DE102007001192A1 - Apparatus and method for determining a level and a temperature of a fluid - Google Patents

Abstract

The present invention relates to an apparatus and a method for determining a level and a temperature of a fluid. In order to provide an even more compact device and a more efficient measuring method, it is proposed that a sensor voltage (U <SUB> mess </ SUB>) and a measuring current (I <SUB> mess </ SUB>) before and after a current ( I <SUB> heating </ SUB>) caused heating of the heating wire (21) for calculating an electrical resistance (R) are measured.

Description

The The present invention relates to an apparatus and a method for determining a fill level and a temperature of a Fluid.

Especially from the motor vehicle sector, the need is known, the To monitor the level and temperature of an engine oil. This scope is numerical and thus also economically important. engine oils On the other hand, because of their role as lubricants and at the same time transport medium for waste heat also over operate over a very wide temperature range and can over Duration attack various materials. In the automotive field In addition, high demands are placed on reliability and reliability Longevity of such a device also in contact with a put relatively aggressive fluid. As an application in the automotive sector A very hard requirement profile, the present becomes Invention hereinafter without limitation in its field of application only against the background of the special use for monitoring Level and temperature of an engine oil in an internal combustion engine a motor vehicle shown.

For the electrothermal level measurement becomes a measuring arrangement based on a heating or hot wire perpendicular or is mounted at a certain angle in the engine oil. The Length of the hot wire is to be chosen so that both at maximum and at minimum oil level the Measuring range of the wire not exceeded or fallen below becomes. The resistance of the hot wire is proportional to the temperature of the wire, so it has PTC characteristics. According to the state of Technology is the hot wire for level measurement with a time limited current pulse with constant current strength heated. The at the beginning of the current pulse and at the end of the current pulse on the hot wire falling voltages are measured and for level determination used. At a high oil level, the wire is supplied electrical heating power delivered to a large extent to the surrounding oil. The wire heats up so only slightly, so that only a small increase in resistance is measurable. At low oil level, however the wire is mostly in the air. There Air is a poor conductor of heat, is little electric Heat output and the fluid can the heating wire only in small Cool the measurements. This heats the wire comparatively strong. This big warming has a big one Voltage difference between the two measured voltages Episode. The voltage difference is thus inversely proportional to Filling level.

From the EP 1 180 667 A2 a device for determining a filling level is known in which, as a function of a respective fill level of a fluid, measured values of a heating wire cooled over a different sized area by the fluid are recorded. This component is operated in the form that a respective voltage drop is measured at the beginning and at the end of a defined energization of the heating wire. For temperature measurement, a corresponding sensor element in the form of an NTC resistor is provided. In a very compact design, the devices for both measurements are arranged in a common elongate housing, which is arranged in an oil pan of a motor vehicle engine in the form of only one component. A device according to the disclosure of EP 1 180 667 A2 has basically proven itself in practical use.

Next are from the unpublished patent applications DE 10 2005 053 278.0 and 10 2005 053 539.9 A method for the combined measurement of level and temperature of an engine oil and very compact devices for implementing such methods known. Based on the heating characteristics of the heat and sensor wires, the oil temperature and oil level are determined. These teachings are based on precise regulation of a heating current in order to be able to analyze a heating curve measured under defined electrical conditions by means of resistance values.

task It is the object of the present invention to provide an even more compact device and a more efficient measuring method using a heating wire to provide PTC or PTC resistor characteristics.

These The object is achieved by the features of the independent claims solved by a measuring voltage and a measuring current before and after heating caused by a heating current of the heating wire for calculating an electrical resistance of Heating wire to be measured. Accordingly, a device according to the invention is characterized characterized in that an evaluation circuit means for voltage measurement when exposed to the sensor wire as a fluid temperature sensor with having a measuring current and by connection to a calculator with integrator at the same time via determination of a cooling behavior is designed as a level sensor.

