A portable gas detector

Abstract

The utility model provides a portable gas detection instrument belongs to gas detection technical field, include: external probe, semiconductor type sensor and catalytic combustion type sensor, semiconductor type sensor and catalytic combustion type sensor are installed in the inside of external probe simultaneously, external probe is designed with convenient replacement interface, is convenient to replace, the appearance of external probe adopts cylinder or oval, installs two gas sensors and temperature sensor, semiconductor sensor works in the lower state of gas concentration, and catalytic combustion sensor works in the higher state of gas concentration, realizes complementary advantages, and the signal of gas sensor is temperature compensated to obtain more accurate detection data, and the current temperature can also be displayed simultaneously by the detection instrument, the characteristics of sensor probe miniaturization are reserved, and the probe is convenient to replace, is convenient in narrow space application, has no influence to the structure of gas detection instrument itself, and is convenient for production reform.

Description

Technical Field

[0001] This utility model belongs to the field of gas detection technology, specifically relating to a portable gas detector. Background Technology

[0002] Town gas includes piped natural gas, liquefied petroleum gas, and manufactured coal gas. As a clean energy source, gas is becoming increasingly popular in urban residents and industrial sites. Due to the inherent dangers of gas, gas companies take various measures to ensure gas safety, especially safety inspections.

[0003] Currently, there are various technologies and products available for the safety inspection of gas pipelines, each targeting different application scenarios. When conducting pipeline inspections or in-home safety inspections, the most common and cost-effective testing instrument is a portable gas detector that utilizes the principle of natural diffusion. Its purpose is to detect gas leaks, and it must be lightweight and reliable.

[0004] Different pressure ratings and different causes of leaks lead to varying gas diffusion rates, resulting in different gas concentrations at different application sites. Even within the same site, gas concentrations can differ at different locations and heights, with higher concentrations near the leak. This creates diverse requirements for gas detectors in field applications. Users desire high sensitivity at low concentrations for timely leak detection, along with a wide measurement range to meet specific field needs. However, this presents a dilemma. Traditional portable gas detectors, especially those with external probes, typically have probes mounted on flexible metal hoses. Due to structural limitations and application requirements, the probe usually only houses a single gas sensor.

[0005] Gas sensors based on different principles have different characteristics. Assuming the probe size of the detection instrument is controlled, sensors for detecting flammable gases generally fall into two categories based on their working principle: semiconductor and catalytic combustion. Semiconductor sensors have high sensitivity but a small detection range (generally less than 20% LEL); catalytic combustion sensors have a large detection range (up to 100% LEL), but because they are broad-spectrum, they are easily affected by interference from other gas components, resulting in poor practical performance in low-concentration ranges.

[0006] Therefore, due to the limitations of sensor characteristics, gas detectors using external probes based on the natural diffusion principle can only have a certain sensitivity within a certain measurement range. Currently, there are two common types: one is low-range, high-sensitivity, using semiconductor gas sensors; the other is large-range, using catalytic combustion sensors.

[0007] Additionally, when a low-range sensor is exposed to a gas environment with a high concentration that exceeds its range, its performance will be affected, and it will take a long time to recover to normal, thus affecting its use in the field.

[0008] In addition, gas detectors with external probes are prone to sensor damage due to impacts, requiring complete machine repair and replacement, which is quite troublesome. Utility Model Content

[0009] This invention addresses existing technical problems by using a semiconductor sensor to detect low concentrations and a catalytic combustion sensor to detect high concentrations, achieving a wide measurement range and high detection accuracy. It also protects the low-range sensor in high-concentration gas conditions and utilizes microprocessor data processing to achieve temperature compensation for the gas sensor detection signal, resulting in more accurate detection data. The detector can also display the current temperature and adopts a replaceable modular design for easy maintenance and replacement of vulnerable parts.

