Vibration limit sensor with optimized inductive drive

Abstract

Vibration limit sensor (1) with an inductive drive with - a currentable coil (2) with a coil core (5) which is arranged at least partially axially overlapping with the coil (2), - a permanent magnet (7) aligned in the axial direction (A), wherein a first end (71) of the permanent magnet (7) is held in a magnet receptacle (9), wherein the coil (2) and the permanent magnet (7) are movable relative to each other and are mounted on one side on a fixed part and on the other side on a movable part coupled to a oscillating diaphragm (11), wherein - at least two air gaps are formed between the stationary part and the moving part, wherein - a first air gap (21) is formed between the coil core (5) and a second end (72) of the permanent magnet (7) and - a second air gap (22) between the stationary and the moving part exists, characterized in that the magnet receptacle (9) is formed in at least two parts with a sleeve (91) for holding the permanent magnet (7) and a steering section (92) connected to the sleeve (91) and is made at least partially of a magnetically non-conductive material.

Description

[0001] The present invention relates to a vibration limit level sensor with inductive drive according to the preamble of patent claim 1.

[0002] Vibration point level sensors with inductive drives are known, for example, from the applicant's EP 2 209 110 B1. The prior art vibration point level sensors with inductive drives are characterized by their suitability for higher ambient temperatures compared to vibration point level sensors with piezoelectric drives.

[0003] In an embodiment known from EP 2 209 110 B1, a permanent magnet is coupled via a magnet receptacle to an oscillating membrane with a tuning fork arranged thereon, and can be excited to oscillate by a coil arranged stationary in a housing of the vibration limit level sensor. The coil is arranged on a coil carrier in a coil receptacle for magnetic field steering and has a coil core, also for magnetic field steering. A first air gap formed between the permanent magnet and the coil core is arranged within an axial extension of the coil. A second air gap is formed between the cylindrical magnet receptacle and the likewise cylindrical coil receptacle.

[0004] The vibration limit level sensor is designed in such a way that a magnetic field inducing current flow in the coil excites the permanent magnet to oscillate in the axial direction and / or an oscillation of the permanent magnet induces a voltage in the coil.

[0005] The problem with vibration limit level sensors known from the state of the art is that a parasitic path of the magnetic field forms between the magnet holder, which surrounds the permanent magnet, and the pole of the permanent magnet facing away from the membrane. This path is lost for the drive power of the inductive drive, so that the efficiency of the drive decreases.

[0006] It is the object of the present invention to provide a vibration limit level sensor with an inductive drive which has an increased efficiency.

[0007] This object is achieved by a vibrating level switch having the features of patent claim 1. Advantageous further developments are the subject of dependent patent claims.

[0008] A vibration limit level sensor according to the invention with an inductive drive having an energizable coil with a coil core that is arranged at least partially axially overlapping with the coil, and an axially aligned permanent magnet, wherein a first end of the permanent magnet is held in a magnet receptacle, and wherein the coil and the permanent magnet are movable relative to one another and are mounted on the one hand on a fixed part and on the other hand on a movable part coupled to a membrane designed to vibrate, wherein at least two air gaps are formed between the fixed part and the movable part, wherein a first air gap is formed between the coil core and a second end of the permanent magnet and a second air gap exists between the fixed and the movable part, is characterized in thatthat the magnetic receptacle is at least partially made of a magnetically non-conductive material.,

[0009] By partially constructing the magnet holder from a non-magnetic material, the magnetic field guidance can be positively influenced. In particular, the non-magnetic part of the magnet holder can be arranged in such a way that parasitic paths—i.e., paths of the magnetic field lines that do not contribute to the force development of the electromagnet—can be reduced or even eliminated. Reducing these parasitic paths improves the efficiency of the drive and increases the achievable output power.

[0010] In such a vibration limit level sensor, the coil can be fixedly mounted, with the permanent magnet then coupled to the membrane and the magnet holder being connected to the membrane as a movable part.

[0011] Such a design is easy to implement because only the permanent magnet is mounted on the oscillating membrane via the magnet mount. Therefore, no electrically operated components need to be movably mounted and supplied with power.