According to a method of the invention, a distinction is made between energizing the heating and sensor wires between a heating current and a sensor or measuring current. In particular, the heating current is an unregulated, relatively high current, while the measuring current is a regulated and very low current, the only resistance measurement outside a heating of the Heating and sensor wire is used. Thus, according to the invention, calculation or determination of an electrical resistance is no longer carried out during the heating of the heating wire caused by the application of a current pulse. In a cooling method proposed here, the heating of the thermoelectric sensor wire and the measurement of the resistance characteristic of the sensor wire during the cooling phase is carried out by temporally separate and the different sized streams. By determining the resistance, the measurement result is largely insensitive to tolerance fluctuations in the measuring current / measuring voltage used.

Of the Heating current is in a preferred embodiment The invention some 100 mA and can be turned on and off. A regulation of the heating current is preferably not necessary so that a z. B. executed in the form of a transistor adjustable current or voltage source can be omitted. The measuring current and / or the measuring voltage are chosen on the other hand sufficiently small, so that the converted in the sensor wire electrical power this only insignificantly heated additionally and tolerance-related Fluctuations of the measuring current and / or the measuring voltage thus a have negligible influence on the measurement result.

Preferably is measured at a measuring interval using a plurality of Measurements determined a corresponding number of measuring points. Out The measuring points can be multiplied by the width of each Sampling interval is an area under the cooling curve be approximated.

One inventive method also works at high levels reliably, since due to the different heat conduction coefficients between air and fluid at different fluid level heights give different heating curves of the heating wire. These Cooling curves close over the time axis thus seen in the measuring intervals of defined length also different sized areas, the one easily determined thermal energy content of the heating or Specify sensor wire. Thus, inaccuracies are just at high Fluid levels largely avoided as they occur in known devices and methods.

According to the invention in addition to the level measurement for the measurement of Temperature of the fluid no additional temperature sensor provided, z. B. in the form of a separate NTC resistor. In one inventive combination sensor is for Both measurements thus advantageously only one sensor element in the form of a heating wire in contact with the to be monitored Fluid is.

In order to can additionally with a device according to the invention to determine a level height also a respective fluid temperature determined with sufficient accuracy become. For determination of fluid temperature and filling level of the fluid is advantageously only one more measurement interval required, that at least in an initial range of two different Evaluation process is used as it were.

By the elimination of a separate NTC resistor for temperature measurement a fluid, as known in the art, is already directly achieved a cost saving, but also no additional Evaluation circuit for the evaluation of highly nonlinear Characteristic curve of an NTC sensor output signal is required. Of the Elimination of this separately to be arranged evaluation logic for the NTC sensor output leads to a reduction in the size of the sensor or sensor housing and also to a reduction in size in terms of to an evaluation circuit. The evaluation circuit can now on a accommodated comparatively smaller circuit board or PCB become. Next leads now the saving of a scheme for the heating current to advantages in terms of energy consumption and manufacturing costs.

following the invention with reference to an embodiment Based on illustrations of the drawing to show other features and advantages explained in more detail.

In the drawing show in each sketched sectional views:

1 an embodiment of a device according to the invention;

2 : A representation of the embodiments of 1 Vertically cut in a plane leading to the plane of the sectional view of 1 is vertical;

3 : An illustration of a known device in the section plane of 1 ;

4 : A representation of the known device in a sectional plane according to 2 ;

5a and 5b : a diagram for representing basic temperature profiles over time with a number of measuring points for determining a heating curve according to a method not previously published;

6a and 6b : one diagram each for Representation of fundamental temperature curves over time with a number of measuring points for determining a cooling curve according to a method of the invention with representation of measurement and heating current in the various phases;

7 FIG. 4 is a diagram showing schematic diagrams of cooling curves at two different level levels of a fluid; FIG.

8th FIG. 4: a diagram of a discrete-time resistance measurement of an initial state and a cooling curve of a thermoelectric wire and FIG

9a and 9b Two diagrams for determining an oil level as a function of several variables and

10 : a block diagram of an electronics with connected sensor wire.

about the different pictures will become below for the same elements always use the same reference numerals. Without Limitation of the invention to this particular application below only one use of the devices for the determination of Level and temperature of engine oil in an internal combustion engine of a motor vehicle and described.

