WO1986007145A1 - Sensor arrangement - Google Patents

Sensor arrangement Download PDF

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Publication number
WO1986007145A1
WO1986007145A1 PCT/DE1986/000181 DE8600181W WO8607145A1 WO 1986007145 A1 WO1986007145 A1 WO 1986007145A1 DE 8600181 W DE8600181 W DE 8600181W WO 8607145 A1 WO8607145 A1 WO 8607145A1
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WO
WIPO (PCT)
Prior art keywords
coil
measuring
measuring tube
sensor arrangement
arrangement according
Prior art date
Application number
PCT/DE1986/000181
Other languages
German (de)
French (fr)
Inventor
Klaus Dobler
Hansjörg Hachtel
Karl Roll
Original Assignee
Robert Bosch Gmbh
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Publication of WO1986007145A1 publication Critical patent/WO1986007145A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
    • G01D5/2006—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils
    • G01D5/2013—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils by a movable ferromagnetic element, e.g. a core
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
    • G01D5/2006—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils
    • G01D5/202—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils by movable a non-ferromagnetic conductive element

Definitions

  • the invention is based on a sensor arrangement according to the type of the main claim.
  • the sensor consists of a measuring tube and a coil which is wound in one layer and uniformly on a core and is connected to a voltage divider or bridge circuit.
  • This results in an S-shaped calibration curve.
  • their flattening at the beginning and at the end falsifies the measurement result.
  • It is known to linearize the course of the calibration curve with the aid of amplifiers whose amplification factor changes as a function of the input voltage level.
  • each individual sensor type is assigned a specially adapted electronics unit.
  • the amplification factor in electronic units designed in this way is relatively strongly dependent on the level of the ambient temperature because of the necessary connection with non-linear resistors.
  • the sensor arrangement according to the invention with the characterizing features of the main claim has the opposite partly that the calibration curve is almost linear over the entire measuring range. There is therefore always a proportional relationship between the measurement signal change ( ⁇ U M ) and the change in immersion depth ( ⁇ S) of the coil in the measuring tube. This is possible with the help of simple structural measures. Furthermore, even with a constant amplification factor over the almost entire measuring range, ie over the entire coil length, a sufficiently precise proportional measuring voltage (U M ) can be generated at the output of the evaluation circuit.
  • FIG. 1 shows a circuit representation of the exemplary embodiment
  • FIG. 2 shows a section through a sensor arrangement in a simplified representation
  • FIG. 3 shows a non-linear calibration curve according to the prior art
  • FIGS. 4, 5 and 6 each show a modification of the exemplary embodiment according to FIG. 2.
  • FIG. 1 shows an evaluation circuit in which an alternating current generator 10 feeds a measuring coil 11 with a high-frequency alternating current.
  • the measuring coil 1 1 is connected to the series resistor 13 to form a voltage divider 14.
  • a resistor 12 is connected in parallel with the measuring coil 11.
  • a diode 15 is connected in series with the series resistor 13.
  • a capacitor 16 is connected in parallel with the resistor 12.
  • Low-pass filter 19 is connected to the tap of the voltage divider 14 for smoothing the measured values.
  • a conventionally known amplifier circuit 20, which has two resistors 21, 22 and an operational amplifier 23, is connected in series with the low-pass filter 19.
  • a metallic measuring core 26 is shown, which is movable in a measuring tube 27.
  • the measuring tube 27 consists of a tubular carrier element 28, 28a made of non-electrically conductive material and an external tubular body 29.
  • the measuring coil 11 is wound in one layer on the carrier element 28.
  • the inner wall of the tubular body 29 has a central cylindrical region 29b and then two conically widening end regions 29a, 29c.
  • the end region 29a is longer than the end region 29c. This results in different radial distances Y between the measuring coil 11 and the inner wall of the tubular body 29.
  • the measuring coil 11 and the tubular body 29 are arranged in a fixed position relative to one another.
  • the measuring core 26 plunges into the measuring tube 27 and thus into the measuring coil 11, ie the measuring coil 11 and the measuring core 26 are moved relative to one another. Because of the eddy current effect, the alternating current resistance of the measuring coil 11 changes. Eddy currents are formed on the electrically highly conductive surface of the inner wall of the tubular body 29 facing the measuring coil 11, which change the alternating current resistance of the measuring coil 11 and thus the applied voltage, ie the measuring coil 11 becomes subdued. This eddy current formation is - provided a homogeneous magnetic field of the measuring coil - dependent on the size of the air gap, ie on the size of the distance Y.
  • the S-shaped calibration curve 30 shown in FIG. 3 is obtained without damping the coil by the tubular body 29 and shows the course of the applied measuring voltage U M over the immersion depth S of the measuring core in the measuring coil.