[0012] Alternatively, the permanent magnet can be mounted in a fixed position, in which case the coil is coupled to the membrane and connected to the membrane, for example, via a coil carrier as a movable part.

[0013] According to the invention, the magnet holder is formed in at least two parts, comprising a magnetically non-conductive sleeve for holding the permanent magnet and a magnetically conductive steering section connected to the sleeve. If the permanent magnet is held in a magnetically non-conductive sleeve, i.e., if the end of the permanent magnet facing the diaphragm is enclosed by the sleeve at least radially, this prevents field lines emerging at the free end of the permanent magnet from being led back via the sleeve directly to the opposite pole of the permanent magnet. The field lines are guided via the steering section and directed to a magnetically effective air gap in the magnetic circuit, thereby exerting a force on the diaphragm.

[0014] The sleeve and / or the steering section are connected to the bolt for optimal power transmission. The connection can be made by screwing, pressing, welding, gluing, or a combination thereof.

[0015] By combining the above-mentioned joining techniques, it is possible to secure a screw connection against loosening by additional welding or gluing.

[0016] In a preferred embodiment, the sleeve is provided with a base in which an internal thread is arranged. The steering section is placed on the bolt and rests against a shoulder of the bolt. The steering section is clamped against this shoulder by means of the internal thread in the sleeve, which interacts with an external thread of the bolt. The sleeve can additionally be secured to the bolt or the steering section by welding, gluing, or otherwise preventing the screw from loosening.

[0017] To maximize the efficiency of the arrangement, the distance between the second end of the permanent magnet and a base area of ​​the steering section should be minimized. In this context, "minimized" means that the distance should be as small as possible, given the materials used and their mechanical properties. If, for example, the sleeve is to be screwed to the bolt, the forces generated when the diaphragm is excited via the bolt must be taken into account when designing the connection between the bolt and the sleeve. Given these constraints, the distance, and thus, in particular, the thickness of the base of the sleeve, should be as small as possible.

[0018] In particular, the sleeve can be flush with the permanent magnet on the membrane side in the axial direction. This means that the sleeve does not extend beyond the permanent magnet in the axial direction, but only encloses its circumference. This makes it possible to have the permanent magnet sit directly on the steering section, thus achieving optimal coupling of the field lines into the steering section.

[0019] If the steering section is connected to the bolt, the sleeve can be tubular. This means, in particular, that the sleeve does not have its own base. For example, the sleeve can then be welded, glued, or otherwise materially connected to the steering section. A force-fitting or form-fitting connection is also conceivable. For example, the sleeve can be screwed or pressed to the steering section. A combination of different connection techniques is also conceivable and advantageous for this connection, e.g., to secure the connection. The steering section can be screwed, pressed, welded, or otherwise connected to the bolt.

[0020] Alternatively, the permanent magnet can be connected directly to the bolt, for example, by screwing it in. To do this, an internal thread is inserted into the permanent magnet, which is then screwed to the bolt. The steering section can then be clamped between the permanent magnet and a shoulder of the bolt, or additionally connected to the bolt.

[0021] In principle, the sleeve can be connected to the steering section in a force-fitting, form-fitting or material-fitting manner, so that during assembly a separately handleable unit is formed which can be connected to the bolt.

[0022] A particularly simple production is possible if the sleeve is made of a rust-proof, weldable, magnetically non-conductive stainless steel, e.g. AISI 316L, preferably WNo. 1.4404.

[0023] A suitable steel according to the American Iron and Steel Institute (AISI) designation, as of June 2018, is 316L. The material number of a suitable steel according to EN 10088-2:2014-12 is 1.4404. This steel also falls under AISI 316L, but has somewhat broader specifications.

[0024] Alternatively, the sleeve can be made of a ceramic material or glass. These would then be glued or otherwise secured to the steering section.

[0025] The magnet holder can have a circumferential collar extending radially away from the membrane on its circumference to guide the magnetic flux. This collar can be arranged, in particular, on the steering section or formed integrally with it.