3 shows a sensor device 0 for determining the level and fluid temperature with a housing 1 made of plastic, which consists of two half shells 2 . 3 is constructed. The two half shells 2 . 3 each have an enlarged diameter in a connecting region in an upper area 4 . 5 which is near its upper end with an inward-facing waistband 6 in a circumferential groove 7 a contact socket 8th intervenes. The housing 1 is along with the contact socket 8th in a connector 9 used, the outside with a screw thread 10 is provided and has known sealing means.

Each connection area 4 . 5 has a radial opening 11 . 12 on. Up to the area of these openings 11 . 12 protrude from the contact socket 8th here are pairs of electrical conductors 13 . 14 and from the case 1 Her pairs of electric wires 15 . 16 into it and are there by welds 17 connected with each other.

The half shell 3 is designed for level measurement. There is a tensioning body near its lower end 18 , which in the longitudinal direction of the half-shell 3 held in it and held by a spring 19 from the connection area 4 is biased away. This clamping body 18 has a pin 20 through which a heating wire 21 is deflected by 180 °, in the half shell 3 extends over a substantial portion of its length and with the two ladders 15 connected is. This heating wire 21 is current flowing through the level measurement. It is more or less cooled by the medium to be measured depending on the level, so that its total electrical resistance changes accordingly and can be determined by measuring the electrical variables of the level.

The half shell 2 has a recess in its lower end face 22 with a temperature responsive sensor element 23 , here an NTC element. This NTC sensor element 23 is outward over the ladder 16 connected, are transmitted by the corresponding temperature signals.

The 4 shows the half shell 3 now alone and opposite to the sectional view of 3 turned by 90 degrees. To recognize is in turn the clamping body 18 with the pin 20 which the heating wire 21 spans and diverts. The heating wire 21 runs so U-shaped, with its two each one leg of the U-forming areas in 2 With 21 ' and 21 '' be designated.

For mounting the illustrated sensor device 0 First, all built-in parts in the two half shells 2 . 3 and the contact socket 8th built-in. Then you weld a half shell 2 . 3 to the contact socket 8th and then connects the other half shell 2 . 3 with the first half shell 2 . 3 For example, by clipping, welding, caulking or staples. Then you welded the already connected half shells 2 . 3 , with the contact socket 8th , In the final assembly, the unit is in the connector 9 used with external hexagon contour, which has integrated sealant. Subsequently, the arrangement with the sensors arranged separately 21 . 23 finished for temperature and level measurement by rolling. In a mounting position, a connection is made via electrical lines on the contact socket 8th in the in the 3 and 4 indicated way.

In this embodiment, now only one sensor is required for the temperature and level measurement 21 whose signals are now evaluated independently by two methods. The determination of a fluid temperature and a fluid level measurement will be described below with reference to the figures 5a , Federation 6a , b received.

By an approach according to the invention simplifies the of 3 Her known construction in an embodiment in the in 1 shown way: The opposite the heating wire 21 as far as possible thermally decoupled recess 22 with the sensor element arranged therein protected 23 deleted without substitution. This can be the half shell 2 be shortened. The half shell 2 But it can also be completely eliminated, as is also a leader 16 is no longer needed. This would make the heating wire 21 be brought into good contact with the fluid directly without the need of flood holes, whereby by a concrete shaping of the half shell 3 In a manner known to those skilled in a required protection and mechanical stability of the device is ensured.

Furthermore, the elimination of a second sensor required according to the prior art also simplifies the wiring in the region of the radial openings 11 . 12 considerably. Finally, in the contact socket 8th only one pair of wires 13 led to the outside. This is in the contact socket 8th Also from reaching space available here to accommodate a not shown evaluation circuit. The evaluation circuit is formed in an embodiment of the invention also equal as a connection member for a LIN or CAN bus or other data network.