  • the flattenings at the beginning and at the end of the calibration curve 30 are caused by the linearity error of the voltage divider 14 or bridge circuit and by the inhomogeneous magnetic field of the measuring coil. This inhomogeneous magnetic field of the measuring coil is due to the lower formation of the magnetic field at the two ends of the measuring coil.
  • the windings of the left and right half of the coil work together to generate the alternating magnetic field, whereas, at the end of the measuring coil, either the windings on the left or right thereof are missing. These deviations from the homogeneity are greater the closer you get to the two coil ends. If the air gap to the measuring tube 27 is enlarged in the two end regions of the measuring coil compared to the central region, the eddy current formation in the end regions is reduced, so that the measuring coil is less damped by the tubular body 29 in the end regions. The measuring coil 11 is therefore less damped in the end regions 29a, 29c with the low magnetic field than in the middle region 29b with the high magnetic field.
  • the magnetic field of the measuring coil 11 can be influenced to such an extent that both the linearity errors of the voltage divider 14 or bridge circuit and the measuring errors of the coil 11 caused by the usually inhomogeneous magnetic field are compensated for.
  • FIG. 4 shows a modification of the exemplary embodiment according to FIG. 2.
  • the measuring coil 11 is wound on a sleeve 35 made of non-electrically conductive material, which is movable in a metallic measuring tube 36.
  • the meas tube 36 has a uniform inner diameter over its entire length.
  • the sleeve 35 has a central region 35b with the same wall thickness and two end regions 35a, 35c which reinforce conically towards the ends of the sleeve 35, so that the openings of the sleeve 35 are reduced.
  • the end region 35c which is first inserted into the measuring tube 36, is shorter than the other end region 35a and has a larger diameter at the end of the sleeve 35.
  • the sleeve 35 is arranged on a metallic core 37, which has the same function as the tubular body 29 in FIG. 2.
  • the measuring coil 11 If the measuring coil 11 is immersed in the measuring tube 36 with the sleeve 35 and the core 37 arranged fixed to it, the measuring coil 11 generates eddy currents on the surface of the core 37 which change the AC resistance of the measuring coil 11. Since in the area 35a, 35c this surface of the core 37 is further away from the measuring coil 11, the eddy current formation in these areas is also less than in the area 35b. As already described above, the measuring coil 11 is damped differently, so that a linear calibration curve is produced at the output of the evaluation circuit.
  • the measuring coil 11 is preferably wound in one layer on a core 40, preferably made of non-electrically conductive material, which is movable in a metal measuring tube 41.
  • the measuring tube 41 itself has a uniform inner diameter over its entire length.
  • a sleeve 42 or 43 made of metallic material is arranged on the inner wall of the measuring tube 41.
  • 3 eide sleeves 42, 43 are conical and each taper towards the opening of the measuring tube 41.
  • the opening diameter of the measuring tube is smaller than its inner diameter in the area Ula between the two sleeves k 2, 43.
  • the sleeve 42 can be made shorter than the sleeve 43. Both Sleeves 42, 43 have approximately the same opening diameter.
  • the S-shaped characteristic curve shown in FIG. 3 is based on the change in the AC resistance of the measuring coil due to the known eddy current effect.
  • the formation of the eddy currents on the metallic inside of the measuring tube 41 can be changed by the sleeves 42, 43 so that the calibration curve in FIG. 3 is almost linear. If the measuring core 40 with the measuring coil 11 is now immersed in the measuring tube 41, the distance Y between the measuring coil 11 and the inside of the measuring tube 41 increases due to the sleeve 42, the deeper the measuring core 40 penetrates into the measuring tube 41. Corresponding to this change in the distance Y, based on the eddy current formation in the measuring tube 41 with a constant inner diameter, more eddy currents are generated.
  • the measuring coil 11 is damped differently and thus the calibration curve is linearized. If the measuring core 40 is located in the region 41a of the measuring tube 41 with a constant inner diameter, i.e. Without an additional sleeve 42, 43, a linear calibration curve is also generated.
  • FIG. 6 shows a reversal of the embodiment of Figure 5.
  • B. PVC, Plexiglas tubular body 45, the measuring coil 11 is wound.
  • a metallic sleeve 47 or 48 is arranged on the metallic measuring core 46 at both ends. Both sleeves 47, 48 are designed to expand conically towards the respective ends of the measuring core 1 + 6.
  • the sleeve 47 which first dips into the tubular body 45, can be shorter than the sleeve 48. Between the two sleeves 47, 48 there is again a region 46a with a constant diameter.
  • the mode of operation when the measuring core 46 is immersed in the tubular body 45 is described analogously to that in FIG. 5.
  • the sleeve 47 corresponds to the sleeve 42 and the sleeve 48 corresponds to the sleeve 43 in their mode of operation.
  • the sensor arrangement can also be operated using the inductive method. The same conditions apply accordingly.

