Constant-temperature electronic nose system with adaptive flow control and control method of constant-temperature electronic nose system

Abstract

The invention discloses a constant-temperature electronic nose system with self-adaptive flow control and a control method of the constant-temperature electronic nose system. The device comprises a gas source conditioning module, a constant-temperature gas chamber, a gas transmission module, a gas detection module and a control module, the gas source conditioning module comprises a filter and a mass flow controller, the constant-temperature gas chamber comprises a heat preservation shell, a sample container, a heater and a temperature sensor are arranged in the heat preservation shell, and the gas inlet end of the filter is connected with a first external carrier gas source; the air outlet end of the filter is connected with the air inlet end of the mass flow controller, the air outlet end of the mass flow controller is connected with an air inlet connector in the top of the sample container through a first connecting pipeline, and an air outlet connector in the top of the sample container is connected with the air inlet end of the air conveying module through a second connecting pipeline. The gas outlet end of the gas transmission module is connected with the gas inlet of the gas detection module. The carrier gas flow can be automatically adjusted according to the actual response of the gas sensor, and saturation of the gas sensor is avoided while the signal intensity is ensured.

Description

An adaptive flow control thermostatic electronic nose system and its control method Technical Field

[0001] This invention relates to the field of intelligent warehousing technology, and in particular to an adaptive flow control thermostatic electronic nose system and its control method. Background Technology

[0002] An electronic nose is an intelligent gas detection system that mimics the olfactory sense of a living organism. It uses a gas sensor array combined with pattern recognition algorithms to identify and classify complex odors. Headspace analysis is a commonly used sample pretreatment technique in electronic nose detection. It involves collecting and analyzing the gas after it has reached equilibrium above the sample, offering advantages such as simple sample pretreatment and minimal interference. In existing electronic nose systems, the carrier gas flow rate is a critical parameter. Insufficient flow rate leads to slow headspace gas transmission, weak sensor response signals, and long detection cycles; excessive flow rate may result in insufficient sensor response time, or cause response saturation or even damage to some sensitive sensors. It can also deplete the headspace sample too quickly, leading to signal instability.

[0003] Currently, carrier gas flow control in electronic nose systems often employs open-loop setting or simple closed-loop stabilization control based on flow sensors. This means that operators preset a fixed flow rate value based on experience, and the system maintains this constant flow rate through a mass flow controller (MFC). However, in practical applications, the volatile components, concentrations, and release kinetics of different samples vary significantly, making it difficult to simultaneously meet the optimized detection needs of multiple samples with a fixed carrier gas flow rate. For high-concentration volatile gases in samples, a fixed carrier gas flow rate may saturate the sensor; for low-concentration volatile gases, the signal may be too weak, affecting detection accuracy. Operators need to repeatedly experiment to find the optimal flow rate, a cumbersome and inefficient process. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an adaptive flow control thermostatic electronic nose system and its control method. This system can automatically adjust the carrier gas flow rate based on the actual response of the gas sensor in the gas detection module, ensuring signal strength while avoiding gas sensor saturation, thereby improving the sensitivity, stability, and adaptability of gas acquisition and detection.

[0005] To solve the above problems, the present invention adopts the following technical solution:

[0006] This invention discloses an adaptive flow control thermostatic electronic nose system, comprising a gas source conditioning module, a thermostatic gas chamber, a gas delivery module, a gas detection module, and a control module. The gas source conditioning module includes a filter and a mass flow controller. The thermostatic gas chamber includes an insulated shell, within which are disposed a sample container for containing a sample to be tested, a heater for heating, and a temperature sensor for detecting the internal temperature of the insulated shell. The inlet of the filter is connected to a first external carrier gas source, and the outlet of the filter is connected to the inlet of the mass flow controller. The outlet of the mass flow controller is connected to the inlet port at the top of the sample container via a first connecting pipe, and the outlet port at the top of the sample container is connected to the inlet of the gas delivery module via a second connecting pipe. The first and second connecting pipes pass through the insulated shell, and the outlet of the gas delivery module is connected to the inlet of the gas detection module. The control module is electrically connected to the mass flow controller, the heater, the temperature sensor, the gas delivery module, and the gas detection module.

