DE102022128511A1 - Manufacturing, calibration and measurement correction procedures as well as inductive distance sensor - Google Patents

Abstract

Methods are proposed for the simplified manufacture and calibration of inductive distance sensors of a series of distance sensors, comprising a determination of fit parameters of a fit function which describes the relationship between an upper distance deviation as a function of the distance deviation at a maximum distance and a lower distance deviation as a function of the distance deviation at the maximum distance.

Description

The invention relates to a manufacturing, calibration and measurement value correction method for self-adjusting inductive distance sensors. Furthermore, the present invention relates to an inductive distance sensor that can be manufactured and calibrated accordingly.

Inductive distance sensors for determining a distance measurement value depending on the distance to a target object are well known from the state of the art. However, the distance measurement values determined by the known inductive distance sensors depend on the ambient temperature. This leads to a large thermal dependency, especially when determining distance measurement values for a large distance, which is why the determined distance measurement values have a temperature-related measurement error.

So far, it has not been possible to achieve a largely temperature-independent measurement operation through a robust design of the inductive distance sensors known from the state of the art. In order to achieve reliable measurement operation over a wide temperature range, it is known from the state of the art that during production each individual distance sensor is individually measured at the limits of a permissible temperature range in order to determine individual compensation parameters that allow the respective temperature-related measurement error to be compensated for in later measurement operation. Such individual compensation measures for all produced individual distance sensors of a certain distance sensor type or a series of distance sensors are time-consuming, since test measurements must be carried out at different ambient temperatures in order to determine the compensation parameters. This leads to high production costs.

The object of the present invention is to overcome the disadvantages known from the prior art. In particular, the object of the present invention is to provide a method and a correspondingly produced distance sensor in order to simplify the negative influence of temperature on the determined distance measurement values.

This object is achieved by the inventive manufacturing method according to claim 1, the inventive calibration method according to claim 8 and the inventive measured value correction method according to claim 9. Furthermore, the object is achieved by a distance sensor according to the invention according to claim 10.

Advantageous developments of the invention are described in the subclaims. The scope of the invention includes all combinations of at least two of the features disclosed in the description, the claims and/or the figures.

To avoid repetition, features disclosed according to the device should also be considered as disclosed according to the method and should be claimable. Likewise, features disclosed according to the method should also be considered as disclosed according to the device and should be claimable.

• Zunächst erfolgt das Bereitstellen eines ersten induktiven Distanzsensoren und wenigstens eines zweiten induktiven Distanzsensoren der Serie der Distanzsensoren, wobei jeder der induktiven Distanzsensoren eine Distanzbestimmungseinheit zum Bestimmen eines Distanzmesswerts in Abhängigkeit eines Abstandes zu einem Zielobjekt innerhalb eines definierten Messbereichs mit einer festgelegten Maximaldistanz und eine Temperaturabgleichseinheit zum temperaturbasierten Korrigieren des Distanzmesswerts innerhalb eines definierten Temperaturbereichs, der zwischen einer oberen Temperatur und einer unteren Temperatur festgelegt ist.

The calibration method according to the invention for inductive distance sensors of a series of distance sensors comprises the following method steps:

• First, a first inductive distance sensor and at least one second inductive distance sensor of the series of distance sensors are provided, wherein each of the inductive distance sensors has a distance determination unit for determining a distance measurement value as a function of a distance to a target object within a defined measuring range with a specified maximum distance and a temperature adjustment unit for temperature-based correction of the distance measurement value within a defined temperature range, which is set between an upper temperature and a lower temperature.

The measuring range extends up to a maximum distance and is fixed for the distance sensors and/or defined in advance. The maximum distance can preferably be taken from a corresponding data sheet. The inductive distance sensor can only determine the distance of the target object using the distance determination unit if the target object is within the measuring range. In other words, the target object can be detected at a maximum distance that corresponds to the maximum distance.

The temperature adjustment unit is designed for temperature-based correction of the distance measurement value within a defined temperature range. The temperature range extends between an upper and a lower temperature, wherein it is preferred if the upper temperature is positive and/or greater than 0°C and the lower temperature is negative and/or less than 0°C. The complete functionality of the distance sensor is only ensured within the temperature range, i.e. a distance measurement value determined within the scope of the present invention lies within guaranteed tolerances.

Furthermore, tempering means are provided for influencing the ambient temperature of the distance sensors in such a way that the ambient temperature corresponds at least to the upper temperature and/or the lower temperature and in particular to an average temperature, wherein the average temperature lies between the lower and the upper temperature.

The temperature control means are preferably designed as a hair dryer, in particular as a hot air dryer. Alternatively, the temperature control means are preferably also designed as a temperature control chamber and/or temperature test cabinet.

