Inductance type proximity switch capable of resisting strong electromagnetic interference

Abstract

The invention provides an inductance type proximity switch resistant to strong electromagnetic interference. The inductance type proximity switch comprises a metal shell, an inductance coil, a metal rear cover, a shielding cable, a functional circuit board, a power supply filtering circuit board and pouring sealant. The metal shell is a metal cylinder with the rear end open and the front end fully closed, the inductance coil is arranged at the metal closed position of the front end of the metal shell and connected with one end of the functional circuit board through a contact pin, and the other end of the functional circuit board is connected with the power filter circuit board through an insulated wire. The rear end of the metal shell is connected with the metal rear cover in a laser welding mode, a wire passing hole is formed in the metal rear cover, a shielding cable is connected with the power supply filtering circuit board through the wire passing hole, and the interior of the metal shell is sealed through pouring sealant. The inductance type proximity switch resistant to strong electromagnetic interference is achieved through the good structure shielding performance and the excellent EMI filter circuit, and the phenomena that the inductance type proximity switch is sensitive and unstable in work in a complex electromagnetic environment are avoided.

Description

Technical Field

[0001] The invention relates to an inductive proximity switch capable of resisting strong electromagnetic interference. Background Art

[0002] Proximity switch is also called proximity sensor or contactless position switch. It is a position switch that can be operated without mechanical contact with moving parts. When the moving body approaches the switch to a certain position, the switch sends an electrical signal, which converts the movement information and existence information of the detected object into electrical signals, thereby realizing signal transmission and control. It has the characteristics of no mechanical wear and fatigue damage, high product positioning accuracy, stable performance, long service life, low power consumption, strong working reliability, and fast response. At present, traditional proximity switches on the market can only work in some relatively simple electromagnetic environments. Once exposed to scenes with slightly stronger interference and slightly larger radiation, the interference will be conducted or radiated along the cable or non-metallic shell into the interior of the proximity switch, causing abnormal voltage or current to be generated in the internal circuit of the proximity switch, resulting in unstable output of the proximity switch or even failure to work. For example, the power supply module disclosed in CN204669218U is used for a proximity switch, and is provided with a common-mode filter module and a differential-mode filter module. After a series of processed power supplies, various types of spikes and noise signals can be effectively suppressed to ensure voltage stability, thereby further improving the reliability of the proximity switch and extending the service life of the proximity switch. However, it does not disclose the conditions that can prevent interference caused by the environment in which the proximity switch is located. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an inductive proximity switch that is resistant to strong electromagnetic interference.

[0004] The present invention is achieved through the following technical solutions.

[0005] The present invention provides an inductive proximity switch capable of resisting strong electromagnetic interference; comprising:

[0006] The metal shell is a metal cylinder with an opening at the rear end and a fully enclosed front end;

[0007] The inductor coil is fixed to the inner wall of the front end of the metal shell by welding;

[0008] A functional circuit board is fixed to the front end of the metal housing, one end of which is electrically connected to the inductor coil via a pin;

[0009] A power filter circuit board is fixed to the rear end of the metal housing and connected to the other end of the functional circuit board through a wire;

[0010] A metal back cover is sealed and connected to the rear end of the metal shell by laser welding, and a wire hole is provided on the metal back cover;

[0011] A shielded cable passes through the wire passing hole and is electrically connected to the power filter circuit board by welding. The shielding layer of the shielded cable is welded and fixed to the metal shell.

[0012] Potting glue completely fills the internal space of the metal shell.

[0013] The rear surface of the metal shell is nickel-plated. The ground wire of the power filter circuit board and the shielding layer of the shielded cable are both fixed to the metal shell by welding.

[0014] The functional circuit board includes:

[0015] An LC oscillation circuit, which includes an inductor L2 and a capacitor C6. One end of the inductor L2 and the capacitor C6 is connected to the 2nd pin of the control chip U1, and the other end of the inductor L2 and the capacitor C6 is connected to the 5th pin of the control chip U1.

[0016] A distance adjustment circuit, which includes a control chip U1, resistors R8 - R11. The 3rd pin of the control chip U1 is connected to the resistor R8. The other end of the resistor R8 is respectively connected to the resistor R9 and the resistor R10. The resistor R9 and the resistor R10 are commonly connected to the resistor R11. The other end of the resistor R11 is connected to the 5th pin of the control chip U1.