Abstract

A measurement coil (11) is incorporated in a voltage divider circuit (14) or bridge circuit. It is wound on a carrier (28) which is a good electric insulator and is moved in relation to a measurement core (26). The carrier (28) is fixed in a stationary position on the inner wall (29) of a measurement tube (27). The inner wall (29), which is a good electrical conductor, has at the ends areas which preferably taper outwards (29a, 29c) so that the measurement coil (11) is attenuated in a different manner. The voltage recorded at the output of the circuits thus has a linear characteristic curve corresponding to the movement of the measurement coil (11) relative to the measurement tube (27). It is possible to balance out the linearity errors in the voltage divider circuit (14) or bridge circuit, as well as the measurement errors in the measurement coil (11) due to the inhomogeneous magnetic field.

Description

SensoranordnungSensor arrangement
Stand der TechnikState of the art
Die Erfindung geht aus von einer Sensoranordnung nach der Gattung des Hauptanspruchs. Bei einer bekannten Anordnung besteht der Sensor aus einem Meßrohr sowie einer Spule, die einlagig und gleichmäßig auf einen Kern gewickelt ist und in eine Spannungsteiler- oder Brückenschaltung geschaltet ist. Dabei ergibt sich eine S-förmige Eichkurve. Deren Abflachungen am Anfang und am Ende verfälschen aber das Meßergebnis. Es ist bekannt, mit Hilfe von Verstärkern, deren Verstärkungsfaktor sich abhängig von der Eingangsspannungshöhe ändert, den Verlauf der Eichkurve zu linearisieren. Dies hat jedoch den Nachteil, daß jedem einzelnen Sensortyp eine speziell dafür angepaßte Elektronikeinheit zuzuordnen ist. Ferner ist der Verstärkungsfaktor bei so konzipierten Elektronikeinheiten wegen der dazu notwendigen Beschaltung mit nicht linearen Widerständen relativ stark von der Höhe der Umgebungstemperatur abhängig.The invention is based on a sensor arrangement according to the type of the main claim. In a known arrangement, the sensor consists of a measuring tube and a coil which is wound in one layer and uniformly on a core and is connected to a voltage divider or bridge circuit. This results in an S-shaped calibration curve. However, their flattening at the beginning and at the end falsifies the measurement result. It is known to linearize the course of the calibration curve with the aid of amplifiers whose amplification factor changes as a function of the input voltage level. However, this has the disadvantage that each individual sensor type is assigned a specially adapted electronics unit. Furthermore, the amplification factor in electronic units designed in this way is relatively strongly dependent on the level of the ambient temperature because of the necessary connection with non-linear resistors.
Vorteile der ErfindungAdvantages of the invention
Die erfindungsgemäße Sensoranordnung mit den kennzeichnenden Merkmalen des Hauptanspruchs hat demgegenüber den Vor teil, daß die Eichkurve über den gesamten Meßbereich nahezu linear verläuft. Es besteht somit stets ein proportionales Verhältnis zwischen Meßsignalänάerung (Δ UM ) und Eintauchtiefenänderung (ΔS) der Spule in das Meßrohr. Dies ist mit Hilfe einfacher baulicher Maßnahmen möglich. Ferner kann auch bei einem konstanten Verstärkungsfaktor über den nahezu gesamten Meßbereich, d.h. über die gesamte Spulenlänge, eine hinreichend genaue proportionale Meßspannung (UM) am Ausgang der Auswerteschaltung erzeugt werden.The sensor arrangement according to the invention with the characterizing features of the main claim has the opposite partly that the calibration curve is almost linear over the entire measuring range. There is therefore always a proportional relationship between the measurement signal change (Δ U M ) and the change in immersion depth (ΔS) of the coil in the measuring tube. This is possible with the help of simple structural measures. Furthermore, even with a constant amplification factor over the almost entire measuring range, ie over the entire coil length, a sufficiently precise proportional measuring voltage (U M ) can be generated at the output of the evaluation circuit.
Durch die in den Unt eransprüchen aufgeführten Maßnahmen sind vorteilhafte Weiterbildungen und Verbesserungen der im Hauptanspruch angegebenen Merkmale möglich.Advantageous further developments and improvements of the features specified in the main claim are possible through the measures listed in the subclaims.
Zeichnungdrawing
Ein Ausführungsbeispiel der Erfindung ist in der Zeichnung dargestellt und in der nachfolgenden .Beschreibung näher erläutert. Es zeigen Figur 1 eine schaltungsgemäße Darstellung des Ausführungsbeispiels, Figur 2 einen Schnitt durch eine Sensoranordnung in vereinfachter Darstellung, Figur 3 eine nicht lineare Eichkurve nach dem Stand der Technik und die Figuren 4 , 5 und 6 je eine Abwandlung des Ausführungsbeispiels nach Figur 2.An embodiment of the invention is shown in the drawing and explained in more detail in the description below. 1 shows a circuit representation of the exemplary embodiment, FIG. 2 shows a section through a sensor arrangement in a simplified representation, FIG. 3 shows a non-linear calibration curve according to the prior art, and FIGS. 4, 5 and 6 each show a modification of the exemplary embodiment according to FIG. 2.
Beschreibung des AusführungsbeispielsDescription of the embodiment
