POSITION SENSOR FOR DETERMINING THE POSITION OF A VALVE STUD OF AN ACTIVATOR VALVE

Description

Field of invention

[0001] The invention relates to a position sensor for determining the position of a valve stem of a control valve.

[0002] Control valves typically require position sensors to detect the position of the valve element so that the positioner can precisely adjust the position. Absolute measurement methods are preferred for this purpose, as a reference measurement is not possible in a process plant, and the valve position must be immediately set to the desired opening cross-section after a malfunction or during plant start-up. Due to the harsh environmental conditions in process plants, non-contact measurement methods are preferred. State of the art

[0003] Magnetic or optical stroke measurement methods are frequently used in position sensors for control valves, where a specific pattern is scanned by a sensor. This pattern either extends over the entire stroke range, or multiple sensors are used that scan a uniform pattern. Publications EP 2 834 601 B1 and EP 861 417 B1 describe such sensors.

[0004] Furthermore, sensor arrangements are known in which coil arrangements are used as sensor elements, which are traversed by metallic elements and either detect a change in flux by means of induction or measure frequency changes. An example of this is described in publication DE 100 48 435 A1.

[0005] Publication EP 1 083 408 B1 discloses the use of connecting coils embedded in a printed circuit board in series for angle of rotation measurements. Publication EP 3 365 634 B1 further discloses the cyclical supply of such coils with alternating current, such that a first part of the coils is supplied with alternating current and a remaining part is unenergized.

[0006] Publication EP 1 158 266 A1 describes a displacement measuring system comprising an encoder, a sensor which includes an inductive element to which the encoder is electromagnetically coupled, and an evaluation unit for a sensor signal, wherein the sensor and encoder are positionable relative to each other. This displacement measuring system is fundamentally suitable for position measurement on pneumatic cylinders, for measuring valve positions, or in grippers.

[0007] However, specific designs for the requirements of control valves, as well as options for adapting to different, especially large, stroke lengths, are not known. Furthermore, the known coil arrangements are not suitable for low-energy applications. Task

[0008] The object of the invention is to provide a position sensor for control valves that is cost-effective and suitable for different, in particular large stroke lengths and for low-energy applications. Solution

[0009] This problem is solved by the subject matter of the independent claim. Advantageous embodiments of the subject matter of the independent claim are identified in the dependent claims. The wording of all claims is hereby incorporated by reference into this description.

[0010] The use of the singular should not exclude the plural, and the same applies in reverse, unless otherwise stated.

[0011] To solve the problem, a valve stem with a position sensor for determining the position of the valve stem of a control valve is proposed. This sensor has a pointer that is coupled to the valve stem in such a way that it is carried along by the stem as it moves. The pointer is made of a magnetically and / or electrically conductive material and / or carries at least one passive electronic component. Passive electronic components can be, for example, coils, capacitors, or resistors. The position sensor has a plurality of modules, each module consisting of a printed circuit board on which at least one flat coil is printed. Each module is arranged such that the pointer sweeps across the at least one flat coil without contact when the valve stem moves. The shape and dimensions of all modules are identical. Each of these modules has identical flat coils.The modules are designed to be connected equidistantly and linearly. This makes the position sensor particularly suitable for different, even large, stroke lengths.

[0012] To enable the modules to be connected without alignment errors, the module circuit boards are shaped like two identical rectangles, arranged parallel to each other along the length of the respective module and touching each other, but offset from one another along the module's length. This creates a staggered edge along the length of the valve stem. Furthermore, the flat coils are printed on the circuit boards in such a way that, when two modules are connected, the flat coils overlap along the length of the valve stem. This is advantageous for signal measurement, as there is no interruption when the pointer moves from one module to the next, ensuring a continuous signal measurement.

[0013] More precise spacing between the modules is achieved by having the circuit boards of the modules have positioning features, e.g. in the form of holes or bores.

[0014] Several modules are arranged in a housing. The housing has a slot through which the pointer can protrude to sweep across at least one flat coil. This provides effective protection against environmental influences, for example in a process plant.

[0015] The housing features centering elements that engage complementarily with the positioning features of the module circuit boards. This ensures that the modules are precisely aligned equidistant from one another. At the same time, the need to manufacture multiple housings is eliminated. The centering elements can, for example, take the form of pins that engage in corresponding holes.

[0016] The position sensor also has a measuring transducer or an electronic evaluation circuit that measures a signal at the at least one flat coil, which allows conclusions to be drawn about the relative position of the pointer and the at least one flat coil.

