Sensor element of an inductive proximity or distance sensor containing coil arrangement having electrically-conductive shielding with flange completely enclosing the coil arrangement and method for operating the sensor element
A sensor element of an inductive proximity sensor or distance sensor contains a coil arrangement with at least one excitation coil and at least one receiving coil and includes an electrically conductive shielding which contains a shielding cup that surrounds the coil arrangement laterally and on the rear face. A method operates the sensor element. The shielding of the sensor element further contains a flange which is provided on the front face of the sensor element, is connected to the shielding cup in an electrically conductive manner, and completely surrounds the coil arrangement.
1. A sensor element of an inductive proximity sensor or distance sensor, the sensor element comprising:
a shielding comprising a flange and a shielding cup, the shielding being electrically-conductive, the flange being connected to the shielding cup in an electrically conductive manner, the shielding cup having a first longitudinal end and a second longitudinal end disposed opposite from the first longitudinal end; and
a coil arrangement comprising at least one excitation coil and at least one receiving coil;
wherein the shielding cup surrounds the coil arrangement laterally and with the second longitudinal end;
wherein the flange is connected to the first longitudinal end of the shielding cup;
wherein the flange completely encloses the coil arrangement;
wherein the excitation coil is connected to a voltage-controlled current source, which provides the excitation current of the excitation coil;
wherein, for controlling the voltage-controlled current source, a signal shaper is provided for shaping a temporal current course of the excitation current;
wherein the signal shaper contains a bandpass filter which suppresses lower-frequency and higher-frequency signal components; and
wherein an addition of a direct current voltage on the output signal of the signal shaper is provided.
2. The sensor element according to claim 1 , wherein the shielding cup is made from one piece.
3. The sensor element according to claim 1 , wherein the shielding cup and the flange are made from one piece.
4. The sensor element according to claim 1 , wherein the flange is implemented as a metal film.
5. The sensor element according to claim 1 , wherein the at least one excitation coil is disposed behind the at least one receiving coil in a direction away from the flange.
6. The sensor element according to claim 1 , wherein the coil arrangement is arranged on a multi-layer board.
7. The sensor element according to claim 6 , wherein the shielding cup has at least one cantilever extension for fixing the shielding cup on the multi-layer board.
8. The sensor element according to claim 1 , wherein an ohmic resistor is connected in parallel to the excitation coil.
9. The sensor element according to claim 1 , wherein a microcontroller for providing a digital output signal for controlling the signal shaper is provided.
10. The sensor element according to claim 9 , wherein a two-stage amplifier is provided for amplifying a measuring voltage provided by the at least one receiving coil.
11. The sensor element according to claim 10 , wherein at least a first amplifier stage of the two-stage amplifier is a capacitor-coupled transimpedance amplifier.
12. The sensor element according to claim 1 , further comprising a sensor housing having a depth and a width, the width being greater than the depth, the depth being related to a measuring direction;
wherein the coil arrangement and the shielding are arranged in the sensor housing.
13. A method for operating the sensor element of claim 1 , wherein a distance of a measuring object from the sensor element is determined;
wherein a temporal course of an excitation current flowing in the at least one excitation coil is set in such a way that a background signal contained in a measuring voltage or in an output signal of an amplifier, said background signal being present without the measuring object, is minimized; and
wherein the excitation current is set depending on the temperature of the at least one excitation coil.
14. The method according to claim 13 , wherein a current maximum of the excitation current flowing in the at least one excitation coil is set in such a way that the background signal is minimized.
15. The method according to claim 13 , wherein the background signal is subtracted from the output signal of the amplifier.
16. The method according to claim 13 , wherein the measuring object is made from a selected material and the temporal current course the excitation current and/or a current maximum are set to maximize sensitivity of the sensor element to the measuring object made from the selected material.
17. The method according to claim 13 , wherein the at least one excitation coil comprises a first excitation coil and a second excitation coil; and
wherein the first and the second excitation coils are supplied with the excitation current at the same time.
18. The method according to claim 13 , wherein magnetic and/or electrical properties of the measuring object are determined by evaluating an output signal of the amplifier in terms of a signal maximum and/or a temporal signal course.
19. A method for operating the sensor element of claim 1 , wherein a distance of a measuring object from the sensor element is determined; and
wherein a temporal course of an excitation current flowing in the at least one excitation coil is set in such a way that a background signal contained in a measuring voltage or in an output signal of an amplifier, said background signal being present without the measuring object, is minimized.
20. A method for operating the sensor element of claim 1 , wherein a distance of a measuring object from the sensor element is determined; and
wherein a temporal course of an excitation current flowing in the at least one excitation coil is set depending on a temperature of the at least one excitation coil.
21. A sensor element of an inductive proximity sensor or distance sensor, the sensor element comprising:
a shielding comprising a flange and a shielding cup, the shielding being electrically-conductive, the flange being connected to the shielding cup in an electrically conductive manner, the shielding cup having a first longitudinal end and a second longitudinal end disposed opposite from the first longitudinal end; and
a coil arrangement comprising at least one excitation coil and at least one receiving coil;
wherein the shielding cup surrounds the coil arrangement laterally and with the second longitudinal end;
wherein the flange is connected to the first longitudinal end of the shielding cup;
wherein the flange completely encloses the coil arrangement;
wherein the excitation coil is connected to a voltage-controlled current source, the voltage-controlled current source providing an excitation current of the excitation coil;
wherein a microcontroller for providing a digital output signal for controlling a signal shaper for shaping a temporal current course of the excitation current is provided;
wherein a two-stage amplifier is provided for amplifying a measuring voltage provided by the at least one receiving coil; and
wherein at least a first amplifier stage of the two-stage amplifier is a capacitor-coupled transimpedance amplifier.
22. The sensor element according to claim 21 , wherein a signal attenuator is provided between the first amplifier stage and a second amplifier stage.
23. The sensor element according to claim 22 , wherein the microcontroller contains a function block which provides a digital control signal for the signal attenuator, which furthermore contains a time delay, the delayed time of which depends on a temporal signal course of the output signal of the amplifier; and
wherein the delayed time is set in such a way that an attenuation of the signal occurring between the first and second amplifying stages occurs in a region of a signal maximum such that overcontrolling the first and second amplifier stages is avoided.