Temperature-stabilized sensor unit for distance determination

Abstract

Temperature-compensated sensor unit (1) for determining the distance to an electrically conductive object, comprising an LC resonant circuit (2) with a coil (3) and a capacitor (4), control means (5) which are designed such that the LC resonant circuit (2) can be excited by an oscillation, in particular a current and / or a voltage, evaluation means (6) which are designed such that a parameter change of the LC resonant circuit (2) caused by the electrically conductive object can be detected and / or evaluated, an auxiliary resistor (7) which is electrically connected to the coil (3) at a common contact (12), a printed circuit board (8) as well as an amplifier unit (9) with an input contact (10) and an output contact (11), wherein the input contact (10) is connected to the common contact (12) of the coil (3) and the auxiliary resistor (7) and the output contact (11), in particular single-pole, is connected to the capacitor (4), wherein the amplifier unit (9) is arranged such that the voltage drop across the auxiliary resistor (7) can be amplified and output at the output contact (11), characterized by that the coil (3) in the circuit board (8) is formed by a first conductor track section (13) which forms a first conductor track resistance (14) and that the auxiliary resistance (7) in the circuit board (8) is formed by a second conductor section (15) which forms the auxiliary resistance (7) as a second conductor resistance (16) and wherein the first conductor section (13) and the second conductor section (15) are thermally coupled and magnetically decoupled.

Description

[0001] The present invention relates to a temperature-stabilized sensor unit for determining the distance of an electrically conductive object according to claim 1.

[0002] Sensor units for determining the distance of an electrically conductive object are known from the prior art.

[0003] One embodiment of the known sensor unit comprises an oscillation circuit with an LC resonant circuit and evaluates the damping of the oscillation that arises due to the eddy currents induced in the metallic object.

[0004] The resonant circuit comprises a coil as an inductor and a capacitor as a capacitance. Electrical energy is applied via a control mechanism such that the LC resonant circuit oscillates electrically, and energy is periodically exchanged between the magnetic field of the coil and the electric field of the capacitor. The time-varying magnetic field of the coil induces eddy currents in metallic objects, which leads to damping of the oscillation and / or energy loss in the resonant circuit.

[0005] Using evaluation tools, such parameter changes in the resonant circuit can now be detected in order to identify the presence of electrically conductive objects within the detection range of the sensor unit. The distance between the metallic object and the coil can also be determined from the magnitude of the damping.

[0006] Real coils exhibit other electrical properties besides their actual inductance. These include electrical resistance, also known as line resistance, which leads to conduction losses and thus a voltage drop across the coil. This also causes damping in the resonant circuit and therefore energy loss. If the coil windings are made of copper, the electrical resistance is also highly temperature-dependent, which is why a temperature change negatively affects the measurement result of the sensor unit.

[0007] From DE 10 2011 115 922 A1 of the applicant, a sensor unit and a method for at least partially compensating for the loss resistance are known. This increases the sensitivity of the sensor unit. However, the high temperature dependence of the copper coil wire remains. It was therefore proposed to use an alloy with low temperature dependence instead of copper. The disadvantage is that these alloys have a higher specific resistance and thus also higher losses. The sensor unit known from DE 10 2011 115 922 A1 is able to compensate for these losses and thus achieve highly sensitive and temperature-stable measurement results.

[0008] However, when using a standard copper wire coil, an additional temperature sensor is still necessary to reduce the influence of temperature on the copper's conduction losses. This sensor actively compensates for parameter changes caused by temperature variations.

[0009] However, despite using copper as the conductor material, it would be preferable to compensate for the temperature dependency directly, rather than via an additional temperature sensor. This is because an additional temperature sensor is often unable to accurately replicate the temperature of the measuring coil.

[0010] Furthermore, DE 10 2015 112 431 A1 is known from the prior art, which describes the formation of a coil by a conductor track section, whereby the reference frequency of the coils is varied to avoid magnetic coupling.

[0011] The object of the present invention is therefore to overcome the disadvantages known from the prior art. In particular, it is an object of the present invention to provide a sensor unit for distance determination using an LC resonant circuit in which the influence of temperature on the distance determination can be almost completely compensated.

[0012] This problem is solved by a sensor unit according to the invention as described in claim 1.