[0017] If the stroke of the control valve changes due to a movement of the valve stem, the pointer influences measurable physical quantities of the at least one flat coil, enabling the transducer to measure a corresponding signal.

[0018] Such a position sensor for control valves can be manufactured very cost-effectively, particularly due to the design of the modules as printed circuit boards with printed flat coils. The small distance at which the pointer sweeps across the at least one module also allows for low energy consumption and a strong signal. Furthermore, a number of modules appropriate to the stroke length can be used, extending the measuring range of the position sensor beyond the length of a single module. The stroke lengths detectable with the position sensor are therefore not limited to the length of a circuit board, and it is also unnecessary to provide different circuit boards of appropriate length for each valve type. This standardization also reduces manufacturing costs.

[0019] Higher accuracy in position determination is achieved when the valve stem with position sensor has multiple flat coils arranged in pairs such that the coils in each pair generate opposing signals. This can be ensured by appropriately selecting the shape and orientation of the flat coils. For example, they can be triangular or trapezoidal.

[0020] When the opposing signals are evaluated together, the accuracy increases because interfering effects, such as temperature influences, affect both flat coils of a pair equally. The signals can be easily evaluated differentially. This involves dividing the difference between the measured values ​​of the two flat coils of a pair by their sum. In such a position sensor, this pair of flat coils represents the smallest meaningful unit that can be addressed individually.

[0021] The flat coils in this system are triangular in shape. The two flat coils in a pair are also arranged symmetrically to each other. This means that, for example, the first of the two flat coils in a pair can be positioned on the circuit board with the base of its triangular shape pointing downwards and the opposite point facing upwards, while the arrangement of the second flat coil in the pair is reversed. Both flat coils then produce signals that are not only opposite in direction but also otherwise exhibit identical behavior. The triangular shape of the flat coils makes it particularly easy to achieve a linear dependence of the signals on the relative position of the flat coil and the pointer. The typical operating frequency of such coils is in the range of a few hundred kHz to a few MHz.

[0022] Particularly consistent position determination is achieved when all flat coils, or in the case of paired arrangements, all pairs of flat coils, are positioned so that they overlap by the same amount along the length of the valve stem. Then, for every possible position, there is a flat coil or coil pair that is just being swept by the pointer and therefore provides a clearly measurable signal. In particular, there are no interruptions at the transition from one flat coil or coil pair to the next.

[0023] Preferably, the modules are electrically connected by spring contacts. These can be standardized and help to determine the distance between the modules.

[0024] The pointer is preferably made of aluminum, sheet metal, ferrite or brass.

[0025] Depending on the material the pointer is made of, the transducer can measure signals in different ways to allow conclusions to be drawn about the relative position of the pointer and the at least one flat coil. If the material is magnetically conductive, e.g., ferrite, the pointer changes the magnetic resistance of the flat coil as it passes over the at least one module. If, on the other hand, the material is only electrically but not magnetically conductive, e.g., aluminum or brass, eddy currents are generated when the flat coils are supplied with alternating current, and these eddy currents have a damping effect.

[0026] The materials mentioned are advantageous, among other reasons, because of their malleability and easy availability.

[0027] Alternatively, the pointer can also be designed as a printed circuit board with at least one passive electronic component.

[0028] The sweeping over of at least one module can be particularly even and at a fixed distance if at least one rail and / or a slide is provided, so that the pointer is guided parallel to the valve rod along the modules by means of the rail and / or the slide.

[0029] Such a slide can preferably be made of a plastic, and more preferably of a bearing material. Furthermore, with this design, it can be advantageous if the pointer is clipped onto the slide. This simplifies, among other things, the mounting of the position sensor. It is important that the rails, and if applicable, the slide and the pointer, are connected with minimal play and that the rails are aligned parallel to the central axis of movement of the valve stem. Only in this way is a consistent distance between the pointer and the module(s) reliably ensured across the entire stroke range of the valve stem. The circuit boards of the modules must also be fixed in the same manner.

[0030] The guidance described above can be implemented in a particularly compact way using at least one rail if the at least one rail is located on the modules.

