Dual-redundancy inductive proximity switch

Abstract

The application provides a dual-redundancy inductive proximity switch, which comprises a connector, a shell, a cover plate, a first circuit board, a second circuit board, a plurality of support columns, a gasket and an induction head; the induction head comprises an induction head cover, a coil and a magnetic core; the induction head cover is fixedly connected with the shell through laser welding; the magnetic core is U-shaped; a magnetic shielding cover is sleeved on the coil; the coil is glued on the inner column of the magnetic core and is filled with silicone rubber; after the magnetic core is bonded in the induction head cover, the induction head cover is filled with filling glue. The circuit design of the two circuit boards adopts a thick film integrated manner; and the debugging resistor and the capacitor in the circuit are selected as patch components and are welded on the printed board. In the design, the series, generalization and combination are fully considered; the mutual interference problem of the induction heads of the dual-redundancy proximity switch is solved in the limited space size; the stable function and performance of the dual-redundancy proximity switch are realized; and the application has certain guiding significance in the proximity switch design field.

Description

Technical Field

[0001] This invention belongs to the field of proximity switch design, and specifically relates to a dual-redundant inductive proximity switch. Background Technology

[0002] Redundancy design is increasingly being used in systems. While internationally, multiple single-redundant proximity switches are often used to achieve redundancy in systems, Chinese systems tend to use a single multi-redundant proximity switch. Currently, the most commonly used multi-redundant proximity switch in domestic equipment is dual-redundant; therefore, the research and development of dual-redundant proximity switches is imperative and has broad application prospects.

[0003] Because inductive proximity switches are highly reliable and widely used, this invention is a dual-redundant function implemented based on inductive proximity switches. However, the design of dual-redundant proximity switches presents two major challenges compared to single-redundant designs.

[0004] On the one hand, dual-redundant inductive proximity switches operate on the principle of electromagnetic induction. The coupling characteristics of electromagnetic waves determine from the design principle that mutual interference between the two induction coils in a dual-redundant inductive proximity switch is inevitable. Therefore, reducing the mutual interference between the two proximity switches within a limited space is of great significance for realizing the function and performance of dual-redundant proximity switches and plays a decisive role in the successful development of dual-redundant inductive proximity switches.

[0005] On the other hand, the two sets of induction coils and detection circuits in a dual-redundant inductive proximity switch will inevitably exhibit some performance differences due to factors such as component batches, manufacturing processes, etc., especially under temperature variations. Furthermore, dual-redundant proximity switches require high output consistency and synchronization. This increases the uncertainty of overall performance when the two sets of induction coils and detection circuits operate together, such as requiring higher accuracy and response time for approach and distance switching. Therefore, improving circuit stability and consistency, and reducing design discrepancies and uncertainties, plays a crucial role in enhancing the performance of dual-redundant inductive proximity switches.

[0006] The above two technical challenges hinder the application of dual-redundant proximity switches, and there are no precedents for the research and application of dual-redundant proximity switches in China, making it a completely blank field. Summary of the Invention

[0007] This invention addresses the current single-inductive proximity switches by proposing a dual-redundant inductive proximity switch from an engineering application perspective. This invention focuses on solving the anti-interference problem and improving the stability and consistency of dual redundancy, realizing the function and performance of dual-redundant inductive proximity switches, and also providing design methods and ideas for more redundant inductive proximity switches.

[0008] The technical solution of the present invention is: a dual-redundant inductive proximity switch, comprising a connector 1, a housing 2, a cover plate 3, a first circuit board 5, a second circuit board 6, several support pillars, a washer 8, and a sensing head 10;

[0009] The housing 2 has a multi-stage cavity inside, one end of which is fixed to the connector 1, and the outer wall of the housing near the other end is connected to the sensing head 10 by laser welding 9.

[0010] The cover plate 3 is used to close the shell 2, and glue is applied before closing;

[0011] The first circuit board 5 and the second circuit board 6 are located inside the cavity. The two circuit boards are parallel to each other and are supported and fixed by several pillars to maintain a distance.

