Gas sensor with shock resistance

Abstract

The utility model provides a gas sensor with shock resistance, which comprises an upper shell, a lower shell, a black element, a white element and a connecting circuit board, the upper shell and the lower shell enclose to form a placing cavity, the black element, the white element and the connecting circuit board are all positioned in the placing cavity, the connecting circuit board is provided with a first welding position and a second welding position, and the first welding position and the second welding position are positioned in the placing cavity. The black element is welded to the first welding position, the white element is welded to the second welding position, a plurality of connecting pins are arranged on the end face, opposite to the first welding position and the second welding position, of the connecting circuit board and penetrate through the lower shell, the black element and the white element comprise heating wires, the number of the heating wires is at least two, and the number of the heating wires is at least two. The heating wires are mutually wound into a plurality of groups of twisted shapes, and the surface area of the heating wires is increased through a special winding mode, so that the welding area of the black element, the white element and the connecting circuit board is increased, the sensor has the advantage of high sensitivity, and meanwhile, the shock resistance of the black element and the white element is also improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of sensors, and in particular relates to a gas sensor with shock resistance. Background Art

[0002] With the development of the times, the Internet of Things (IoT) is increasingly affecting people's lives. The IoT uses sensors based on various principles as the perception layer to obtain underlying information. The indicators detected by these sensors can be physical quantities or chemical quantities. As the eyes and tentacles of the IoT, they provide basic data for the IoT. The IoT has been increasingly used in various levels of production and life. For example, the content of flammable gases and toxic and harmful gases in various factories, mining, hospitals, schools, homes and other places is closely related to people's lives and property. When the content of flammable gases exceeds the standard, it will cause explosions, fires and other malignant accidents, seriously endangering people's lives and property safety. The concentration of toxic and harmful gases exceeding the allowable range will endanger people's health. For some gases, such as flammable gases, there is an allowable safety range for their content in the air. The upper limit of this safety value is called the lower explosion limit. Taking hydrogen as an example, the lower explosion limit is 4%. Due to these particularities, the gas sensors used are required to have outstanding advantages such as fast response speed, wide detection range and low cost. In addition, the gas sensors used in handheld detectors need to be powered by batteries. The traditional catalytic combustion principle sensor consists of three parts: a housing (including connecting pins), a connecting circuit board and a Wheatstone bridge. The housing provides physical support and protection for the internal structure of the sensor. It is usually made of explosion-proof materials such as stainless steel and metal sand core to ensure that when the high-temperature components inside the sensor fail, the danger will not spill out of the housing. The connecting circuit board is used to form a connected and conductive loop between the black element and the white element to ensure that the electrical signal generated by the reaction can be output externally. The Wheatstone bridge is the core part of the detection, which consists of a black element, a white element and their corresponding matching resistors. The black element is the place where flameless combustion of the gas to be tested occurs; the white element is a compensation element, which is exactly the same as the black element in structure and basic materials, but does not contain the catalyst required for detection, so it can provide temperature and humidity compensation for the black element; although the process conditions of the black element and the white element are the same, there is still a slight difference in resistance value, and this difference is compensated by the matching resistors of the black and white elements. By adjusting the resistance value of the matching resistor, the output of the bridge arm of the Wheatstone bridge can be 0 when there is no gas to be tested. When the gas to be tested undergoes flameless combustion on the black element, the heat generated will cause the Wheatstone bridge, which was originally in equilibrium, to lose balance and output a voltage value as a detection signal. By detecting this voltage value, the concentration of the gas to be tested can be accurately quantified.