[0031] In a valve stem with a position sensor, as just described, it is particularly advantageous if the pointer is coupled to the valve stem by a drive ring on the stem. A pin attached to the pointer runs in a slot or groove in the drive ring in such a way that the pointer follows vertical movements of the valve stem but is decoupled from rotational movements or slight twisting of the stem. The valve stem sometimes has radial play in the plain bearings of the valve cover or the valve body of the control valve. The valve stem is also subject to bending due to forces from the process medium. The aforementioned coupling device between the pointer and the valve stem, which only transmits vertical movements of the valve stem, does not transmit any bending, guide play, or twisting of the valve stem to the position sensor guide.The position sensor will then function reliably even if the valve stem is not secured against rotation. The drive ring can be equipped with a spring element, for example, to fix the pin in place.

[0032] If the pointer has a shielding casing made of an electrically and / or magnetically conductive material and / or is grounded, wherein the shielding casing encloses the pointer and the at least one module in a vicinity of the pointer, the at least one module itself can be designed to be particularly cost-effective, as special shielding of it can be dispensed with.

[0033] A simple encapsulated circuit board, protected against environmental influences (e.g., climate, humidity), can serve as the module. Such a shielding sleeve is connected to the pointer and carried along by it. It therefore only shields the area of ​​the at least one module where the signal for position determination must be measured. The sleeve is designed to enclose the module at a sufficient distance to prevent signal distortion. Grounding of the shielding sleeve is ensured by its connection to the pointer, which in turn is connected to the valve stem. Ferrite is a particularly advantageous material for the shielding sleeve.

[0034] The simplest way to connect the position sensor is to connect the transducer to each flat coil, or, in the case of paired coils, to each pair of flat coils, via a number of parallel lines, such that it can measure the signal independently of the other flat coils. The control of the lines to the flat coils or pairs of flat coils can be implemented, for example, using a multiplexer.

[0035] A more compact and less wired, but electronically more complex, position sensor can be wired if the transducer is connected to each flat coil, or in the case of paired coils, to each pair of flat coils, via a data bus. For this purpose, each flat coil, or in the case of paired coils, has a chip with its own digital identifier on its circuit board, allowing the transducer to measure the signal independently of the other flat coils. Ideally, all flat coils or pairs of flat coils can be controlled via a single data bus line that connects all of the aforementioned chips.

[0036] Preferably, the measurement method is selected from: differential choke, differential transformer, inductance measurement of the coils, damping by eddy currents.

[0037] In the measuring arrangement as a differential choke (see glossary), the flat coils are connected individually or in pairs as bridge resistors.

[0038] If the differential transformer is to be used as the measuring arrangement, the pointer can be additionally equipped with a coil that serves as the primary coil for the transformer circuit. Alternatively, corresponding to each coil pair on the circuit board, a further, third flat coil can serve as the primary coil.

[0039] As the pointer passes over the flat coils, it changes their magnetic resistance, provided it is magnetically conductive. These changes can be detected by measuring their inductance. This measuring principle is particularly preferred due to its simplicity. Furthermore, energy consumption is very low, since a voltage only needs to be applied to each individual coil for the duration of the inductance measurement.

[0040] When an electrically conductive pointer sweeps across the flat coils, eddy currents are generated in the pointer, which have a damping effect when the coils are supplied with alternating current. This damping can also be used as a measurement principle.

[0041] The position sensor's transducer preferably also includes a microcontroller. This enables particularly efficient control of the flat coils and signal evaluation. Furthermore, the same controller can be used for position sensors with varying numbers of modules.

[0042] Particularly low energy consumption of the position sensor can be achieved by configuring the transducer in such a way that, after an initialization phase, only the flat coil or coil pair with the strongest signal and its immediate neighbors are activated.

[0043] During the initialization phase, the signals from each flat coil or coil pair can be compared to determine the current position of the pointer. Alternatively, this position can be stored in the transducer from the previous measurement.

[0044] The task is also solved by a control valve with a valve rod with a position sensor, as described above.

[0045] The task is also solved by a process engineering system with a control valve, as just described.

[0046] Further details and features will become apparent from the following description of preferred embodiments in conjunction with the figures. The respective features can be implemented individually or in combination. The possibilities for solving the problem are not limited to the embodiments shown. For example, range specifications always include all intermediate values ​​not explicitly stated and all conceivable sub-intervals.