[0010] The specific technical solution adopted is as follows: A portable gas detector includes: an external probe, a semiconductor sensor, and a catalytic combustion sensor; the external probe simultaneously installs the semiconductor sensor and the catalytic combustion sensor. The semiconductor sensor operates at low gas concentrations, while the catalytic combustion sensor operates at high gas concentrations. By utilizing the complementary advantages of the two sensors, gas detection based on the principle of natural diffusion is achieved, resulting in a wide measurement range and high detection accuracy. Furthermore, a control circuit protects the low-range sensor when it is in a high-concentration gas environment. The external probe has a built-in temperature sensor to detect the temperature at the site. Through data processing by a microprocessor, temperature compensation is achieved for the gas sensor detection signal to obtain more accurate detection data. The external probe has an LED at the top for illumination, making it easy to use; The external probe is designed with a convenient replacement interface, which can be connected to the extension probe tube for easy probe replacement.

[0011] Furthermore, the external probe consists of a housing and a cover plate, with the sensor components inside the housing; The cover plate has a through-hole pin, and the inner side of the cover plate matches the outer shell structure. The pin on the inner side of the cover plate is welded with wires to connect to the sensor component and LED light. The outer side of the cover plate has an external thread interface for fixing and electrical connection with the extension probe of the detector, so as to facilitate easy replacement. The cover plate is assembled with the outer shell and fixes the sensor component.

[0012] This utility model provides a structural method for an external probe, which adopts a cylindrical shell and two gas sensors are vertically mounted to achieve a compact size; the semiconductor sensor and the catalytic combustion sensor are respectively mounted on two circuit boards, and then the two circuit boards are vertically mounted together to form a sensor component.

[0013] Furthermore, the top of the cylindrical shell has multiple second air inlets facing the semiconductor sensor; the periphery of the side wall of the cylindrical shell has multiple first air inlets facing the catalytic combustion sensor, to ensure that the sensor can receive the gas to be detected through natural diffusion.

[0014] This utility model provides another structural method for an external probe, which adopts an elliptical shell and two sensors are installed side by side to achieve a compact size; the semiconductor sensor and the catalytic combustion sensor are installed side by side on the same circuit board to form a sensor component.

[0015] Furthermore, the top of the elliptical cylindrical shell has two sets of perforations, one facing the semiconductor sensor and the other the catalytic combustion sensor, to facilitate the natural diffusion of the gas being measured through the perforations.

[0016] Furthermore, the inner wall of the elliptical cylindrical shell has supporting ribs to support the circuit board of the sensor component; Furthermore, the top of the elliptical cylindrical casing has two openings for positioning LED light-emitting diodes to achieve illumination.

[0017] Compared with the prior art, the advantages and positive effects of this utility model are as follows: 1. This utility model cleverly integrates a conventional semiconductor sensor and a catalytic combustion sensor into an external probe. This ingenious installation method ensures a compact size while leveraging the complementary advantages of the two sensors to meet engineering requirements. It avoids the inconvenience of carrying different products for different site needs, achieving gas detection based on the principle of natural diffusion. Furthermore, a control circuit protects the low-range sensor in high-concentration gas environments. By having the semiconductor sensor operate at lower gas concentrations and the catalytic combustion sensor at higher concentrations, it achieves high-sensitivity detection in both low-concentration and high-concentration ranges, while also protecting the low-range sensor and extending its lifespan. This makes the gas detector more practical and eliminates the hassle of purchasing and carrying multiple instruments.

[0018] 2. When this utility model is in use, the temperature sensor inside the probe detects the temperature at the scene. Through data processing by the microprocessor, temperature compensation is achieved for the gas sensor detection signal to obtain more accurate detection data. At the same time, the detector can also display the current temperature.

[0019] 3. In the field of use, if the environment is dark or the illumination is low and the situation cannot be clearly seen, the LED at the probe end can be lit by operating the button switch on the detector, eliminating the trouble of carrying other lighting equipment.

[0020] 4. This utility model utilizes a convenient connection method between the sensor probe and the detector, which allows for easy disassembly and replacement of the sensor probe, eliminating the hassle of whole-machine repair and replacement, reducing usage costs, and saving maintenance time.