[0007] In this scheme, during testing, the sample to be tested is placed in a sample container, which is then sealed. The control module controls the heater to heat the ambient temperature inside the insulation shell to a set temperature range and maintain it within that range. After standing for T minutes, the sample to be tested is allowed to fully volatilize. Next, the first external carrier gas source outputs carrier gas through a filter to a mass flow controller. The control module controls the mass flow controller to deliver carrier gas to the sample container at an initially set output flow rate. The gas delivery module delivers the volatilized gas generated by the sample to the top of the sample container to the gas detection module. The gas detection module detects the volatilized gas and sends the generated response signal to the control module. The control module calculates a comprehensive response characteristic value based on the response signal, compares the comprehensive response characteristic value with a preset target response characteristic value range, and adjusts the output flow rate of the mass flow controller according to the comparison result until the comprehensive response characteristic value is within the preset target response characteristic value range. Then, within a preset detection time, the gas sensor in the gas detection module detects the volatilized gas and sends the generated response signal to the control module. The control module processes the response signal to obtain the detection result.

[0008] Preferably, the first connecting pipe is equipped with a flow sensor for detecting the gas flow rate within the first connecting pipe, and the flow sensor is electrically connected to the control module. This facilitates the control module obtaining accurate output flow rate from the mass flow controller.

[0009] Preferably, the insulation shell is further equipped with a circulating fan to ensure a uniform temperature field inside the insulation shell. The circulating fan is electrically connected to the control module. The operation of the circulating fan promotes gas circulation within the insulation shell, resulting in a more uniform temperature field inside the insulation shell.

[0010] Preferably, the gas delivery module includes a solenoid valve, a sampling pump, and a cleaning pump. The gas outlet at the top of the sample container is connected to the first gas inlet of the solenoid valve via a second connecting pipe. The second gas inlet of the solenoid valve is connected to a second external carrier gas source. The first gas outlet of the solenoid valve is connected to the gas inlet of the gas detection module via the sampling pump. The second gas outlet of the solenoid valve is connected to the gas inlet of the gas detection module via the cleaning pump. The solenoid valve, sampling pump, and cleaning pump are electrically connected to the control module.

[0011] During detection, the control module connects the first inlet and the first outlet via a solenoid valve, while disconnecting the second inlet and the second outlet. The cleaning pump is off, but the sampling pump operates, delivering the volatile gas from the top of the sample container to the gas detection module. After detection, the control module disconnects the first inlet and the first outlet via a solenoid valve, while connecting the second inlet and the second outlet. The sampling pump is off, but the cleaning pump operates, delivering carrier gas supplied by a second external carrier gas source to the gas detection module. This cleans the gas detection module, removing residual gas and volatile components, providing a clean and stable initial state for the next detection.

[0012] Preferably, the gas detection module includes a housing, within which a detection gas chamber is provided. The detection gas chamber comprises, from top to bottom, a first gas guiding chamber, an upper gas chamber, a second gas guiding chamber, a middle gas chamber, a third gas guiding chamber, and a lower gas chamber. An air inlet is provided at the top of the housing, communicating with the first gas guiding chamber. The first gas guiding chamber is inverted funnel-shaped. The upper, middle, and lower gas chambers are all cylindrical. The diameters of the upper and lower gas chambers are both D, and the diameter of the middle gas chamber is E, where D > E. The second gas guiding chamber has a circular cross-section with its diameter gradually decreasing from top to bottom. The third air guide chamber has a circular cross-section with a diameter that gradually increases from top to bottom. The bottom of the housing is provided with an air outlet that communicates with the lower air chamber. The upper air chamber is provided with a first horizontal partition, and the top of the lower air chamber is provided with a second horizontal partition. The first horizontal partition has a plurality of first vent holes evenly distributed on it, and the second horizontal partition has a plurality of second vent holes evenly distributed on it. The diameter of the first vent holes is larger than the diameter of the second vent holes. Three gas sensors are evenly spaced on the side wall of the middle air chamber, and three gas sensors are provided on the bottom surface of the lower air chamber. The gas sensors are electrically connected to the control module.

