Sensor element and inductive sensor

Abstract

A sensor element (10) has a circuit board (11) which has at least one plane with a printed coil (12). The printed coil (12) has at least one first through-hole (15) which is arranged outside the outermost coil winding (13). A shielding ring (17) is arranged between the first through hole (15) and the outermost coil winding (13). An inductive sensor has several such sensor elements (10).

Description

Technical Field

[0001] The invention relates to a sensor element. Furthermore, the invention relates to an inductive sensor having several sensor elements. Background Art

[0002] Inductive sensors have a housing in which a sensor element is mounted. The number of possible windings that a coil of the sensor element has is limited by the surface of the sensor element. It is of course desirable for the coil to have as many windings as possible, since the signal sensitivity of the coil increases with the number of windings. High signal sensitivity has a positive effect on the evaluability, EMC sensitivity and switching frequency of the sensor. In addition, the number of possible coil windings is limited by other elements that must be arranged in the same plane as the coil. On the one hand, these are through-holes, which are provided to electrically connect several coils of the sensor element arranged in different planes to each other. On the other hand, these are shielding rings, which are provided to electrically shield the coil from the surroundings. This is particularly important when the inductive sensor is to be installed in a metallic environment. The sensor housing often does not have a sufficiently high electrical conductivity in order to ensure a sufficient degree of shielding from the surroundings, so that the sensor without a shielding ring in the installed state has an unacceptably high sensitivity to interference.

[0003] An object of the invention is to provide a sensor element having as high a number of coil windings as possible on a predetermined surface. Another object is to provide an inductive sensor having a sensor element. Summary of the invention

[0004] The sensor element has a circuit board. The circuit board has at least one plane, on which the printed coil is arranged. The printed coil has at least one first through hole, which is electrically connected to the printed coil. A through hole is to be understood as an electrical through contact (plated through hole) between the planes of the circuit board, which is in particular achieved by an inwardly metallized pore in the substrate of the circuit board. The first through hole is arranged outside the outermost coil winding of the printed coil. The first through hole is arranged on the plane of the printed coil and optionally extends through an existing additional plane of the circuit board. A shield is arranged between the first through hole and the outer coil winding. For example, the shield can consist of copper.

[0005] The advantage of this arrangement of the shielding ring is that the first through hole can be arranged on the edge of the circuit board. Thus, compared with other possible designs of the sensor element, the largest surface of the circuit board can be covered by the winding of the printed coil, so that a high signal sensitivity of the sensor element can be achieved.

[0006] Additionally, the arrangement of the first through-holes on the edge of the circuit board advantageously allows the first through-holes to be designed as half-through-holes or half-holes (plated half-holes). This can be achieved in particular by initially producing a circuit board that is larger than can be reliably mounted in the housing of the inductive sensor. All first through-holes are produced as through-contact apertures on the edge of the circuit board. The circuit board is then cut to size in such a way that the outer diameter of the circuit board corresponds to the inner diameter of the sensor housing. In this case, the first through-holes are halved so that they occupy less circuit board surface area than full apertures and thus a larger proportion of the circuit board surface is available for printing the coils.

[0007] In order to shield the printed coil well from the metallic environment of the sensor element, it is preferred that the electrical connection between the first through hole and the outer coil winding of the printed coil has an electrical connection point to the shielding ring on the plane. Thus, the electrical connection is made via the shield without having to electrically insulate the shield. The short circuit of the electrical connection to the shielding ring achieves an optimal electrical shielding of the printed coil.

[0008] In principle, the sensor element can be implemented with only one plane and thus also with only one printed coil. However, in order to achieve a higher signal sensitivity, it is preferred that the sensor element has several parallel planes. In this case, in each case one printed coil is arranged on each of these planes. The printed coils of several planes are respectively electrically connected to one another via through-holes. In this case, the first through-hole is used to contact the printed coil on its outermost coil winding.

[0009] Furthermore, in each case, one shielding ring is arranged on each plane. The shielding rings of the planes are preferably not directly electrically connected to one another. Instead, each shielding ring is only electrically connected to the printed coil of its plane. The electrical connection between the shielding rings is therefore only indirectly via the printed coil.

[0010] Furthermore, it is preferred that the printed coil has at least one second through hole, which is arranged inside the innermost coil winding. In each case, the first through hole is provided for electrical contacting the outermost coil winding of the coil, while the second through hole is used for electrical contacting on the innermost coil winding.

