A liquid chromatograph EMC protection method based on electromagnetic interference

Abstract

The present invention provides an EMC protection method for a liquid chromatograph based on electromagnetic interference, and relates to the technical field of liquid chromatograph protection, specifically comprising the following steps: partitioning the cavity of the liquid chromatograph, determining the radiation source, and using a compartment-type shielding structure to layout the liquid chromatograph through simulation modeling and combining electromagnetic test data; designing a shielding protection structure for the optical path system, flow path system, injection system, temperature control system, and body cover; selecting a magnetic conductive material as the material of the liquid chromatograph; dividing the cable distribution into a strong current signal area and a weak current signal area, and using a magnetic ring to wrap the cable; and using a star-shaped grounding method to make the grounding resistance of the liquid chromatograph lower than the upper limit. The present invention comprehensively utilizes module layout, shielding, material selection, cable selection, electromagnetic simulation, and pre-test protection design to further improve the electromagnetic compatibility performance of the high-performance liquid chromatograph and further enhance the electromagnetic protection capability of the chromatograph.

Description

Technical Field

[0001] The invention relates to the technical field of liquid chromatography protection, and in particular to an EMC protection method for a liquid chromatograph based on electromagnetic interference. Background Art

[0002] High performance liquid chromatography analysis technology is a conventional separation technology. With the development of mass spectrometry technology, liquid chromatography-mass spectrometry technology, referred to as LC-MS system, has the excellent characteristics of high efficiency separation and ultra-high sensitivity. Liquid chromatography is its separation system, and mass spectrometry is its detection system. LC-MS system is widely used in many fields such as biochemical analysis, food safety, environmental monitoring, drug analysis, clinical medicine, etc. With the rapid development of LC-MS system, higher requirements are also put forward for the high performance liquid chromatograph that matches it. In particular, the safety of high performance liquid chromatograph needs to pay attention to electromagnetic compatibility design to improve the electromagnetic interference resistance of liquid products and reduce the degree of electromagnetic interference of products to the environment.

[0003] During the application period, reliability and anti-electromagnetic interference capability are the most important. R&D personnel should use various methods to improve the reliability of instrument system components and structures, enhance their electromagnetic anti-interference capability, and meet the use requirements of modern high-performance liquid chromatography. Since there are many electromagnetic interference factors in high-performance liquid chromatography and the sources of electromagnetic interference are relatively complex, instrument R&D personnel should comprehensively analyze the electromagnetic interference of high-performance liquid chromatography and take effective measures to eliminate interference factors, enhance the electromagnetic anti-interference capability of the instrument high-performance liquid chromatography, and ensure the normal operation of the high-performance liquid chromatography system.

[0004] With the continuous improvement of the application scope and technical content of HPLC, the use conditions or environment of HPLC system tends to be stricter. Different external environments will cause different electromagnetic interference to the operation of HPLC. Therefore, in the design and testing process of HPLC system, in addition to the design based on the HPLC itself, it is also necessary to optimize the design and specific analysis in combination with the corresponding use environment to find out the main interference factors under specific conditions. Therefore, it is necessary to provide an EMC protection method for liquid chromatography based on electromagnetic interference, and to design electromagnetic anti-interference measures in a targeted manner to ensure that the application quality of instruments can be improved, their operation effect can be enhanced, their development system can be optimized, and a working environment for HPLC without electromagnetic interference can be gradually created to fundamentally solve various electromagnetic interference problems. Summary of the invention

[0005] Based on the above problems, the object of the present invention is to provide an EMC protection method for a liquid chromatograph based on electromagnetic interference.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A liquid chromatograph EMC protection method based on electromagnetic interference comprises the following steps:

[0008] Step 1: Obtain the cavity layout of the liquid chromatograph, divide the cavity of the liquid chromatograph into zones, determine the radiation source, and layout the liquid chromatograph by using a compartment shielding structure through simulation modeling and combining electromagnetic test data;

[0009] Step 2: Design a shielding protection structure for the optical system, flow system, injection system, temperature control system and outer cover of the liquid chromatograph;

[0010] Step 3: The material of the liquid chromatograph is selected from magnetic conductive materials;

[0011] Step 4: Divide the cable distribution of the liquid chromatograph into a strong current signal area and a weak current signal area, and use a magnetic ring to wind the cable;

[0012] Step 5: adopt a star grounding method to make the grounding resistance of the liquid chromatograph lower than the upper limit value.