In Figur 1 ist eine Auswerteschaltung dargestellt, in der ein Wechselstromgenerator 10 eine Meßspule 11 mit einem hochfrequenten Wechselstrom speist. Die Meßspule 1 1 ist mit dem Vorwiderstand 13 zu einem Spannungsteiler 14 verschaltet. Parallel zur Meßspule 11 ist ein Widerstand 12 geschaltet. In Reihe zum Vorwiderstand 13 liegt eine Diode 15. Ferner ist parallel zum Widerstand 12 ein Kondensator 16 geschaltet. Ein aus einem Widerstand 17 und einem Kondensator 18 bestehender Tiefpaß 19 ist zur Glättung der Meßwerte mit dem Abgriff des Spannungsteilers 14 verbunden. Ferner ist in Reihe zum Tiefpaß 19 eine herkömmlich bekannte Verstärkerschaltung 20 geschaltet, die zwei Widerstände 21, 22 und einen Operationsverstärker 23 aufweist.1 shows an evaluation circuit in which an alternating current generator 10 feeds a measuring coil 11 with a high-frequency alternating current. The measuring coil 1 1 is connected to the series resistor 13 to form a voltage divider 14. A resistor 12 is connected in parallel with the measuring coil 11. A diode 15 is connected in series with the series resistor 13. Furthermore, a capacitor 16 is connected in parallel with the resistor 12. One consisting of a resistor 17 and a capacitor 18 Low-pass filter 19 is connected to the tap of the voltage divider 14 for smoothing the measured values. Furthermore, a conventionally known amplifier circuit 20, which has two resistors 21, 22 and an operational amplifier 23, is connected in series with the low-pass filter 19.
In Figur 2 ist ein metallischer Meßkern 26 dargestellt, der in einem Meßrohr 27 beweglich ist. Das Meßrohr 27 besteht aus einem, aus nicht elektrisch leitfähigem Stoff bestehendem rohrförmigen Trägerelement 28, 28a und einem außenliegenden Rohrkörper 29. Auf dem Trägerelement 28 ist die Meßspule 11 einlagig gewickelt. Die Innenwand des Rohrkörpers 29 hat einen mittleren zylindrischen Bereich 29b und anschließend zwei sich konisch erweiternde Endbereiche 29a, 29c. Der Endbereich 29a ist länger als der Endbereich 29c. Somit ergeben sich unterschiedliche radiale Abstände Y zwischen Meßspule 11 und der Innenwand des Rohrkörpers 29. Die Meßspule 11. und der Rohrkδrper 29 sind ortsfest zueinander angeordnet.In Figure 2, a metallic measuring core 26 is shown, which is movable in a measuring tube 27. The measuring tube 27 consists of a tubular carrier element 28, 28a made of non-electrically conductive material and an external tubular body 29. The measuring coil 11 is wound in one layer on the carrier element 28. The inner wall of the tubular body 29 has a central cylindrical region 29b and then two conically widening end regions 29a, 29c. The end region 29a is longer than the end region 29c. This results in different radial distances Y between the measuring coil 11 and the inner wall of the tubular body 29. The measuring coil 11 and the tubular body 29 are arranged in a fixed position relative to one another.
Soll eine Position eingestellt oder eine Längenänderung bestimmt werden, so taucht der Meßkern 26 in das Meßrohr 27 und somit in die Meßspule 11 ein, d.h. die Meßspule 11 und der Meßkern 26 werden relativ zueinander bewegt. Dabei verändert sich wegen des Wirbelstromeffektes der Wechselstromwiderstand der Meßspule 11. Auf der der Meßspule 11 zugewandten, elektrisch gut leitfähigen Oberfläche der Innenwand des Rohrkörpers 29 bilden sich Wirbelströme, die den Wechselstromwiderstand der Meßspule 11 und damit die anliegende Spannung verändern, d.h. die Meßspule 11 wird gedämpft. Diese Wirbelstromausbildung ist - ein homogenes Magnetfeld der Meßspule vorausgesetzt - abhängig von der Größe des Luftspalts, d.h. von der Größe des Abstandes Y. Je größer dieser Abstand Y ist, desto schwächer ist die Wirbelstromausbildung, und die Meßspule wird schwächer gedämpft. Bei Verwendung einer gleichmäßig gewickelten Meßspule 11 ergibt sich - ohne Bedämpfung der Spule durch den Rohrkörper 29 - die in Figur 3 dargestellte S-förmige Eichkurve 30, die den Verlauf der anliegenden Meßspannung UM über die Eintauchtiefe S des Meßkerns in der Meßspule aufzeigt. Die Abflachungen am Anfang und am Ende der Eichkurve 30 sind durch den Linearitätsfehler der Spannungsteiler- 14 bzw. Brückenschaltung und durch das inhomogene Magnetfeld der Meßspule bedingt. Dieses inhomogene Magnetfeld der Meßspule ist auf die geringere Ausbildung des magnetischen Feldes an den beiden Enden der Meßspule zurückzuführen. Im mittleren Bereich der Meßspule wirken zur Erzeugung des magnetischen Wechselfeldes die Windungen der linken und der rechten Spulenhälfte zusammen, während hingegen am Ende der Meßspule entweder die links oder rechts davon liegenden Wicklungen fehlen. Diese Abweichungen von der Homogenität sind dabei umso größer, je näher man zu den beiden Spulenenden kommt. Wird nun in den beiden Endbereichen der Meßspule der Luftspalt zum Meßϊohr 27 gegenüber dem mittleren Bereich vergrößert, so wird die Wirbelstromausbildung in den Endbereichen verringert, so daß die Meßspule in den Sndbereichen durch den Rohrkörper 29 weniger gedämpft wird. Es wird also die Meßspule 11 in den Sndbereichen 29a, 29c mit dem geringen magnetischen Feld weniger gedämpft als im mittleren Bereich 29b mit dem hohen magnetischen Feld. Das magnetische Feld der Meßspule 11 kann dadurch soweit beeinflußt werden, daß sowohl die Linearitätsfehler der Spannungsteiler- 14 bzw. άer Brückenschaltung, als auch die durch das üblicherweise inhomogene Magnetfeld bedingten Meßfehler der Spule 11 ausgeglichen werden.If a position is to be set or a change in length is to be determined, the measuring core 26 plunges into the measuring tube 27 and thus into the measuring coil 11, ie the measuring coil 11 and the measuring core 26 are moved relative to one another. Because of the eddy current effect, the alternating current resistance of the measuring coil 11 changes. Eddy currents are formed on the electrically highly conductive surface of the inner wall of the tubular body 29 facing the measuring coil 11, which change the alternating current resistance of the measuring coil 11 and thus the applied voltage, ie the measuring coil 11 becomes subdued. This eddy current formation is - provided a homogeneous magnetic field of the measuring coil - dependent on the size of the air gap, ie on the size of the distance Y. The larger this distance Y, the weaker the eddy current formation, and the measuring coil is damped less. When using a uniformly wound measuring coil 11, the S-shaped calibration curve 30 shown in FIG. 3 is obtained without damping