[0013] The three gas sensors in the middle chamber and the three gas sensors in the lower chamber form a six-channel sensor array.

[0014] The airflow flows from top to bottom through the detection chamber, which is gourd-shaped. The middle chamber, located in the middle, has a smaller diameter than the upper and lower chambers, making it a constricted section. This causes the airflow to accelerate and redistribute, facilitating full contact with the gas sensor. The diameter of the first vent on the first horizontal partition is larger than the diameter of the second vent on the second horizontal partition. The airflow first passes through the first horizontal partition, where it is dispersed into multiple relatively coarse jets that impact the gas sensor located on the side wall of the middle chamber. This enhances the contact between the gas and the sensitive layer of the gas sensor. Subsequently, the gas converges in the third air guide cavity region and passes through the smaller-diameter second vent on the second horizontal partition. Under shearing action, it generates more small-scale eddies and turbulence, which further promotes the homogenization of the gas before flowing through the gas sensor in the lower chamber.

[0015] Preferably, the three gas sensors in the lower gas chamber are located directly below the three gas sensors in the middle gas chamber.

[0016] Preferably, both the air inlet and outlet are straight pipes and coaxial with the detection chamber. That is, the air inlet, outlet, and detection chamber are coaxial.

[0017] Preferably, the sample container includes a cup body, a sealing film, and a membrane-breaking sampling cap. The sealing film is used to seal the top opening of the cup body. The membrane-breaking sampling cap includes a cap body and an annular clamping mechanism. The annular clamping mechanism is used to fit around the outside of the top of the cup body and lock it in place. The annular clamping mechanism is located below the cap body. The annular clamping mechanism and the cap body are sealed together by an annular flexible connecting membrane. The cap body can rotate relative to the annular clamping mechanism. The cap body is provided with an air inlet and an air outlet that penetrate the cap body. The air inlet and air outlet are symmetrically arranged on the left and right sides of the cap body. The bottom surface of the cap body is provided with a membrane-breaking structure for piercing the sealing film. The membrane-breaking structure includes multiple conical thorns arranged at equal intervals along the circumference.

[0018] The sample to be tested is placed inside the cup, and the top opening of the cup is sealed with a sealing film. The annular clamping mechanism of the sampling cap is then placed on the outside of the top of the cup, and the annular clamping mechanism is tightened to lock it in place and seal the cup. The cup is left to stand for T minutes to allow the sample to fully volatilize. Afterward, the cap is pressed down so that the conical piercing contacts the sealing film. The cap is then rotated so that the conical piercing creates an arc-shaped cut in the sealing film. Throughout the process, the annular clamping mechanism and the cup maintain a perfect static seal. Carrier gas is introduced into the cup through the gas inlet on the cap, and the volatile gas generated by the sample in the headspace of the cup is delivered to the gas detection module by the gas delivery module.

[0019] The present invention provides a control method for an adaptive flow control thermostatic electronic nose system, used in the aforementioned adaptive flow control thermostatic electronic nose system, comprising the following steps:

[0020] S1: Place the sample to be tested in the sample container, seal the sample container, and control the heater to heat the constant temperature chamber to the set temperature range and maintain it within the set temperature range. Let it stand for T minutes.

[0021] S2: The first external carrier gas source outputs carrier gas to the mass flow controller. The control module controls the mass flow controller to deliver carrier gas to the sample container at the initially set output flow rate. The gas delivery module delivers the volatile gas generated by the sample to be tested at the top of the sample container to the gas detection module. The gas sensor in the gas detection module detects the volatile gas and sends the generated response signal to the control module.

[0022] S3: The control module calculates the comprehensive response characteristic value based on the response signals generated by all gas sensors, compares the comprehensive response characteristic value with the preset target response characteristic value range, and adjusts the output flow of the mass flow controller according to the comparison result until the comprehensive response characteristic value is within the preset target response characteristic value range.