[0021] The implementation of the above functions still retains the miniaturized characteristics of the sensor probe, which is convenient for use in narrow spaces, and does not affect the structure of the gas detector itself, making it easy to modify and produce. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a circuit diagram of the probe end of a portable gas detector according to the present invention; Figure 2 This is a circuit diagram of the detector end of a portable gas detector according to the present invention; Figure 3 This is a three-dimensional structural diagram of a portable gas detector according to the present invention; Figure 4 This is a schematic diagram of the first angle structure of the cylindrical outer shell of the sensor of this utility model; Figure 5 This is a schematic diagram of the second angle structure of the cylindrical outer shell of the sensor of this utility model; Figure 6 This is a schematic diagram of the internal structure of the cylindrical shell of the sensor of this utility model; Figure 7 This is a schematic diagram of the first angle structure of the elliptical cylindrical shell of the sensor of this utility model; Figure 8 This is a schematic diagram of the second angle structure of the elliptical cylindrical shell of the sensor of this utility model; Figure 9 This is a schematic diagram of the internal structure of the elliptical cylindrical shell of the sensor of this utility model; The components are: 1. External probe; 2. Extension probe tube; 101. Housing; 102. Cover plate; 103. Anti-fooling post; 104. Pin; 105. First air inlet; 106. Second air inlet; 107. Catalytic combustion sensor; 108. Circuit board one; 109. Circuit board two; 110. Semiconductor sensor. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of this utility model, the present utility model will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0026] Example 1, such as Figures 1-9 As shown, this application provides a portable gas detector. When using a gas detector with an external probe 1 in the field, the probe needs to be extended to a place that is inconvenient to reach in order to detect gas leaks. Therefore, the probe needs to be relatively small in size to be practical.

[0027] This patent integrates both a semiconductor sensor and a catalytic combustion sensor, both commonly used in the industry, into an external probe 1. This ingenious installation method ensures a compact size while leveraging the complementary advantages of the two sensors to meet engineering requirements. It avoids the awkwardness of carrying different products due to different needs on site, achieves gas detection based on the principle of natural diffusion, and protects the low-range sensor from high-concentration gas environments through a control circuit.

[0028] The gas detector with external probe 1 is used for gas leak detection in confined spaces. When the environment is dark or the illumination is low, it is inconvenient to check the situation on site. Therefore, an illumination circuit has been added to the probe.

[0029] The external probe 1 of this patent is an independent component with a convenient replacement interface. When the sensor probe is damaged, it is easy to replace, reducing after-sales maintenance and waiting time, and making it convenient to use.

[0030] The aforementioned semiconductor sensor 110 and catalytic combustion sensor 107 have dimensions that are basically in line with industry standards. In this case, the semiconductor sensor TGS2611-E00 from Figaro, a leading company in the industry, has dimensions of Ф10x13, and the catalytic combustion sensor N55A from the same company has dimensions of Ф12x10. Both of these sensors have mature technology, reliable supply, and guaranteed quality.

[0031] Figaro's TGS2611-E00 semiconductor sensor incorporates internal filter material, giving it high selectivity and interference resistance. This prevents it from being affected by external factors when measuring low-concentration gases, resulting in more accurate measurement of the target gas.

[0032] The external probe 1 is typically cylindrical in shape, with dimensions of approximately Ф22x37. The specific dimensions are determined by each manufacturer. Generally speaking, the smaller the dimensions, the more convenient it is for field use.

[0033] This patent provides two technical solutions for simultaneously installing gas sensors based on two different technical principles inside an external probe 1, allowing for complementary advantages and expanding the lighting and temperature detection circuits.

[0034] Option 1 Two sensors are mounted vertically, such as Figure 4-6 As shown, the housing 101 is a cylindrical housing with external dimensions of Ф22x38. The semiconductor sensor 110 and the catalytic combustion sensor 107 are respectively mounted on two circuit boards, namely circuit board one 108 and circuit board two 109. The two circuit boards are then vertically mounted together to form a sensor component, in order to minimize the size of the probe.

[0035] The top of the cylindrical housing 101 has multiple second air inlets 106 facing the semiconductor sensor 110; the periphery of the side wall of the cylindrical housing has multiple first air inlets 105 facing the catalytic combustion sensor 107, to ensure that the sensor can receive the gas to be detected by natural diffusion.

[0036] The inner wall of the cylindrical shell has supporting ribs to support the circuit board of the sensor component.