[0012] The sensing head 10 includes a sensing head cover, a coil, and a magnetic core. The sensing head cover is fixed to the housing 2 by laser welding. A positioning plate is provided in the cover to position the two magnetic cores. The magnetic cores are U-shaped, and the two magnetic cores are placed in parallel with their open ends facing the sensing end face of the sensing head cover. A magnetic shielding cover is fitted on the coil to prevent the two coils from interfering with each other. The coil is glued to the inner post of the magnetic core and encapsulated with silicone rubber. After the magnetic core is glued inside the sensing head cover, it is encapsulated with potting compound.

[0013] The circuit design on the first circuit board 5 and the second circuit board 6 adopts thick film integrated circuits, and the debugging resistors and thermistors in the circuit are surface mount components soldered on the printed circuit board.

[0014] Furthermore, the magnetic core is made of ferrite material.

[0015] Furthermore, the sensing head cover is a non-magnetic metal cuboid thin-walled structure. The outer side of the bottom surface of the cuboid is the sensing end face, which is the starting point of the test distance between the target and the product. The opening end is provided with a stepped rectangular hole for positioning with the outer surface of the rectangular boss of the shell.

[0016] Furthermore, the sensing end face is designed with a thickness of 0.2–0.3 mm, an outer wall thickness of 0.8–1 mm, and a connection wall thickness of 0.4–0.6 mm.

[0017] Furthermore, the circuit modules on the circuit board are mounted on the printed circuit board, which is positioned by the inner hole and steps of the housing and fastened by screw rings and secured with thread-locking adhesive.

[0018] Furthermore, the magnetic shielding cover of the coil is made of soft magnetic alloy 1J50 material.

[0019] Furthermore, the coil is made of QZYTWC-1 / 180 non-magnetic enameled wire.

[0020] Furthermore, the plurality of pillars are three in number, namely the first pillar 7, the second pillar 11 and the third pillar 12. One end of the first pillar 7 is fixedly connected to the cover plate, and the other end is fastened to the second pillar 11. The second pillar 11 supports and installs the first circuit board, and at the same time fastens the second circuit board to the third pillar 12. One end of the third pillar 12 supports and installs the second circuit board, and the other end is fixedly connected to the housing.

[0021] Furthermore, the integrated circuit on the circuit board includes a hysteresis resistor, a signal feedback resistor, a state transition resistor, a proximity switch circuit module, a resonant capacitor, and an induction coil; the high-side power supply is connected to an external DC power supply of 16V to 36V, the power ground is connected to the external power supply ground line, and the output is an open-collector (OC) output switch signal.

[0022] Invention Effects

[0023] The technical effects of this invention are as follows: Compared with the prior art, the specific effects produced by this invention are as follows:

[0024] The circuit adopts a thick-film integrated circuit approach. Compared with discrete components, the circuit shows significant improvements in power consumption, AC / DC operating point, bandwidth, and temperature drift, greatly enhancing the measurement accuracy of the dual-redundant proximity switch. After experimental screening, the pass rate of the thick-film integrated circuit module is approximately 12% higher than that of the circuit built with discrete components. On the other hand, the resonant part of the inductive proximity switch circuit can first couple and interfere with other parts of the product, and secondly, it may generate an antenna effect due to defects in the printed circuit board design, radiating interference to a wider range of supporting systems. The thick-film integrated circuit eliminates the potential for antenna effects and encapsulates the circuit in a metal package. Based on the principle of electrical shielding, this greatly improves the electromagnetic compatibility performance of the product, enabling the product to pass the electromagnetic compatibility tests of the relevant systems on the first attempt.

[0025] In the circuit board, the debugging resistors and thermistors are not integrated; instead, they are surface-mount components soldered onto the printed circuit board. During the integration design process, considering product verifiability, key testing points in the circuit are led out to the integrated module pins for convenient module inspection and testing. After using this method for debugging and temperature compensation, compared to a design without temperature compensation, the product's normal operating temperature range is increased by 42%, and the debugging cycle is shortened by 57% compared to not setting debugging resistors and test points. By selecting different values ​​for the debugging resistors, the circuit's performance consistency is significantly improved, and the module scrap rate decreases from approximately 6% to approximately 1%.