[0003] The black element is composed of three parts: heating wire, coating layer and catalyst, and the white element is composed of heating wire and coating layer. Both black and white elements are welded to the welding position on the connecting circuit board by means of conductive silver paste and other means. The principle of catalytic combustion is that the catalyst needs to be heated to a high temperature of more than 300 degrees, so that the gas to be tested can be detected by flameless combustion on the catalyst. The function of the heating wire is to provide energy for the black and white elements and heat the black and white elements to the corresponding target temperature value. The heating wire is usually composed of platinum wire, gold wire, palladium wire and other components with high stability and ductility. The coating layer is generally composed of viscous porous materials such as aluminum oxide and silicon oxide, and is wrapped around the periphery of the heating wire according to the preset shape, which provides a protection for the heating wire and a carrier for the catalyst. The coating layer is a porous material such as silicon oxide and aluminum oxide. The catalyst will be fixed in the holes of the coating layer by physical adsorption or chemical grafting. The catalyst plays a role in assisting the flameless combustion reaction of the gas to be tested. It can be a precious metal material or a high-temperature resistant material such as an oxide with catalytic effect.

[0004] The difference between the white element and the black element is that the white element does not contain a catalyst. Other materials and preparation processes are the same as those of the black element to ensure that the resistance values ​​and various performances of the black and white elements are as close as possible in the absence of the gas to be tested.

[0005] In traditional catalytic combustion sensors, in order to ensure that a high amount of heat is obtained with a small size, the diameter of the heating wire is very small, usually only a few microns. In order to ensure that a certain amount of catalyst is adsorbed, the coating layer needs a certain thickness and volume to meet the requirements, so the weight of the coating material is much greater than the weight of the heating wire. However, there are many vibration scenarios during the use and transportation of sensors. The heating wire can easily break due to the weight of the coating layer during the vibration, causing the sensor to fail. In addition, when there is silicone vapor in the environment, the gas will be adsorbed in the porous structure of the coating layer, and under the action of temperature, it will become silicon, thereby blocking the air inlet, causing the catalyst inside the coating layer to be unable to contact the gas, and even the surface catalyst is covered by silicon, resulting in sensitivity attenuation, which is often called silicone poisoning. The sensor is also required to have low power consumption.

[0006] Among the detection principles of gas sensors, gas sensors based on the catalytic combustion principle have been widely used due to their advantages such as fast response speed, wide detection range, low cost, and small size, especially in the field of combustible gas and high-concentration toxic and harmful gas detection.

[0007] The gas sensors based on the catalytic combustion principle currently available on the market have the defects of poor resistance to induction, high power consumption, low sensitivity, and serious silicone poisoning due to the particularity of their structure. Utility Model Content

[0008] The technical problem to be solved by the utility model is to provide a gas sensor with good anti-vibration effect and anti-vibration performance in view of the deficiencies existing in the above technical solutions.

[0009] The utility model adopts the following technical solution to solve the technical problem: a gas sensor with shock resistance, comprising an upper shell, a lower shell, a black element, a white element and a connecting circuit board, the upper shell and the lower shell enclose a placement cavity, the black element, the white element and the connecting circuit board are all located in the placement cavity, a first welding position and a second welding position are arranged on the connecting circuit board, the black element is welded on the first welding position, the white element is welded on the second welding position, a plurality of connecting pins are arranged on one end face of the connecting circuit board facing away from the first welding position and the second welding position, and the connecting pins pass through the lower shell, the black element and the white element comprise heating wires, at least two heating wires are arranged, the heating wires are mutually twisted into a plurality of groups of twists, and a plurality of groups of the twists are mutually twisted into braids.

[0010] Furthermore, a catalytic layer is provided on the braid, and the catalytic layer is wrapped around the outer surface and the inner side of the braid.

[0011] Furthermore, the shock-resistant gas sensor further comprises a filter element, a breathable membrane and a PTFE ring, and the filter element, the breathable membrane and the PTFE ring are sequentially stacked on the connecting circuit board.

[0012] Furthermore, the shock-resistant gas sensor also includes a first thermal insulation pad, which is embedded in the PTFE ring.

[0013] Furthermore, the shock-resistant gas sensor also includes a second thermal insulation pad, on which a through hole adapted to the connecting pin is opened, and the second thermal insulation pad passes through the connecting pin to contact the connecting circuit board.