2 shows analogously to the representation of 4 an embodiment in which the above-mentioned simplifications and savings of separate components have been implemented more concrete, without causing an external appearance or dimensions of the sensor device 0 would have been changed: the contact socket 8th is now with the connector 9 made in one piece. The connection areas 4 . 5 omitted. The electrical conductors 13 . 15 are integrally formed and are poured.

In principle, now also the half shell 3 with the contact socket 8th and the fitting 9 be made in one piece, so that in an assembly only the heating wire 21 at a free end of the ladder 15 would have to be connected. Instead of a construction of clamping body 18 with separate elastic element 19 In a not further concretely illustrated embodiment of the invention, the elasticity of the material for tensioning the heating wire 21 be used.

In one embodiment, this is a tensioning body 18 with a spring element 19 formed in one piece and in particular integrally with the housing 1 the device 0 connected or molded to this. This is one in the 1 and 2 Dashed area A around the pin 20 C-shaped or S-shaped, for example by arrangement of notches or recesses 24 with corresponding transition radii. The area A can thus be deflected or compressed elastically in a required area itself in a predetermined manner.

A non-pre-published measuring method will now be described with reference to the drawings of FIG 5a and 5b In a stationary case, the temperature of the heating wire in contact with the fluid corresponds 21 that of the fluid. According to the non-pre-published approaches mentioned in the introduction, a rectangular pulse with a constant current is applied to the heating wire over the duration of a measuring interval 21 created to measure a heating curve. When measuring the fluid temperature, the heating wire 21 a constant current I flows through it during a measuring interval for a period Δt of approximately 400 ms. Due to the current flow, the heating wire heats up 21 and its ohmic resistance R _sens rises. Depending on a respective initial or stationary starting temperature and a high or low fluid level FS, the continuous measurement results in a substantially square curve of the resistance in a range B up to a heating or current flow time of T = 100 ms R _sens or the temperature of the heating wire 21 over time t.

In 5a is a curve corresponding voltage or resistance values of a heating wire 21 drawn at a high and a low fluid temperature over time t. In a region B, with a sufficiently good approximation, there is a quadratic relationship between a respective time t at the heating wire 21 tapped voltage U _sens and time t. According to 5b is from a time t _o to a time t _1, a current I _sens in the form of a regulated rectangular pulse to the heating wire 21 the device 0 created.

According to the in 5a From a point in time t 'points now no continuous measurement, but a measurement of the above the heating wire 21 decreasing voltage U _sens at several times. These measuring points have an equidistant spacing of approximately 1 to approximately 4 ms from each other. In the present embodiment, the temporal distance between measuring points is selected to be 2 ms. Values U _sens (t '), which can be converted by R _sens (t) = U _sens (t) / I _{sens, are} determined by the measured values at the respective sampling instants t. Now, using known approximation methods, a compensation curve f as a function of second order is passed through these determined values R _sens (t). Here is a method with minimization of the square of the deviations of the respective measuring points to the curve f application. As a distance from the start of the defined energization of the heating wire 21 is accurately known at t _o up to a first measuring point at a point in time t ', a resistance value R _sens (t _o ) can now be determined backwards on the basis of this compensating curve f or of the resistance _profile R _sens (t). The calculated based on the resistance _curve R _sens (t) Wi The resistance R _sens (t _o ) then outputs a stationary start temperature of the heating wire via a read-only memory or look-up table 21 which has coincided with the fluid temperature.

In a method for determining a fluid level, the above for determining a stationary initial temperature of the heating wire 21 or a fluid temperature measured values up to a time t ₁ over a total time .DELTA.t of the energization viewed from here about 400 ms. As shown by 5a With larger level differences at time t _1, significant differences in the measured voltage difference ΔU1 at low and ΔU2 at high level FS occur. This behavior was used in known methods: The hot wire is thus heated with a temporary current pulse with constant current. The voltages dropping on the hot wire at the beginning of the current pulse and at the end of the current pulse are measured and used to determine the filling level. At low levels, the wire heats up, resulting in a large voltage difference ΔU between the two measured voltages. At high level, the voltage difference is comparatively low. The voltage difference is thus inversely proportional to the level height. At lower level differences, however, a difference in the voltage difference at time t ₁ is much less pronounced. Thus, a resolution of known methods is therefore not sufficiently secure in the critical range of high fluid levels. Also, considering a slope of the compensation curve f at an extrapolated start time t _o or another fixed predetermined time as a measure of a level FS would already be relatively inaccurate due to the approximation used.