[0026] 3. The product casing adopts a split structure, consisting of three parts: the shell, the cover plate, and the sensor head cover. This allows for a more reasonable layout of the size, strength, and rigidity of each component, avoids the need for machining thin-walled parts with long and narrow holes, improves the manufacturability of the parts and the manufacturability of the product assembly, and facilitates product installation and debugging.

[0027] 4. The product adopts an all-metal sealed structure, protecting internal components, circuit boards, and parts from corrosion by salt spray, mold, and acidic atmospheres. The sensor head is laser-sealed and welded to the housing after positioning, making the welding process simple and easy to operate. The socket uses GJB599 series hermetic electrical connector sockets, which can achieve good sealing performance.

[0028] 5. The sensing surface is integrated with the outer shell, which protects the internal magnetic core and coil from external environmental corrosion, ensuring reliable and sensitive product detection. The sensing head cover is made of TC4-R titanium alloy, which meets the material selection requirements, making the sensing head highly resistant to mechanical forces and impacts, and not easily damaged.

[0029] 6. Welding and potting are used to connect components, ensuring the airtightness of the product cavity, reducing shell stress, increasing shell strength, improving corrosion and damp heat resistance, and preventing high-frequency harmonics from escaping from shell gaps, further enhancing the product's electromagnetic compatibility performance. In field testing, this structural design was verified to withstand environmental conditions, ensuring the normal operation of the product's electrical functions.

[0030] 7. Traditional sensors mostly use hollow coils, which reduces manufacturing difficulty but also causes loss of magnetic field energy. Adding a magnetic core inside the coil confines the magnetic field within a certain range, ensuring that the number of turns is reduced and the coil's Q value is increased under the same inductance conditions. This allows for sensitivity to weaker magnetic field changes and increases the measurement range.

[0031] 8. The magnetic core is made of ferrite material, which has a resistivity much greater than that of metal materials, thus suppressing the generation of eddy currents. It is an ideal magnetic core material for eddy current proximity switches. At the same time, in order to ensure the product's adaptability to high and low temperature environments, the magnetic core material should have a small permeability to temperature coefficient.

[0032] 10. The geometry of the magnetic core affects the coil's shielding, leakage inductance, winding, and installation. The product's magnetic core is designed with a can-shaped structure, providing excellent magnetic shielding performance while facilitating coil lead-out and core-coil frame installation. The R2KG material used in the core is easily magnetized, has a low residual magnetic flux density, and a resistivity much greater than that of metallic materials, thereby suppressing eddy current generation, reducing eddy current losses, and improving the product's detection distance and sensitivity.

[0033] The 11 coils are wound without a frame using tooling, making full use of the winding space of the magnetic core, reducing the gap with the magnetic core, improving the coil quality factor, and generating stable inductance.

[0034] The 12-induction coil shielding makes the magnetic flux distribution generated by the induction coil more concentrated, and allows the magnetic circuit that originally directly connected the two induction coils through space to pass through the shielding, reducing direct interference between the induction coils and reducing mutual interference of eddy currents induced by the induction coils on the target, thus reducing indirect interference between the induction coils. Attached Figure Description

[0035] Figure 1 Eddy current model

[0036] Figure 2 Eddy current equivalent circuit

[0037] Figure 3 Parallel resonant equivalent circuit

[0038] Figure 4 Schematic diagram of a dual-redundant inductive proximity switch circuit

[0039] Figure 5 Integrated circuit diagram

[0040] Figure 6 Overall structure diagram of dual-redundant inductive proximity switch

[0041] Figure 7 Structure diagram of dual-redundant inductive proximity switch sensing head cover

[0042] Figure 8 Structure diagram of magnetic shielding cover for dual-redundant inductive proximity switch

[0043] Figure 9 Dimensions of the magnetic shielding cover for a dual-redundant inductive proximity switch

[0044] Figure 10 Dual-redundant inductive proximity switch core structure diagram