[0014] Furthermore; the shock-resistant gas sensor also includes a PCB circuit board, which is installed on an end face of the lower shell facing away from the upper shell, and an explosion-proof sealing filling layer is arranged between the lower shell and the PCB circuit board, and the PCB circuit board and the explosion-proof sealing filling layer are both provided with circular holes for the connecting pins to pass through.

[0015] Furthermore, the diameter of the heating wire is 0.001-0.5 mm, and the heating wire is any one of platinum wire, gold wire or palladium wire.

[0016] Furthermore, the filter element is any one of activated carbon, carbon fiber cotton or modified fiber cotton.

[0017] Furthermore, the upper shell and the lower shell are any one of PP, PC, PPO, ABS, glass fiber single or composite material or stainless steel, copper, aluminum metal thin shell or metal powder metallurgy cover.

[0018] Furthermore, the explosion-proof sealing filling layer is any one of fireproof plugging material, explosion-proof putty or epoxy resin.

[0019] The beneficial effect of the shock-resistant gas sensor provided by the utility model is that the surface area of ​​the heating wire is increased by a special winding method, thereby increasing the welding area of ​​the black element, the white element and the connecting circuit board, so that the sensor has the advantage of high sensitivity, and also increases the shock resistance of the black element and the white element. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the explosion of the overall structure of the gas sensor with shock resistance provided by the utility model;

[0021] Figure 2 This is an installation diagram of the black element and the white element in the gas sensor with shock resistance provided by the utility model;

[0022] Figure 3 Another installation diagram of the black element and the white element in the shock-resistant gas sensor provided by the utility model. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0024] See also Figure 1-2 , a gas sensor with shock resistance provided by the utility model includes an upper shell 1, a lower shell 11, a black element 6, a white element 7 and a connecting circuit board 8, the upper shell 1 and the lower shell 11 are enclosed to form a placement cavity, the black element 6, the white element 7 and the connecting circuit board 8 are all located in the placement cavity, a first welding position 611 and a second welding position 711 are arranged on the connecting circuit board 8, the black element 6 is welded on the first welding position 611, the white element 7 is welded on the second welding position 711, a plurality of connecting pins 9 are arranged on one end surface of the connecting circuit board 8 facing away from the first welding position 611 and the second welding position 711, and the connecting pins 9 pass through the lower shell 11, the black element 6 and the white element 7 include heating wires, at least two of the heating wires are arranged, the heating wires are mutually twisted into a plurality of groups of twists, and a plurality of groups of the twists are mutually twisted into braids.

[0025] In this embodiment, a catalytic layer (not shown) is disposed on the braid, and the catalytic layer is wrapped around the outer surface and the inner side of the braid.

[0026] In this embodiment, the shock-resistant gas sensor further includes a filter element 2 , a breathable membrane 3 and a PTFE ring 4 , and the filter element 2 , the breathable membrane 3 and the PTFE ring 4 are sequentially stacked on the connecting circuit board 8 .

[0027] In this embodiment, the shock-resistant gas sensor further includes a first thermal insulation pad 5 , and the first thermal insulation pad 5 is embedded in the PTFE ring 4 .

[0028] In this embodiment, the shock-resistant gas sensor further includes a second thermal insulation pad 10 , on which a through hole adapted to the connecting pin 9 is provided, and the second thermal insulation pad 10 passes through the connecting pin 9 to contact the connecting circuit board 8 .

[0029] In this embodiment, the shock-resistant gas sensor also includes a PCB circuit board 13, which is installed on an end surface of the lower shell 11 facing away from the upper shell 1, and an explosion-proof sealing filling layer 12 is arranged between the lower shell 11 and the PCB circuit board 13, and both the PCB circuit board 13 and the explosion-proof sealing filling layer 12 are provided with round holes for the connecting pin 9 to pass through.