In the present embodiment of the invention, a fill-level sensor operating according to the hot-wire principle is used, in which a predetermined current flow through the sensor wire causes a temperature increase in the wire. Since the wire used in the present embodiment also has a PTC characteristic, when the temperature of the wire increases, an increase in electrical resistance occurs, as in FIG 6a indicated. During this heating process, the electrical heating energy is partially released to the surrounding media. The energy difference from the supplied electrical energy and the heat energy emitted heats the hot wire. Due to the different coefficients of thermal conductivity of air and fluid, different fill level heights cause different heating curves of the hot wire, as already described above. In contrast to that with reference to the illustrations of 5a and 5b described method is now differentiated _{according to the} invention between a measuring current I _mess and a heating current I. He follows it up 6b a clear of 5b deviating current course.

The temporal diagrams of 6a and 6b show the basic timing of a measurement by a method according to the invention: The sensor resistance has the temperature of the surrounding oil at the beginning of the measurement, and thus the resistance R _{o associated} with a specific temperature. First, therefore, during a time t _mess1, the initial _resistance R _{o of} the sensor wire is measured with a small measurement current I _mess and a small measurement voltage U _mess . Since the resistance of the sensor wire used increases substantially linearly with the temperature, the initial temperature of the wire and thus the oil temperature can be determined from this measurement, without the measurement itself significantly influencing the result by additional heating. During a subsequent period t _heating of the sensor is heated by a _heating compared to the measurement current I _measured substantially larger heating current I. This increases the electrical resistance R of the wire. Then, during a phase t _mess2, the electrical resistance of the sensor wire is determined with the aid of a small measuring current I _mess2 . As this again only a small electrical power is delivered to the sensor wire, the sensor wire cools. This also reduces the wire resistance well measurable. After a waiting period, after which the sensor wire has resumed the temperature of the oil, the measurement can be restarted.

The effects of level changes on the cooling characteristics of the sensor wire are shown in the figure of 7 sketched in the form of a sketch for high and low oil level with the same oil temperature and the same heating current. When the oil level is low, the wire cools slowly, so the sensor resistance changes slowly. When the oil level is high, the wire cools down very quickly, so the resistance of the sensor has quickly decreased to the initial value R _o .

• 1. Der Anfangswiderstand R_o wird vor Beginn des Heizens gemessen, aus dem Anfangswiderstand R_o wird eine ursprüngliche Öltemperatur bestimmt. Die Bestimmung des Anfangswiderstands R_o erfolgt mit mehreren Widerstandsmessungen während der Zeit t_mess1 auch in Form zeitdiskreter Messung gemäß der Abbildung von 8.
• 2. Ein Widerstandswert R_max wird zum Abschluss der Heizphase bestimmt, also nach Ablauf der Phase t_heiz. Durch unterschiedliche Heizströme I_heiz und/oder Heizspannungen U_heiz und verschiedene Füllstände wird der Sensordraht während der Heizperiode unterschiedlich stark aufgeheizt. Dementsprechend ist auch ein maximal erreichter Sensorwiderstand R_max verschieden. Dieser maximale Sensorwiderstand R_max wird aus den gemessenen Widerstandswerten der Abkühlkurve ermittelt. Dazu wird in zeitlich äquidistanten Abständen Δa der Widerstand des Drahtes während der Abkühlphase gemessen, wie in 8 angedeutet. Aus diesen Werten ist mit geeigneten Methoden, hier durch Ermittlung einer Ausgleichskurve unter Anwendung bekannter Approximationsverfahren, der maximale Widerstand R_max nach dem Heizvorgang zu bestimmen.
• 3. Schließlich wird eine Widerstandssumme R_sum bestimmt. Durch Summation der gemessenen Widerstandswerte der Abkühlkurve des thermoelektrischen Drahtes erhält man eine Messgröße, aus der mit Hilfe der bekannten Öltemperatur und des maximal gemessenen Widerstands R_max der Ölstand bestimmt werden kann. Um die Verarbeitung in einem Mikrocontroller zu erleichtern, kann eine Verkleinerung der Widerstandssumme erfolgen, indem jeweils der Anfangswert R_o vom gemessenen Widerstand subtrahiert wird.