[0045] Figure 11 Engineering drawing of dual-redundant inductive proximity switch coil

[0046] Explanation of reference numerals in the attached drawings: 1-Connector; 2-Housing; 3-Cover plate; 4-Screw; 5-First circuit board; 6-Second circuit board; 7-First support; 8-Washer; 9-Laser weld; 10-Induction head; 11-Second support; 12-Second support Detailed Implementation

[0047] See Figures 1-11 The objective of this invention is achieved through the following technical means: this design method suppresses the mutual interference between the two sets of induction coils inside the dual-redundant proximity switch and greatly improves design stability. Thus, while ensuring the performance indicators of the proximity switch, such as sensing range, size, weight, and power consumption, dual-redundant functionality and performance are achieved. This method has strong engineering practicality and provides certain guiding significance in the field of dual-redundant inductive proximity switch design.

[0048] The dual-redundant switch designed in this invention includes a connector 1, a housing 2, a cover plate 3, a first circuit board 5, a second circuit board 6, several pillars, a washer 8, and a sensing head 10.

[0049] 1. The circuit design and considerations for the switch are as follows:

[0050] 1. Based on the relative permeability of the induction target, the induction range, and the sensitivity requirements of the proximity switch, an eddy current physical model is established. The parameter values ​​in the model, namely the equivalent inductance L of the induction coil and the resonant frequency ω of the resonant circuit, are determined, serving as the theoretical guidance for the design. Using the values ​​of the equivalent inductance L and the resonant frequency ω of the resonant circuit, combined with the calculations of the final equivalent theoretical formulas 13 and 14, the selection of components in the proximity switch circuit design is determined, thus completing the circuit design.

[0051] First, a simplified eddy current model is established, as follows: Figure 1 As shown, for ease of analysis, the eddy current loop inside the target is equivalent to a short-circuit loop, which is equivalent to a one-turn closed inductor coil.

[0052] The short-circuit loop parameters are as follows:

[0053] r i =0.525r as (1)

[0054] r a =1.39r as (2)

[0055]

[0056] In the formula:

[0057] r i —Equivalent inner radius of the short-circuit loop, cm;

[0058] r a —Equivalent outer radius of the short-circuit loop, cm;

[0059] r as —Outer radius of the coil, cm;

[0060] h—Eddy current penetration depth, cm;

[0061] ρ—Target resistivity, Ω·cm;

[0062] f—current frequency, Hz;

[0063] μ r —Relative permeability.

[0064] Short-circuit ring eddy current loss power P e for:

[0065]

[0066] In the formula:

[0067] ω — angular frequency of the alternating magnetic field, rad / s;

[0068] B m —Maximum magnetic flux density, T.

[0069] Impact on P e Factors include the angular frequency ω of the alternating magnetic field and the maximum magnetic induction intensity B. m The resistivity ρ of the target and the range of eddy current formation, etc.

[0070] Among the factors affecting eddy current loss, the magnetic field distribution plays a decisive role in sensitivity and linear range. To achieve a large linear range, a large axial distribution range of the magnetic field is required; to achieve high sensitivity, a large change in eddy current loss power is required when the target moves axially, i.e., a large gradient in axial magnetic field strength.

[0071] The inner diameter, outer diameter, and thickness of the coil will have a certain impact on the magnetic field strength-detection distance Bx characteristic, and the relationship between them is relatively complex. The outer diameter of the coil has a significant impact on the magnetic field distribution range and the gradient of magnetic field strength variation. The larger the outer diameter of the coil, the larger the linear range, but the lower the sensitivity; the smaller the outer diameter of the coil, the higher the sensitivity, but the smaller the linear range. The linear range is approximately 1 / 3 to 1 / 5 of the outer diameter of the coil. Changes in the inner diameter and thickness of the coil only result in slight differences in sensitivity near the coil.

[0072] Eddy current equivalent circuit as follows Figure 2 As shown, the short-circuit ring resistor is R2 and the inductor is L2.