[0030] In this embodiment, the diameter of the heating wire is 0.001-0.5 mm, and the heating wire is any one of platinum wire, gold wire or palladium wire.

[0031] In this embodiment, the filter element 2 is any one of activated carbon, carbon fiber cotton or modified fiber cotton.

[0032] In this embodiment, the upper shell 1 and the lower shell 11 are any one of PP, PC, PPO, ABS, glass fiber single or composite material or stainless steel, copper, aluminum metal thin shell or metal powder metallurgy cover.

[0033] In this embodiment, the explosion-proof sealing filling layer 12 is any one of fireproof plugging material, explosion-proof putty or epoxy resin.

[0034] The special winding method increases the surface area of ​​the heating wire, thereby increasing the welding area of ​​the black element, the white element and the connecting circuit board, and also increases the amount of catalyst adhesion, so that the sensor has the advantage of high sensitivity, while also increasing the shock resistance of the black element and the white element.

[0035] Specifically, the upper shell 1 and the lower shell 11 can be made of a single or composite material such as PP, PC, PPO, ABS, glass fiber, etc., or can also be made of stainless steel, copper, aluminum and other metal thin shells or metal powder metallurgy covers. The upper shell 1 provides physical support and protection for the entire sensor; the filter element 2 can be activated carbon, carbon fiber cotton, modified fiber cotton, etc., which can adsorb or decompose dust or organic volatiles, reduce interference, and improve accuracy; the breathable membrane 3 supports the filtered material in the filter element 2, and also allows the gas to pass through the filter element 2 and enter the sensor; the PTFE ring 4 supports the breathable membrane 3; the thermal insulation pad is placed in the PTFE ring 4, and the first welding position 61 is provided on the connected circuit board 8 1 and the second welding position 711; wherein the black element 6 is prepared by an in-situ growth method; a connecting pin 9 is provided on the side of the connecting circuit board 8 facing away from the black element 6 and the white element 7, one end of the connecting pin 9 is fixedly connected to the connecting circuit board 8, and the other end passes through the lower shell 11, so as to transmit the voltage value output by the Wheatstone bridge to the outside; it adopts gold-plated material to increase wear resistance, and the first thermal insulation pad 5 is the same as the second thermal insulation pad 10, which can not only isolate the black element 6 and the white element 7, but also play a role in heat preservation; the explosion-proof sealing filling layer 12 is filled with an explosion-proof sealing filler, which can be a fire-proof plugging material, explosion-proof glue, epoxy resin, etc.; the PCB circuit board 13 plays the role of encapsulating the entire sensor.

[0036] Specifically, in this embodiment, the black element 6 and the white element 7 are wound with 9 heating wires, and the 9 heating wires are divided into three parts. First, three heating wires are woven into a loose braid. After the three groups are woven, the three groups of braids are woven into a thick braid. The purpose of this design is to increase the contact area between the black element 6 and the white element 7 and the connection circuit board 8, so that there are more attachment points. The outer surface and the inner side of the braid are covered with a catalytic layer.

[0037] The gas sensor with shock resistance of the present application is assembled in the following order:

[0038] 1. Measure the resistance of the black element 6 and the white element 7;

[0039] 2. Pair the black element 6 and the white element 7 with similar resistance values ​​and put them in the input sensor for use;

[0040] 3. Calculate the length that needs to be reserved when welding and connecting the circuit board 8 according to the length and weight of the black component 6 and the white component 7, so as to ensure that the black component 6 and the white component 7 are neither in a tight state nor too loose after being welded to the first welding position 611 and the second welding position 711;

[0041] 4. Weld the matched black element 6 to the first welding position 611;

[0042] 5. Solder the matched white components 7 to the second soldering positions 711 on the corresponding connecting circuit board 8;

[0043] At the same time, in order to increase the shock resistance of the black element 6 and the white element 7, the heating wire is wound in a secondary twist to obtain the black element 6 and the white element 7. Before winding, the quenched heating wire is first wound into a twist in a relaxed state. After winding, the twist is wound into a loose braid in the same way to obtain the black element 6 and the white element 7.