[0017] A protection circuit, which includes a bidirectional transient voltage suppression diode TVS3 and a rectifier diode D2. The bidirectional transient voltage suppression diode TVS3 is connected in parallel between the emitter and the collector of the output triode Q2. The anode of the rectifier diode D2 is connected to the pad BU1 through the resistor R12.

[0018] An output circuit, which includes an output triode Q2. The base of the output triode Q2 is connected to the 7th pin of the control chip U1 through the resistor R7. The collector of the output triode Q2 is connected to the pad OUT1 through the magnetic bead CZ2.

[0019] In the protection circuit, the 8th pin of the control chip U1 is also connected to the emitter of the output triode Q2 and the resistor R5. The other end of the resistor R5 is connected to the 6th pin of the control chip U1 through the magnetic bead CZ1.

[0020] The power filter circuit board includes:

[0021] A differential mode filter circuit, which includes bidirectional transient voltage suppression diodes TVS1, TVS2, a resistor R1, a capacitor C1, and a rectifier diode D1. TVS1 is connected between the positive and negative poles of the power supply. TVS2 is connected in parallel between the output line and the negative pole of the power supply. One end of the resistor R1 is connected to the positive line, and the other end is connected to the negative pole of the power supply through the capacitor C1 and the rectifier diode D1.

[0022] The common-mode filter circuit includes a common-mode inductor L1, and capacitors CY1 and CY2. The pin 1 of the common-mode inductor L1 is connected to a resistor R1, the pin 2 is connected to a capacitor C6, and the pins 3 and 4 are grounded through the capacitors CY1 and CY2 respectively.

[0023] The filter circuit suppresses broadband interference through the cooperation of a differential-mode filter circuit and a common-mode filter circuit.

[0024] The power supply filter circuit board also includes a power supply circuit, which is composed of a voltage-regulating diode DZ1, an adjustment triode Q1, and a resistor R2. The cathode of the voltage-regulating diode DZ1 is connected to the capacitor CY1, the anode is connected to the base of the adjustment triode Q1, the resistor R2 is connected in parallel between the base and the collector of the adjustment triode Q1, the collector of the adjustment triode Q1 is connected to the capacitor CY2, and the emitter is connected to the pad BU.

[0025] The shielding layer coverage rate of the shielded cable is more than 95%, and the potting glue is an epoxy resin material.

[0026] The material of the metal shell is aluminum alloy, and the surface is treated by nickel plating.

[0027] The beneficial effects of the present invention are as follows: the electromagnetic interference resistance of the proximity switch is increased. In terms of structure, the all-metal + laser welding method is adopted to ensure that interference cannot radiate into the switch interior through holes and seams; a shielded wire is used on the cable, and the shielding layer is connected to the metal shell of the inductive proximity switch, so that the wire core for transmitting signals is completely inside the shielding layer, cutting off the coupling path for interference to conduct into the cable; in terms of circuit, a differential-mode + common-mode combined filtering method is adopted to achieve the filtering characteristics of multiple types and wide frequencies; the phenomenon that the inductive proximity switch is prone to sensitivity and unstable operation in a complex electromagnetic environment is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of the present invention;

[0029] Figure 2 is a schematic principle diagram of the present invention;

[0030] Figure 3 is a schematic circuit structure diagram of the power supply filter circuit board of the present invention;

[0031] Figure 4 is a schematic circuit structure diagram of the functional circuit board of the present invention;

[0032] In the figure: 1 - metal shell, 2 - inductor coil, 3 - metal rear cover, 4 - shielded cable, 5 - functional circuit board, 6 - power supply filter circuit board, 7 - potting glue, 8 - LC oscillation circuit, 9 - output circuit, 10 - distance adjustment circuit, 11 - protection circuit, 12 - power supply circuit, 13 - filter circuit. DETAILED DESCRIPTION OF THE INVENTION

[0033] The technical solution of the present invention will be further described below, but the scope of protection is not limited thereto.

[0034] An inductive proximity switch resistant to strong electromagnetic interference; comprising:

[0035] A metal housing 1, which is a metal cylinder with an open rear end and a fully enclosed front end. The metal housing adopts an aluminum alloy cylinder structure with an open rear end and a fully enclosed front end, and is surface nickel-plated (thickness 5μm - 10μm). This not only enhances the conductivity and corrosion resistance of the housing, but also forms a fully metal sealed structure with the metal rear cover through laser welding, completely blocking the possibility of external electromagnetic interference invading the internal circuit through gaps or holes. The high magnetic permeability of the aluminum alloy material (thickness 1.5mm - 2.5mm) further improves the electromagnetic shielding efficiency.