[0026] In particular, a second air gap can be formed between the collar and a yoke for returning the magnetic field, which contributes to the force effect of the drive.

[0027] The yoke can be sleeve-shaped and in particular rotationally symmetrical to a longitudinal axis of the drive.

[0028] Overall, a rotationally symmetrical design of the drive is advantageous because in this way a large number of components of the drive can be rotationally symmetrical and thus, for example, designed as turned parts.

[0029] A rotationally symmetrical structure also has positive effects on the acting forces, as these also act symmetrically.

[0030] Furthermore, the yoke can be formed with a base, with the coil core being arranged at the base, preferably formed integrally with it. By essentially completely guiding the magnetic field outside the air gaps, stray magnetic fields can be reduced and the magnetic resistance of the magnetic circuit can be reduced, thereby further increasing the efficiency of the drive.

[0031] Designing the magnetic field-carrying components of the drive with as few components as possible also has a positive effect on the magnetic resistance of the magnetic circuit and thus has a positive effect on the performance of the drive.

[0032] The present invention will be explained in detail below using exemplary embodiments with reference to the accompanying figures. They show: Fig. 1 a longitudinal section through a vibration limit level sensor with inductive drive according to the state of the art, Fig. 2 a longitudinal section through a vibration limit level sensor with inductive drive according to the present application, Fig. 3 a variant of the vibration limit sensor of the Fig. 2 with tubular sleeve and Fig. 4 another variant of the vibration limit sensor of the Fig. 2, where the sleeve is completely omitted.

[0033] In the figures, unless otherwise stated, the same reference symbols designate the same components with the same function.

[0034] Fig. 1 shows a longitudinal section through a vibration limit level sensor 1 with inductive drive according to the prior art.

[0035] The vibration limit level sensor 1 has an inductive drive, which essentially consists of a coil 2 mounted in a housing 13, a coil core 5 arranged inside the coil 2, and a permanent magnet 7 mounted on an oscillating membrane 11 via a magnet holder 9 and a bolt 15. The permanent magnet 7 is arranged in the magnet holder 9 with a first end 71, which in the present embodiment corresponds to the south pole of the permanent magnet 7. The permanent magnet 7 is glued into a recess in the magnet holder 9 and is thus integrally connected to it. The magnet holder 9 is screwed to the bolt 15, which is formed integrally with the membrane 11, and is thus coupled to it.

[0036] A movement of the magnet holder 9 is transmitted to the diaphragm 11 in such a way that a movement of the permanent magnet 7 causes a movement of the diaphragm 11 and vice versa. Mechanical oscillators 12 are arranged on a side of the diaphragm 11 opposite the magnet holder 9, which execute a lateral pivoting movement upon a movement of the permanent magnet 7 in the axial direction A.

[0037] The coil 2 of the inductive drive is fixedly mounted in the housing 13 of the vibration limit level sensor 1 and penetrated by the coil core 5. The coil core 5 and the magnet holder 9 are both made of magnetically conductive material, so that these components ensure guidance of the magnetic field generated by the coil 2 and the permanent magnet 7. Surrounding the coil 2 is a cylindrical yoke 17 made of magnetically conductive material, which also guides the magnetic field and thus closes the magnetic circuit. A first air gap 21 is formed between the coil core 5 and a second end 72 of the permanent magnet 7. When the coil 2 is energized, the permanent magnet 7 is drawn towards the coil core 5 due to the magnetic field generated by the energization, or - depending on the orientation of the generated magnetic field - is repelled by it.

[0038] The coil core 5 is mounted on the yoke 17 at the rear, ie at an end of the vibration limit level sensor 1 facing away from the membrane 11, and extends approximately up to half of an axial extent of the coil 2 in the axial direction A. The permanent magnet 7 is arranged opposite the coil core 7 in the axial direction A and forms a first air gap 21 with it, the permanent magnet 7 being mounted with its first end 71 in the magnet holder 9.