[0044] like Figure 3 As shown, in the present application, the black component 6 and the white component can also be fixed on the connecting circuit board 8 by mechanical parts, wherein the mechanical parts are V-shaped metal parts.

[0045] The outer surface of the heating wire of the black element 6 in the present application is wrapped with a catalytic layer, while the white element 7 is not, wherein the heating wire is made of materials with high thermal stability such as platinum wire, palladium wire, gold wire, etc., with a diameter between 0.001-0.5mm, preferably 0.005-0.1mm, and the material is preferably platinum wire. The catalyst is loaded onto the heating wire by an in-situ growth method, and the catalyst can be selected from one or a mixture of nanoparticles of precious metals such as ruthenium, rhodium, gold, platinum, iridium, palladium, etc., or a mixture of one or a mixture of metal oxides with certain catalytic activity such as tin oxide and copper oxide, preferably nanoparticles of precious metals. And the white element 7 is directly composed of the same heating wire as the black element 6. The heating wire is first quenched by the outer flame of an alcohol lamp before use, and the flame temperature during quenching is 200-600 degrees, preferably 250-350 degrees. The ductility of the heating wire after quenching is greatly provided, which is not only helpful for winding the coil but also beneficial to the shock resistance of the sensor.

[0046] The heating wire is immersed in a growth liquid containing a catalyst precursor. The catalyst precursor is a precious metal acid or salt compound. The precursor is dissolved in a mixture of glycerol, ethyl carbonate, polyvinylidene fluoride and other solvents, and the heating wire is immersed therein again. The heating wire containing the growth liquid is placed in a dark room equipped with an infrared lamp of a specific wavelength for weak reduction for 24 hours. Then, a programmed temperature is adopted in a high temperature box under nitrogen protection to allow the active components in the precursor to grow in situ onto the heating wire.

[0047] White element 7 is a heating wire prepared by the same method without loading a catalyst.

[0048] Embodiment 1:

[0049] 1. Quench a platinum wire with a diameter of 10um at 320 degrees at a quenching speed of 1mm / s;

[0050] 2. Weave the 20 mm quenched platinum wire into a loose twist shape under a microscope;

[0051] 3. Weave the loose twist into a loose braid under a microscope;

[0052] 4. Cut the braid 2 into 3 mm long segments to obtain the white element 7;

[0053] 5. Dissolve 1 g of chloroplatinic acid in a mixture of 0.7 ml of glycerol, 0.1 ml of ethyl carbonate, 0.1 ml of polyvinylidene fluoride, and 0.1 ml of perfluorosulfonic acid proton solution to obtain a catalyst precursor;

[0054] 6. Place the white element 7 obtained in 4 into the precursor in 5;

[0055] 7. Place the 6 substances in an infrared reduction chamber for 24 hours;

[0056] 8. Place the mixture in 7 in a muffle furnace under nitrogen protection and perform secondary reduction by programmed temperature rise. The temperature rise mode is 40 degrees for 10 minutes; 100 degrees for 5 minutes; 300 degrees for 5 minutes; 600 degrees for 10 minutes, and the temperature rise rate is 1°C / min.

[0057] 9. The reaction product in 8 is naturally cooled to room temperature under nitrogen protection and then taken out to obtain the black element 6 loaded with the catalyst;

[0058] 10. Weld the black element 6 and the white element 7 to the first welding position 611 and the second welding position 711 respectively. When welding, mainly weld the braids at both ends of the braid, which can further enhance the shock resistance.