[0013] Advantageous embodiments of the invention are described in the dependent claims. The scope of the invention includes all combinations of at least two features disclosed in the description and / or the claims and / or the figures.

[0014] The temperature-compensated sensor unit according to the invention for determining the distance of an electrically conductive object comprises an LC resonant circuit with an inductor and a capacitor. The LC resonant circuit, which can also be called a resonant circuit or LC parallel resonant circuit, comprises a capacitor and an inductor. The inductor, which can also be called an inductor, and the capacitor, which can also be called a capacitance, are connected in parallel.

[0015] Furthermore, the sensor unit according to the invention comprises control means configured such that the LC resonant circuit can be excited by an oscillation, in particular by a current and / or a voltage. Preferably, the control means comprise an electronic switch, in particular a transistor, to excite the oscillation in the LC resonant circuit by means of a switching operation.

[0016] Furthermore, the sensor unit according to the invention comprises evaluation means designed such that a parameter change of the LC resonant circuit caused by the electrically conductive object can be detected. The parameter change is preferably a voltage and / or a current and / or a power, which is detected in the LC resonant circuit by means of measurement technology.

[0017] Preferably, the oscillation and / or vibration is an electrical energy with which the resonant circuit is actuated.

[0018] Furthermore, the sensor unit according to the invention includes an auxiliary resistor which is electrically connected to the coil via a common contact. In other words, the coil and the auxiliary resistor form a series circuit.

[0019] Furthermore, it is provided that the sensor unit according to the invention comprises a single- or multi-layer printed circuit board and an amplifier unit.

[0020] The amplifier unit according to the invention comprises an input contact and an output contact, wherein the input contact is electrically connected to the common contact and thus to the coil and the auxiliary resistor, in particular directly. The output contact of the amplifier unit is electrically connected to the capacitor, in particular via a single-pole connection.

[0021] Furthermore, it is provided within the scope of the invention that the amplifier unit is arranged in such a way that the voltage dropping across the auxiliary resistor, which is present at the input contact, can be amplified and output at the output contact.

[0022] According to the invention, the coil in the circuit board is formed by a first conductor track section and includes a first conductor track resistance and / or forms the first conductor track resistance.

[0023] Furthermore, according to the invention, the auxiliary resistor is also formed in the printed circuit board by a second conductor track section and thus forms a second conductor track resistance, wherein the first conductor track section and the second conductor track section are positioned and / or designed in the printed circuit board in such a way that they are thermally coupled and magnetically decoupled.

[0024] According to the invention, the coil is thus designed as a printed circuit board coil and / or PCB coil, and the auxiliary resistor as a printed circuit board auxiliary resistor and / or PCB auxiliary resistor.

[0025] Within the scope of the present invention, it was recognized that by designing the coil as a PCB component and the auxiliary resistor as a PCB component and / or as the first and second conductor track sections, an optimal simulation of the thermal behavior of the coil's conductor resistance can be achieved by the auxiliary resistor. According to the invention, the influence of temperature fluctuations on the measurement result of the sensor unit according to the invention is thus further reduced or almost completely prevented.

[0026] Advantageously, the present invention enables the temperature of the coil to be determined using the auxiliary resistor on the same substrate material and / or on the same conductor material. This advantageously results in good thermal coupling between the coil and the auxiliary resistor, which is why the influence of temperature can be particularly well compensated by the inventive design of the sensor unit.

[0027] Further development envisages that the second conductor track section, which forms the auxiliary resistor, exhibits a meandering and / or bifilar profile, particularly a circular bifilar profile, at least partially in plan view. Advantageously, the auxiliary resistor can thus be implemented with the lowest possible inductance, thereby also achieving low magnetic coupling between the auxiliary resistor and the coil.

[0028] In a further development of the sensor unit according to the invention, the printed circuit board comprises a first layer and at least one second layer. In other words, the printed circuit board comprises at least two layers with conductive traces. Advantageously, a conductive trace section in the first layer can thus, in a top view, run at least partially above a conductive trace section in the at least second layer. This allows for particularly good thermal coupling between the first conductive trace section of the PCB coil and the second conductive trace section of the auxiliary resistor.