[0013] Preferably, in step one, equivalent modeling is performed on the PCB board, and an independent shielding space is set for the PCB board in combination with the clock signal spectrum, operating frequency and electromagnetic noise distribution of the resonant frequency of the PCB board.

[0014] Preferably, a detachable CPU absorbing plate is provided inside the independent shielding space, and a waveguide vent is provided on the side wall of the independent shielding space.

[0015] Preferably, in step 2, the electric field and magnetic field strength simulation is performed on the outer cover of the body, and the needle simulation result is used to determine the optimal solution for the wall thickness of the chassis and the diameter of the ventilation hole in the outer cover of the body.

[0016] Preferably, in step 2, the outer cover of the body adopts an integrated structure, and the outer cover of the body is surface-treated by a plastic spraying process, and the gaps in the outer cover of the body are filled with conductive material.

[0017] Preferably, the conductive material is at least one of conductive foam, absorbing material and copper foil.

[0018] Preferably, in step 2, the window of the injection system is provided with a visual shielding structure, and the visual shielding structure includes a tubular motor and a shielding film wrapped around the motor shaft of the tubular motor, and a positioning optical coupler and a guide rail are fixed on the frame of the window; the shielding film is provided with a metal strip on the side relative to the motor shaft, and a metal cavity magnetic strip is provided on the side of the frame of the window away from the tubular motor, and the shielding film moves along the direction of the guide rail under the drive of the tubular motor, and when the metal strip contacts the metal cavity magnetic strip, the tubular motor stops.

[0019] Preferably, the shielding film is made of a flexible material with a conductive network layer etched on the surface, and the transparency is greater than 80%; the shielding effectiveness of the shielding film is in the range of 50-60dB.

[0020] Preferably, the magnetic conductive material is at least one of iron, aluminum and stainless steel.

[0021] Preferably, in step four, a single-core / multi-core shielded cable is used in the weak current signal area.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The present invention provides an EMC protection method for a liquid chromatograph based on electromagnetic interference, which comprehensively utilizes module layout, shielding, material selection and cable selection as well as electromagnetic simulation and pre-test protection design, further improves the electromagnetic compatibility performance of a high performance liquid chromatograph, further enhances the electromagnetic protection capability of the chromatograph, comprehensively improves the electromagnetic anti-interference capability of the high performance liquid chromatograph, and enhances the compatibility and reliability of the chromatograph in the application field. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a liquid chromatograph EMC protection method based on electromagnetic interference;

[0025] Figure 2 It is the EMI prediction result before the structural shielding in the present invention;

[0026] Figure 3 It is the EMI prediction result after structural shielding in the present invention;

[0027] Figure 4 It is an electric field radiation phase diagram under the first circuit board layout of the present invention;

[0028] Figure 5 It is an electric field radiation phase diagram under the second circuit board layout of the present invention;

[0029] Figure 6 It is a magnetic field radiation phase diagram under the first circuit board layout of the present invention;

[0030] Figure 7 It is a magnetic field radiation phase diagram under the second circuit board layout of the present invention;

[0031] Figure 8 It is the electric field radiation phase diagram of the chassis aperture of the present invention with a size of 380 mm*1.5 mm*1.5 mm (length*width*depth);

[0032] Fig. 9 It is the magnetic field radiation phase diagram of the chassis hole of the present invention with a size of 380mm*1.5mm*1.5mm (length*width*depth);

[0033] Fig.10 This is a schematic diagram of the PCB board compartment shielding case compartment structure in the present invention;

[0034] Fig.11 It is a structural schematic diagram of the upper cover of the PCB board compartment type shielding cover in the present invention;

[0035] Fig.12 It is a structural schematic diagram of a visual shielding structure in the sample injection system of the present invention;

[0036] Fig.13 It is the test result of the electromagnetic compatibility test radiation emission (3-meter darkroom method) of the product before EMC protection;

[0037] Fig.14 It is the test result of electromagnetic compatibility test radiation emission (3-meter darkroom method) of the product after EMC protection;

[0038] Reference numerals:

[0039] 1-positioning optical coupler; 2-metal cavity magnetic strip; 3-metal strip; 4-shielding film; 5-slide rail; 6-motor cover;

[0040] 7- tubular motor; 8- column; 9- CPU absorbing patch; 10- waveguide ventilation hole. DETAILED DESCRIPTION

[0041] In order to make the purpose and technical solution of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0042] In the description of the present application, it should be understood that the terms "length", "up", "down", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0043] like Figure 1-Figure 14 As shown, the present invention provides an EMC protection method for a liquid chromatograph based on electromagnetic interference, comprising the following steps:

[0044] Step 1: Figure 2-Figure 7 As shown, according to the functional characteristics of each module of the high performance liquid chromatograph and the actual application perspective, a protective design is performed on the cavity layout of each module to reduce electromagnetic interference.