[0073] The complex impedance Z1 of the coil is:

[0074] Z1=R1+jωL1 (5)

[0075] The short-circuit ring resistor R2 is:

[0076]

[0077] When the target approaches the coil, it becomes a coupled inductor, and there is a mutual inductance coefficient M between the coil and the target. The mutual inductance coefficient M is:

[0078]

[0079] In the formula:

[0080] x — the detection distance between the coil and the target;

[0081] ω — Oscillation frequency.

[0082] The mutual inductance coefficient increases as the distance between the coil and the target decreases.

[0083] The equivalent complex impedance Z of the coil after being affected by the target eddy current effect is:

[0084]

[0085] The equivalent resistance R is:

[0086]

[0087] The equivalent inductance L is:

[0088]

[0089] The quality factor Q is:

[0090]

[0091] The variations in the coil's inductance, impedance, and quality factor are related to the target's geometry, size, resistivity ρ, and permeability μ, as well as the coil's geometric parameters, current frequency, and the distance between the coil and the target. The target's resistivity ρ, permeability μ, distance x between the coil and the target, and the angular frequency ω of the coil's excitation current are all related to the coil's impedance through eddy current and magnetic effects. The coil impedance Z is a function of these parameters, i.e., Z = f(ρ, μ, x, ω).

[0092] When the target parameters and coil parameters remain constant, the coil's inductance L, impedance Z, and quality factor Q depend only on the distance x between the target and the coil, becoming single-valued functions of distance x.

[0093] (L, Z, Q) = u(I²) = Fx (12)

[0094] The conversion circuit can use any of the parameters L, Z, and Q to convert them into electrical quantities for measurement.

[0095] Since it is an inductive proximity switch, the L is measured using a resonant circuit method.

[0096] A resonant circuit converts changes in the equivalent inductance of a coil into changes in voltage or current. The coil and capacitor form an LC parallel resonant circuit. Compared to the impedance method, which directly utilizes the coil's impedance, this improves the nonlinearity of the measurement circuit and is more widely used. In addition to the inductance L, the coil also has a resistance R. The equivalent circuit of the parallel resonant circuit is as follows: Figure 3 As shown.

[0097] The resonant frequency ω of the parallel resonant circuit is:

[0098] ω=2πf

[0099]

[0100] At the point of circuit resonance, its equivalent impedance Z0 is at its maximum, which is:

[0101]

[0102] In the formula:

[0103] R′——Equivalent loss resistance of the circuit.

[0104] Therefore, the eddy current physical model can be equivalent to an LC oscillating circuit. The internal dimensions of the sensing head are designed based on the sensing head material and system requirements. The optimal parameters of the magnetic core structure and induction coil are iteratively designed based on space requirements, target, detection distance, and enameled wire performance, with the induction coil's quality factor Q being the primary reference. After determining the required specifications within the sensing head, impedance matching and resonant frequency ω are configured using the conditioning circuit on the circuit board to achieve the function and performance of a proximity switch. When changes in distance cause a change in the inductance L of the induction coil within the sensing head, both the equivalent impedance and resonant frequency of the circuit change; therefore, the circuit impedance or resonant frequency can be used for measurement.

[0105] To reduce the discreteness caused by too many components, improve performance and stability, and reduce cost, risk, and debugging difficulty, the circuit board design adheres to the principles of modularity and integration, employing a thick-film integration method. This significantly enhances the performance and stability of the detection circuit board.

[0106] The circuit block diagram of this invention is as follows: Figure 4 As shown, considering factors such as reducing product size, improving product performance, and lowering costs and risks, the product circuitry utilizes a thick-film integrated circuit design. After testing and long-term use verification, its quality has proven to be stable and reliable. The product is designated BHM-S-13, and its dimensions are as follows. Figure 5 As shown in the diagram, the proximity switch circuit module is the main component. An external 16V-36V power supply is connected to the module's VS+ pin, and the external power supply ground is connected to the module's GND pin. The module's YL_JH terminal serves as the proximity switch output. The induction coil is inside the sensing head and connected to the module's GND and LC terminals via two leads. A parallel tuning capacitor is connected to the induction coil to adjust the circuit impedance and resonant frequency. A hysteresis resistor, soldered to the printed circuit board and connected to the module's RH1 and RH2 terminals, is mainly used to adjust the proximity switch hysteresis distance. A signal feedback resistor, also connected to the printed circuit board and connected to the module's RF and VZ10 terminals, is mainly used to adjust the induction coil's external radiated power. A state transition resistor, connected to the printed circuit board and connected to the module's RD and VZ10 terminals, is mainly used to adjust the product's output distance from the approach point to the distance from the point of origin.