[0029] In this context, it is further specified that the first conductor track section and / or the second conductor track section runs section by section in the first layer and the at least second layer. In other words, the first and / or second conductor track section runs in a first area within the first layer of the printed circuit board and in at least a second area within the at least second layer of the printed circuit board.

[0030] Furthermore, the position of the printed circuit board can change multiple times during the first and / or second conductor track segment, with vias, particularly standardized vias, being used to connect the conductor track segments on different layers. This advantageously allows for good thermal coupling between the first and second conductor track segments.

[0031] Further development envisages that, in plan view, the first conductor track section is formed and / or positioned in a first printed circuit board sub-area and the second conductor track section is formed and / or positioned in a second printed circuit board sub-area, wherein the first printed circuit board sub-area surrounds and / or encloses the second printed circuit board sub-area on its periphery and / or is nested.

[0032] This also results in particularly good and / or almost identical thermal coupling between the first conductor track section, especially the coil, and the second conductor track section, especially the auxiliary resistor. Advantageously, the thermal behavior of the coil can thus be replicated very accurately.

[0033] It is further preferred that, in plan view, the first printed circuit board section is formed and / or positioned, in particular, directly, laterally and / or, in particular, directly adjacent to the second printed circuit board section. In other words, with this lateral and / or adjacent arrangement between the first and the second printed circuit board section, there is no partial and / or complete overlap of the first conductor track section and the second conductor track section.

[0034] It is particularly preferred that the first printed circuit board section, in particular completely, extends and / or is formed in the first layer and that the second printed circuit board section, in particular completely, extends and / or is formed in at least the second layer, wherein in plan view the first printed circuit board section and the second printed circuit board section overlap at least partially and / or are arranged one above the other in the vertical direction.

[0035] In a particularly preferred embodiment, the first conductor track section is designed to have a larger conductor track cross-section than the second conductor track section. This particularly preferred embodiment of the present invention results in a shorter length and / or overall extent of the second conductor track section compared to the first conductor track section, leading to lower AC current losses within the PCB coil. Furthermore, this also results in comparatively lower magnetic coupling in the auxiliary resistor due to its shortened length.

[0036] Furthermore, it is intended that, for further training purposes, the monitored parameter change of the LC resonant circuit is a voltage and / or a current.

[0037] Finally, it is further provided that the ratio between the conductor resistance and the auxiliary resistance corresponds to a factor of 0.2 to 5. Preferably, the ratio is selected depending on the gain factor of the amplifier unit according to the invention in order to simulate the voltage drop across the conductor resistance of the coil and thus to generate a virtual operating point.

[0038] The invention is explained in more detail below by way of example with reference to the drawings. The combination of features shown as examples in the embodiments illustrated can be supplemented by further features according to the above explanations, in accordance with the properties of the sensor unit according to the invention that are necessary for a specific application. Likewise, individual features can be omitted in the described embodiments, also in accordance with the above explanations, if the effect of this feature is not important in a specific application.

[0039] In the drawings, elements of the same function and / or structure are designated with the same reference symbol.

[0040] They show, in: Fig. 1: A schematic representation of a temperature-compensated sensor unit according to the invention for determining the distance of an electrically conductive object according to a first exemplary embodiment, in Fig. 2: an electrical equivalent circuit diagram of the coil and the auxiliary resistor, in Fig. 3a-d: each a schematic representation of a possible design of coil and auxiliary resistor as PCB components, and in Fig. 4-d: a schematic representation of possible designs of the auxiliary resistor as a PCB resistor.

[0041] The Fig. Figure 1 shows a temperature-compensated sensor unit 1 according to the invention for determining the distance of an electrically conductive object according to a preferred embodiment.

[0042] The sensor unit 1 according to the invention comprises an LC resonant circuit 2 with a coil 3 and a capacitor 4.

[0043] The coil 3 and the capacitor 4 are directly electrically connected to each other via a first conductor section 19 and are indirectly connected to each other via a second conductor section 20 through an amplifier unit 9.

[0044] The LC resonant circuit 2 can also be subjected to oscillation via control means 5 which are not shown in detail, in order to subject the resonant circuit 2, for example, to an electrical voltage or an electric current.

[0045] Furthermore, the sensor unit 1 also includes evaluation means 6, not shown in detail, which are designed in such a way that a parameter change of the LC resonant circuit 2 caused by the electrically conductive object can be detected and evaluated.