[0045] Obtain the cavity layout of the liquid chromatograph, partition the liquid chromatograph cavity, partition the signal processing circuit system and the power supply system, partition the strong current and weak current, and partition the interference source and signal source.

[0046] After the internal mechanical layout of each module, the radiation module is determined, and then analysis and simulation are carried out to analyze the radiation effect of each circuit radiation module; the various functional modules in the chromatographic system have complex structures, the radiation interference source of the circuit system PCB board is a time-varying current, and the structural design around the interference source will also affect the change of the interference source, so the radiation interference of the PCB circuit board is complex and difficult to troubleshoot.

[0047] Therefore, it is necessary to perform equivalent modeling on the PCB radiation source, optimize the mechanical structure and optimize the PCB board layout, through simulation modeling, and combine the electromagnetic compatibility prediction and measured results, such as Figure 4-Figure 7 The figure shows the electric field radiation and magnetic field radiation of the circuit board under two different layout conditions. The product is re-arranged and rectified according to the simulation results. The electromagnetic radiation source simulates the -Y direction of the injection, and from the perspective of circuit board layout, the closer the distance to the ventilation hole on the rear panel of the product, the higher the electric field and magnetic field radiation. Therefore, in terms of circuit board layout, areas with relatively weak electric and magnetic field radiation are preferred to ensure that the circuit board is not affected by electromagnetic interference.

[0048] Through simulation modeling, combined with electromagnetic test data, a compartment shielding structure is adopted to re-layout the liquid chromatograph, and an independent shielding space is set for the PCB board to perform spatial area shielding treatment on the chip. Generally, it is designed as a shielding box or shielding cover mode, and a suitable CPU absorbing plate 9 is selected to be pasted on the corresponding position of the compartment shielding cover of the PCB board, and the interference source is shielded in a targeted manner, replacing the existing shielding box that completely covers the PCB board, and reducing the diffuse reflection of electromagnetic waves in the shielding box or shielding box due to the different working frequencies of different chips, thereby forming mutual interference. For the power module in the PCB board, since reasonable ventilation and heat dissipation are required, while taking into account its electromagnetic radiation problem, a waveguide ventilation hole 10 is added at the position of its shielding cover. The independent shielding space is combined with different working frequencies, and different inner wall thicknesses, materials and conductive spray materials or conductive fabrics of the compartment shielding cavity can be selected to design, that is, the shielding space is processed in a targeted manner.

[0049] like Figure 1 As shown in the figure, before the product was rectified for electromagnetic shielding, the electromagnetic noise was Test01. In the electromagnetic spectrum range of 0-1GHz, there was a concentrated 25MHz frequency multiplication interference, and the amplitude was about 25dBμV. After the implementation of the electromagnetic rectification plan, the electromagnetic interference in the full spectrum range was significantly improved, specifically, the 25MHz frequency multiplication interference in the spectrum of 300-800MHz was weakened or even disappeared. The electromagnetic interference amplitude in the 0-300MHz spectrum range was reduced by 5dBμV.

[0050] Step 2: Since the structure of the chromatography system is relatively complex, the detection system includes an optical path system, the infusion pump system includes a flow path system, the automatic sampler system includes an external motion mechanism sample injection system, and the column thermostat includes a temperature control system for column insulation. Each module needs to process and control its own data, and each module needs to transmit and communicate data. Therefore, it is necessary to design a shielding protection structure for the optical path system, flow path system, sample injection system, temperature control system and body cover of the liquid chromatograph.