The temperature control devices make it possible to influence the ambient temperature of the respective distance sensor in order to carry out test measurements within the framework of the manufacturing process described here and the calibration procedure explained later.

Furthermore, the invention provides that the at least two distance sensors are positioned relative to the target object at a first test distance and at least a second test distance, wherein the test distances lie within the measuring range and the first test distance is selected to be greater than the at least second test distance.

In other words, the target object or the respective distance sensor is positioned at a first test distance and at a second test distance and possibly at further test distances.

Furthermore, according to the invention, a distance measurement value is determined by means of each of the at least two distance sensors at each of the at least two test distances at the upper, lower and middle temperatures.

In order to carry out the measurements at different temperatures, the respective distance sensors are tempered accordingly using the tempering agents.

Preferably, the mean temperature corresponds to the room temperature, which is why no temperature control by means of the temperature control means needs to be carried out when determining the distance measurement values at the first test distance and at least the second test distance at the mean temperature.

A further method step included according to the invention provides for determining an upper distance deviation for the first test distance and the at least second test distance. The upper distance deviation is determined by forming a difference between the determined distance measurement value at the upper temperature and the determined distance measurement value at the middle temperature, wherein the upper distance deviation is determined for each of the at least two distance sensors and for any test distances.

A further method step included in the present manufacturing method according to the invention provides for the determination of an upper fit function with at least one fit parameter for the upper distance deviation at the at least second test distance, and in particular at all further test distances, as a function of the upper distance deviation at the first test distance, in particular at the largest test distance, for the respective distance sensors;

In other words, an upper fit function with at least one fit parameter is determined for the upper distance deviation of the at least two distance sensors for the second test distance and possibly for further test distances, whereby the dependence of the second test distance and possibly of further test distances is each mapped to the upper distance deviation at the first - and thus largest - test distance;

According to the invention, it was recognized that the distance deviation for large distances is large compared to distance deviations for small distances. Therefore, the determined distance deviations for the second test distance and possibly for further test distances are standardized in relation to the largest distance deviation.

In other words, this method step includes determining an upper fit function, which has at least one fit parameter, for the second distance deviation of all distance sensors, such that for each of the at least two distance sensors, the second distance deviation is mapped as a function of the upper distance deviation at the first - and thus largest - test distance. Furthermore, an upper fit function, which has at least one fit parameter, for a third or fourth or further distance deviation of all distance sensors is determined, such that for each of the at least two distance sensors, the third or fourth or further distance deviation is mapped as a function of the upper distance deviation at the first - and thus largest - test distance.

Furthermore, the invention also provides for the determination of a lower distance deviation for all test distances by forming the difference between the determined distance measurement value at the lower temperature and the determined distance measurement value at the average temperature for each distance sensor.

According to the invention, a lower fit function is then determined with at least one fit parameter for the lower distance deviations at the at least second test distance for each of the at least two distance sensors as a function of the lower distance deviation at the first test distance for the respective distance sensor. Here, the procedure is similar to the upper distance deviation in order to determine the lower fit function.

This gives us an upper and a lower fitting function for the upper temperature and for the lower temperature for the second test distance. We also get an upper and a lower fitting function for each additional test distance.

Subsequently, according to the invention, the fit parameters and/or the upper and lower fit functions for each of the at least two test distances are stored in storage means, which are included in the temperature adjustment unit, in all inductive distance sensors.

In summary, in the present invention, for a first selection of the distance sensors of the series of distance sensors, a distance measurement value is determined at the at least two test distances at the upper, middle and lower temperatures. From these determined distance measurement values, the upper and lower distance deviation of all distance sensors at the first test distance, the second test distance and further test distances can then be determined by forming the difference.

The upper fit functions can then be determined for the upper distance deviation at the second test distance - and possibly for each additional test distance. Furthermore, a lower fit function can be determined for the lower distance deviation at the second test distance - and possibly for each additional test distance.

The upper and lower fit functions are then stored in the storage means included in the respective temperature adjustment unit.

This first selection of distance sensors involves at least two distance sensors. In concrete terms, this means two sensors or three sensors or ten, twenty, thirty or more distance sensors.

All other distance sensors, which include the fit functions stored in the storage means, are then calibrated only by a calibration method according to the invention, which will be explained in more detail later. For this purpose, a distance measurement value is determined using the respective distance sensor at the at least two test distances only at the middle temperature. For the upper and lower temperatures, within the scope of the present invention, only one distance measurement value needs to be determined for the first - and thus largest - test distance. From this, the applicable relationship for the other test distances can then be determined. According to the invention, this advantageously leads to a significant time saving.

In a further development, the manufacturing method according to the invention provides that the first test distance is selected such that it is in the range of 20% below the maximum distance and the maximum distance, wherein preferably the first test distance corresponds to the maximum distance.