[0059] The sensor obtained by the above method was subjected to vibration test and silicone poisoning test. The changes in the detection performance of the sensor before and after the experiment are shown in Table 1 below:

[0060]

[0061] Table 1 Test results data

[0062] The present application uses an in-situ growth method to directly generate a catalytic layer on the heating wire without adding a coating layer, which can solve the problem of poor shock resistance of the sensor due to the heavy weight of the coating layer; it also makes it impossible for silicone vapor to be adsorbed on the heating wire, thereby failing to generate a silicon component covering the catalytic layer, thereby solving the problem of silicone poisoning of the sensor; it also solves the problem of the energy required by the sensor during operation from traditional heating of the entire coating layer to heating only the heating wire, thereby requiring less heat and low power consumption.

[0063] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A gas sensor with shock resistance, characterized in that: The invention comprises an upper shell (1), a lower shell (11), a black element (6), a white element (7) and a connecting circuit board (8); the upper shell (1) and the lower shell (11) are enclosed to form a placement cavity; the black element (6), the white element (7) and the connecting circuit board (8) are all located in the placement cavity; a first welding position (611) and a second welding position (711) are arranged on the connecting circuit board (8); the black element (6) is welded on the first welding position (611); the white element (7) is welded on the second welding position (711); a plurality of connecting pins (9) are arranged on one end surface of the connecting circuit board (8) facing away from the first welding position (611) and the second welding position (711); and the connecting pins (9) pass through the lower shell (11); the black element (6) and the white element (7) comprise heating wires; at least two heating wires are arranged; the heating wires are intertwined to form a plurality of groups of twisted braids; and the plurality of groups of twisted braids are intertwined to form braids.

2. A gas sensor with shock resistance as claimed in claim 1, characterized in that: A catalytic layer is arranged on the braid, and the catalytic layer wraps around the outer surface and the inner side of the braid.

3. A gas sensor with shock resistance as claimed in claim 1, characterized in that: The shock-resistant gas sensor further comprises a filter element (2), a breathable membrane (3) and a PTFE ring (4), wherein the filter element (2), the breathable membrane (3) and the PTFE ring (4) are sequentially stacked on the connecting circuit board (8).

4. A gas sensor with shock resistance as claimed in claim 3, characterized in that: The shock-resistant gas sensor further comprises a first thermal insulation pad (5), wherein the first thermal insulation pad (5) is embedded in the PTFE ring (4).

5. A gas sensor with shock resistance as claimed in claim 4, characterized in that: The shock-resistant gas sensor further comprises a second thermal insulation pad (10), the second thermal insulation pad (10) being provided with a through hole adapted to the connecting pin (9), the second thermal insulation pad (10) passing through the connecting pin (9) and contacting the connecting circuit board (8).

6. A gas sensor with shock resistance as claimed in claim 5, characterized in that: The shock-resistant gas sensor further comprises a PCB circuit board (13), the PCB circuit board (13) being mounted on an end surface of the lower shell (11) facing away from the upper shell (1), an explosion-proof sealing filling layer (12) being arranged between the lower shell (11) and the PCB circuit board (13), and both the PCB circuit board (13) and the explosion-proof sealing filling layer (12) being provided with a circular hole for the connecting pin (9) to pass through.

7. A gas sensor with shock resistance as claimed in claim 1, characterized in that: The diameter of the heating wire is 0.001-0.5 mm, and the heating wire is any one of platinum wire, gold wire or palladium wire.

8. A gas sensor with shock resistance as claimed in claim 3, characterized in that: The filter element (2) is any one of activated carbon, carbon fiber cotton or modified fiber cotton.

9. A gas sensor with shock resistance as claimed in claim 6, characterized in that: The upper shell (1) and the lower shell (11) are any one of PP, PC, PPO, ABS, glass fiber single or composite material, stainless steel, copper, aluminum metal thin shell, or metal powder metallurgy cover.

10. A gas sensor with shock resistance as claimed in claim 6, characterized in that: The explosion-proof sealing filling layer (12) is any one of fireproof plugging material, explosion-proof putty or epoxy resin.

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