[0107] Meanwhile, to facilitate product proximity characteristic adjustment and temperature compensation, the adjustment resistor and thermistor are not integrated, but are instead surface-mount components soldered onto the printed circuit board.

[0108] 1. The design and considerations for the specific components in the switch are as follows:

[0109] The cover and housing are connected by screws and sealed with sealant. The sensor head cover and housing are laser welded together. The cable lead-out holes between the housing and the connector are filled with glue to ensure absolute sealing inside the housing cavity. The two circuit boards are supported by pillars and fixed in the center of the cavity. This prevents the deformation of the structural components from affecting the circuit and makes good use of the cavity space, thus promoting product miniaturization.

[0110] The socket and housing are fastened together using standard parts; the cover plate is fastened to the housing using standard parts; the sensor head and housing are welded together using laser welding technology; the coil and magnetic core inside the sensor head are encapsulated in potting compound within the sensor head cover. The components are connected using welding, standard parts fastening, and potting compounding, simplifying the process and improving reliability and stability.

[0111] The magnetic core is made of ferrite, which is easily magnetized, has a low residual magnetic flux density, and a resistivity much greater than that of metal materials, which helps to reduce eddy current losses. It also has a small permeability wall temperature coefficient, making it an ideal magnetic core material for proximity switches and improving stability under temperature changes.

[0112] The geometry of the magnetic core affects the shielding, leakage inductance, winding, and installation of the coil. To meet product requirements, a U-shaped magnetic core was developed, which has excellent magnetic shielding performance, low leakage inductance, and convenient coil lead-out and installation.

[0113] Magnetic shielding covers are installed on the two sets of induction coils to make the magnetic flux generated by the induction coils more concentrated and narrower in direction, thereby reducing electromagnetic interference between them.

[0114] The sensing head is the sensitive element of the product, consisting of a sensing head cover, a magnetic core, and a coil. The coil is bonded to the inner post of the magnetic core with X98-11 adhesive and then encapsulated with GD401 silicone rubber. The magnetic core is bonded to the inside of the sensing head cover with DG-3S epoxy adhesive and then encapsulated with GOET-1080RL tough epoxy resin potting compound.

[0115] The BHM-S-13 proximity sensor circuit module is mounted on a printed circuit board (PCB). The PCB is positioned using housing bores and steps, then secured with threaded rings and Loctite 243 threadlocker to prevent loosening. To improve circuit board versatility, PCB I and PCB II are designed with the same layout.

[0116] Sensor headgear, such as Figure 7 As shown, it is designed as a non-magnetic metal cuboid structure. The outer side of the bottom surface of the cuboid is the sensing end face, which is the starting point of the test distance between the target and the product.

[0117] The sensing surface is integrated with the outer shell, protecting the internal magnetic core and coil from external environmental corrosion and ensuring reliable and sensitive product detection. The sensing head cover features a thin-walled structure, allowing the internal magnetic core and coil to fully utilize space to increase the detection distance. To meet design requirements for structural strength, corrosion resistance, and solderability, the sensing head cover is made of TC4-R titanium alloy, meeting material selection requirements and providing the sensing head with strong resistance to mechanical forces and impacts, making it less prone to damage.

[0118] The stepped rectangular hole at the opening of the sensor head cover is used for positioning with the outer surface of the rectangular boss on the housing, and the joint is connected to the housing by laser sealing welding.