[0047] The exemplary embodiments are shown schematically in the figures. Identical reference numbers in the individual figures denote identical or functionally equivalent elements, or elements corresponding to each other in terms of their functions. Specifically, the figures show: Fig. 1 a schematic representation of a position sensor with a simple module having a pair of triangular flat coils; Fig. 2 a schematic representation of a control valve with a position sensor according to the invention having a module with three pairs of flat coils; Fig. 3 a schematic representation of a position sensor on a control valve in which the pointer is decoupled from rotations of the valve stem; Fig. 4 a schematic representation of a position sensor on a control valve in which the pointer has a shielding cover; Fig. 5 a further schematic representation of the position sensor made of Fig. 4 ; Fig. 6 a schematic representation of a plurality of connected modules with positioning devices in a housing with centering devices; and Fig. 7 a schematic representation of a plurality of connected modules with positioning devices without an associated housing.

[0048] Fig. 1 Figure 1 shows a module 100 and the pointer 110 of a position sensor according to the invention. The module consists of a printed circuit board 120 on which two triangular flat coils 130, 135 are printed. The terminals 140, 145 of the flat coils are also shown. The pointer 110 is typically a "passive" piece of metal or sheet metal that can move without contact at a small distance (typically a few mm) above the module 100. The pointer 110 changes the inductance of the flat coils 130, 135 through the degree of overlap, since the metal content in the respective air coil changes.

[0049] The pointer can be magnetic and / or electrically conductive, depending on which effect is to be measured and evaluated. Preferably, the pointer is magnetically conductive, and the inductance of the flat coils 130 and 135 is considered. The flat coils 130 and 135 are configured as a coil pair. This means, in particular, that they are arranged point-symmetrically: the wide end of the first flat coil 130 is located next to the pointed end of the second flat coil 135, and vice versa. This arrangement causes the signals generated or measured with the flat coils 130 and 135 to exhibit opposite behavior: while, for example, the signal of coil 130 decreases due to a shift of the pointer 130, the signal of the other coil 135 increases accordingly. The measurements on the two coils therefore complement each other and can thus provide more accurate results.The differential arrangement of the two flat coils 130, 135 eliminates effects such as temperature dependencies, interference coupling, etc., since these affect both flat coils equally. In . Fig. 1 When the pointer 110 moves downwards, the inductance of the first flat coil 130 increases, while the inductance of the second flat coil 135 decreases.

[0050] The evaluation circuit (not shown) generates the signals S F1 (increasing) and S F2 (decreasing) when the pointer 110 moves downwards. The following calculation formula yields a stable, interference-resistant signal that depends on the pointer position h: S diff h = S F 2 h − S F 1 h / S F 2 h + S F 1 h

[0051] The energy consumption of such a position sensor is so low that a 4-20 mA power supply, as commonly used in the process industry for valve control, is perfectly sufficient. Sensors with inductive measuring principles and planar coils are generally very cost-effective, since the sensor base can be manufactured by printing conductive traces onto printed circuit board material. Possible measuring methods include, for example, differential chokes, differential transformers, inductance measurement of the coils, changing the transformer coupling of a transmitting coil into two receiving coils, or damping of the coils using eddy currents.

[0052] In Fig. 2 A cross-section through a control valve 200, equipped with a position sensor according to the invention, is shown. The valve cone 210 is driven by the pneumatic actuator 220 via the valve stem 230. To determine the position of the valve cone or the valve stem, the pointer 240 of the position sensor is fixedly attached to the valve stem 230. This pointer sweeps across the module 250 of the position sensor, which is mounted next to the valve stem, as far as the stroke of the valve cone extends. For the stroke range over which positions are to be measured, three pairs 260, 265, 270 of flat coils, as described above, are arranged on the module 250 in this example. To enable uniform and uninterrupted measurement, the coil pairs 260, 265, 270 are arranged offset in such a way that the successive coil pairs overlap by the same amount in the longitudinal direction of the valve rod 230.In this design, the pointer 240 must be slightly longer than in a version with only one coil pair. Typical stroke measuring ranges are 15-40 mm.

[0053] In Fig. 3 A position sensor according to the invention is shown, which is decoupled from the rotational movements of the valve stem 300. For this purpose, two guide rails 340, 345 are provided parallel to the module 310 – again in an embodiment with three pairs 320, 325, 330 of flat coils – on which the pointer 350 is guided. The pointer 350 thus always remains at a constant distance parallel to the module 310. The coupling of the pointer 350 to the valve stem 300 is effected by a drive ring 360 on the valve stem and a drive pin 370 rigidly connected to the pointer 350, which is moved longitudinally along the valve stem by the drive ring 360, but has sufficient play in the tangential direction. The drive ring 360 is rigidly connected to the valve stem 300.The drive pin 370 is smooth and either rests on the upper surface of the drive ring 360, being pressed onto the drive ring by a spring element (not shown), or the drive pin is guided in a form-fitting manner in an elongated hole (not shown) of the drive ring.