[0036] Furthermore, an inductance coil 2, which is fixed to the inner wall of the front closed part of the metal housing 1 by welding; the inductance coil is fixed to the inner wall of the front closed part of the metal housing by welding, and is directly connected to the functional circuit board through pins, shortening the signal transmission path and reducing the coupling risk of high-frequency interference. The functional circuit board is fixed to the front end of the metal housing, and uses the shielding effect of the metal housing to isolate the interference of the external electromagnetic field on the sensitive circuit.

[0037] Furthermore, a functional circuit board 5, which is fixed to the front end of the metal housing 1, and one end thereof is electrically connected to the inductance coil 2 through pins; the power supply filter circuit board is connected to the functional circuit board through a wire, and the ground wire and the shielding layer of the shielding cable are both welded to the nickel-plated metal housing, forming a unified low-impedance grounding path, effectively discharging the interference current and avoiding signal distortion caused by ground potential floating.

[0038] Furthermore, a power supply filter circuit board 6, which is fixed to the rear end of the metal housing 1 and is connected to the other end of the functional circuit board 5 through a wire;

[0039] Furthermore, a metal rear cover 3, which is hermetically connected to the rear end of the metal housing 1 by laser welding, and a wire passing hole is provided on the metal rear cover 3; a shielding cable 4 passes through the wire passing hole and is electrically connected to the power supply filter circuit board 6 by welding, and the shielding layer of the shielding cable 4 is welded and fixed to the metal housing 1; the shielding cable (shielding layer coverage rate ≥ 95%) passes through the wire passing hole of the metal rear cover, and the shielding layer is welded to the metal housing, so that the wire core is completely in shielding protection, cutting off the path of external interference entering the circuit through the cable conduction. The tight fit between the wire passing hole and the shielding cable further reduces electromagnetic leakage.

[0040] Furthermore, the potting adhesive 7 completely fills the internal space of the metal housing 1. The epoxy resin potting adhesive (temperature resistance range: -40°C to 150°C) completely fills the internal space of the metal housing and forms an insulating, moisture-proof and shock-proof protective layer after curing. At the same time, it fixes the internal components, avoids poor circuit contact caused by mechanical vibration, and helps to suppress the high-frequency radiation interference of the internal circuit.

[0041] Furthermore, the rear end surface of the metal housing 1 is nickel-plated, and the ground wire of the power filter circuit board 6 and the shielding layer of the shielding cable 4 are both fixed to the metal housing 1 by welding.

[0042] Furthermore, the functional circuit board 5 includes: an LC oscillation circuit 8, the LC oscillation circuit 8 includes an inductor L2 and a capacitor C6, one ends of the inductor L2 and the capacitor C6 are connected to the 2nd pin of the control chip U1, and the other ends of the inductor L2 and the capacitor C6 are connected to the 5th pin of the control chip U1; a distance adjustment circuit 10, the distance adjustment circuit 10 includes a control chip U1, resistors R8 to R11, the 3rd pin of the control chip U1 is connected to the resistor R8, the other end of the resistor R8 is respectively connected to the resistors R9 and R10, the resistors R9 and R10 are commonly connected to the resistor R11, and the other end of the resistor R11 is connected to the 5th pin of the control chip U1; the inductor L2 and the capacitor C6 achieve high-stability oscillation through the control chip U1, and cooperate with the resistors R8-R11 in the distance adjustment circuit to accurately adjust the detection distance. The closed-loop feedback design of the control chip U1 enhances the anti-interference ability and ensures that a stable signal can still be output in a strong electromagnetic environment.