[0023] S4: Within the preset detection time, the gas sensor in the gas detection module detects the volatile gas and sends the generated response signal to the control module. The control module processes the response signal to obtain the detection result.

[0024] Preferably, step S3 includes the following steps:

[0025] S31: The control module acquires the response signal generated by each gas sensor in the current sampling window and calculates the response characteristic value of each gas sensor in the current sampling window;

[0026] The response characteristic value r of the i-th gas sensor in the k-th sampling window i,k The calculation formula is as follows:

[0027]

[0028] x i，k (t)=(s i (t)-b i,k ) / b i,k ,

[0029]

[0030] Among them, t k Let T be the starting time of the k-th sampling window. w s is the sampling window length. i (t) represents the response signal of the i-th gas sensor at time t, b i，kLet [t] be the baseline value of the i-th gas sensor in the k-th sampling window. k -T b , t k ] represents the baseline sub-window before the start of the k-th sampling window, T b The length of the baseline sub-window;

[0031] S32: The control module calculates the comprehensive response characteristic value R corresponding to the current sampling window based on the response characteristic values ​​of all gas sensors in the current sampling window;

[0032] The comprehensive response feature value R corresponding to the kth sampling window k The calculation formula is as follows:

[0033]

[0034] Among them, w i is the weighting coefficient corresponding to the i-th gas sensor, and n is the number of gas sensors, 1≤i≤n;

[0035] S33: The control module compares the comprehensive response feature value R corresponding to the current sampling window with the preset target response feature value range, where the target response feature value range is [R]. L R U ],

[0036] If R < R L If the output flow rate of the mass flow controller is increased by the preset value ΔQ, then proceed to step S31.

[0037] If R > R U If the output flow rate of the mass flow controller is reduced by the preset value ΔQ, then proceed to step S31.

[0038] If R L ≤R≤R U Then proceed to step S4.

[0039] The beneficial effects of this invention are: (1) It can automatically adjust the carrier gas flow rate according to the actual response of the gas sensor in the gas detection module, and avoid gas sensor saturation while ensuring signal strength, thereby improving the sensitivity, stability and adaptability of gas collection and detection. (2) The sealed container containing the gas to be tested is dynamically sealed and controlled by the membrane rupture sampling cover. The opening shape is controllable and the sealing performance is not affected by the membrane rupture action. (3) The detection chamber is gourd-shaped. The first horizontal baffle disperses the airflow into multiple relatively coarse jets, which converge and remix in the contracted middle chamber. The second horizontal baffle generates more small-scale eddies and turbulence under shearing action, which is conducive to further homogenization of the gas. The gas sensors in the middle and lower chambers can collect gas fingerprint information under different heights and flow field conditions, thereby improving the representativeness and stability of the detection signal. Attached Figure Description

[0040] Figure 1 is a schematic diagram of the embodiment;

[0041] Figure 2 is a schematic diagram of the gas detection module;

[0042] Figure 3 is a schematic diagram of the structure of the membrane-breaking sampling cover;

[0043] Figure 4 is a bottom view of the cover;

[0044] Figure 5 is a schematic diagram of the ring clamping mechanism.

[0045] In the diagram: 1. Filter, 2. Mass flow controller, 3. Flow sensor, 4. Insulated housing, 5. Sample container, 6. Heater, 7. Temperature sensor, 8. Circulating fan, 9. Solenoid valve, 10. Sampling pump, 11. Cleaning pump, 12. Gas detection module, 13. Data acquisition card, 14. Computer, 15. Controller, 16. Housing, 17. First gas guide chamber, 18. Upper gas chamber, 19. Second gas guide chamber, 20. Middle gas chamber, 21. Third gas guide chamber, 22. Lower gas chamber, 23. Inlet, 24. Outlet, 25. First horizontal partition, 26. Second horizontal partition, 27. Gas sensor, 28. Cup body, 29. Membrane rupture sampling cover, 30. Cover body, 31. Annular clamping mechanism, 32. Flexible connecting membrane, 33. Inlet port, 34. Outlet port, 35. Conical spike. Detailed Implementation