[0054] The pointer 350 is guided along the rails 340, 345 with virtually no friction. To ensure this, the pointer can be equipped with a separate carriage (not shown) that runs on the rails 340, 345. The rails can be designed as sliding rods. The carriage has the advantage that, particularly in the area of ​​the sliding bushings, it can be made of a non-metallic material optimized, for example, for particularly low friction. Bearing materials are especially well-suited for this purpose. The pointer 350, which is preferably magnetic and / or electrically conductive, and thus typically made of ferrite, sheet metal, or other metallic materials, can preferably be clipped or pushed onto the at least partially non-metallic carriage. However, many other suitable connection methods are also known.

[0055] Alternatively (not shown), the pointer can be designed as a printed circuit board on which at least one passive electronic component, e.g., a coil or a capacitor, is mounted. Due to the lower stability of such a pointer, a design with guide rails is particularly advantageous.

[0056] One embodiment of the position sensor as shown in Fig. 3 This is therefore useful because valve stems in pneumatically actuated control valves are often not secured against rotation. The typical rotations of just a few degrees are sufficient to significantly affect the position determination with the measurement principles suitable for the position sensor if the pointer is rigidly connected to the valve stem. This can be compensated for during signal evaluation, for example, by using additional coils to measure the distance between the pointer and the module. The in Fig. 3 However, the depicted design is less complicated and less prone to errors.

[0057] In process industry applications, it is advantageous to shield the flat coils of the position sensor against environmental influences, especially interference fields. However, the larger the strokes to be measured, the more complex this becomes. Therefore, for particularly large strokes, it can be advantageous to connect the shielding to the pointer, as shown in the [reference]. Fig. 4 and Fig. 5 can be seen.

[0058] Due to the larger stroke, the module shown there, 400, 500, is equipped with 7 pairs of flat coils, which are arranged in an offset, overlapping manner as already described. The module can be easily protected against environmental influences such as dust or moisture (e.g., by encapsulating the circuit board).

[0059] The pointer 410, 510, which is connected to the valve stem 420, 520, has a shielding sleeve 430, 530. This sleeve is rigidly connected to the pointer and thus participates in the stroke movement of the pointer and valve stem. The shielding sleeve 430, 530 surrounds the area of ​​the module 400, 500 where the pointer is located and where the measurement is being taken. It is dimensioned to provide sufficient shielding against electromagnetic interference. The shielding sleeve is designed to maintain a sufficiently large distance from the flat coils so that it cannot distort the signal being measured.

[0060] In the execution of Fig. 4 and 5 The shielding sleeve has a U-shaped cross-section in the longitudinal direction of the valve stem 420, 520. Fig. 4 (Oblique view) shows how the shielding shell 430 surrounds the module 400.

[0061] Fig. 5 Figure 1 shows a side view. It is particularly evident that the shielding sleeve 530 extends sufficiently along the length of the valve stem 520 to cover and thus shield the area relevant for measurement. The shielding sleeve 430, 530 can be conductively connected to the pointer 410, 510 and thus typically also to the valve stem 420, 520, which generally provides grounding (GND). To further optimize the shielding properties, a cable connection to the evaluation electronics is also possible.

[0062] If even larger stroke ranges need to be measured, or if very different stroke ranges need to be detectable by otherwise identical position sensors, it is advantageous to provide versions of the position sensor according to the invention with multiple modules. The length of the printed circuit boards to be manufactured can then be kept small and uniform. In particular, very long printed circuit boards can be avoided, as their production is cost-intensive. Such a design is described in the Fig. 6 and Fig. 7 to see.

[0063] In Fig. 6 Two modules 600 and 605 are shown, each comprising four pairs of flat coils arranged in an offset, overlapping manner as previously described. To ensure that this arrangement continues seamlessly at the module joints, the printed circuit boards (PCBs) from which the modules are constructed have a correspondingly large offset step at each end. To guarantee that the coil spacing is sufficiently precise from one module to the next, the modules feature positioning features, in this case in the form of positioning holes 610, which accommodate centering elements. These centering elements are implemented as index pins 620, which are part of the common housing 630 in which the modules are contained. The length of the housing is designed to accommodate the required number of modules. Power and signals can be supplied and disconnected, for example, via a cable gland (not shown).