In the context of further development, the upper and lower fitting functions correspond to a linear approximation.

It was recognized that if at least two or more distance sensors are measured and the determined values of the upper or lower distance deviation are mapped as a function of the respective greatest distance, a linear relationship results.

The linear relationship between the upper and lower distance deviation (D _x ) can be described for the second test distance (X=2) as follows: $${\text{D}}_2\left(\text{D1}\right)={\text{a}}_2{\text{<figure-callout id="1" label="D" filenames="DE102022128511A1\_0006.png" state="{{state}}">D</figure-callout>}}_1+{\text{<figure-callout id="2" label="b" filenames="DE102022128511A1\_0006.png" state="{{state}}">b</figure-callout>}}_2$$

D2

obere bzw. untere Distanzabweichung an der zweiten Testdistanz

a2

Steigung als Fitparameter

D1

obere bzw. untere Distanzabweichung an der ersten Testdistanz

b2

y-Achsenabschnitt als Fitparameter,

The respective D ₂ values can thus be determined from the previously determined value for the first test distance. The following applies:

D2

upper or lower distance deviation at the second test distance

a2

Slope as a fit parameter

D1

upper or lower distance deviation at the first test distance

b2

y-intercept as fit parameter,

This linear relationship can be used to determine the upper and lower distance deviations of other distance sensors from individual measurements. This means that each individual distance sensor does not have to be measured during production.

Alternatively, the fit function can also be formed by a quadratic approximation. Depending on the sensor type and/or the defined temperature range and/or the specified measuring range, the assignment rule, which can be determined from the individual upper and lower distance deviations for the second test distance and further test distances, can also have a quadratic relationship.

Furthermore, it is provided in a further development that the current ambient temperature (Tact) is determined by a temperature sensor included in the distance sensor, in particular a temperature sensor, or that the current ambient temperature (Tact) is read out via an external temperature sensor using an interface included in the distance sensor (3). The current temperature can thus advantageously be determined precisely, with an average between the upper and lower fit function being able to be implemented by interpolation. This advantageously makes it possible to further reduce the negative effects of the temperature on a determined distance measurement value.

As part of a further development, the lower temperature is selected such that it is in the range of the lowest temperature of the temperature range and at most 20% above the lowest temperature of the temperature range, with the lower temperature preferably corresponding to the lowest temperature of the temperature range. Furthermore, in this context it is also provided that the upper temperature is selected such that it is in the range of the highest temperature of the temperature range and at most 20% of the temperature range below the highest temperature of the temperature range, with the upper temperature preferably corresponding to the highest temperature of the temperature range.

In a further development, it is provided that at least two distance sensors, preferably all distance sensors to be measured, are mounted on a holder for carrying out the method for producing inductive distance sensors. The holder thus advantageously includes the individual test distances for which the distance measurement values are to be determined. Furthermore, the holder is preferably designed in such a way that it is also operatively connected to the temperature control means in order to influence the ambient temperature.

• Zunächst erfolgt das Bereitstellen eines induktiven Distanzsensors der Serie von Distanzsensoren, wobei anschließend das Bestimmen des jeweiligen Distanzmesswerts für den jeweiligen Distanzsensoren an den wenigstens zwei Testdistanzen bei der mittleren Temperatur erfolgt.

Furthermore, within the scope of the present invention, protection is also claimed for a calibration method for an inductive distance sensor from the series of distance sensors that were produced in particular according to the manufacturing method according to the invention. The calibration method according to the invention comprises the following steps:

• First, an inductive distance sensor from the series of distance sensors is provided, followed by determining the respective distance measurement value for the respective distance sensors at the at least two test distances at the average temperature.

Preferably, activation of the tempering agents is not necessary here, since the average temperature is room temperature, in particular 25°C.

Subsequently, according to the invention, the respective distance measurement value for the respective distance sensor is determined at the first - and thus largest - test distance at the upper temperature and at the lower temperature.

These determined distance measurements are then preferably stored in the storage means of the temperature adjustment unit.

• Auswerten eines aktuellen Temperaturmesswerts Tact eines internen Temperatursensors oder eines über eine Schnittstelle verbundenen externen Temperatursensors zum Festlegen eines hinsichtlich der mittleren Temperatur unteren Arbeitsbereichs oder oberen Arbeitsbereichs des Distanzsensors;

Furthermore, within the scope of the present invention, protection is also claimed for a measured value correction method for an inductive distance sensor of the series of distance sensors, wherein the distance sensor was previously calibrated using the calibration method according to the invention. The measured value correction method according to the invention comprises the following steps:

• Evaluating a current temperature measurement value Tact of an internal temperature sensor or an external temperature sensor connected via an interface to determine a lower working range or upper working range of the distance sensor with regard to the average temperature;

Select the upper or lower fitting function depending on the upper or lower working range.