[0046] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0047] Example: An adaptive flow control thermostatic electronic nose system according to this example, as shown in Figures 1 to 5, includes a gas source conditioning module, a thermostatic gas chamber, a gas delivery module, a gas detection module, and a control module. The gas source conditioning module includes a filter 1 and a mass flow controller 2. The thermostatic gas chamber includes an insulated shell 4, which contains a sample container 5 for holding the sample to be tested, a heater 6 for heating, a temperature sensor 7 for detecting the internal temperature of the insulated shell 4, and a circulating fan 8 for making the internal temperature field of the insulated shell 4 uniform. The gas delivery module includes a solenoid valve 9, a sampling pump 10, and a cleaning pump 11. The inlet of the filter 1 is connected to a first external carrier gas source, and the outlet of the filter 1 is connected to the inlet of the mass flow controller 2. The outlet of the mass flow controller 2 is connected to the inlet port 33 on the top of the sample container 5 through a first connecting pipe. The thermostatic shell 4 is equipped with... A first through hole is matched with the first connecting pipe, through which the first connecting pipe passes. A flow sensor 3 for detecting the gas flow rate in the first connecting pipe is provided on the first connecting pipe. The gas outlet 34 at the top of the sample container 5 is connected to the first gas inlet of the solenoid valve 9 through the second connecting pipe. A second through hole matched with the second connecting pipe is provided on the insulation shell 4, through which the second connecting pipe passes. The second gas inlet of the solenoid valve 9 is connected to the second external carrier gas source. The first gas outlet of the solenoid valve 9 is connected to the gas inlet of the gas detection module 12 through the sampling pump 10. The second gas outlet of the solenoid valve 9 is connected to the gas inlet of the gas detection module 12 through the cleaning pump 11. The control module is electrically connected to the mass flow controller 2, the flow sensor 3, the heater 6, the temperature sensor 7, the circulating fan 8, the solenoid valve 9, the sampling pump 10, the cleaning pump 11, and the gas detection module 12, respectively.

[0048] The sample container 5 includes a cup body 28, a sealing film, and a membrane-breaking sampling cap 29. The sealing film is used to seal the top opening of the cup body 28. The membrane-breaking sampling cap 29 includes a cap body 30 and an annular clamping mechanism 31. The annular clamping mechanism 31 is used to fit around the top of the cup body 28 and lock it in place. The annular clamping mechanism 31 is located below the cap body 30. The annular clamping mechanism 31 and the cap body 30 are sealed together by an annular flexible connecting membrane 32. The cap body 30 can rotate relative to the annular clamping mechanism 31. The cap body 30 is provided with an air inlet 33 and an air outlet 34 that penetrate the cap body 30. The air inlet 33 and the air outlet 34 are symmetrically arranged on the left and right sides of the cap body 30. The bottom surface of the cap body 30 is provided with a membrane-breaking structure for piercing the sealing film. The membrane-breaking structure includes four conical thorns 35 that are evenly spaced along the circumference.

[0049] In this design, a filter removes moisture, oil, and particulate impurities that may be present in the carrier gas, preventing contamination of subsequent gas paths and sensors. A mass flow controller precisely sets and adjusts the carrier gas flow rate, providing controllable flow conditions for subsequent detection. A flow sensor allows the control module to obtain accurate real-time output flow from the mass flow controller.

[0050] The insulation shell features a double-layer structure, comprising an inner shell and an outer shell, with insulation material filling the interlayer to reduce heat loss and improve temperature control accuracy. A PTC heater is used to heat the air inside the insulation shell. A temperature sensor is positioned near the sample container area to monitor the internal air temperature in real time. A circulating fan promotes gas circulation within the insulation shell, resulting in a more uniform temperature field. The sample container is placed on a sample holder inside the insulation shell. A sampling pump, in detection mode, delivers headspace gas from the sample container to the gas detection module; a purging pump, in purging mode, introduces clean carrier gas to purge the gas path and gas detection module.