[0037] The top of the cylindrical housing has four openings for mounting and positioning light-emitting diodes on the LED board to achieve illumination.

[0038] The cover plate 102 is assembled with the cylindrical housing, and the cover plate 102 presses down on the sensor component.

[0039] The pins inside the cover plate 102 are soldered to wires that connect to the sensor circuit board and LEDs.

[0040] Option 2 Two sensors are installed side by side, such as Figure 7-9 As shown, the housing 101 adopts an elliptical cylindrical shape with external dimensions of 13x30x27 mm. The semiconductor sensor 110 and the catalytic combustion sensor 107 are mounted side by side on the same circuit board to form a sensor component, in order to minimize the size of the probe.

[0041] The top of the elliptical cylindrical shell has two sets of perforations, which are directly opposite the semiconductor sensor 110 and the catalytic combustion sensor 107, respectively, so that the gas to be measured can diffuse in naturally through the perforations.

[0042] The inner wall of the elliptical cylindrical shell has supporting ribs to support the circuit board of the sensor component.

[0043] The top of the elliptical cylindrical housing has two openings for positioning LED light-emitting diodes to provide illumination.

[0044] The cover plate 102 is assembled with the elliptical cylindrical housing, and the cover plate 102 presses down on the sensor component.

[0045] The pins inside the cover plate 102 are soldered to wires that connect to the sensor circuit board and LEDs.

[0046] The cover plate 102 and the interface have threads on the outside and are circular or elliptical in shape on the inside, and are assembled with the two types of shells mentioned above respectively.

[0047] The cover plate 102 has a through-type 9-pin connector 104 embedded in its center. Its structure is the so-called "male" type, as shown in the figure. The 9-pin connector 104 is embedded in the cover plate 102 by molding. The inner end of the connector 104 is an open type to facilitate the soldering of wires, so as to make electrical connection with the sensor circuit board through wires. The outer end of the connector 104 mates with the corresponding female connector. The cover plate 102 is also designed with a foolproof post 103, which is parallel to the connector 104 and set at the same height.

[0048] The extension probe 2 of the detector is equipped with a female connector at its end, which makes it easy to connect with the male connector on the outside of the cover plate 102. The female and male connectors are locked with a nut, making the installation convenient, secure and waterproof.

[0049] This design makes it easy to replace the probe, allowing for the connection of probes with different shapes or the replacement of damaged probes, greatly simplifying the user experience and eliminating the need for overall machine maintenance.

[0050] The extension probe 2 is a flexible metal tube with internal wires that connect to the circuitry of the detector. This connection method enables both electrical and mechanical connections between the sensor probe and the detector.

[0051] To further protect the sensor probe, a rubber protective sleeve is installed on the outside of the probe to cushion it in case of impact.

[0052] Circuit function introduction, sensor component circuit function introduction: The semiconductor sensor TGS2611 operates at 5V, while the catalytic combustion sensor N55A operates at 2.5V. The gas detector supplies power to the sensors independently.

[0053] RL is the load resistor of semiconductor sensor CG1. Ra and Rb, together with the C and D terminals of catalytic combustion sensor CG2, form a typical Whitworth bridge circuit, which facilitates the output of sensor signals.

[0054] Rt is a thermistor, which, together with resistor R0, forms a temperature detection circuit to facilitate the detection of the temperature around the probe, thereby enabling temperature compensation for the gas sensor.

[0055] HL1 to HL4 are white light-emitting diodes, controlled by a microprocessor, to provide illumination at the probe end.

[0056] JP1 is the connector plug, which is the pin inside the cover plate, and it connects with the extension probe.

[0057] The aforementioned circuit is installed on the circuit board of the sensor component, forming the sensor's detection circuit, and is connected to the circuit of the gas detector via wires.

[0058] Circuit description of the gas detector: The gas detector's circuit consists of a microprocessor IC1, a battery and power supply circuit, a display circuit, a communication circuit, an audible and visual alarm circuit, and operation buttons. All circuit functions are processed and controlled by the microprocessor IC1.

[0059] The battery and power supply circuit, display circuit, communication circuit, and audible and visual warning circuit are all conventional designs and will not be described in detail here.