In other words, in this step, either the upper or the lower fitting function should be selected depending on the current temperature for the stored mean temperature. It should be noted that the mean temperature was used in the calibration process when creating the complete measurement curve.

Determining corrected distance measurement values by correcting the distance measurement values determined with the distance determination unit at the average temperature, in particular the test distances at the average temperature, depending on the distance deviation at the first test distance and the respective upper or lower fit function; It is pointed out that these distance measurement values at the average temperature are within the scope of the calibration process according to the invention. These values were determined for each individual distance sensor in the calibration process and stored in each distance sensor, in particular in the storage means provided, in order to correct them with regard to the current ambient temperature.

This process step is preferably carried out once and then stored as a constant in the storage means. It is therefore not necessary for the corrected distance measurement values to be determined multiple times in the measurement value correction process, which has a positive effect on the computing time.

In other words, the distance values recorded at the mean temperature at the respective test distances are corrected at the upper or lower temperature depending on the fit function and the maximum test distance, in particular the first test distance X1.

The temperature-compensated distance measurements are now calculated from the determined test distance values at the middle temperature and the corrected distance measurements at the upper and lower temperatures depending on the current temperature (Tact).

Depending on these temperature-compensated distance measurements and the current measuring distance, the current temperature-compensated measuring distance is calculated, in particular by means of interpolation.

Through interpolation, the required correction values can be calculated approximately for any temperature value within the permissible temperature range and for any distance measurement value within the permissible measurement range. This makes it possible to determine the respective temperature-compensated distance measurement value using the stored fit functions;

As part of the measurement value correction process, various interpolation steps are carried out. First, an interpolation is carried out between the current ambient temperature and the upper and middle or lower and middle temperature in order to interpolate the measurement curves in relation to the current temperature. An interpolation is also carried out with regard to the current measurement value in order to interpolate it in relation to the recorded test distances. In this way, the current measurement distance can be determined.

• Eine Distanzbestimmungseinheit zum Bestimmen eines Distanzmesswerts in Abhängigkeit eines Abstandes zu einem Zielobjekt, wobei das Zielobjekt innerhalb eines Messbereichs positionierbar ist. Der Messbereich erstreckt sich bis zu einer festgelegten Maximaldistanz. Die Maximaldistanz wurde im Vorfeld festgelegt. Bevorzugt kann die Maximaldistanz aus einem Datenblatt ausgelesen werden.

Finally, within the scope of the present invention, protection is also claimed for an inductive distance sensor for determining a distance, wherein the distance sensor according to the invention was produced in particular by the production method according to the invention and comprises the following:

• A distance determination unit for determining a distance measurement value depending on a distance to a target object, whereby the target object can be positioned within a measuring range. The measuring range extends up to a specified maximum distance. The maximum distance was specified in advance. Preferably, the maximum distance can be read from a data sheet.

The distance determination unit preferably further comprises at least one coil to determine the distance to the target object.

A temperature adjustment unit for temperature-based correction of the distance measurement value within a defined temperature range set between an upper and a lower temperature.

In addition, storage means, which are specifically included in the temperature adjustment unit, for storing the fit parameters and/or the upper and lower fit functions for each of the at least two test distances.

According to the invention, the temperature adjustment unit is designed such that an adjustment of the recorded distance measurement values can be carried out by means of interpolation, such that the fit parameters and/or the upper and lower fit functions are used.

Examples of implementation:

• 1: eine schematische Darstellung eines erfindungsgemäßen Distanzsensors einer Serie von Distanzsensoren nach einem bevorzugten Ausführungsbeispiel;
• 2: eine perspektivische Ansicht einer Halterung zum Positionieren von mehreren Distanzsensoren, um Messungen zum Bestimmen eines Distanzmesswerts durchzuführen;
• 3a/b: jeweils Darstellungen des Drift-Verhaltens mehrerer Distanzsensoren der Serie von Distanzsensoren bei einer unteren und einer oberen Temperatur jeweils im Vergleich zu einer mittleren Temperatur sowie
• 4a-d: grafische Darstellungen der ermittelten Distanzabweichung für eine zweite und eine dritte Testdistanz in Abhängigkeit der Distanzabweichung bei der ersten Testdistanz, um für diese Testdistanzen eine obere und eine untere Distanzabweichung zu bestimmen.