[0011] Furthermore, it is preferred that the sensor element has more first through holes than second through holes. Here, in order to connect the printed coils to each other, only the same number of first through holes as the second through holes that the sensor element has are required. Only this number of first through holes is electrically connected to the printed coil. The further first through holes are electrically insulated from the printed coil. Here, use is made of the fact that the first through holes are arranged in an annular manner around the printed coil and the shielding ring in the circuit board. If only the same number of first through holes as is required for electrically contacting the printed coil is arranged, part of the circuit board surface in this annular region will remain unused. By filling this area with further first through holes, the redundant first through holes can contribute to the electrical shielding of the printed coil from the metallic environment.

[0012] The shielding ring attached to the edge of the circuit board must have a certain minimum width. The arrangement of the shielding ring between the printed coil and the first through-hole has a further advantage: the shielding ring can be designed to have a certain width, which in particular is a maximum of 200 μm in the plane. As a result, the surface consumption of the shielding ring on the circuit board is minimized, so that more surface is available for the coil winding. In the case of very large coils, of course, a wider shielding ring can also be selected. Nevertheless, the outer diameter of the first outer winding of the coil can be greater than the outer diameter of the sensor element, the through-hole of which is arranged inside the shielding ring. The advantages of the sensor element according to the invention are therefore particularly evident for very small constructions. However, even with larger constructions, the present invention also offers small advantages.

[0013] According to the previously described aspect of the invention, the inductive sensor has several sensor elements. In particular, these sensor elements all have the same circuit board. Therefore, all sensor elements can be combined in a single circuit board, which can then be mounted on the end face of the sensor housing.

[0014] In a preferred embodiment of the inductive sensor, the inductive sensor has three sensor elements, which are arranged one above the other on a common circuit board. Here, the first sensor element is set as a first receiving element. The second sensor element is set as a second receiving element. The second sensor element is electrically connected to the first sensor element. The setting as a receiving element is carried out in particular by connecting the corresponding sensor element to a voltmeter. The third sensor element is arranged between the first sensor element and the second sensor element. The third sensor element is set as a transmitting element and is electrically insulated from the first sensor element and the second sensor element. The setting as a transmitting element is carried out in particular by electrically connecting the third sensor element to a pulse shaper. Such an inductive sensor can identify all metal objects without a reduction factor under the same switching distance. This characteristic is advantageous in the use when the material of the object to be detected can be changed or when non-ferrous metals with large switching distances are to be recorded. The shielding of the printed coil by the shielding ring also makes the inductive sensor highly sensitive when installed in a metal material. The function of the inductive sensor is not disturbed by strong electromagnetic fields. Therefore, the inductive sensor can be used, for example, in induction curing or welding equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Exemplary embodiments of the invention are depicted in the drawings and are explained in more detail in the following description.

[0016] FIG. 1 shows a schematic plan view of a sensor element according to the prior art.

[0017] FIG. 2 schematically shows how several printed coils are connected to each other in a sensor element according to the prior art.

[0018] Figure 3 A schematic illustration of a plan view of a sensor element according to an exemplary embodiment of the present invention is shown.

[0019] Figure 4 It is schematically shown how several printed coils in a sensor element according to an exemplary embodiment of the invention are connected to one another.

[0020] Figure 5 An inductive sensor according to an exemplary embodiment of the invention is schematically shown. DETAILED DESCRIPTION

[0021] FIG. 1 shows a plane of a sensor element 10 according to the prior art (sensor element of the inductive sensor BES08KP of Balluff GmbH, Germany). A printed coil 12 is arranged on a circular circuit board 11. The printed coil has an outermost winding 13 and an innermost winding 14, at which the conductor path of the printed coil 12 ends in each case. Five first through-holes 15 penetrate the circuit board 11 orthogonally to the plane. One of these first through-holes 15 is electrically connected to the outermost coil winding 13. Five second through-holes 16 are arranged inside the printed coil 12 and penetrate the circuit board 11 orthogonally to the plane. One of the second through-holes 16 is electrically connected to the innermost coil winding 14. The sensor element has several planes, on which the printed coil 12 is arranged in each case. In each case, a pair of first through-holes 15 and second through-holes 16 are used here to electrically connect the printed coil 12 of a plane to the printed coil 12 of an adjacent plane. The shielding ring 17 is realized in the form of edge metallization of the circuit board 11. The shielding ring is partially broken in two locations in order to be able to contact the conductor plates 11 by means of two fastening elements 18 and thus fix them in the sensor housing. In the plane, the shielding ring has a width of 300 μm. A distance of 100 μm remains free between the shielding ring 17 and the first through-hole 15. The first through-hole 15 has a diameter of 500 μm in each case. A distance of 100 μm again remains free between the first through-hole 15 and the outermost coil winding 13. Therefore, in the edge region of the circuit board 11, an area with a width of 1.050 μm is not available for printing the coil 12.