[0060] There are many choices for microprocessor IC1, with typical chips including ATmega, STM32, HT, and PIC series. The following describes the signal detection and circuit control related to this patent.

[0061] The signal from the semiconductor sensor 110 is connected to the AD1 channel of the microprocessor IC1, the temperature signal is connected to the AD2 channel, and the Whitworth bridge circuit of the catalytic combustion sensor 107 is connected to the internal operational amplifier circuit. The IO1 output port of the microprocessor IC1 controls the MOSFET T2 through the current-limiting resistor R2 to achieve controllable power output and provide power to the semiconductor sensor 110; The IO2 output port of the microprocessor IC1 controls the EN pin of the LDO chip IC2 through the current-limiting resistor R3 to achieve controllable power output and provide power to the catalytic combustion sensor 107; The IO3 output port of microprocessor IC1 controls MOSFET T1 via current-limiting resistor R4 to supply power to LED, thereby controlling the LED's on / off state and achieving lighting control; resistor R1 is used for current limiting to restrict the current passing through the LED.

[0062] The button AJ1 is connected to the IO4 input port of the microprocessor IC1 to detect button actions; Chip IC2 is a linear LDO that performs power supply voltage conversion to provide power to the catalytic combustion sensor 107.

[0063] JP2 is the connector plug, which is the plug for extending the probe and connecting to the external probe.

[0064] The following describes the usage process and circuit application.

[0065] At the application site, staff members used portable detectors, turned on the power switch, and detected leaking gas near gas pipelines and related gas equipment. When the gas concentration exceeded the standard, the detector issued an audible and visual alarm to alert the testing personnel.

[0066] Initially, the semiconductor sensor 110 is in the working state, while the catalytic combustion sensor 107 is in the off state. When the gas concentration is low (e.g., less than 10% LEL), the display is based on the detection signal of the semiconductor sensor 110. When the gas concentration rises to 13% LEL, the microprocessor automatically turns on the power supply to the catalytic combustion sensor 107, and the display is still based on the detection signal of the semiconductor sensor 110. When the gas concentration continues to rise to 16% LEL, the display is based on the detection signal of the catalytic combustion sensor 107, and the power supply to the semiconductor sensor 110 is turned off to save power and prevent the semiconductor sensor 110 from being affected by high gas concentrations. When the gas concentration is below 16% LEL, the semiconductor sensor 110 is powered on again, and the display is based on the detection signal of the catalytic combustion sensor 107. When the gas concentration is below 13% LEL, the power supply to the catalytic combustion sensor 107 is turned off to save power, and the display is based on the detection signal of the semiconductor sensor 110.

[0067] This method enables the semiconductor sensor 110 to operate at low concentrations and the catalytic combustion sensor 107 to operate at high concentrations, while also promptly shutting down unused sensors, thus protecting the sensors, reducing product power consumption, and extending battery life.

[0068] In this case, the semiconductor sensor selected is the Figaro TGS2611-E00. This sensor has internal filter material, which gives it high selectivity and anti-interference ability, and makes it particularly effective in responding to target gases (such as methane in natural gas). It avoids external influences when the gas concentration is low, making its measurement of target gases more accurate and sensitive.

[0069] Interfering gases encountered in daily life, such as alcohol, acetic acid, VOCs, and hairspray volatiles, typically range in concentration from several hundred ppm to around 1000-2000 ppm, especially common in home kitchens. Because catalytic combustion sensors are broad-spectrum, these substances can also trigger a reaction in the sensor 107, easily leading to false alarms or misdiagnosis of leaks. Therefore, catalytic combustion sensors are not effective in low-concentration ranges. This patent utilizes the anti-interference capabilities, selectivity, and high sensitivity in low-range conditions of semiconductor sensors for gas detection in low-concentration areas. Furthermore, when the target gas concentration in the environment is high, even low concentrations of interfering gases in daily life have negligible impact on the test results. Therefore, catalytic combustion sensors are used for detection in high-concentration ranges.

[0070] As a gas detector, a resolution of ±1% is generally required. For a detector using a catalytic combustion sensor with a range of 100% LEL, the resolution is 1% LEL; for a detector using a semiconductor sensor with a range of 10% LEL, the resolution is 0.1% LEL. This method achieves the goal of high sensitivity in a low range and a large range, while avoiding the interference issues that catalytic combustion sensors are prone to in low concentration ranges in practical applications.