Embodiments of the invention are shown in the drawings and are explained in more detail below with further details and advantages. In detail:

• 1 : a schematic representation of a distance sensor according to the invention of a series of distance sensors according to a preferred embodiment;
• 2 : a perspective view of a holder for positioning several distance sensors to perform measurements to determine a distance measurement value;
• 3a /b: representations of the drift behavior of several distance sensors of the series of distance sensors at a lower and an upper temperature, each compared to a mean temperature and
• 4a -d: graphical representations of the determined distance deviation for a second and a third test distance depending on the distance deviation at the first test distance in order to determine an upper and a lower distance deviation for these test distances.

The 1 shows the schematic structure of an inductive distance sensor 3 according to a first embodiment. The distance sensor 3 comprises a distance determination unit 2 with an LC resonant circuit 11, having a coil 12 and a capacitor 13. The LC resonant circuit 11 is excited by an oscillator 14, which is also included in the distance determination unit 2, by means of a high-frequency control current.

A target object to be detected influences the oscillation that develops in the oscillating circuit 11, since the inductance of the coil 12 changes depending on the distance of the target object. This change in the amplitude and/or frequency of the oscillation can be determined in particular via a measuring voltage, so that a sensor signal S can be indirectly generated that represents the distance of the target object from the distance sensor 3.

The illustrated embodiment of the distance sensor 3 further comprises an integrated temperature sensor 7 to detect the current ambient temperature Tact of the distance sensor 3.

Furthermore, the distance sensor 3 has a temperature adjustment unit 4, which receives the sensor signal S of the distance determination unit 2 and the current ambient temperature Tact from the temperature sensor 7 as input variables.

In the temperature adjustment unit 4, the sensor output data O is generated, which represents the temperature-corrected distance measurement value to be determined by the distance sensor 3. The sensor output data O can then be further processed in an external application.

The temperature adjustment unit 4 also has storage means 10. According to the invention, the distance measurement values are adjusted by the temperature adjustment unit 4 with regard to the temperature-related drift. Therefore, the storage means 10 comprise an assignment rule for temperature-based calibration and/or production of the distance measurement values, which can be generated by standardization from the sensor signal S in order to generate distance measurement values compensated with regard to the current ambient temperature Tact as sensor output data O.

The assignment rule stored in the storage means 10 comprises at least one upper and one lower fit function, each of which comprises at least one fit parameter and was generated within the scope of the manufacturing method according to the invention.

Preferably, the individual fit parameters are stored in a look-up table in the storage means 10. Using the assignment rule, the temperature adjustment unit 4 calculates the deviation of the determined distance measurement value from the distance measurement value at the average temperature from the measured temperature Tact and thus determines a temperature-compensated distance measurement value as the sensor output variable O.

• Zunächst wird der aktuelle Temperaturmesswert Tact, der mittels des internen Temperatursensors 7 ermittelt wurde, erfasst und mit der hinterlegten mittleren Temperatur verglichen, um somit einen unteren oder einen oberen Arbeitsbereich des Distanzsensors 3 zu wählen.

Specifically, the temperature adjustment unit 4 is set up so that the measured value correction method according to the invention can be carried out. The measured value correction method according to the invention comprises the following processing steps:

• First, the current temperature measurement value Tact, which was determined by means of the internal temperature sensor 7, is recorded and compared with the stored average temperature in order to select a lower or an upper working range of the distance sensor 3.

When activating the lower working area, the at least one lower fit function is used. When activating the upper working area, the at least one upper fit function is used. All fit functions were generated within the scope of the inventive manufacturing method for a specific series of the inventive distance sensors and stored on the storage means 10.

Subsequently, corrected distance measurement values are determined by correcting the test distance measurement values stored in the storage means 10, which were determined in advance at the average temperature, depending on the first distance and the upper or lower fit function.

This is followed by determining the temperature-compensated distance measurement value O, which depends on the current temperature Tact and the previously determined corrected distance measurement values.

An approximation method, in particular interpolation, is used to calculate the corresponding values in order to map the current ambient temperature from the upper temperature range or the lower temperature range. In addition, further interpolation is carried out in order to approximately determine all distance measurement values that lie between the measured test distances.

In summary, a computational temperature compensation is proposed, which uses determined compensation data and determined fit functions, whereby an approximation to intermediate values with regard to temperature and position is carried out by means of interpolation.

The temperature-compensated distance measurement value O is then output on the output side. This is also fed to a control or regulating device and/or a display device, which is shown here as an external unit 16.

The fit parameters and/or the upper and lower fit functions are determined during sensor manufacture and/or sensor calibration and stored in the respective distance sensor 3 so that the output-side distance measurement values O can be temperature compensated with respect to the current temperature Tact.

The 2 shows a holder 1 designed as a mounting plate 15 with several slots 17 in order to position an inductive distance sensor 3 on each slot 17.