[0022] FIG2 shows how two printed coils 12a, 12b of different planes of the sensor element are connected to one another via through-holes 15, 16, which are not depicted. Furthermore, shielding rings 17a, 17b of the two printed coils 12a, 12b are depicted. These shielding rings 17a, 17b have an electrical connection 20 on the outer edge of the circuit board 11. All shielding rings of all planes of the sensor element 10 are directly connected to one another via this electrical connection 20. This electrical connection 20 is electrically connected to the system of printed coils 12 connected via through-holes 15, 16 at a single connection point 21.

[0023] Figure 3The plane of the sensor element 10 according to an exemplary embodiment of the present invention is shown. Compared with the sensor element 10 according to the prior art, the circuit board 11 is not metallized on its edge. Instead, the first through hole 15 in the form of a half through hole is arranged on the edge of the circuit board 11. The printed coil 12 is connected to the printed coil 12 of the other plane of the sensor element 10 in the same way as in the prior art by the first through hole 15 connected to the outermost coil winding 13 and the second through hole 16 connected to the innermost coil winding 14. Although the sensor element 10 has six second through holes 16 arranged around the center point, it has fifteen first through holes 15. However, only six of these first through holes 15 are used to contact the printed coil 12, while the remaining nine first through holes 15 are not connected to one of the printed coils 12, but these printed coils are electrically shielded from the surrounding environment. The shielding ring 17 is arranged between the first through hole 15 and the outermost coil winding 13 on the circuit board 11. The shielding ring is short-circuited to the connection between the outermost coil winding 13 and the first through hole 15 at the connection point 22.

[0024] exist Figure 4 2 is depicted, the shielding rings 17a, 17b are electrically connected to each other via two printed coils 12a, 12b of different planes at a connection point 22a, 22b per plane of electrical connection to the printed coils 12a, 12b in each case. There is no need for separate electrical connections of the shielding rings 17a, 17, one below the other, as depicted in FIG. 2 for the prior art.

[0025] By implementing the first through-hole 15 as a half-through-hole, the space requirement of the first through-hole on the imaginary axis between the edge of the circuit board 11 and its center corresponds to their radius instead of their diameter. When the aperture of the first through-hole 15 is implemented by the circuit board 11 with the same diameter as in the exemplary embodiment of the prior art, the space requirement is therefore only 275 μm. The distance between the first through-hole and the shielding ring 17 is 100 μm. The shielding ring 17 can be designed to have a width of only 100 μm. The distance between the shielding ring 17 and the outermost winding of the printed coil 12 is also 100 μm, so that an annular area with a width of 525 μm around the printed coil 12 is not available for the winding of the printed coil 12. Compared with the prior art, this width of the unusable edge area of ​​the circuit board 11 can therefore be halved.

[0026] Figure 5An inductive sensor 30 is shown, which is designed as a proximity switch. A first sensor element 10a and a second sensor element 10b are electrically connected to each other. In addition, the sensor elements are respectively connected to a voltmeter 31 for reading the voltage. A third sensor element 10c is arranged between the two sensor elements 10a, 10b. The third sensor element is connected to a pulse shaper 32 of an oscillator. The first two sensor elements 10a, 10b serve as receiving elements and the third sensor element 10c serves as a transmitting element. When a metal object 40 is brought close to the inductive sensor 30 and moves along a trajectory s towards the inductive sensor 30, the object 40 is identified when the switching distance is not met.