the coil by the tubular body 29 and shows the course of the applied measuring voltage U M over the immersion depth S of the measuring core in the measuring coil. The flattenings at the beginning and at the end of the calibration curve 30 are caused by the linearity error of the voltage divider 14 or bridge circuit and by the inhomogeneous magnetic field of the measuring coil. This inhomogeneous magnetic field of the measuring coil is due to the lower formation of the magnetic field at the two ends of the measuring coil. In the middle area of the measuring coil, the windings of the left and right half of the coil work together to generate the alternating magnetic field, whereas, at the end of the measuring coil, either the windings on the left or right thereof are missing. These deviations from the homogeneity are greater the closer you get to the two coil ends. If the air gap to the measuring tube 27 is enlarged in the two end regions of the measuring coil compared to the central region, the eddy current formation in the end regions is reduced, so that the measuring coil is less damped by the tubular body 29 in the end regions. The measuring coil 11 is therefore less damped in the end regions 29a, 29c with the low magnetic field than in the middle region 29b with the high magnetic field. The magnetic field of the measuring coil 11 can be influenced to such an extent that both the linearity errors of the voltage divider 14 or bridge circuit and the measuring errors of the coil 11 caused by the usually inhomogeneous magnetic field are compensated for.
In Figur 4 ist eine Abwandlung des Ausführungsbeispiels nach Figur 2 dargestellt. Die Meßspule 11 ist auf eine aus nicht elektrisch leitendem Stoff hergestellte Hülse 35 gewickelt, die in einem metallischen Meßrohr 36 beweglich ist. Das Meß röhr 36 hat über seine ganze Länge einen einheitlichen Innendurchmesser. Die Hülse 35 weist einen mittleren Bereich 35b mit gleicher Wandstärke auf und zwei sich konisch zu den Enden der Hülse 35 hin verstärkende Endbereiche 35a, 35c, so daß die Öffnungen der Hülse 35 verkleinert werden. Der Endbereich 35c, der zuerst in das Meßrohr 36 eingeführt wird, ist kürzer als der andere Endbereich 35a ausgebildet und hat am Ende der Hülse 35 einen größeren Durchmesser. Die Hülse 35 ist auf einem metallischen Kern 37 angeordnet, der die gleiche Funktion hat wie der Rohrkörper 29 in Figur 2.FIG. 4 shows a modification of the exemplary embodiment according to FIG. 2. The measuring coil 11 is wound on a sleeve 35 made of non-electrically conductive material, which is movable in a metallic measuring tube 36. The meas tube 36 has a uniform inner diameter over its entire length. The sleeve 35 has a central region 35b with the same wall thickness and two end regions 35a, 35c which reinforce conically towards the ends of the sleeve 35, so that the openings of the sleeve 35 are reduced. The end region 35c, which is first inserted into the measuring tube 36, is shorter than the other end region 35a and has a larger diameter at the end of the sleeve 35. The sleeve 35 is arranged on a metallic core 37, which has the same function as the tubular body 29 in FIG. 2.
Taucht die Meßspule 11 mit der zu ihr ortsfest angeordneten Hülse 35 und dem Kern 37 in das Meßrohr 36 ein, so erzeugt die Meßspule 11 auf der Oberfläche des Kerns 37 Wirbelströme, die den Wechselstromwiderstand der Meßspule 11 verändern. Da im Bereich 35a, 35c diese Oberfläche des Kerns 37 weiter von der Meßspule 11 entfernt ist, ist die Wirbelstromausbildung in diesen Bereichen auch geringer als im Bereich 35b. Wie bereits oben beschrieben, wird dadurch die Meßspule 11 unterschiedlich gedämpft, so daß am Ausgang der Auswerteschaltung eine lineare Eichkurve entsteht.If the measuring coil 11 is immersed in the measuring tube 36 with the sleeve 35 and the core 37 arranged fixed to it, the measuring coil 11 generates eddy currents on the surface of the core 37 which change the AC resistance of the measuring coil 11. Since in the area 35a, 35c this surface of the core 37 is further away from the measuring coil 11, the eddy current formation in these areas is also less than in the area 35b. As already described above, the measuring coil 11 is damped differently, so that a linear calibration curve is produced at the output of the evaluation circuit.
In Figur 5 ist eine weitere Abwandlung des Ausführunβsbeispiels dargestellt. Die Meßspule 11 ist auf einen vorzugsweise aus nicht elektrisch leitfähigem Stoff hergestellten Kern 40 vorzugsweise einlagig aufgewickelt, der in einem metallichen Meßrohr 41 beweglich ist. Daß Meßrohr 41 selbst hat über seine ganze Länge einen einheitlichen Innendurchmesser. In beiden Öffnungen des .Meßrohrs 41 ist je eine Hülse 42 bzw. 43 aus metallischem Werkstoff an der Innenwand des Meßrohrs 41 angeordnet. 3eide Hülsen 42 , 43 sind konisch ausgebildet und verjüngen sich jeweils zur Öffnung des Meßrohrs 41 hin. Dadurch ist jeweils der Öffnungsdurchmesser des Meßrohrs kleiner als sein Innendurchmesser im Bereich Ula zwischen den beiden Hülsen k 2 , 43. Die Hülse 42 kann dabei kürzer ausgebildet sein als die Hülse 43 . Beide Hülsen 42, 43 haben aber etwa gleichen Öffnungsdurchmesser.A further modification of the exemplary embodiment is shown in FIG. The measuring coil 11 is preferably wound in one layer on a core 40, preferably made of non-electrically conductive material, which is movable in a metal measuring tube 41. The measuring tube 41 itself has a uniform inner diameter over its entire length. In both openings of the measuring tube 41, a sleeve 42 or 43 made of metallic material is arranged on the inner wall of the measuring tube 41. 3 eide sleeves 42, 43 are conical and each taper towards the opening of the measuring tube 41. As a result, the opening diameter of the measuring tube is smaller than its inner diameter in the area Ula between the two sleeves k 2, 43. The sleeve 42 can be made shorter than the sleeve 43. Both Sleeves 42, 43 have approximately the same opening diameter.