By means of a holding attachment 18, a target object 6 is attached at a precisely predetermined distance relative to each of the distance sensors 3, so that during a measuring process of the distance sensor 3, a distance measurement value can be generated at a defined distance.

The entire holder 1 with the distance sensors 3 and the pre-assembled target objects 6 can be placed in a temperature chamber as part of the manufacturing method according to the invention, so that the sensor-target arrangement operates at a temperature T predetermined by the temperature chamber. The ambient temperature of the distance sensors 3 can thus advantageously be influenced.

The holder 1 comprises a total of sixteen slots 17, with six distance sensors each arranged graphically on one slot 17. Furthermore, a holding attachment 18 is shown for each of the two distance sensors 3, which allows the precise positioning of a target object 6.

The temperature control chamber thus forms the temperature control means 5 in order to produce and/or calibrate up to sixteen distance sensors 3 simultaneously.

By determining distance measurement values using the distance sensors 3, their temperature dependence can be recorded and thus compensated.

The holder 1 advantageously makes it possible to carry out a thermal investigation for several distance sensors 3 simultaneously, which is why time can be saved with regard to the production of the inductive distance sensors 3.

The holder 1 not only has slots 17, but also includes conductor tracks, electronics for reading the distance measurement values and a temperature sensor for recording the current ambient temperature Tact. The temperature sensor is connected to all distance sensors 3 via an interface in order to transmit the current ambient temperature Tact, which is influenced by the temperature chamber and recorded by the temperature sensor.

The holder 1 can thus be used within the scope of the manufacturing method according to the invention and/or the calibration method according to the invention in order to simultaneously manufacture and/or calibrate several distance sensors.

Within the scope of the inventive manufacturing method for inductive distance sensors 3 of a series of distance sensors, at least two distance sensors 3 are positioned relative to a target object 6 by means of a holding attachment 18. The at least two distance sensors 3 can be positioned on the slots 17 for this purpose, wherein in addition to a mechanical alignment, an energetic and a communicative coupling of the individual distance sensors 3 also takes place.

Advantageously, a distance measurement value can thus be determined for each of the distance sensors 3, whereby 18 different test distances X1, X2, X3 can be realized by using different holding attachments.

Specifically, the determination of a distance measurement value in the manufacturing method according to the invention takes place at least at a first test distance X1 and a second test distance X2. However, it is preferred if at least three test distances are measured in the context of the manufacturing method according to the invention.

Advantageously, distance measurements can be determined at an upper temperature, a lower temperature and an average temperature.

In the embodiment now described, the upper temperature corresponds to 90°C, the lower temperature to -35°C and the middle temperature to 25°C.

Thus, a measurement curve can be recorded for each of the at least two distance sensors 3 at the three temperatures.

An upper and a lower distance deviation are then determined from the individual measurement curves. To determine the upper distance deviation, the determined distance measurement value at the upper temperature is subtracted from the determined distance measurement value at the middle temperature for each test distance. To determine the lower distance deviation, the determined distance measurement value at the lower temperature is subtracted from the determined distance measurement value at the middle temperature for each test distance.

In the 3a is the lower distance deviation and in the 3b the upper distance deviation, which can be determined from several individual measurements.

A total of 40 distance sensors 3 were measured over the entire measuring range, which extends up to a maximum distance X _max . In this embodiment, the distance deviation is available as a 16-bit value. The distance deviation thus extends in a range from 0 to 65535.

From the comparison of the individual measurement curves in the 3a It can be seen that the scatter of the lower distance deviation increases with increasing distance of the target object 6 from the respective distance sensor 3. In other words, at the lower temperature of -35°C, an increasing scatter occurs between the individual distance sensors 3 with increasing distance, which can be attributed to the low temperature. Furthermore, it was recognized within the scope of the invention that this characteristic curve can be approximately reproduced by selecting at least 2 test distances. The position of the first test distance X1, the second test distance X2 and a third test distance X3 is entered on the X-axis as an example.

Also from the 3b It can be seen that the scatter of the upper distance deviation of the individual distance sensors is particularly evident at a large distance.

In summary, it can be determined from the course of the lower and upper distance deviation that for small distances to be measured, which in this case are approximately in the range of nine millimeters, the temperature-related deviations due to drift are very small, i.e. close to 0.

For a distance to be measured of sixteen millimeters, which in this case corresponds to the maximum distance X _max , the deviations due to drift are significantly higher.

It is therefore advantageous to carry out calibration measurements for temperature compensation when large distances are to be measured.

After the lower and upper distance deviations have been determined for at least two test distances, the invention now provides that a lower fit function is determined for each test distance, which maps the lower distance deviation at the respective test distance as a function of the lower distance deviation at the first test distance. Furthermore, an upper fit function is also determined accordingly, which maps the upper distance deviation at the respective test distance as a function of the upper distance deviation at the first test distance.