Based on a determination of the following measured variables, a current oil level can now be determined. According to the illustrated cooling method, the determination of three measured quantities is required:

• 1. The initial resistance R _o is measured before the start of heating, from the initial resistance R _o , an original oil temperature is determined. The determination of the initial resistance R _o is carried out with several resistance measurements during the time t _mess1 also in the form of time-discrete measurement according to the illustration of 8th ,
• 2. A resistance value R _max is determined at the end of the heating phase, ie after the end of the phase t _heating . By different heating currents I _heating and / or heating _voltages U _heater and different levels of the sensor wire is heated to different degrees during the heating season. Accordingly, a maximum reached sensor resistance R _{max is} different. This maximum sensor resistance R _max is determined from the measured resistance values of the cooling curve. For this purpose, the resistance of the wire during the cooling phase is measured in time equidistant intervals Δa, as in 8th indicated. From these values, by means of suitable methods, here by determining a compensation curve using known approximation methods, the maximum resistance R _max can be determined after the heating process.
• 3. Finally, a resistance _sum R _{sum is} determined. By summation of the measured resistance values of the cooling curve of the thermoelectric wire, a measured variable is obtained from which the oil level can be determined with the aid of the known oil temperature and the maximum measured resistance R _max . In order to facilitate the processing in a microcontroller, a reduction of the resistance sum can be carried out by subtracting in each case the initial value R _o from the measured resistance.

The method described above is made independent of the sampling time in a non-illustrated embodiment in that the respective resistance value is multiplied by the sampling interval. Graphically, this approach is interpreted as integration of the area under the cooling curve, as indicated by the hatched area in 7 indicated. The method described above has already due to a use of a lot of individual measuring points on a lower sensitivity of the level measurement against interference. Thus, a calculation R (t) = U _mess (t) / I _mess (t) is carried out continuously with automatic error compensation. A respective software computing concept can be integrated in a microcontroller using various integration methods, eg. B. a Newton approach.

The following procedure is used to determine the oil level: The oil level or level is to be calculated as a function of three variables as level = f (R _o , R _sum , R _max) . The pictures of the 9a . 9b show typical curves of a resistive sum at high and low levels as a function of R _max at a certain temperature. A representation as a family of characteristics is in 9a and as a 3-dimensional area in 9b outlined. The oil level is calculated according to this function with the measured input variables in a microcontroller. For this purpose, a suitable look-up table can be used.

Regarding a saving of space in the controller expedient However, a calculation of the level over applied a multivariate polynomial. So only the Coefficients of each term are stored. These coefficients or the values of the look-up table are by suitable measurements to investigate.

The block diagram of 10 shows a possible realization of a circuit suitable for the method as part of a device. A microcontroller switches the heating current I _heating and / or the heating voltage U _heating , which is obtained from the supply voltage of the entire sensor, via a switching transistor S ₁ . The measuring current I _mess and / or the measuring voltage U _mess can be obtained from the regulated voltage from the voltage regulator and can also be switched by the controller via a switching transistor S ₂ . After the resistance measurement and the calculation of the level, the output of the result z. B. via a PWM signal or via a suitable bus system, such. B. LIN.

The The method described above is especially for high temperature applications suitable because the heating current is only switched on or off, d. H. the power loss in a control transistor is minimal, thereby also the problems with the self-heating of the power transistor reduce. In addition, cost reductions are possible in several places, since no voltage reference is required, a heater drive transistor can be dimensioned comparatively small, a current control circuit is not mandatory and also a number of precision components reduced in the form of resistors or resistor arrays and also PCB area due to smaller number of components Is saved. Finally, another improvement the measurement accuracy achieved by that in the above Method the size of the measuring current is not in the Result of the measurement, which results in a significant factor of inaccuracy Compared to previous methods is eliminated.