Auch beim Ausführungsbeispiel nach Figur 5 beruht die in Figur 3 dargestellte S-förmige Kennlinie auf der Änderung des Wechselstromwiderstandes der Meßspule durch den bekannten Wirbelstromeffekt. Die Ausbildung der Wirbelströme auf der metallischen Innenseite des Meßrohrs 41 ist durch die Hülsen 42, 43 so zu verändern, daß die Eichkurve in Figur 3 nahezu linear verläuft. Taucht nun der Meßkern 40 mit der Meßspule 11 in das Meßrohr 41 ein, so wird aufgrund der Hülse 42 der Abstand Y zwischen der Meßspule 11 und der Innenseite des Meßrohrs 41 immer größer, je tiefer der Meßkern 40 in das Meßrohr 41 eindringt. Entsprechend dieser Änderung des Abstands Y werden, bezogen auf die Wirbelstromausbildung im Meßrohr 41 bei konstantem Innendurchmesser, mehr Wirbelströme erzeugt. Dadurch wird abhängig von der jeweiligen Eintauchtiefe des Meßkerns 40 die Meßspule 11 un- terschiedlich bedämpft und somit deren Eichkurve linearisiert. Befindet sich der Meßkern 40 im Bereich 41 a des Meßrohrs 41 mit konstantem Innendurchmesser, d.h. ohne zusätzliche Hülse 42, 43, so wird ebenfalls eine lineare Eichkurve erzeugt.In the exemplary embodiment according to FIG. 5 too, the S-shaped characteristic curve shown in FIG. 3 is based on the change in the AC resistance of the measuring coil due to the known eddy current effect. The formation of the eddy currents on the metallic inside of the measuring tube 41 can be changed by the sleeves 42, 43 so that the calibration curve in FIG. 3 is almost linear. If the measuring core 40 with the measuring coil 11 is now immersed in the measuring tube 41, the distance Y between the measuring coil 11 and the inside of the measuring tube 41 increases due to the sleeve 42, the deeper the measuring core 40 penetrates into the measuring tube 41. Corresponding to this change in the distance Y, based on the eddy current formation in the measuring tube 41 with a constant inner diameter, more eddy currents are generated. Depending on the respective immersion depth of the measuring core 40, the measuring coil 11 is damped differently and thus the calibration curve is linearized. If the measuring core 40 is located in the region 41a of the measuring tube 41 with a constant inner diameter, i.e. Without an additional sleeve 42, 43, a linear calibration curve is also generated.
Gelangt nun der Meßkern 40 in den Bereich der Hülse 43 so ist zur Linearisierung der Eichkurve wieder eine Änderung des Wirbelstromeffektes notwendig. Durch die Verringerung des Abstandes Y zwischen der Wicklungsoberfläche der Meßspule 11 und der Innenseite der Hülse 43 und somit des Meßrohrs 41 werden mehr Wirbelstrδme erzeugt als im Bereich mit dem konstanten Innendurchmesser d. Dadurch wird ein größerer Spannungsabfall an der Meßspule 11 bewirkt, der somit eine lineare Meßkurve ermöglicht. Figur 6 zeigt eine Umkehrung des Ausführungsbeispiels nach Figur 5. Auf einen aus vorzugsweise nicht elektrisch leitfähigem Stoff hergestellten 6z. B. PVC , Plexiglas) Rohrkörper 45 ist die Meßspule 11 aufgewickelt. Auf dem metallischen Meßkern 46 ist an beiden Enden je eine metallische Hülse 47 bzw. 48 angeordnet. Beide Hülsen 47, 48 sind zu den jeweiligen Enden des Meßkerns 1+6 hin konisch erweiternd ausgebildet. Die Hülse 47, die zuerst in den Rohrkörper 45 eintaucht kann kürzer als die Hülse 48 ausgebildet sein. Zwischen den beiden Hülsen 47, 48 befindet sich wieder ein Bereich 46a mit konstantem Durchmesser. Die Wirkungsweise beim Eintauchen des Meßkerns 46 in den Rohrkörper 45 ist analog zu der in Figur 5 beschrieben. Dabei entspricht die Hülse 47 der Hülse 42 und die Hülse 48 der Hülse 43 in ih¬rer Wirkungsweise.If the measuring core 40 now reaches the area of the sleeve 43, a change in the eddy current effect is again necessary for the linearization of the calibration curve. By reducing the distance Y between the winding surface of the measuring coil 11 and the inside of the sleeve 43 and thus the measuring tube 41, more eddy currents are generated than in the area with the constant inside diameter d. This causes a larger voltage drop across the measuring coil 11, which thus enables a linear measurement curve. Figure 6 shows a reversal of the embodiment of Figure 5. On a 6z made of preferably non-electrically conductive material. B. PVC, Plexiglas) tubular body 45, the measuring coil 11 is wound. A metallic sleeve 47 or 48 is arranged on the metallic measuring core 46 at both ends. Both sleeves 47, 48 are designed to expand conically towards the respective ends of the measuring core 1 + 6. The sleeve 47, which first dips into the tubular body 45, can be shorter than the sleeve 48. Between the two sleeves 47, 48 there is again a region 46a with a constant diameter. The mode of operation when the measuring core 46 is immersed in the tubular body 45 is described analogously to that in FIG. 5. The sleeve 47 corresponds to the sleeve 42 and the sleeve 48 corresponds to the sleeve 43 in their mode of operation.
Selbstverständlich sind auch andere geometrische Formen, z.B. Ringe, als die hier aufgeführten Hülsen möglich. In allen Fällen ist dabei eine Verstärkung des Wirbelstromeffektes am Beginn und am Ende der Meßspule durch eine Veränderung des Abstandes zwischen der Meßspule und der Kernoberfläche bzw. der Meßrohrinnenwand wichtig. Auch ist eine einstückige Herstellung denkbar.Of course, other geometric shapes, e.g. Rings than the sleeves listed here possible. In all cases it is important to amplify the eddy current effect at the beginning and at the end of the measuring coil by changing the distance between the measuring coil and the core surface or the inner tube of the measuring tube. A one-piece production is also conceivable.
Die Sensoranordnung kann auch nach dem induktiven Verfahren betrieben werden. Dabei gelten sinngemäß die gleichen Verhältnisse. The sensor arrangement can also be operated using the inductive method. The same conditions apply accordingly.

