fixed resistor 322 it is not necessary for the fixed resistor 322 to be brought into contact with the fluid and it is sufficient if only the first conductor 312 is brought into contact with the fluid.
- the other of the voltage dividers is formed by two adjustable resistors 341 and 342.
- the resistors 341 and 342 are resistors whose resistance value can be changed and are preferably designed as digital potentiometers.
- the evaluation unit 10 is configured in such a way that it adjusts or changes the resistance values of the resistors 341 and 342 in such a way that the measuring bridge 340 is balanced when the AC voltage U0 is initially applied.
- the conductor arrangement 300 has only one first conductor 321, which is designed as a wire.
- the first conductor 321 is connected at connections 302 to lines of the measuring bridge 340.
- the connections 302 in the embodiment shown in FIGS. 8 and 9 are screwable connections, but it is also possible to design the connections as clamp or plug connections. As a result, the holding structure 301 can be easily assembled and removed.
- the first conductor 321 is laid as a loop and is arranged in a plane parallel to a bottom surface 304 of the holding arrangement 301.
- a frame 306 is formed around the bottom surface 304 so that the holding arrangement 301 is formed as a recessed housing in which a small proportion of the fluid is present.
- the first conductor 321 is guided over deflection points 308 and is pretensioned by means of elastic elements in order to compensate for a change in length due to heating in the current-carrying state and a change in shape or length of the holding arrangement 301 in the event of a temperature change.
- the elastic elements are designed as spring elements 310 and 312.
- a first spring element 310 biases the first conductor 321 in a direction toward an outside of the loop.
- a second spring element 312 biases the first conductor 321 towards an inner side of the loop in that two opposite sections of the first conductor 321 are drawn together by the second spring element 312. In this way, contact of the first conductor 321 with itself or with other elements of the conductor arrangement 300 is reliably prevented. As a result, short-circuiting of the first conductor 321 can be reliably prevented.
- a change in shape or length of the holding arrangement 301 due to a change in temperature can be compensated for.
- elevations 314 or projections are arranged, which make contact with the first conductor 321 further reliably prevent with itself or with surrounding elements.
- the elevations 314, which are cylindrical in the example shown in FIGS. 8 and 9, also limit a spatial expansion of a frozen section in the area of the first conductor 321, so that the frozen section of the aqueous urea solution quickly after a start of heating is defrostable.
- the holding arrangement 301 has two hollow cylinders 316 in a central area on the outside, into which pins of a lid or a cover (not shown) can be inserted or into which screws can be screwed in order to connect the lid to the holding arrangement 301.
- the cover rests on the frame 306 of the conductor arrangement 300 and is in turn formed with slots or holes so that the fluid can penetrate into the interior of the conductor arrangement 300.
- the cover further prevents the aqueous urea solution or the washing liquid from freezing in the area of the holding arrangement 301 and the risk of mechanical destruction of the holding arrangement 301 or the first conductor 321 is reduced.
- the holding arrangement 301 is not limited to the first conductor 321 and a second conductor can also be arranged on a similar conductor arrangement.
- the conductor arrangement 300 can also be designed in such a way that both the first conductor and the second conductor can be attached to the conductor arrangement 300.
- the two conductors can be routed one above the other in two parallel planes or the second conductor, which is shorter than the first conductor, can also be used as a loop inside the loop of the first conductor, which is optionally also pretensioned by elastic elements , are formed.
- FIG. 10 shows a flowchart of a method 400 that is executed when the measuring bridge 340 shown in FIGS. 8 and 9 is used.
- the method 400 differs from the method 100 shown in FIG. 3 in that a step S10, in which the evaluation unit 10 compares the measuring bridge 340 by setting the resistance values of the two resistors 341 and 342, is carried out before step S1.
- An adjustment of the measuring bridge 340 is carried out as follows.
- the evaluation unit 10 is designed to cause at least one of the two transistor booster stages 61, 62 to apply a direct voltage to the measuring bridge 340.
- the DC voltage has a value of 200 mV. However, the value of the direct voltage can also be between 100 mV and 500 mV.
- the bridge voltage Ub is then recorded and the evaluation unit 10 changes the two adjustable resistors 341 and 342.
- a DC voltage is then again applied to the measuring bridge 340 and the bridge voltage Ub is recorded. This process is carried out until the bridge voltage Ub, which is detected in response to the applied DC voltage, is essentially equal to a voltage of 0V.