[0064] Fig. 7 Figure 700 also shows two modules 705, each with four pairs of flat coils. It can be seen that the modules are connected via electrical contact elements 740, which can be attached, for example, to the underside of the circuit boards at their longitudinal ends. These contact elements are preferably designed as spring contacts, which allow for easy connection and disconnection while also exhibiting good contact properties. Also in Fig. 7 The positioning holes 710 are clearly visible; these serve to accommodate centering pins or index pins and thus ensure precise distances between the flat coils even across the module transitions.

[0065] The electronic components required for the evaluation circuit, such as microcontrollers, amplifiers, passive components, etc., only need to be present on one of the modules. Alternatively, they can be mounted completely separately in another location, which has the advantage that all modules can be identical. The signal-carrying conductors of the various flat coils or pairs of flat coils are routed via the contact elements to this evaluation electronics and processed centrally there.

[0066] An example of signal evaluation will be explained using Table 1. Here, the pairs of flat coils (and thus the measured stroke ranges) are designated by letters (A, B, C, ...), and the individual flat coils of a pair are designated pc_1 and pc_2, respectively. S_C_pc_1 therefore denotes the signal of the first flat coil of the coil pair in stroke range C. The corresponding stable differential signals Sig_diff are generated as described above.

[0067] Table 1 covers the stroke ranges BD, where B starts at h = 0% and D ends at h = 260%. "nd" here means that the signal level is too low for evaluation. For evaluation purposes, ranges are now defined in which the differential signal should be used for stroke measurement, e.g., by specifying limits for the magnitude of the differential signal.

[0068] Table 1 illustrates this for differential signals with a magnitude less than or equal to 0.8 (highlighted area). For area C, the total stroke is the sum of the offset value for area C (i.e., the stroke at which area C is located, measured from stroke 0) plus the measured stroke value, which results from the position of the pointer or the signals of the flat coils in area C.

[0069] The selection of the area to be actively measured can be achieved, for example, by first querying and comparing all signals. Only the signals with the highest level or exceeding a minimum level can be reliably used for stroke measurement. To save power, only a portion of all flat coils relevant for stroke measurement can be activated at any given time, for example, using the following method: First, all flat coils or coil pairs are briefly activated to determine which coil pair has the highest level (starting point finding). Then, only the currently required coil pair and the two directly adjacent ones are activated to detect the transition to the next range. Alternatively, only the currently required coil pair and the one the pointer is moving towards can be activated. Which pair this is is determined by the sign of the time derivative of the stroke. glossary Differential throttle

[0070] Electrically, a measuring device based on the differential choke principle represents a Wheatstone half-bridge consisting of two measuring coils. A ferromagnetic core is adjusted so that, in its zero or rest position, both measuring coils exhibit the same impedance. The bridge circuit is thus balanced, and the measuring voltage is consequently zero. If the core is moved from its zero or rest position, the impedances of the two measuring coils change in opposite directions, and the measuring voltage increases proportionally with the displacement of the core within the measuring range. Differential transformer

[0071] A differential transformer is a special type of transformer. It typically consists of a primary coil and two secondary coils. The latter are connected in series out of phase, causing the voltages at their terminals to subtract from each other. The resulting voltage is zero if and only if the two coils and the entire assembly are symmetrical. If the symmetry is disturbed, an output voltage is generated. The phase of this output voltage relative to the excitation (primary voltage) indicates the direction of the asymmetry, and its value indicates the magnitude of the asymmetry. This principle is frequently used in displacement and rotation measurements. (Adapted from https: / / de.wikipedia.org / wiki / Differentialtransformator) ferrite

[0072] Ferrites are poorly or non-conductive ferrimagnetic ceramic materials made from the iron oxide hematite (Fe₂O₃), less commonly from magnetite (Fe₃O₄), and from other metal oxides or carbonates. Depending on their composition, ferrites are either hard or soft magnetic. The chemical composition of ferrites can be described by the general formula MeO•Fe₂O₃. Soft magnetic ferrites contain additional metals (Me) such as nickel, zinc, manganese, cobalt, copper, magnesium, or cadmium, while hard magnetic ferrites contain barium, strontium, or cobalt.