[0039] The permanent magnet 7 can, for example, be pressed into the magnet holder 9, glued into it, or connected to it in some other way. The magnet holder 9 also has a central opening running in the axial direction A, in which the bolt 15 is arranged. The magnet holder 9 can, for example, be pressed, screwed, or otherwise connected to the bolt 15. The magnet holder 9 is, as described above, pot-shaped and therefore has a circumferential collar 93 running in the axial direction A, which, with an end of the yoke 17 facing the membrane 5, forms a second air gap 22, which likewise contributes to the drive power of the inductive drive.

[0040] By energizing the coil 2, a magnetic field can be induced in the stationary part of the present arrangement, i.e. the coil 2 and the coil core 7, which, with a suitable size and frequency, is suitable for causing the movable part of the present arrangement, i.e. the permanent magnet 7 and the magnet holder 9, to vibrate in the axial direction A. These vibrations are transmitted via the bolt 15 to the diaphragm 11, which is designed to be capable of vibration and is mounted on the housing 13, which transmits the vibrations to vibrating elements 12 arranged on the diaphragm 11, which in this case are designed as a tuning fork. In this way, the vibrations generated by the drive can be transmitted to a space adjacent to the diaphragm 11 and a process medium located therein.

[0041] Conversely, vibrations of the vibrating elements 12 are transmitted via the membrane 11 and the bolt 15 to the magnet holder 9 and in this way induce a current in the coil 2. In this way, an oscillation frequency and / or amplitude or a change in the oscillation frequency and / or amplitude of the vibrating elements 12 can be detected and thus it can be concluded that the vibrating elements 12 are covered with a process medium.

[0042] In the embodiment of the Fig. 1 shows a first path P1, where the field lines should ideally run. The field lines of the magnetic field generated by the coil 2 and the permanent magnet 7 run according to the first path P1 through the permanent magnet 7, the magnet holder 9, to the second air gap 22, via the yoke 17, a base 19 connected to the yoke, the coil core 5, and the first air gap 21 back to the permanent magnet 7, so that both air gaps 21, 22 contribute to the drive power of the inductive drive.

[0043] In the prior art design, however, a parasitic second path P2 is formed by the magnetic field lines. After exiting the permanent magnet 7, the second path P2 runs upwards in the magnet holder 9 and from there, via a coil carrier on which the coil 2 is arranged, jumps to the yoke 17, thereby bypassing the second air gap 22 aligned parallel to the diaphragm 11, so that this portion of the magnetic field lines is lost for the force effect of the drive.

[0044] According to a third path P3, magnetic field lines can also form directly from the magnet holder 9 back into the permanent magnet 7, so that this part of the magnetic field is lost not only in the second air gap 22 but also in the first air gap 21 for the drive power.

[0045] In Fig. 2 shows a longitudinal section through a vibration limit level sensor 1 according to the present application.

[0046] The basic structure of the vibration limit sensor 1 corresponds to that in Fig. 1, with the difference that the magnet holder 9 is formed in two parts according to the present invention. In the present embodiment, the magnet holder 9 is formed from a sleeve 91 in which the permanent magnet 7 is mounted, and a steering section 92 for guiding the magnetic field. The sleeve 91 is made of a magnetically non-conductive material, for example, a weldable, magnetically non-conductive stainless steel.

[0047] To establish a connection to the membrane 11, the steering section 92 has a bore through which the bolt 15 is guided. The sleeve 91 has an internal thread and is screwed onto a corresponding external thread of the bolt 15, so that the steering section 92 is clamped against a shoulder of the bolt 15. To prevent this connection from coming loose, the sleeve 91 is welded to the steering section 92 at certain points or, alternatively, circumferentially, effectively preventing the screw connection from unscrewing. Alternatively, the screw connection can also be secured, for example, using a threadlocker or other locking agent.

[0048] Because the sleeve 91 is made of a magnetically non-conductive material, the magnetic field of the permanent magnet 7 and the coil 2 is guided entirely via the steering section 92 to the second air gap 22 and is thus fully available for the drive power of the inductive drive. Parasitic magnetic field paths, such as those that arise in the prior art, are effectively prevented in this way.