Thus, all test distances X2, X3 with the exception of the first and therefore largest test distance are selected and the determined values of the upper distance deviation of all distance sensors are mapped as a function of the distance deviation at the first test distance.

This then results in the 4a to 4c , where the individual points represent the determined lower distance deviation ( 4a and 4b) and the determined upper distance deviation ( 4c and 4d ) of the 40 distance sensors 3 at the respective test distance. Each individual point is thus formed by one of the measured distance sensors.

The graphical representation of the individual values shows that all values can be described using a linear approximation function.

Specifically, for the second test distance X2, which is 14mm in this case, at a lower temperature of -35°C and an average temperature of 25°C after the 4a Determine the following straight line equation as the lower fitting function: $${\mathbf{D}}_2\left(D_1\right)=0,906{\mathbf{<figure-callout\; id="1"\; label="D"\; filenames="DE102022128511A1\_0006.png"\; state="\{\{state\}\}">D</figure-callout>}}_1-34,571.$$

bestimmen.Furthermore, for the second test distance X2 at an upper temperature of 90°C and an average temperature of 25°C, 4c the upper fit function to $${\mathbf{D}}_2\left(D_1\right)=0,\mathrm{8th}944{\mathbf{<figure-callout\; id="1"\; label="D"\; filenames="DE102022128511A1\_0006.png"\; state="\{\{state\}\}">D</figure-callout>}}_1-31,2\mathrm{<figure-callout\; id="7"\; label="8th"\; filenames="DE102022128511A1\_0006.png"\; state="\{\{state\}\}">8th</figure-callout>}7$$

determine.

und für die untere Temperatur nach der 4b $${\mathbf{D}}_3\left(D_1\right)=0,4583{\mathbf{D}}_1-90,907$$

bestimmen.For the third test distance X3, which in this case is a distance between target object 6 and distance sensor 3 of 9mm, can be used for the selected upper temperature according to the 4d as upper fitting function $${\mathbf{D}}_3\left(D_1\right)=0,421\mathrm{<figure-callout\; id="1"\; label="8th\; D"\; filenames="DE102022128511A1\_0006.png"\; state="\{\{state\}\}">8th</figure-callout>}{\mathbf{D}}_{}{\mathbf{}}_1-\mathrm{8th}\mathrm{8th},592$$

and for the lower temperature after the 4b $${\mathbf{D}}_3\left(D_1\right)=0,45\mathrm{8th}3{\mathbf{<figure-callout\; id="1"\; label="D"\; filenames="DE102022128511A1\_0006.png"\; state="\{\{state\}\}">D</figure-callout>}}_1-90,907$$

determine.

The fit parameters are thus obtained in order to carry out a calibration by determining and storing the assignment rule for each distance sensor in a series in a further process step. The determined fit functions or their fit parameters are then stored in the storage means 10.

These parameters can then be used in the calibration process according to the invention, which is why for all subsequent distance sensors the distance measurement values only need to be determined at the middle temperature for all test distances. For the upper and lower temperatures, however, the distance measurement value only needs to be determined at the first test distance.

As a result, the present invention makes it possible to significantly simplify the calibration of distance sensors in a series of distance sensors, which is why a time advantage can be achieved in the manufacture and/or calibration of the distance sensors. Furthermore, the complexity of the calibration device can also be significantly reduced. A cost advantage is thus achieved by the present invention.

Claims (10)