[0046] Advantageously, the presence and / or distance of the electrically conductive object to the sensor unit 1 can be detected or determined within a detection area that is not graphically represented.

[0047] In the schematic representation, the coil 3 is symbolically represented by a pure inductance 3.1 and by an ohmic resistance and / or a line resistance 3.2, where the line resistance 3.2 replicates the voltage drop caused in the coil 3 due to line losses.

[0048] Coil 3 is also connected to a fixed potential GND via an auxiliary resistor 7. The input contact 10 of the amplifier unit 9 is electrically connected to the common contact 12 of coil 3 and auxiliary resistor 7, thus supplying the applied voltage potential to the amplifier unit 9. Depending on a predefined gain factor, this input potential is amplified by the amplifier unit 9 and output at an output contact 11 of the amplifier unit 9 such that the potential between inductor 3.1 and line resistance 3.2 can be replicated at the output contact 11. Advantageously, the amplifier unit 9 can thus compensate for the voltage drop across the line resistance 3.2 in order to generate the virtual potential between inductor 3.1 and line resistance 3.2 (see dotted line 23).

[0049] For this purpose, it is necessary that the auxiliary resistor 7 replicates the line resistance 3.2 of the coil 3 as closely as possible, whereby the auxiliary resistor 7 should exhibit the same thermal behavior as the line resistance 3.2 of the coil 3.

[0050] Within the scope of the present invention, it is therefore provided that the coil 3 and the auxiliary resistor 7 are each designed as a PCB component in a printed circuit board 8 in order to achieve good thermal coupling between the two components.

[0051] In other words, the coil 3 is implemented in the printed circuit board 8 by a first conductor section 13, which thus forms a first conductor resistance 14. Furthermore, the auxiliary resistor 7 is also implemented in the same printed circuit board 8 by a second conductor section 15, which is why the auxiliary resistor 7 is implemented by a second conductor resistance 16. Advantageously, by designing the coil 3 as a PCB coil 3, an improved simulation of the conductor resistance 3.2 can be achieved by means of the auxiliary resistor 7, since both components can be implemented on the same substrate material and / or with the same conductor material.

[0052] The Fig. 2 shows a schematic representation of the already from the Fig. 1 known coil 3 and auxiliary resistor 7, which are designed as PCB components in an identical circuit board 8 to explain the functionality of the amplifier unit 9 according to the invention in more detail and which are connected in series via a common contact 12.

[0053] The voltage drop U Rs Due to the line losses, especially copper losses, within the coil 3, the voltage is essentially doubled via the auxiliary resistor 7, so that the voltage drop U Rs above the line resistance 3.2 essentially the voltage drop U Rk above the auxiliary resistor 7.

[0054] This voltage U Rs is applied to U by means of the amplifier unit 9 Aamplified. Thus, the output contact 11 of the amplifier unit 9 corresponds to the virtual connection point 21 of the ideal coil, and the resonant circuit 2 can be operated with high Q. As a result, it reacts very sensitively to small losses caused by an electrically conductive object in the detection range of the sensor unit 1 according to the invention.

[0055] It should be noted that the auxiliary resistor 7 or the reduction of the gain factor A of the amplifier unit 9 is designed to ensure that a small virtual loss resistance is maintained in the coil, as otherwise the LC resonant circuit 2 would have an "infinite" quality factor. In this case, the output voltage would approach the limits of the operating voltage of the sensor unit 2.

[0056] In the Fig. Figures 3a-d are schematically represented as specific embodiments of the coil 3 and the auxiliary resistor 7 as the first and second conductor track sections 13, 15.

[0057] In the Fig. In 3a, the coil 3 is formed by a first conductor section 13 in a single-layer printed circuit board 8. The first conductor section 13 comprises several circular conductor loops which, in plan view, circumferentially enclose an inner surface 22. The inductance of the coil 3 can be dimensioned by the number of conductor loops.

[0058] The conductor resistance of coil 3 is determined by the cross-sectional area and the length and / or total extent of the first conductor track section 13 as well as the choice of material and corresponds to the first conductor track resistance 14.