[0071] During use, the temperature sensor inside the probe detects the ambient temperature. Through data processing by the microprocessor, temperature compensation is achieved for the gas sensor's detection signal to obtain more accurate detection data. At the same time, the detector can also display the current temperature.

[0072] In the field of use, if the environment is dark or the illumination is low and the situation cannot be clearly seen, the LED at the end of the sensor probe can be lit by operating the button switch on the detector, thus eliminating the need to carry other lighting equipment.

[0073] This working method achieves both high-sensitivity detection in the low-concentration range and detection in the high-concentration range, while also protecting the sensor in the low-concentration range and extending its service life. This makes the gas detector more practical and eliminates the hassle of purchasing and carrying multiple instruments.

[0074] The convenient connection between the sensor probe and the detector allows for easy removal and replacement of the external probe, eliminating the hassle of whole-machine repair and replacement, reducing operating costs and saving maintenance time. Furthermore, the machine also provides an additional external probe with a different form factor; if one probe fails, the other can be directly replaced, enhancing ease of use.

[0075] The implementation of the above functions still retains the miniaturized characteristics of the sensor probe, which is convenient for use in narrow spaces, and does not affect the structure of the gas detector itself, making it easy to modify and produce.

[0076] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present utility model without departing from the technical solution of the present utility model shall still fall within the protection scope of the technical solution of the present utility model.

Claims

1. A portable gas detector, characterized in that, include: External probe, semiconductor sensor and catalytic combustion sensor; the external probe simultaneously installs a semiconductor sensor and a catalytic combustion sensor. The semiconductor sensor works in the state of low gas concentration, and the catalytic combustion sensor works in the state of high gas concentration. By utilizing the complementary advantages of the two sensors, gas detection based on the principle of natural diffusion is realized, achieving the purpose of wide range and high detection accuracy. Furthermore, the control circuit realizes the protection of the low range sensor when it is in a high concentration gas environment. The external probe has a built-in temperature sensor to detect the temperature at the site. Through data processing by a microprocessor, temperature compensation is achieved for the gas sensor detection signal to obtain more accurate detection data. The external probe has an LED at the top for illumination, making it easy to use; The external probe is designed with a convenient replacement interface, which can be connected to the extension probe tube for easy probe replacement.

2. The portable gas detector as described in claim 1, characterized in that, The external probe includes a housing and a cover plate, with the sensor components inside the housing; The cover plate has a through-hole pin, and the inner side of the cover plate matches the outer shell structure. The pin on the inner side of the cover plate is welded with wires to connect to the sensor component and LED light. The outer side of the cover plate has an external thread interface for fixing and electrical connection with the extension probe of the detector, so as to facilitate easy replacement. The cover plate is assembled with the outer shell and fixes the sensor component.

3. The portable gas detector as described in claim 2, wherein the external probe is characterized in that the outer shell is cylindrical, and the two gas sensors are vertically mounted to achieve a compact size; the semiconductor sensor and the catalytic combustion sensor are respectively mounted on two circuit boards, and then the two circuit boards are vertically mounted together to form a sensor component.

4. The portable gas detector as described in claim 3, wherein the external probe is characterized in that the top of the cylindrical shell has a plurality of second air inlets facing the semiconductor sensor; and the periphery of the side wall of the cylindrical shell has a plurality of first air inlets facing the catalytic combustion sensor, so as to ensure that the sensor can receive the gas to be detected by natural diffusion.

5. The portable gas detector as described in claim 2, wherein the external probe is characterized in that the outer shell is elliptical, and the two sensors are installed side by side to achieve a compact size; the semiconductor sensor and the catalytic combustion sensor are installed side by side on the same circuit board to form a sensor component.

6. A portable gas detector as described in claim 5, characterized in that, The top of the elliptical cylindrical shell has two sets of perforations, which are directly opposite the semiconductor sensor and the catalytic combustion sensor, respectively, to facilitate the natural diffusion of the gas being measured through the perforations.

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