[0073] In a ferrite, there are approximately four oxygen atoms for every three metal atoms. The metals and oxygen form a cubic crystal system within which the alloying elements are embedded. The crystal systems grow into grains of varying sizes. Since the outer boundaries of the grains consist of non-conducting Fe₂O₄, they are electrically insulated from each other. This is particularly important for soft magnetic ferrites because it makes the ferrite material practically non-conducting, thus enabling the production of magnetic cores with extremely low core losses.

[0074] Soft magnetic ferrites are used in electrical engineering as magnetic cores in transformers, switched-mode power supplies, chokes, and coils. In the non-saturated state, high magnetic permeability is possible. Since they are hardly electrically conductive and therefore exhibit virtually no eddy current losses, they are also suitable for high frequencies up to several MHz.

[0075] Hard magnetic ferrites are used as cost-effective permanent magnets, for example in loudspeakers. (According to https: / / de.wikipedia.org / wiki / Ferrite) Flat coil

[0076] A flat coil is a coil in a flat spiral shape. The coil's cross-section can be rectangular, for example. Flat coils are often implemented as a spiral conductor track directly on a printed circuit board. Control valve

[0077] Control valves, also called process or regulating valves, are used to throttle or regulate fluid flows. For this purpose, a closing element is moved within a flow orifice of a valve seat by means of a valve stem and actuator. This allows the flow orifice to be opened or closed, thereby changing the flow rate. pointer

[0078] This refers to an element that is significantly extended in one direction relative to the two directions perpendicular to it. A pointer is typically rod-shaped, but it can also be flattened. The pointer may taper to a point at one end along its length, but this is not mandatory. The name derives from the fact that such an element can be used to indicate something. Reference sign

[0079] 100 Module 110 Pointer 120 Circuit board 130 First flat coil 135 Second flat coil 140 Connections of the first flat coil 145 Connections of the second flat coil 200 Control valve 210 Valve cone 220 Pneumatic actuator 230 Valve stem 240 Pointer 250 Module 260 Pair of flat coils 265 Pair of flat coils 270 Pair of flat coils 300 Valve stem 310 Module 320 Pair of flat coils 325 Pair of flat coils 330 Pair of flat coils 340 Guide rail 345 Guide rail 350 Pointer 360 Drive ring 370 Drive pin 400 Module 410 Pointer 420 Valve stem 430 Shielding cover 500 Module 510 Pointer 520 Valve stem 530 Shielding cover 600 Module 605 Module 610 Positioning provision or positioning hole 620 Centering or index pin 630 Housing 700 Module 705 Module 710 Positioning provision or positioning hole 740 Contact elements cited literature cited patent literature

[0080] DE 100 48 435 A1 EP 861 417 B1 EP 1 083 408 B1 EP 1 158 266 A1 EP 2 834 601 B1 EP 3 365 634 B1

Claims

1. Valve stem comprising position sensor for determining the position of the valve stem (230; 300; 420; 520) of a control valve (200), 1.1 having a pointer (110; 240; 350; 410; 510) which is coupled to the valve stem in such a way that it is carried along by the valve stem when it moves; 1.1.1 wherein the pointer is made of a magnetically and / or electrically conductive material and / or carries at least one passive electronic component; 1.2 having a plurality of modules (100; 250; 310; 400; 500; 600, 605; 700, 705); 1.2.1 wherein each module is formed from a printed circuit board (120) on which at least one flat coil (130, 135) is printed; 1.2.2 wherein each module is arranged in such a way that the pointer sweeps over the at least one flat coil without contact when the valve stem moves; 1.2.3 wherein the shape and dimensions of all modules are identical; 1.2.4 wherein each module has identical flat coils (130, 135); and 1.2.5 wherein the modules are designed in such a way that they can be connected to each other equidistantly and linearly; 1.3 wherein the printed circuit boards (120) of the modules (600, 605; 700, 705) 1.3.1 have the shape of two identical rectangles, 1.3.2 which are arranged parallel in the longitudinal direction of the particular module 1.3.3 and touch each other 1.3.4 however, they are shifted relative to each other in the longitudinal direction of the module, 1.3.5 so that there is an offset between the rectangles; and 1.3.6 wherein the flat coils are printed on the printed circuit boards in such a way that, in the case of two connected modules, there is an overlap of the flat coils on the two modules in the longitudinal direction of the valve stem; 1.4 wherein the printed circuit boards of the modules (600, 605; 700, 705) have positioning provisions (610; 710); 1.5 wherein a plurality of modules (100; 250; 310; 400; 500; 600, 605; 700, 705) are arranged in a housing; 1.5.1 wherein the housing has a slot through which the pointer can protrude into the housing to sweep over the at least one flat coil (130, 135); 1.5.2 and wherein the housing has centering features (620) which engage complementarily with the positioning provisions (610; 710) of the printed circuit boards of the modules in order to align the modules equidistantly to each other; and 1.6 having a measuring transducer; 1.6.1 wherein the measuring transducer measures a signal at the at least one flat coil which allows conclusions to be drawn about the relative position of the pointer and the at least one flat coil.