[0051] During testing, the sample to be tested is placed inside the cup, and the top opening of the cup is sealed with a sealing film (to prevent premature leakage of volatile components during the isothermal equilibrium process). The annular clamping mechanism of the sampling cap is placed on the outside of the top of the cup, and the annular clamping mechanism is tightened to lock it in place and seal the cup. The control module controls the heater and circulating fan to heat the ambient temperature inside the insulation shell to the set temperature range and maintain it within that range. After standing for T minutes, the sample to be tested is allowed to fully volatilize. Next, the cap is pressed down so that the conical spike contacts the sealing film. The cap is rotated so that the conical spike pierces four consecutive, centrally symmetrical arc-shaped cuts in the sealing film, forming a regular, windmill-like opening. Throughout the process, the annular clamping mechanism and the cup maintain a static seal intact. Then, the carrier gas from the first external carrier gas source passes through a filter to the mass flow controller, and the control module controls the mass flow control. The device delivers carrier gas to the sample container at an initially set output flow rate. The control module controls the connection between the first inlet and the first outlet via a solenoid valve, while disconnecting the second inlet and the second outlet. The cleaning pump is not working, but the sampling pump is working, delivering the volatile gas at the top of the sample container to the gas detection module. The gas detection module detects the volatile gas and sends the generated response signal to the control module. The control module calculates a comprehensive response characteristic value based on the response signal, compares the comprehensive response characteristic value with a preset target response characteristic value range, and adjusts the output flow rate of the mass flow controller according to the comparison result until the comprehensive response characteristic value is within the preset target response characteristic value range. Then, within a preset detection time, the gas sensor in the gas detection module detects the volatile gas and sends the generated response signal to the control module. The control module processes the response signal to obtain the detection result. After the test is completed, the control module controls the first air inlet to disconnect from the first air outlet and the second air inlet to connect with the second air outlet via a solenoid valve. The sampling pump does not work, but the cleaning pump works to deliver the carrier gas supplied by the second external carrier gas source to the gas detection module to clean the gas detection module, remove residual gas and volatile components, and provide a clean and stable initial state for the next test.

[0052] The gas detection module 12 includes a housing 16, within which a detection chamber is provided. The detection chamber comprises, from top to bottom, a first gas guiding chamber 17, an upper gas chamber 18, a second gas guiding chamber 19, a middle gas chamber 20, a third gas guiding chamber 21, and a lower gas chamber 22. An air inlet 23 is located at the top of the housing 16, communicating with the first gas guiding chamber 17. The first gas guiding chamber 17 is inverted funnel-shaped. The upper, middle, and lower gas chambers 18, 20, and 22 are all cylindrical. The diameters of the upper and lower gas chambers 18 and 22 are both D, and the diameter of the middle gas chamber 20 is E, where D > E. The cross-section of the second gas guiding chamber 19 is circular, with its diameter gradually decreasing from top to bottom. The cross-section of the third gas guiding chamber 21 is circular, with its diameter gradually increasing from top to bottom. An air outlet communicating with the lower gas chamber 22 is located at the bottom of the housing 16 and is connected to an external activated carbon adsorption tank. The upper gas chamber 18... The upper air chamber 18 is equipped with a first horizontal partition 25, which is located in the middle of the upper air chamber 18. The lower air chamber 22 is equipped with a second horizontal partition 26 at the top. The first horizontal partition 25 has a plurality of first vent holes evenly distributed on it, and the second horizontal partition 26 has a plurality of second vent holes evenly distributed on it. The diameter of the first vent holes is larger than the diameter of the second vent holes. Three gas sensors 27 are evenly spaced on the side wall of the middle air chamber 20, and three gas sensors 27 are provided on the bottom surface of the lower air chamber 22. The gas sensors 27 are electrically connected to the control module.

[0053] The three gas sensors in the lower gas chamber are located directly below the three gas sensors in the middle gas chamber.