[0049] For the present measure to be effective, it is advantageous if the distance d between the first end 71 of the permanent magnet 7, at which the magnetic field lines emerge from the permanent magnet 7, and the entry into the steering section 92 is as small as possible. To achieve this, the sleeve 91, as shown in Fig. 3, for example, be tubular, so that the permanent magnet 7 sits directly on the steering section 92 or - if this is technologically feasible - an internal thread for clamping with the bolt 15 can be introduced directly into the permanent magnet 7. The sleeve 91 could in this way, as in Fig. 4, are also completely eliminated. List of reference symbols 1 vibration level sensor 2 coils 5 coil core 7 Permanent magnet 9 Magnetic holder 11 Membran 12 mechanical oscillators 13 housings 15 bolts 17 yoke 19 Floor 21 first air gap 22 second air gap 71 first end 72 second end 91 sleeve 92 steering section 93 collar A axial direction d distance

Claims

[1] Vibration limit level sensor (1) with an inductive drive with - an energizable coil (2) with a coil core (5) which is arranged at least partially axially overlapping with the coil (2), - a permanent magnet (7) aligned in the axial direction (A), wherein a first end (71) of the permanent magnet (7) is held in a magnet receptacle (9), wherein the coil (2) and the permanent magnet (7) are movable relative to one another and are mounted on the one hand on a fixed part and on the other hand on a movable part coupled to a membrane (11) designed to be capable of oscillation, wherein - at least two air gaps are formed between the fixed part and the movable part, wherein - a first of the air gaps (21) is formed between the coil core (5) and a second end (72) of the permanent magnet (7) and - a second of the air gaps (22) exists between the fixed and the movable part, characterized by that the magnet holder (9) is formed at least in two parts with a sleeve (91) for holding the permanent magnet (7) and a steering section (92) connected to the sleeve (91) and is made at least partially from a magnetically non-conductive material. [2] Vibration limit sensor (1) according to claim 1, characterized by , that - the coil (2) is fixed, - the permanent magnet (7) is coupled to the membrane (11), - wherein the magnet holder (9) is connected to the membrane (11) as a movable part. [3] Vibration limit level sensor (1) according to claim 1, characterized by , that - the permanent magnet (7) is fixed, - the coil (2) is coupled to the membrane (11), - wherein a coil carrier is connected to the membrane (11) as a movable part. [4] Vibration limit sensor (1) according to one of the preceding claims, characterized by that the sleeve (91) and / or the steering section (92) is connected to the membrane (11) via a bolt (15), in particular screwed and / or welded and / or glued and / or pressed. [5] Vibration limit sensor (1) according to one of the preceding claims, characterized by that a distance (d) between the second end (72) of the permanent magnet (7) and a bottom region of the steering section (92) is minimized. [6] Vibration limit sensor (1) according to one of the preceding claims, characterized by that the sleeve (91) is tubular. [7] Vibration limit sensor (1) according to one of the preceding claims, characterized bythat the sleeve (91) is connected to the steering section (92) in a force-fitting, form-fitting or material-fitting manner. [8] Vibration limit sensor (1) according to one of the preceding claims, characterized by that the sleeve (91) is flush with the permanent magnet (7) on the membrane side in the axial direction (A). [9] Vibration limit sensor (1) according to one of the preceding claims, characterized by that the sleeve (91) is made of a rust-proof, weldable, magnetically non-conductive stainless steel, in particular AISI 316L, preferably WNo. 1.4404. [10] Vibration limit sensor (1) according to one of the preceding claims, characterized by that the magnet holder (9) has on its circumference a circumferential collar (93) extending radially away from the membrane (11) for guiding the magnetic flux. [11] Vibration limit sensor (1) according to claim 10, characterized bythat the second air gap (21) is formed between the collar (93) and a yoke (17) for returning the magnetic field. [12] Vibration limit sensor (1) according to claim 11, characterized by that the yoke (17) is sleeve-shaped. [13] Vibration limit sensor (1) according to claim 12, characterized by that the yoke (17) is formed with a base (19), wherein the coil core (5) is arranged on the base (19), preferably formed in one piece therewith.

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