- the measuring bridge 340 can be balanced reliably. This procedure is advantageously carried out when commissioning or starting a detection of the thermal conductivity in order to initially adjust the measuring bridge 340.
- the evaluation unit 10 can be designed so that it filters out a signal component of the bridge voltage Ub which corresponds to the single frequency of the alternating voltage U0 applied to the measuring bridge 340.
- the amplitude of this signal component of the bridge voltage Ub can be used as a measure for the detuning of the measuring bridge 340 and the evaluation unit 10 is designed so that it changes the resistance value of the adjustable resistors 341 and 342 in step S10 in such a way that the signal component of the bridge voltage that the corresponds to the simple frequency of the applied alternating voltage Ub, is essentially 0 V.
- This procedure offers the advantage that a detuning of the measuring bridge 340 can be detected during a measuring operation. Accordingly, detunings of the measuring bridge 340, which occur, for example, as a result of heating during operation, can be detected and the measuring bridge 340 can then be adjusted.
- FIG. 11 shows a folding arrangement 501 according to an embodiment, which is covered by a cover 502.
- the folding arrangement 501 and the cover 502 have congruent holes 504 and 506, respectively, into which pins 508 can be inserted.
- the holding arrangement 501 and the cover 502 can also be connected to one another by screws or rivets.
- the holes have, for example, a thread for the screw or are designed in such a way that a rivet can be supported therein.
- the cover 502 has two slots 510 through which the fluid, the property of which is to be determined, can communicate with a conductor 521 designed as a wire.
- the holding arrangement 501 shown in FIG. 11 also differs from the previous embodiments in that the conductor 521 is arranged in a groove section 512. Accordingly, the sections outside of the groove section 512 correspond to the elevations according to the previous embodiments.
- the conductor 521 can be connected to a measuring bridge, such as the measuring bridge 340 according to the previous embodiment, via two contact pins 514. Furthermore, the conductor 521 is pretensioned via an elastic element, in particular the spring element 516, so that a change in length of the conductor 312 and / or a change in length or shape of the holding arrangement 510 due to a change in temperature can be compensated for. As a result, the conductor 521 formed as a wire can be reliably prevented from being destroyed.
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Abstract
Description
Claims
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DE102020111862 | 2020-04-30 | ||
DE102020115467 | 2020-06-10 | ||
DE102020131192.3A DE102020131192A1 (en) | 2020-04-30 | 2020-11-25 | Device and method for determining a thermal conductivity of a fluid, liquid container and vehicle |
PCT/EP2021/061124 WO2021219709A1 (en) | 2020-04-30 | 2021-04-28 | Device and method for ascertaining the thermal conductivity of a fluid |
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EP4143553A1 true EP4143553A1 (en) | 2023-03-08 |
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EP21723172.9A Pending EP4143553A1 (en) | 2020-04-30 | 2021-04-28 | Device and method for ascertaining the thermal conductivity of a fluid |
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US (1) | US20230168215A1 (en) |
EP (1) | EP4143553A1 (en) |
CN (1) | CN116261660A (en) |
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WO (1) | WO2021219709A1 (en) |
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DE102020134912A1 (en) | 2020-04-30 | 2021-11-04 | AST (Advanced Sensor Technologies) International GmbH | Sensor arrangement for a fluid, fluid tank and use of the sensor arrangement |
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FI92440C (en) * | 1993-08-23 | 1994-11-10 | Vaisala Oy | Detector and method for observing the presence of a liquid and / or a change thereof |
DE10123920B4 (en) | 2001-05-17 | 2006-02-02 | Robert Bosch Gmbh | Integrated microstructure sensor element for detecting thermodynamic quantities of a fluid |
DE102016205776A1 (en) | 2016-04-07 | 2017-10-12 | Robert Bosch Gmbh | Calorimetric determination of a gas concentration |
-
2020
- 2020-11-25 DE DE102020131192.3A patent/DE102020131192A1/en active Pending
-
2021
- 2021-04-28 WO PCT/EP2021/061124 patent/WO2021219709A1/en unknown
- 2021-04-28 US US17/922,467 patent/US20230168215A1/en active Pending
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DE102020131192A1 (en) | 2021-11-04 |
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WO2021219709A1 (en) | 2021-11-04 |
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