[0027] In the following, three exemplary embodiments of inductive sensors have been compared with one another. Here, in each case, sensor elements 10a to 10c have been used which have the same number of planes and in each case have a diameter of a circuit board 11 of 18 mm. The circuit board 11 has been mounted in a sensor housing and the inductive sensor has been set to a nominal switching distance of 8 mm. In a first comparative example VB1, sensor elements 10a to 10b have been used which differ from the sensor element 10 of the prior art depicted in FIGS. 1 and 2 in the absence of a shielding ring 17. In a second comparative example VB2, sensor elements 10a to 10c have been used according to the prior art depicted in FIGS. 1 and 2. In example B1 according to the invention, sensor elements 10a to 10c have been used which correspond to Figure 3 and Figure 4 An exemplary embodiment of the invention is depicted. The oscillator amplitude detected by means of the voltmeter 31 has been measured in three cases respectively. In the first case, the inductive sensor 30 has not been installed in a metallic environment and no object 40 has been brought close to the inductive sensor. In the second case, the inductive sensor 30 has not been installed in a metallic environment and an object 40 has been brought up to a distance of 8 mm from the inductive sensor 30. In the third case, the inductive sensor 30 has been flush mounted in a surrounding environment made of high-grade steel and no object 40 has been brought close to the inductive sensor. The measured oscillator amplitudes are listed in Table 1:

[0028] Table 1

[0029] VB1 VB2 B1 No object / Not installed 1,000mV 1,000mV 1,000mV Object / Not Installed 900mV 990mV 950mV No object / installed 800mV 995mV 980mV

[0030] As can be seen from these values, in the comparative example VB1, the sensor elements 10a to 10c without the shielding ring 17 are more affected by the installation than by the metal object 40 to be identified. In the comparative example VB2, the change in the oscillator amplitude due to the installation is smaller than the change in the oscillator amplitude due to the metal object 40 to be identified. Nevertheless, the two changes are close to each other, which makes the evaluation difficult and makes the inductive sensor 30 susceptible to interference. In the example B1 according to the present invention, the inductive sensor 30 is more affected by the installation situation than in the comparative example VB2. However, this is not a problem because there is a significant difference between the oscillator amplitude in the installation position and the oscillator amplitude due to the object 40 to be identified. Regardless of the surrounding environment in which the inductive sensor 30 is installed, it can reliably identify the metal object 40. This is achieved by having more coil windings with the same diameter as the circuit board 11 than in the second comparative example VB2.

Claims

1. A sensor element (10, 10a-c), comprising a circuit board (11), the circuit board having at least one plane, the at least one plane having a printed coil (12, 12a-b), wherein the printed coil (12, 12a-b) has at least one first through hole (15), the at least one first through hole being arranged outside the outermost coil winding (13), characterized in that: A shielding ring (17, 17a-b) is arranged between the first through hole (15) and the outermost coil winding (13).

2. The sensor element (10, 10a-c) according to claim 1, characterized in that The first through hole (15) is implemented as a half through hole.

3. The sensor element (10, 10a-c) according to claim 1 or 2, characterized in that The electrical connection between the first through hole (15) and the outermost coil winding (13) has an electrical connection point (22) to the shielding ring (17, 17a-b).

4. The sensor element (10, 10a-c) as claimed in one of claims 1 to 3, characterized in that The sensor element has several planes, wherein the printed coils (12, 12a-b) of a plurality of planes are electrically connected to each other through through holes (15, 16).

5. The sensor element (10, 10a-c) according to claim 4, characterized in that The shielding rings (17, 17a-b) of the plane are not directly electrically connected to each other.

6. The sensor element (10, 10a-c) according to one of claims 1 to 5, characterized in that The printed coil (12, 12a-b) has at least one second through hole (16) arranged inside the innermost coil winding (14).

7. The sensor element (10, 10a-c) according to claim 6, characterized in that The sensor element has more first through holes (15) than second through holes (16).

8. An inductive sensor (30) having several sensor elements (10a-c) according to one of claims 1 to 7.

9. The inductive sensor (30) according to claim 8, characterized in that The inductive sensor has three sensor elements (10a-c) which are arranged one above the other on a common circuit board (11), wherein - the first sensor element (10a) is arranged as a first receiving element, - a second sensor element (10b) is arranged as a second receiving element and is electrically connected to the first sensor element (10a), and A third sensor element (10c) arranged between the first sensor element (10a) and the second sensor element (10b) is provided as a transmitting element and is electrically insulated from the first sensor element (10a) and the second sensor element (10b).

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