Claims

Ansprüc he Expectations
1. Sensoranordnung mit einer Spule (11) und einem relativ zu dieser bewegten Element (26), die von Wechselstrom durchflossen ist und in eine Spannungsteilerschaltung (14) oder in eine Brückenschaltung geschaltet ist, dadurch gekennzeichnet, daß die Spule (11) Bereiche (29a, 29b, 29c) aufweist, in denen ihr magnetisches Wechselfeld unterschiedlich gedämpft wird, so daß die am Ausgang der Schaltung abgegriffene Spannung eine lineare Kennlinie, bezogen auf die Relativbewegung der Spule (11) zum Element (26), hat.1. Sensor arrangement with a coil (11) and an element (26) which is moved relative to the latter and through which alternating current flows and is connected into a voltage divider circuit (14) or into a bridge circuit, characterized in that the coil (11) has regions ( 29a, 29b, 29c), in which their alternating magnetic field is damped differently, so that the voltage tapped at the output of the circuit has a linear characteristic curve, based on the relative movement of the coil (11) to the element (26).
2. Sensoranordnung nach Anspruch 1, dadurch gekennzeichnet, daß die Spule (11) auf einen Träger (28) aus elektrisch nicht leitendem Werkstoff gewickelt ist und daß ein ortsfest zur Spule (11) angeordnetes elektrisch gut leitendes Meßrohr (27) Bereiche (29a, 29b, 29c) mit unterschiedlichen radialen Abständen (Y) zwischen der Spule (11) und der Meßrohr-Innenseite (29) aufweist (Figur 2).2. Sensor arrangement according to claim 1, characterized in that the coil (11) is wound on a carrier (28) made of electrically non-conductive material and that a fixedly arranged to the coil (11) arranged electrically well-conductive measuring tube (27) areas (29a, 29b, 29c) with different radial distances (Y) between the coil (11) and the inside of the measuring tube (29) (FIG. 2).
3. Sensoranordnung nach Anspruch 1 und/oder 2, dadurch gekennzeichnet, daß das Meßrohr (27) in den Bereichen (29a, 29c) an den Enden der Spule (11) sich nach außen zunehmend erweiternde Abstände (Y) zwischen der Spule (11) und dem Meßrohr (27) aufweist.3. Sensor arrangement according to claim 1 and / or 2, characterized in that the measuring tube (27) in the areas (29a, 29c) at the ends of the coil (11) outwardly increasing distances (Y) between the coil (11th ) and the measuring tube (27).
4. Sensoranordnung nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß sich die Bereiche (29a, 29c) an den beiden Enden des Meßrohrs (27) zu den Öffnungen hin konisch erweitern. 4. Sensor arrangement according to one of claims 1 to 3, characterized in that the regions (29a, 29c) at the two ends of the measuring tube (27) widen conically towards the openings.
5. Sensoranordnung nach Anspruch 1, dadurch gekennzeichnet, daß die Spule (11) auf einen vorzugsweise nicht elektrisch leitenden Meßkern (40) gewickelt ist und daß ein relativ zur Spule beweglich angeordnetes metallisches Meßrohr (41) an seinen beiden Enden Bereiche mit unterschiedlichen radialen Abständen (Y) zwischen Spule (11) und der Meßrohrinnenseite aufweist. (Figur 5).5. Sensor arrangement according to claim 1, characterized in that the coil (11) is wound on a preferably non-electrically conductive measuring core (40) and that a metal measuring tube (41) which is movably arranged relative to the coil has regions at both ends with different radial distances (Y) between the coil (11) and the inside of the measuring tube. (Figure 5).
6. Sensoranordnung nach Anspruch 5, dadurch gekennzeichnet, daß der Abstand (Y) von beiden Enden des Meßrohrs (41) her zunimmt und das Meßrohr (41) einen mittleren Bereich (41a) mit konstantem Innendurchmesser (d) aufweist.6. Sensor arrangement according to claim 5, characterized in that the distance (Y) from both ends of the measuring tube (41) increases and the measuring tube (41) has a central region (41a) with a constant inner diameter (d).
7. Sensoranordnung nach Anspruch 1, dadurch gekennzeichnet, daß die Spule (11) auf ein vorzugsweise elektrisch nichtleitendes Meßrohr (45) gewickelt ist und daß ein relativ zum Meßrohr (45 ) beweglicher metallischer Meßkern (46) an seinen Enden Bereiche (47, 48) mit unterschiedlichen radialen Abständen (Y) zwischen der Spule (11) und dem Meßkern (46) und einen mittleren 3ereich (46a) mit konstantem Abstand aufweist und daß die Bereiche ( 47 , 48} konisch zu den Enden des Meßkerns (46) hin zunehmen (Figur 6).7. Sensor arrangement according to claim 1, characterized in that the coil (11) is wound on a preferably electrically non-conductive measuring tube (45) and that a relative to the measuring tube (45) movable metallic measuring core (46) at its ends regions (47, 48th ) with different radial distances (Y) between the coil (11) and the measuring core (46) and a middle 3 area (46a) with a constant distance and that the areas (47, 48} conical towards the ends of the measuring core (46) increase (Figure 6).
8. Sensoranordnung nach Anspruch 1, dadurch gekennzeichnet, daß die Spule (11) auf eine Hülse (35) aus nicht elektrisch leitendem Material aufgewickelt ist, die an den beiden Enden der Spule (11) Bereiche (35a, 35c) mit einer dickeren Wandstärke aufweist und daß die Hülse (35) auf einem Kern (37) aus metallischem Werkstoff angeordnet ist (Figur 4).8. Sensor arrangement according to claim 1, characterized in that the coil (11) is wound on a sleeve (35) made of non-electrically conductive material, the regions (35a, 35c) with a thicker wall thickness at the two ends of the coil (11) and that the sleeve (35) is arranged on a core (37) made of metallic material (Figure 4).
9. Sensoranordnung nach Anspruch 8, dadurch gekennzeichnet, daß in den Bereichen (35a, 35c) an den beiden Enden der Hülse (35) die radialen Abstände (Y) zwischen der Spule ( 1 1 ) und der metallischen Oberfläche des Kernes (46) unterschiedlich groß sind. . 9. Sensor arrangement according to claim 8, characterized in that in the areas (35a, 35c) at the two ends of the sleeve (35) the radial distances (Y) between the coil (1 1) and the metallic surface of the core (46) are different sizes. ,
10. Sensoranordnung nach einem der Ansprüche 1, bis 9, dadurch gekennzeichnet, daß die Bereiche (29a, 29c; 35a, 35c; 42, 43; 47, 48) mit den unterschiedlichen radialen Abständen (Y) unterschiedlich lang sind. 10. Sensor arrangement according to one of claims 1 to 9, characterized in that the areas (29a, 29c; 35a, 35c; 42, 43; 47, 48) with the different radial distances (Y) are of different lengths.
PCT/DE1986/000181 1985-05-24 1986-05-02 Sensor arrangement WO1986007145A1 (en)