In order to is inventively in addition to a simple installation in a sump also a simplified construction with clear Potential savings in a manufacturing and an operating method disclosed. An inventive device is Moreover, it can be easily integrated into existing systems.

0

sensor device all in all

1

casing made of plastic

2

half shell

3

half shell

4

connecting area

5

connecting area

6

Federation

7

groove

8th

Contact socket

9

Fitting / connector with external hexagon

10

Screw thread on 9

11

radial perforation

12

radial perforation

13

electrical Through line

14

electrical Through line

15

electrical conductor pair

16

electrical conductor pair

17

welding

18

tensioning body

19

spring element

20

Pin / deflection hooks for heating wire

21

heating wire

22

recess

23

sensor element

24

recess

FS

level

A

elastic range of 3

B

initial region

I _sens

measuring current

U _sens

measuring voltage

R _sens

Heat wire resistance

.DELTA.U

voltage difference

t

Time (Time axis)

t ₀

Start time

t ₁

end time

t '

time a first measuring point

T

end an approximation

.delta.t

total time the defined current supply

f (t)

regression curve

I _mess

measuring current

U _mess

measuring voltage

I _{am heating}

heating

U _heating

heating voltage

R

measured Resistance of the wire

R _o

initial resistance

R _max

maximum resistance

t _mess1

measurement interval before heating the wire

t _heating

heating interval

t _mess2

measuring interval after heating the wire

.DELTA.a

discreet time step

S ₁

transistor as a switch for the heating current / heating voltage

S ₁

transistor as a switch for the measuring current / measuring voltage

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1180667 A2 [0004, 0004]
• - DE 102005053278 [0005]
• - DE 102005053539 [0005]

Claims (6)

Method for determining a fill level and a temperature of a fluid, in which, as a function of a respective filling level, electrical measured values are recorded at a heating wire which is cooled by the fluid over a variable range, characterized in that a measuring voltage (U _mess ) and a measuring current ( I _mess ) before and after heating by a heating current (I _heating ) heating of the heating wire ( 21 ) for calculating an electrical resistance (R) of the heating wire ( 21 ) are measured. Method according to the preceding claim, characterized characterized in that over the time of cooling an area under a curve (R (t)) of the sensor wire resistance (R) as a measure of a current fluid level (level) is determined. Device for determining a filling level and a temperature of a fluid, in which means are provided for receiving, as a function of a respective fill level, electrical measured values at a heating wire cooled over a different sized range by the fluid, characterized in that the device for implementing a method according to one of the preceding claims, characterized in that means are provided for switching on and off a heating current (I _heating ) and a regulated measuring current (I _mess ) different therefrom, the heating wire ( 21 ) has a PTC or PTC characteristic and the heating wire ( 21 ) is formed with an evaluation circuit by means for voltage measurement when exposed to the measuring current (I _mess ) as a fluid temperature sensor and by connection to an arithmetic unit. Device according to the preceding claim 1, characterized in that the heating wire ( 21 ) U-shaped in or on an elongated housing ( 1 ) is arranged under tension with a deflection in a region (A) and is connected via two connection elements with the evaluation circuit, wherein a clamping body ( 18 ) and a spring element ( 19 ) are integrally formed and in particular also integrally with a housing ( 1 ) of the device ( 0 ) are connected or formed on this. Device according to one of the two preceding claims, characterized in that the evaluation circuit for investigating a time course of a cooling behavior of the heating wire ( 21 ) when exposed to a constant measuring current (I _mess ) over measuring intervals (t _mess1 , t _mess2 ) of about 200 ms to about 800 ms, but preferably about 400 ms in length, is formed when determining value pairs of time and associated resistance , Device according to one of the preceding claims 3 to 5, characterized in that the evaluation circuit a Integrator includes.