[0059] The auxiliary resistor 7 is positioned inside the circular conductor loops of the coil 3. In other words, the inner surface 22 encompasses the auxiliary resistor 7, which is formed by the second conductor section 15.

[0060] The second conductor section 15 comprises a forward conductor and a return conductor, each consisting of several conductor subsections running horizontally or vertically in plan view. Each conductor subsection of the forward conductor can be assigned to a conductor subsection of the return conductor, with the respective conductor subsections of the forward and return conductors running parallel to each other and directly adjacent, and carrying opposite currents when energized.

[0061] In other words, the forward and return conductors run directly adjacent and / or parallel and / or spirally and / or interlocked, such that all conductor track sections of the forward conductor can be assigned to a directly adjacent conductor track section of the return conductor with opposite current flow.

[0062] In other words, the auxiliary resistor 7 has a bifilar shape, with the forward and return conductors being spiral-shaped and interleaved.

[0063] This has the advantage that the opposing current flow in the forward and return conductors essentially cancels itself out. Thus, magnetically induced voltages compensate each other, so that essentially no current is induced between the output contacts of the auxiliary resistor 7. This enables the low magnetic coupling according to the invention between the coil 3 and the auxiliary resistor 7, whereby the second conductor resistance 16 is formed depending on the cross-sectional area of ​​the second conductor section, the length of the second conductor section, and the material of the conductor section 15.

[0064] Due to the arrangement of the first conductor track section 13 and the second conductor track section 15 in the same position on the printed circuit board 8, and in close proximity or almost immediately adjacent, good thermal coupling can be achieved. This ensures that the auxiliary resistor 7 replicates the thermal behavior of the coil 3 and / or, in other words, experiences essentially the same positive or negative temperature input simultaneously.

[0065] The Fig. Figure 3b shows an alternative embodiment of the coil 3 and the auxiliary resistor 7.

[0066] Coil 3 is identical to the embodiment shown in the Fig. 3a is formed and includes the first conductor track section 13, which comprises several circular conductor loops.

[0067] The auxiliary resistor 7 now comprises a second conductor track section 15, which corresponds to the embodiment of the Fig. 3a also has a bifilar course, but is not spiral or nested, but has a U-shaped course in top view.

[0068] Specifically, the second conductor section 15 comprises a forward and a return conductor, each of which has a U-shaped or inversely U-shaped course in plan view, with the forward and return conductors running directly adjacent to each other and carrying an opposite current flow when energized.

[0069] Additionally, the embodiment differs according to the Fig. 3b also by the positioning of the coil 3 relative to the auxiliary resistor 7. The first conductor track section 13 runs in a first circuit board sub-area 17, which is arranged directly adjacent to a second circuit board sub-area 18, which comprises the second conductor track section 15. Advantageously, good thermal coupling between the coil 3 and the auxiliary resistor 7 can thus also be achieved in this embodiment.

[0070] The embodiment according to the Fig. 3c essentially corresponds to the embodiment shown in the Fig. 3b, since the coil 3 and the auxiliary resistor 7 are arranged in two immediately adjacent circuit board sections 17, 18 in order to achieve the thermal coupling according to the invention between the first conductor section 13 and the second conductor section 15.

[0071] In contrast to the embodiment according to the Fig. In the top view shown in 3b, the auxiliary resistor 7 does not have a bifilar but a meandering path. In this meandering path, the second conductor section 15 comprises several vertically oriented conductor subsections that are arranged directly adjacent to each other and each carry an opposing current flow when externally energized.

[0072] The Fig. Figure 3d shows another variant of the first and second conductor track sections 13, 15, in order to form the coil 3 and the auxiliary resistor 7 as PCB components.

[0073] According to the exemplary embodiment of the Fig. 3a The auxiliary resistor 7 is arranged in the inner surface 22 of the coil 3. The second conductor section 15 now comprises several semicircular conductor loops, each semicircular conductor loop being directly adjacent to at least one other semicircular conductor loop. In other words, the second conductor section again comprises a bifilar configuration to prevent the induction of a current in the auxiliary resistor due to the opposing current flow direction of adjacent conductor loops.

[0074] The Fig. Figures 4a-d show further preferred embodiments for forming the auxiliary resistor 7 within the printed circuit board 8 through the second conductor track section 15.