[0054] Both the inlet and outlet are straight pipes and coaxial with the detection chamber. The height of both inlet and outlet is 10mm, and the inner diameter is 3mm. This design is used to stabilize the inflow velocity profile, reduce turbulence, and provide repeatable boundary conditions for subsequent flow field organization.

[0055] The three gas sensors in the middle chamber and the three gas sensors in the lower chamber form a six-channel sensor array. The six gas sensors are MEMS metal oxide gas sensors with different sensitive materials or different parameter configurations to form complementary responses to different types of volatile organic compounds, thereby improving the overall recognition capability.

[0056] For example, the sample to be tested is fresh longan fruit stored under cold chain conditions. Headspace gases generated at different storage stages are collected for freshness / shelf life identification. Six gas sensors are used: the first gas sensor, the second gas sensor, the third gas sensor, the fourth gas sensor, the fifth gas sensor, and the sixth gas sensor. The first gas sensor is highly sensitive to alcohols, showing a strong response to fermentation-related volatiles such as ethanol; the second gas sensor is highly sensitive to aldehydes, showing a strong response to oxidation-related volatiles such as acetaldehyde; the third gas sensor is highly sensitive to ketones, showing a strong response to volatiles such as acetone; the fourth gas sensor is highly sensitive to ammonia / amines, showing a strong response to putrefactive amines; the fifth gas sensor is highly sensitive to sulfur-containing volatiles, showing a strong response to odor markers such as hydrogen sulfide and thiols; and the sixth gas sensor is highly sensitive to hydrophobic VOCs, showing a strong response to fruit aroma-related components such as terpenes and aromatic volatiles. By using the differentiated responses of the above six channels, more distinctive odor fingerprint information can be obtained, improving the stability and adaptability of longan storage status identification.

[0057] The airflow flows from top to bottom through the detection chamber, which is gourd-shaped. The middle chamber, located in the middle, has a smaller diameter than the upper and lower chambers, making it a constricted section. This causes the airflow to accelerate and redistribute, facilitating full contact with the gas sensor. The diameter of the first vent on the first horizontal partition is larger than that of the second vent on the second horizontal partition. The airflow first passes through the first horizontal partition, where it is dispersed into multiple relatively coarse jets that impact the gas sensor located on the side wall of the middle chamber. This increases the effective contact area and contact time between the gas and the sensitive layer of the gas sensor. Subsequently, the gas converges in the third air guide chamber area and passes through the smaller-diameter second vent on the second horizontal partition. Under shearing action, it generates more small-scale eddies and turbulence, which further promotes uniform mixing of the gas. Afterward, the gas flows through the gas sensor in the lower chamber, and the detected exhaust gas is discharged from the outlet at the bottom of the casing to the external activated carbon adsorption tank.

[0058] The control module includes a data acquisition card 13, a computer 14, and a controller 15. The data acquisition card 13 is electrically connected to the computer 14 via the controller 15. The controller can be a microcontroller, embedded processor, or programmable logic controller, etc., to control and acquire data from the mass flow controller, flow sensor, heater, temperature sensor, circulating fan, solenoid valve, sampling pump, and cleaning pump. The analog or digital signals from the six gas sensors are transmitted to the computer via the data acquisition card. The computer is used for data storage, visualization, and subsequent signal processing and pattern recognition. The controller can communicate with the computer, and the computer can issue commands such as detection tasks, parameter settings, and cleaning control to the controller.

[0059] This invention can automatically adjust the carrier gas flow rate according to the actual response of the gas sensor, ensuring signal strength while avoiding gas sensor saturation, thereby improving the sensitivity, stability, and adaptability of gas acquisition and detection. The invention uses a ruptured sampling cap to dynamically seal and control the rupture of the sealed container containing the gas to be tested, with controllable opening morphology and unaffected sealing by the rupture action. The detection chamber is gourd-shaped; the first horizontal baffle disperses the airflow into multiple relatively coarse jets, which converge and remix in the contracting middle chamber. The second horizontal baffle generates more small-scale eddies and turbulence under shearing action, which is beneficial for further homogenization of the gas. Gas sensors in the middle and lower chambers can collect gas fingerprint information under different heights and flow field conditions, thereby improving the representativeness and stability of the detection signal.