[0119] During operation, eddy current losses occur at the cylindrical bottom of the sensing head cover. Therefore, the sensing surface should be as thin as possible while ensuring structural strength and manufacturability. Based on the factory's existing equipment processing capabilities and the structure of similar proximity switch sensing heads cover, the sensing surface thickness is designed to be 0.3mm, the outer wall thickness to be 1mm, and the wall thickness at the connection point to be 0.5mm. After strength analysis, this meets the product's mechanical environment requirements.

[0120] Shielding cover such as Figure 8 As shown, shielding electromagnetic fields requires the use of soft magnetic alloys. Joint simulation iterations were conducted based on the magnetic properties of various materials combined with spatial dimensions. The selection of the magnetic material was primarily based on a comprehensive consideration of factors such as the versatility of its application, the maturity of its processing technology, and available inventory. Ultimately, 1J50 material was chosen.

[0121] Due to structural space limitations, the initial dimensions of the shielding cover need to be defined for simulation software to assess its shielding effect. The optimal external dimensions will be determined through continuous iteration, considering both the shielding function and the potential for eddy current losses. For example... Figure 9 As shown.

[0122] The magnetic core is designed with a U-shaped structure, such as Figure 11 As shown, traditional sensors mostly use hollow coils, which reduces manufacturing difficulty but also results in magnetic field energy loss. Adding a magnetic core inside the coil confines the magnetic field within a certain range, ensuring that the number of turns is reduced and the coil's Q value is increased while maintaining the same inductance. This allows for sensitivity to weaker magnetic field changes and expands the measurement range.

[0123] Eddy current loss W in magnetic core e for:

[0124]

[0125] In the formula:

[0126] R – radius of the inner cylinder of the magnetic core; ρ – resistivity of the magnetic core material.

[0127] As shown in Equation 15, eddy current loss is inversely proportional to the resistivity of the core material. To reduce eddy current loss, a material with higher resistivity should be selected. Ferrite, as a soft magnetic material, is easily magnetized, but its residual magnetic flux density is low after the external magnetic field is removed. Furthermore, the resistivity of ferrite materials is much greater than that of metallic materials, thus suppressing eddy current generation, making it an ideal core material for eddy current proximity switches. Simultaneously, to ensure the product's adaptability to high and low temperature environments, the core material should have a small permeability-to-temperature coefficient. Generally, MnZn and R2KG ferrites are suitable for frequencies below 1MHz, while NiZn ferrite materials are required for higher frequencies.

[0128] The geometry of the magnetic core affects the shielding, leakage inductance, winding, and mounting of the coil. The product's magnetic core is designed with a can-shaped structure, such as... Figure 10 As shown, it possesses excellent magnetic shielding performance, while facilitating coil lead-out and the installation and mating of the magnetic core with the coil frame. The magnetic core utilizes highly stable R2KG manganese-zinc ferrite material with high initial permeability, low specific loss coefficient, and low temperature coefficient over a wide temperature range. R2KG material is easily magnetized, has a low residual magnetic flux density, and its resistivity is much greater than that of metallic materials, thereby suppressing eddy current generation, reducing eddy current losses, and improving the product's detection distance and sensitivity. The inner surface of the magnetic core is sprayed with H30-12 insulating varnish to insulate it from the coil.

[0129] The coil is designed as a toroidal structure, such as Figure 11 As shown. To improve the coil quality factor, after simulation analysis and full-temperature performance tests, QZYTWC-1 / 180 non-magnetic enameled wire with 300-500 turns was selected. The coil was wound without a frame using a tooling, making full use of the winding space of the magnetic core, reducing the gap with the magnetic core, improving the coil quality factor, and generating a stable inductance.

[0130] Ferrite was chosen as the magnetic material because its low permeability and high resistivity help reduce energy loss in the induction coil, improve detection distance and sensitivity, and lower power consumption. Furthermore, its low temperature coefficient ensures good performance consistency at both high and low temperatures, which is beneficial for improving the performance stability of dual-redundant proximity switches. Compared to proximity switches using ferrite cores and other cores, ferrite cores offer approximately 24% wider normal operating temperature range and an 8% increase in detection distance. Testing the on / off point of the dual-channel switch at high and low temperatures showed that the change using ferrite cores was less than 0.2 mm, while the change using other materials reached 0.4 mm.