[0043] Further, there is a protection circuit 11, which includes a bidirectional transient voltage suppressor diode TVS3 and a rectifier diode D2. The bidirectional transient voltage suppressor diode TVS3 is connected in parallel between the emitter and collector of the output triode Q2. The anode of the rectifier diode D2 is connected to the pad BU1 through a resistor R12. There is an output circuit 9, which includes an output triode Q2. The base of the output triode Q2 is connected to the 7th pin of the control chip U1 through a resistor R7. The collector of the output triode Q2 is connected to the pad OUT1 through a bead CZ2. In the protection circuit 11, the 8th pin of the control chip U1 is also connected to the emitter of the output triode Q2 and a resistor R5. The other end of the resistor R5 is connected to the 6th pin of the control chip U1 through a bead CZ1. In the protection circuit, the bidirectional transient voltage suppressor diode TVS3 and the rectifier diode D2 can quickly absorb surge voltage and reverse current, preventing the output triode Q2 from being damaged due to overvoltage or reverse current. The bead CZ2 suppresses the high-frequency noise of the output signal, ensuring the purity and reliability of the output signal. The power supply filter circuit board 6 includes: a differential-mode filter circuit, which includes bidirectional transient voltage suppressor diodes TVS1, TVS2, a resistor R1, a capacitor C1, and a rectifier diode D1. TVS1 is connected between the positive and negative poles of the power supply. TVS2 is connected in parallel between the output line and the negative pole of the power supply. One end of the resistor R1 is connected to the positive line, and the other end is connected to the negative pole of the power supply through the capacitor C1 and the rectifier diode D1. A common-mode filter circuit, which includes a common-mode inductor L1 and capacitors CY1, CY2. The 1st pin of the common-mode inductor L1 is connected to the resistor R1, the 2nd pin is connected to the capacitor C6, and the 3rd and 4th pins are grounded through the capacitors CY1, CY2 respectively. The filter circuit 13 suppresses broadband interference through the cooperation of the differential-mode filter circuit and the common-mode filter circuit. The inductance value of the common-mode inductor L1 is 10 mH to 50 mH, and the capacitance values of the capacitors CY1, CY2 are 0.1 μF to 1 μF.

[0044] The differential-mode filter circuit (TVS1, TVS2, capacitor C1, etc.) suppresses the interference between power lines, and the common-mode filter circuit (common-mode inductor L1, capacitors CY1 / CY2) suppresses the common-mode interference between the power line and the ground wire. The two work together (the inductance value of the common-mode inductor is 10 mH to 50 mH, and the capacitance value of the capacitor is 0.1 μF to 1 μF), covering broadband interference (10 kHz to 1 GHz), and significantly improving the anti-interference ability of the power supply end.

[0045] Further, the power supply filtering circuit board 6 further includes a power supply circuit 12, which is composed of a voltage stabilizing diode DZ1, an adjustment triode Q1 and a resistor R2. The cathode of the voltage stabilizing diode DZ1 is connected to the capacitor CY1, the anode is connected to the base of the adjustment triode Q1, the resistor R2 is connected in parallel between the base and the collector of the adjustment triode Q1, the collector of the adjustment triode Q1 is connected to the capacitor CY2, and the emitter is connected to the pad BU. The power supply circuit realizes voltage stabilization through the voltage stabilizing diode DZ1 and the adjustment triode Q1, and the resistor R2 provides a bias current to ensure that the functional circuit board and the filtering circuit can still obtain a stable working voltage under input voltage fluctuations or strong interference, avoiding malfunction caused by voltage fluctuations.

[0046] Further, the shielding layer coverage rate of the shielding cable 4 is more than 95%, and the potting glue 7 is made of epoxy resin material, and the temperature resistance range is -40°C to 150°C.

[0047] Further, the material of the metal shell 1 is aluminum alloy, the thickness is 1.5 mm - 2.5 mm, and the surface is treated by nickel plating, and the thickness of the nickel plating is 5 μm - 10 μm. Through multiple protection measures such as a full-metal shielding structure, grounding of the shielding cable, differential and common-mode collaborative filtering, and potting glue filling, the present invention forms a three-level anti-interference system of "structural shielding - conduction isolation - circuit filtering", enabling the proximity switch to still maintain high-precision detection and stable output in a strong electromagnetic environment (such as near industrial frequency converters and high-voltage equipment), and solving the technical problem that traditional products are easily interfered and fail.

Claims

1. An inductive proximity switch resistant to strong electromagnetic interference, characterized in that, Comprising: A metal housing (1), which is a metal cylinder with an open rear end and a fully enclosed front end; An inductor coil (2), which is fixed to the inner wall of the front end enclosure of the metal housing (1) by welding; A functional circuit board (5), which is fixed to the front end of the metal housing (1), and one end of which is electrically connected to the inductor coil (2) through pins; A power filter circuit board (6), which is fixed to the rear end of the metal housing (1) and is connected to the other end of the functional circuit board (5) through a wire; A metal back cover (3), which is hermetically connected to the rear end of the metal housing (1) by laser welding, and a wire passing hole is provided on the metal back cover (3); A shielded cable (4), which passes through the wire passing hole and is electrically connected to the power filter circuit board (6) by welding, and the shielding layer of the shielded cable (4) is welded and fixed to the metal housing (1); Potting glue (7), which completely fills the internal space of the metal housing (1).