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DEP3518771.9 1985-05-24
DE3518771 1985-05-24
DE19853534460 DE3534460A1 (en) 1985-05-24 1985-09-27 SENSOR ARRANGEMENT
DEP3534460.1 1985-09-27

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EP0339983A2 (en) * 1988-04-29 1989-11-02 LUCAS INDUSTRIES public limited company Movement transducer
WO1990004152A1 (en) * 1988-10-11 1990-04-19 Radiodetection Limited Homopolar inductive displacement sensor
FR2646505A1 (en) * 1989-04-29 1990-11-02 Teves Gmbh Alfred RACE SENSOR, IN PARTICULAR FOR THE PEDAL OF A BRAKING SYSTEM
DE4328712A1 (en) * 1993-08-26 1995-03-02 Foerster Inst Dr Friedrich Method and device for testing elongated objects, optionally with cross-section deviating from circularity

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DE68926970T2 (en) * 1988-01-22 1997-03-13 Data Instr Inc Linear position sensor, particularly suitable for hydraulic and pneumatic cylinders
GB8809575D0 (en) * 1988-04-22 1988-05-25 Penny & Giles Potentiometers L Linear displacement transducers
DE102010005550A1 (en) 2010-01-22 2011-07-28 Christian-Albrechts-Universität zu Kiel, 24118 Method for determining mechanical properties of magnetostrictive materials

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US3891918A (en) * 1971-03-23 1975-06-24 James F Ellis Linear displacement transducer utilizing an oscillator whose average period varies as a linear function of the displacement
DE2653943A1 (en) * 1976-11-27 1978-06-01 Dieter Hans Viebach Analogue inductive converter system for length or angle measurements - operates using inductance coil with movable core whose permeability continuously varies
DE2816596A1 (en) * 1978-04-17 1979-10-25 Vdo Schindling Contactless measurement of distance or angle travelled - using coil with former outer dia. which varies along core path
GB1558206A (en) * 1977-11-02 1979-12-19 Tioxide Group Ltd Position indicator

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Publication number Priority date Publication date Assignee Title
US3513408A (en) * 1968-08-01 1970-05-19 Tri Metrics Displacement transducer oscillator with movable tapered magnetic core
US3891918A (en) * 1971-03-23 1975-06-24 James F Ellis Linear displacement transducer utilizing an oscillator whose average period varies as a linear function of the displacement
DE2653943A1 (en) * 1976-11-27 1978-06-01 Dieter Hans Viebach Analogue inductive converter system for length or angle measurements - operates using inductance coil with movable core whose permeability continuously varies
GB1558206A (en) * 1977-11-02 1979-12-19 Tioxide Group Ltd Position indicator
DE2816596A1 (en) * 1978-04-17 1979-10-25 Vdo Schindling Contactless measurement of distance or angle travelled - using coil with former outer dia. which varies along core path

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0339983A2 (en) * 1988-04-29 1989-11-02 LUCAS INDUSTRIES public limited company Movement transducer
EP0339983A3 (en) * 1988-04-29 1990-09-26 LUCAS INDUSTRIES public limited company Movement transducer
WO1990004152A1 (en) * 1988-10-11 1990-04-19 Radiodetection Limited Homopolar inductive displacement sensor
GB2241788A (en) * 1988-10-11 1991-09-11 Radiodetection Ltd Homopolar inductive displacement sensor
US5214378A (en) * 1988-10-11 1993-05-25 Radiodetection Limited Homopolar inductive displacement sensor
FR2646505A1 (en) * 1989-04-29 1990-11-02 Teves Gmbh Alfred RACE SENSOR, IN PARTICULAR FOR THE PEDAL OF A BRAKING SYSTEM
DE4328712A1 (en) * 1993-08-26 1995-03-02 Foerster Inst Dr Friedrich Method and device for testing elongated objects, optionally with cross-section deviating from circularity

Also Published As

Publication number Publication date
ES8704261A1 (en) 1987-03-16
EP0222798A1 (en) 1987-05-27
DE3534460A1 (en) 1986-11-27
ES555295A0 (en) 1987-03-16

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