[0131] Adding an induction coil shield to the coil makes the magnetic flux generated by the induction coil more concentrated. The magnetic circuit that originally directly connected the two induction coils through space passes through the shield, reducing direct interference between the induction coils and reducing mutual interference of eddy currents induced by the induction coils on the target, thus reducing indirect interference between the induction coils.

Claims

1. A dual-redundant inductive proximity switch, characterized in that, It includes a connector (1), a housing (2), a cover plate (3), a first circuit board (5), a second circuit board (6), several pillars, gaskets (8), and a sensor head (10); The housing (2) has a multi-stage cavity inside. One end is fixed to the connector (1), and the outer wall of the housing near the other end is connected to the sensing head (10) by laser welding (9). The cover plate (3) is used to close the shell (2), and glue is applied before closing; The first circuit board (5) and the second circuit board (6) are located in the cavity. The two circuit boards are parallel to each other and are supported and fixed by several pillars to maintain a distance. The sensing head (10) includes a sensing head cover, a coil, and a magnetic core; wherein the sensing head cover is fixed to the housing (2) by laser welding, and a positioning plate is provided in the cover to position the two magnetic cores; the magnetic core is U-shaped, the two magnetic cores are placed in parallel, and the open end faces the sensing end face of the sensing head cover; a magnetic shielding cover is fitted on the coil to avoid mutual interference between the two coils; the coil is glued to the inner column of the magnetic core and potted with silicone rubber; after the magnetic core is glued inside the sensing head cover, it is potted with potting glue; The circuit design on the first circuit board (5) and the second circuit board (6) adopts thick film integrated circuits, and the debugging resistors and thermistors in the circuit are surface mount components soldered on the printed circuit board.

2. The dual-redundant inductive proximity switch as described in claim 1, characterized in that, The magnetic core is made of ferrite material.

3. A dual-redundant inductive proximity switch as described in claim 1, characterized in that, The sensing head cover is a non-magnetic metal cuboid thin-walled structure. The outer side of the bottom surface of the cuboid is the sensing end face, which is the starting point of the test distance between the target and the product. The opening end is provided with a stepped rectangular hole for positioning with the outer surface of the rectangular boss of the shell.

4. A dual-redundant inductive proximity switch as described in claim 3, characterized in that, The induction end face is designed to have a thickness of 0.2–0.3 mm, an outer wall thickness of 0.8–1 mm, and a connection wall thickness of 0.4–0.6 mm.

5. A dual-redundant inductive proximity switch as described in claim 1, characterized in that, The circuit modules on the circuit board are mounted on the printed circuit board, which is positioned by the inner hole and steps of the housing and fastened by screw rings and thread-locking adhesive.

6. A dual-redundant inductive proximity switch as described in claim 1, characterized in that, The magnetic shielding cover of the coil is made of soft magnetic alloy 1J50 material.

7. A dual-redundant inductive proximity switch as described in claim 1, characterized in that, The coil is made of QZYTWC-1 / 180 non-magnetic enameled wire.

8. A dual-redundant inductive proximity switch as described in claim 1, characterized in that, The aforementioned pillars are three in number: a first pillar (7), a second pillar (11), and a third pillar (12). One end of the first pillar (7) is fixedly connected to the cover plate, and the other end is fastened to the second pillar (11). The second pillar (11) supports and installs the first circuit board, and at the same time fastens the second circuit board to the third pillar (12). One end of the third pillar (12) supports and installs the second circuit board, and the other end is fixedly connected to the housing.

9. A dual-redundant inductive proximity switch as described in claim 1, characterized in that, The integrated circuits on the circuit board include a hysteresis resistor, a signal feedback resistor, a state transition resistor, a proximity switch circuit module, a resonant capacitor, and an induction coil; the high-side power supply is connected to an external DC power supply of 16V to 36V, the power ground is connected to the external power supply ground line, and the output is an open collector (OC) output switch signal.

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