[0051] Specifically, there are matching tolerances and gaps between the equipment frame of each module and the outer cover of the machine. The outer cover of the machine is partially sprayed with plastic to form continuous conductivity with the equipment frame of each module. At the same time, based on the requirements of the equipment appearance and the actual shielding effect, screws with good conductivity are selected to fix the outer cover of the machine and the frame, and the number of screws is increased and the screw spacing is reduced to improve the electromagnetic shielding effectiveness.

[0052] Due to processing tolerance and precision issues in mechanical design, matching tolerance will introduce mechanical holes. For this reason, the outer cover of the body adopts an integrated structure, and conductive materials such as conductive foam, absorbing materials, copper foil, etc. can be used for electromagnetic shielding, filling and sealing, and to a certain extent, it plays a shock-absorbing role.

[0053] In order to ensure the normal operation of each module of the high-performance liquid chromatograph, it is usually necessary to perform heat dissipation treatment on the chassis to form air-cooled heat dissipation, and add ventilation holes on the outer cover of the instrument for heat dissipation. The holes will lead to a decrease in shielding effectiveness. Therefore, the wall thickness design of the chassis and the shape and size of the holes need to be simulated to simulate the distribution of electric and magnetic field strengths, and the shape of the holes must be confirmed to ensure the electromagnetic shielding effectiveness.

[0054] like Figure 8-Figure 9 As shown, Figure 8 It is the electric field radiation phase diagram of the chassis hole-380mm*1.5mm*1.5mm (length*width*depth), Fig. 9It is a magnetic field radiation phase diagram of the chassis hole - 380mm*1.5mm*1.5mm (length*width*depth), and the electric field and magnetic field strength simulation is performed on the outer cover of the machine body. The optimal solution for the wall thickness of the chassis and the diameter of the ventilation hole in the outer cover of the machine body is determined based on the simulation results.

[0055] Among them, the automatic sampler module in the unit module of the chromatography system needs to place the sample in the tray of the automatic sampler, so its mechanical linkage mechanism including the drive system such as the motor will be exposed to the external space. The full covering and shielding design is difficult and costly, so the window of the automatic sampler is designed as an automatic shielding visualization system.

[0056] Specifically, the window of the sampling system is provided with a visual shielding structure, in which the micro-tubular motor 7 of the sampling system is covered by a motor cover 6 and a column 8. The structure here can be improved and deformed in combination with the mechanical structure of the actual equipment. The micro-tubular motor 7 is used to drive the motor shaft, and a transparent shielding film 4 is wrapped around the motor shaft. The micro-tubular motor 7 is electronically positioned through an embedded program and runs at a constant speed. When the transparent shielding film 4 runs along the slide rail 5 to the positioning optical coupler 1, the running position is accurately determined by the photoelectric signal. When the transparent shielding film 4 runs along the slide rail 5, the thin film metal strip 3 embedded at the edge of the transparent shielding film 4 is completely in contact with the metal cavity magnetic strip 2 of the automatic sampler, and the motor stops. At this time, the thin film metal strip 3 and the magnetic strip 2 are automatically attracted to form a complete conductor and shielding chamber with the chassis frame.

[0057] The transparent shielding film 4 is a flexible material with a conductive layer and a very fine etching network on it. The shielding effectiveness can reach 50-60dB. The film thickness is usually 100μm and the transparency is greater than 80%. It can achieve excellent visual effects and meet the needs of operators to observe the internal injection process of the automatic sampler and the remaining sample quantity at any time. Because it is a flexible material, it can be bent at different angles with various tracks and can be stretched and retracted freely. This structure is not limited to the automatic sampler module of the chromatography system, and can be applied to various types of equipment that have shielding requirements and require visualization systems.

[0058] Step 3: The material of the liquid chromatograph is a magnetic material; in terms of material selection, in order to improve the electromagnetic shielding environment of the chromatography system, materials such as iron, aluminum, and stainless steel with good magnetic and electrical conductivity should be selected in the material design. The surface treatment process used is intended not to destroy the good electrical conductivity of the material itself.

[0059] Step 4. Divide the cable distribution of the liquid chromatograph into strong current signal area and weak current signal area, high voltage signal area and low voltage signal area, and use magnetic rings of different apertures to wrap the cables 2-3 times to reduce the EMI common mode interference introduced by the cables. For weak signal cables in the chromatography system, single-core or multi-core shielded cables are used. For the connector protection design, a 360-degree full metal shielding method is adopted for the high-speed data communication interface. A metal stamping integrated shielding structure can be used, and a flange structure is used to fully couple the connector with the panel.