2. Valve stem comprising position sensor according to the preceding claim, characterized by 2.1 a plurality of flat coils (130, 135); 2.2 the flat coils being arranged in pairs in such a way that the flat coils of a pair (260, 265, 270; 320, 325, 330) each deliver opposing signals; 2.3 the flat coils (130, 135) each having a triangular shape; and 2.4 the two flat coils of a pair (260, 265, 270; 320, 325, 330) being arranged point-symmetrically to each other.

3. Valve stem comprising position sensor according to either of the preceding claims, characterized in that all flat coils (130, 135) or, in the case of paired arrangements, all pairs (260, 265, 270; 320, 325, 330) of flat coils are arranged in such a way that they overlap by the same amount in the longitudinal direction of the valve stem (230; 300; 420; 520).

4. Valve stem comprising position sensor according to any of the preceding claims, characterized in that the electrical connection of the modules is made by spring contacts (740).

5. Valve stem comprising position sensor according to any of the preceding claims, characterized in that the pointer (110; 240; 350; 410; 510) is made of aluminum, sheet metal, ferrite or brass.

6. Valve stem comprising position sensor according to any of the preceding claims, characterized in that at least one rail (340, 345) and / or one sliding carriage are present; the pointer (110; 240; 350; 410; 510) being guided along the modules (300) by means of the rail and / or the sliding carriage parallel to the valve stem (230; 300; 420; 520).

7. Valve stem comprising position sensor according to the preceding claim, characterized in that the at least one rail (340, 345) is located on the modules (300).

8. Valve stem comprising position sensor according to one of the two preceding claims 6 or 7, characterized 8.1 in that the coupling of the pointer (110; 240; 350; 410; 510) to the valve stem (230; 300; 420; 520) is effected by a drive ring (360) on the valve stem, 8.2 a pin (370) attached to the pointer running in such a way in an elongated hole or groove in the drive ring, 8.2.1 that the pointer follows vertical movements of the valve stem, 8.2.2 but is decoupled from rotational movements of the valve stem.

9. Valve stem comprising position sensor according to any of the preceding claims, characterized 9.1 in that the pointer (110; 240; 350; 410; 510) has a shielding cover (430; 530), 9.2 the shielding cover consisting of an electrically and / or magnetically conductive material and / or being grounded, and 9.3 the shielding cover enclosing the pointer and the at least one module (100; 250; 310; 400; 500; 600, 605; 700, 705) in a vicinity of the pointer.

10. Valve stem comprising position sensor according to any of the preceding claims, characterized in that the measuring transducer is connected to each flat coil (130, 135) or, in the case of paired arrangements, to each pair (260, 265, 270; 320, 325, 330) of flat coils by a plurality of parallel lines in such a way that it can measure the signal independently of the other flat coils.

11. Valve stem comprising position sensor according to any of claims 1 to 9, characterized 11.1 in that the measuring transducer is connected by a data bus to each flat coil (130, 135) or, in the case of paired arrangements, to each pair (260, 265, 270; 320, 325, 330) of flat coils; 11.2 each flat coil, or in the case of paired arrangements, each pair of flat coils on the particular circuit board having a chip with its own digital identification, so that the measuring transducer can measure the signal independently of the other flat coils.

12. Valve stem comprising position sensor according to any of the preceding claims, characterized in that the measurement method selected is from: differential choke, differential transformer, inductance measurement of the coils, damping by eddy currents; and in that the measuring transducer is implemented by a microcontroller.

13. Valve stem comprising position sensor according to any of the preceding claims, characterized in that the measuring transducer is configured in such a way that, after an initialization phase, only the flat coil (130, 135) or the pair (260, 265, 270; 320, 325, 330) of flat coils with the strongest signal and their immediate neighbors are driven.

14. Control valve (200) comprising a valve stem having a position sensor according to any of the preceding claims.

15. Process engineering system comprising a control valve (200) according to the preceding claim.