Manufacturing method for inductive distance sensors (3) of a series of distance sensors (3) with the following method steps: - Providing at least two inductive distance sensors (3) of the series of distance sensors (3), wherein each of the inductive distance sensors (3) ◯ a distance determination unit (2) for determining a distance measurement value as a function of a distance (X1, X2, X _max ) to a target object (6) within a defined measuring range with a specified maximum distance (X _max ) and ◯ a temperature adjustment unit (4) for temperature-based correction of the distance measurement value within a defined temperature range which is set between an upper temperature (To) and a lower temperature (Tu); - Providing temperature control means (5) for influencing the ambient temperature (Tact) of the distance sensors (3) such that the ambient temperature (Tact) corresponds at least to the upper temperature (To) and/or the lower temperature (Tu) and in particular to an average temperature (Tm), wherein the following applies to the average temperature: Tu < Tm < To. - Positioning the at least two distance sensors (3) relative to the target object (6) at a first test distance (X1) and at least one second test distance (d2), wherein the test distances lie within the measuring range and the first test distance (X1) is selected to be greater than the at least one second test distance (X2, X3); - Determining a distance measurement value (X1_To; X2_To; X1_Tu; X2_Tu; X1_Tm; X2_Tm) for each of the at least two distance sensors (3) at the at least two test distances (X1, X2) at the upper temperature (To), the lower temperature (Tu) and an average temperature (Tm), the average temperature (Tm) corresponding in particular to room temperature; - Determining an upper distance deviation (D2) for the respective test distances (X1, X2) by forming the difference between the determined distance measurement value at the upper temperature (X1_To; X2_To) and the determined distance measurement value at the average temperature (X1_Tm; X2_Tm) for each of the at least two distance sensors (3); - Determining an upper fit function with at least one fit parameter for the upper distance deviation at the at least second test distance as a function of the upper distance deviation at the first test distance for the respective distance sensor; - Determining a lower distance deviation (D ₂ ) for the respective test distances X1, X2) by forming the difference between the determined distance measurement value at the lower temperature (X1_Tm; X2_Tm) and the determined distance measurement value at the middle temperature (X1_Tm; X2_Tm); - Determining a lower fit function with at least one fit parameter for the lower distance deviations at the at least second test distance for each of the at least two distance sensors as a function of the lower distance deviation at the first test distance for the respective distance sensor; - Storing the fit parameters and/or the upper and lower fit function for each of the at least two test distances in storage means (10), which are included in the temperature adjustment unit (4), in all inductive distance sensors (3). Procedure according to Claim 1 , characterized in that the first test distance (X1) is selected such that it is in the range of 20% below the maximum distance (X _max ) and the maximum distance (X _max ), wherein preferably the first test distance (X1) corresponds to the maximum distance (X _max ). Method according to one of the preceding claims, characterized in that the upper and lower fitting functions correspond to a linear approximation. Procedure according to Claim 1 or 2 , characterized in that the fitting function corresponds to a quadratic approximation. Method according to one of the preceding claims, characterized in that the current ambient temperature (Tact) is determined by a temperature sensor (7) included in the distance sensor (3) or that the current ambient temperature (Tact) is read out via an external temperature sensor by means of an interface included in the distance sensor (3). Method according to one of the preceding claims, characterized in that the lower temperature (Tu) is selected such that it lies in the range of the lowest temperature of the temperature range and at most 20% above the lowest temperature of the temperature range, wherein preferably the lower temperature corresponds to the lowest temperature of the temperature range and the upper temperature is selected such that it lies in the range of the highest temperature of the temperature range and at most 20% of the temperature range below the highest temperature of the temperature range, wherein preferably the upper temperature corresponds to the highest temperature of the temperature range. Method according to one of the preceding claims, characterized in that at least two distance sensors (3), preferably all distance sensors (3) to be measured are mounted on a holder (1) for carrying out the method for producing inductive distance sensors (3). Calibration method for an inductive distance sensor (3) from a series of distance sensors (3), which is in particular designed according to one of the Claims 1 until 7 was manufactured, comprising the following steps: - providing an inductive distance sensor (3) of the series of distance sensors (3); - determining the respective distance measurement value (X1_Tm; X2_Tm) for the distance sensors (3) at the at least two test distances (X1, X2) at the average temperature (Tm); - determining the respective distance measurement value (X1_To, X1_Tu) for the distance sensors (3) at the first test distance (X1) at the upper (To) and the lower temperature (Tu); Measured value correction method for an inductive distance sensor (3) which is calibrated using the calibration method according to Claim 8 was calibrated, with the following steps: - evaluating a current temperature measurement value (Tact) of an internal temperature sensor (7) or an external temperature sensor connected via an interface to determine a lower or upper working range of the distance sensor (3) with regard to the average temperature (Tm); - selecting the upper or lower fit function depending on the upper or lower working range; - correcting the distance measurement values determined with the distance determination unit (2) at the average temperature (Tm) depending on the distance deviation at the first test distance and the respective upper or lower fit function; - determining a temperature-compensated distance measurement value depending on the current temperature (Tact) and the corrected distance measurement values and the current distance measurement value. Inductive distance sensor (3) for determining a distance, wherein the distance sensor (3) is designed in particular according to one of the Claims 1 until 8th was manufactured, comprising - a distance determination unit (2) for determining a distance measurement value as a function of a distance to a target object (6) that can be positioned within a measuring range with a specified maximum distance (X _max ), wherein the distance determination unit (2) in particular comprises at least one coil (12) to determine the distance to the target object, - a temperature adjustment unit (4) for temperature-based correction of the distance measurement value within a defined temperature range that is set between an upper and a lower temperature (To, Tu); - storage means (10) that are included in the temperature adjustment unit (4) for storing, - wherein the temperature adjustment unit (4) is designed such that an adjustment of the detected distance measurement values can be carried out by at least one interpolation, wherein the fit parameters and/or the upper and lower fit functions are used.

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