[0060] Step 5: Use a star grounding method to make the grounding resistance of the liquid chromatograph lower than the upper limit. Connect the analog ground and digital ground in the system at a certain point so that the signals refer to the same potential. At the same time, ensure that the working ground of the chromatograph is well connected to the entire conductive cavity of the instrument, that is, the grounding resistance is less than 0.1 ohm.

[0061] like Fig.13 and Fig.14 The following are the test results of the electromagnetic compatibility radiation emission of the product before and after the product rectification under the environmental conditions of room temperature 23℃, humidity 53%, and air pressure 101KPa. Fig.13 This is the test result of the electromagnetic compatibility test radiation emission (3m darkroom) of the product before EMC protection. Fig.14 The test results of electromagnetic compatibility test radiation emission (3-meter darkroom) of the product after EMC protection, where the light curve is the peak value of antenna horizontal polarization measurement; the dark curve is the peak value of antenna vertical polarization measurement. At 30-230MHz, the quasi-peak value must be less than 40dB (μV / m), and at 230MHz-1GHz, the quasi-peak value must be less than 47dB (μV / m). After EMC protection, the peak values ​​of horizontal and vertical polarization measurements are reduced.

[0062] The above are only some embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A liquid chromatograph EMC protection method based on electromagnetic interference, characterized in that: The following steps are involved: Step 1: Obtain the cavity layout of the liquid chromatograph, divide the cavity of the liquid chromatograph into zones, determine the radiation source, and layout the liquid chromatograph by using a compartment shielding structure through simulation modeling and combining electromagnetic test data; Step 2: Design a shielding protection structure for the optical system, flow system, injection system, temperature control system and outer cover of the liquid chromatograph; Step 3: The material of the liquid chromatograph is selected from magnetic conductive materials; Step 4: Divide the cable distribution of the liquid chromatograph into a strong current signal area and a weak current signal area, and use a magnetic ring to wind the cable; Step 5: adopting a star grounding method to make the grounding resistance of the liquid chromatograph lower than an upper limit value; In step 1, equivalent modeling is performed on the PCB board, and an independent shielding space is set for the PCB board in combination with the clock signal spectrum, operating frequency and electromagnetic noise distribution of the resonant frequency of the PCB board; A detachable CPU absorbing sheet is provided inside the independent shielding space, and a waveguide vent is provided on the side wall of the independent shielding space; In step 2, the electric field and magnetic field strength of the outer cover of the body are simulated, and the needle simulation results are used to determine the optimal solution for the wall thickness of the chassis and the diameter of the ventilation holes in the outer cover of the body; The gap of the outer cover of the housing is filled with conductive material; In step 2, the window of the injection system is provided with a visual shielding structure, and the visual shielding structure includes a tubular motor and a shielding film wrapped around the motor shaft of the tubular motor, and a positioning optical coupler and a guide rail are fixed on the frame of the window; the shielding film is provided with a metal strip on the side relative to the motor shaft, and a metal cavity magnetic strip is provided on the side of the frame of the window away from the tubular motor. The shielding film moves along the direction of the slide rail under the drive of the tubular motor, and when the metal strip contacts the metal cavity magnetic strip, the tubular motor stops.

2. The liquid chromatograph EMC protection method based on electromagnetic interference according to claim 1, characterized in that: In step 2, the outer cover of the body adopts an integrated structure, and the outer cover of the body adopts a plastic spraying process for surface treatment.

3. The liquid chromatograph EMC protection method based on electromagnetic interference according to claim 1, characterized in that: The conductive material is at least one of conductive foam, wave absorbing material and copper foil.

4. The liquid chromatograph EMC protection method based on electromagnetic interference according to claim 1, characterized in that: The shielding film is made of a flexible material with a conductive network layer etched on the surface, and the transparency is greater than 80%; The shielding effectiveness of the shielding film ranges from 50 to 60 dB.

5. The liquid chromatograph EMC protection method based on electromagnetic interference according to any one of claim 1, characterized in that: The magnetic conductive material is at least one of iron, aluminum and stainless steel.

6. The liquid chromatograph EMC protection method based on electromagnetic interference according to any one of claim 1, characterized in that: In step four, a single-core / multi-core shielded cable is used in the weak current signal area.

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