[0075] In the Fig. 4a The second conductor section 15 extends in a first layer of the printed circuit board 8 (solid line) and in a second layer of the printed circuit board 8 (dashed line). In other words, the forward conductor of the second conductor section 15 is located in the first layer of the printed circuit board 8, and the return conductor runs in at least the second layer of the printed circuit board 8, with the forward and return conductors being connected to each other centrally via a via along the entire length of the second conductor section 15. Furthermore, in plan view, the forward and return conductors follow essentially identical paths in the different layers in order to form conductor pairs with opposing current flows when externally powered.

[0076] The Fig. Figure 4b shows the design of the auxiliary resistor 7 according to the exemplary embodiment of the Fig. 3d, wherein the second conductor track section 15 comprises several semicircular conductor loops.

[0077] The Fig. Figure 4c shows a variant embodiment of the auxiliary resistor 7 according to the exemplary embodiment of the Fig. 3b, wherein the second conductor track section 15 has a bifilar orientation.

[0078] The Fig. Figure 4d shows a further embodiment of the auxiliary resistor 7, wherein the second conductor track section 15 has a rectangular and / or meandering shape, as already described in connection with the embodiment of the Fig. 3c is known.

Claims

[1] Temperature-compensated sensor unit (1) for determining the distance to an electrically conductive object, comprising an LC resonant circuit (2) with a coil (3) and a capacitor (4), control means (5) which are designed such that the LC resonant circuit (2) can be excited by an oscillation, in particular a current and / or a voltage, evaluation means (6) which are designed such that a parameter change of the LC resonant circuit (2) caused by the electrically conductive object can be detected and / or evaluated, an auxiliary resistor (7) which is electrically connected to the coil (3) at a common contact (12), a printed circuit board (8) as well as an amplifier unit (9) with an input contact (10) and an output contact (11), wherein the input contact (10) is connected to the common contact (12) of the coil (3) and the auxiliary resistor (7) and the output contact (11), in particular single-pole, is connected to the capacitor (4), wherein the amplifier unit (9) is arranged such that the voltage drop across the auxiliary resistor (7) can be amplified and output at the output contact (11), characterized by , that the coil (3) in the circuit board (8) is formed by a first conductor track section (13) which forms a first conductor track resistance (14) and that the auxiliary resistance (7) in the circuit board (8) is formed by a second conductor section (15) which forms the auxiliary resistance (7) as a second conductor resistance (16) and wherein the first conductor section (13) and the second conductor section (15) are thermally coupled and magnetically decoupled. [2] Sensor unit according to claim 1, characterized by , that the second conductor track section (15) has, at least in part, a meandering course and / or a bifilar course, in particular a round bifilar course, in the top view. [3] Sensor unit according to claim 1 or 2, characterized by , that the printed circuit board (8) comprises a first layer and at least one second layer. [4] Sensor unit according to claim 3, characterized by , that the first conductor track section (13) and / or the second conductor track section (15) runs section by section in the first layer and the at least second layer. [5] Sensor unit according to one of the preceding claims, characterized by, that in plan view the first conductor track section (13) is formed in a first printed circuit board sub-area (17) and the second conductor track section is formed in a second printed circuit board sub-area (18), wherein the first printed circuit board sub-area surrounds and / or circumferentially encloses and / or is nested around the second printed circuit board sub-area. [6] Sensor unit according to claim 5, characterized by , that in plan view the first printed circuit board section (17) is formed laterally and / or adjacent to the second printed circuit board section (18). [7] Sensor unit according to claim 5, characterized by , that the first printed circuit board section (17), in particular completely, extends in the first layer and the second printed circuit board section (18), in particular completely, extends in at least the second layer, wherein in plan view the first printed circuit board section (17) and the second printed circuit board section (18) overlap at least partially. [8] Sensor unit according to one of the preceding claims, characterized by , that the first conductor section (13) has a larger conductor cross-section than the second conductor section (15). [9] Sensor unit according to one of the preceding claims, characterized by that the monitored parameter change of the LC resonant circuit is a voltage and / or a current. [10] Sensor unit according to one of the preceding claims, characterized by , that the auxiliary resistor (7) is dimensioned such that the ratio between the first conductor resistance (14) and the second conductor resistance (16) corresponds to a factor of 0.2 to 5.

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