2. The inductive proximity switch against strong electromagnetic interference according to claim 1, characterized in that: The rear end surface of the metal housing (1) is nickel-plated, and the ground wire of the power filter circuit board (6) and the shielding layer of the shielded cable (4) are both fixed to the metal housing (1) by welding.

3. The inductive proximity switch with strong electromagnetic interference resistance according to claim 1, wherein: The circuit printed on the functional circuit board (5) includes: An LC oscillation circuit (8), the LC oscillation circuit (8) includes an inductor L2 and a capacitor C6, one end of the inductor L2 and the capacitor C6 is connected to the 2nd pin of the control chip U1, and the other end of the inductor L2 and the capacitor C6 is connected to the 5th pin of the control chip U1; A distance adjustment circuit (10), the distance adjustment circuit (10) includes a control chip U1, resistors R8 to R11, the 3rd pin of the control chip U1 is connected to the resistor R8, the other end of the resistor R8 is respectively connected to the resistors R9 and R10, the resistors R9 and R10 are commonly connected to the resistor R11, and the other end of the resistor R11 is connected to the 5th pin of the control chip U1; A protection circuit (11), the protection circuit (11) includes a bidirectional transient suppression diode TVS3 and a rectifier diode D2, the bidirectional transient suppression diode TVS3 is connected in parallel between the emitter and the collector of the output triode Q2, and the anode of the rectifier diode D2 is connected to the pad BU1 through the resistor R12; An output circuit (9), the output circuit (9) includes an output triode Q2, the base of the output triode Q2 is connected to the 7th pin of the control chip U1 through the resistor R7, and the collector of the output triode Q2 is connected to the pad OUT1 through the magnetic bead CZ2.

4. The inductive proximity switch resistant to strong electromagnetic interference according to claim 3, wherein: In the protection circuit (11), the 8th pin of the control chip U1 is also connected to the emitter of the output triode Q2 and the resistor R5, and the other end of the resistor R5 is connected to the 6th pin of the control chip U1 through the magnetic bead CZ1.

5. The inductive proximity switch with strong electromagnetic interference resistance according to claim 1, wherein: The circuit printed on the power filter circuit board (6) includes: Differential-mode filtering circuit, including bidirectional transient voltage suppression diodes TVS1, TVS2, resistor R1, capacitor C1 and rectifier diode D1. TVS1 is connected between the positive and negative poles of the power supply. TVS2 is connected in parallel between the output line and the negative pole of the power supply. One end of resistor R1 is connected to the positive line, and the other end is connected to the negative pole of the power supply through capacitor C1 and rectifier diode D1; Common-mode filtering circuit, including common-mode inductor L1 and capacitors CY1, CY2. The No. 1 pin of common-mode inductor L1 is connected to resistor R1, the No. 2 pin is connected to capacitor C6, and the No. 3 and No. 4 pins are grounded through capacitors CY1, CY2 respectively.

6. The inductive proximity switch against strong electromagnetic interference according to claim 5, characterized in that: The filtering circuit (13) suppresses broadband interference through the cooperation of the differential-mode filtering circuit and the common-mode filtering circuit.

7. The inductive proximity switch resistant to strong electromagnetic interference according to claim 1, characterized in that: The power supply filtering circuit board (6) further includes a power supply circuit (12), which is composed of a zener diode DZ1, an adjustment triode Q1 and a resistor R2. The cathode of zener diode DZ1 is connected to capacitor CY1, the anode is connected to the base of adjustment triode Q1, resistor R2 is connected in parallel between the base and the collector of adjustment triode Q1, the collector of adjustment triode Q1 is connected to capacitor CY2, and the emitter is connected to pad BU.

8. The inductive proximity switch with strong electromagnetic interference resistance according to claim 1, characterized in that: The shielding layer coverage rate of the shielded cable (4) is more than 95%.

9. The inductive proximity switch resistant to strong electromagnetic interference according to claim 1, characterized in that: The material of the metal shell (1) is aluminum alloy, and the surface is treated by nickel plating.

10. The inductive proximity switch resistant to strong electromagnetic interference according to claim 1, characterized in that: The potting adhesive (7) is an epoxy resin material.

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