[0060] This embodiment provides a control method for an adaptive flow control thermostatic electronic nose system, used in the aforementioned adaptive flow control thermostatic electronic nose system, comprising the following steps:

[0061] S1: Place the sample to be tested inside the cup, seal the top opening of the cup with sealing film, put the annular clamping mechanism of the membrane breaking sampling cap on the outside of the top of the cup, tighten the annular clamping mechanism to lock the annular clamping mechanism on the top of the cup and seal it, the control module controls the heater and circulating fan to work, heat the ambient temperature inside the heat preservation shell to the set temperature range and maintain it within the set temperature range, let it stand for T minutes to allow the sample to be tested to fully volatilize;

[0062] S2: Press down the cover to make the conical thorn contact the sealing film, rotate the cover to make the conical thorn pierce the sealing film to make an arc-shaped cut, the first external carrier gas source outputs carrier gas to the mass flow controller, the control module controls the mass flow controller to deliver carrier gas to the sample container at the initially set output flow rate, the control module controls the first gas inlet end to connect with the first gas outlet end through the solenoid valve, the second gas inlet end to disconnect from the second gas outlet end, the cleaning pump does not work, the sampling pump works, and delivers the volatile gas at the top of the sample container to the gas detection module, the gas sensor in the gas detection module detects the volatile gas, and the generated response signal is sent to the control module;

[0063] S3: The control module calculates the comprehensive response characteristic value based on the response signals generated by all gas sensors, compares the comprehensive response characteristic value with the preset target response characteristic value range, and adjusts the output flow of the mass flow controller according to the comparison result until the comprehensive response characteristic value is within the preset target response characteristic value range.

[0064] S4: Within the preset detection time, the gas sensor in the gas detection module detects the volatile gas and sends the generated response signal to the control module. The control module processes the response signal to obtain the detection result.

[0065] S5: The control module controls the first air inlet to disconnect from the first air outlet and the second air inlet to connect with the second air outlet via a solenoid valve. The sampling pump does not work, but the cleaning pump works, delivering the carrier gas supplied by the second external carrier gas source to the gas detection module to clean the gas detection module.

[0066] Step S3 includes the following steps:

[0067] S31: The control module acquires the response signal generated by each gas sensor in the current sampling window and calculates the response characteristic value of each gas sensor in the current sampling window;

[0068] The response characteristic value r of the i-th gas sensor in the k-th sampling window i,k The calculation formula is as follows:

[0069]

[0070] x i，k (t)=(s i (t)-b i,k ) / b i,k ,

[0071]

[0072] Among them, t k Let T be the starting time of the k-th sampling window. w s is the sampling window length. i (t) represents the response signal of the i-th gas sensor at time t, b i,k Let [t] be the baseline value of the i-th gas sensor in the k-th sampling window. k -T b , t k ] represents the baseline sub-window before the start of the k-th sampling window, T b The length of the baseline sub-window;

[0073] S32: The control module calculates the comprehensive response characteristic value R corresponding to the current sampling window based on the response characteristic values ​​of all gas sensors in the current sampling window;

[0074] The comprehensive response feature value R corresponding to the kth sampling window k The calculation formula is as follows:

[0075]

[0076] Among them, w i is the weighting coefficient corresponding to the i-th gas sensor, and n is the number of gas sensors, 1≤i≤n;

[0077] S33: The control module compares the comprehensive response feature value R corresponding to the current sampling window with the preset target response feature value range, where the target response feature value range is [R]. L R U ],

[0078] If R < R L If the output flow rate of the mass flow controller is increased by the preset value ΔQ, then proceed to step S31.

[0079] If R > R U If the output flow rate of the mass flow controller is reduced by the preset value ΔQ, then proceed to step S31.

[0080] If R L ≤R≤R U Then proceed to step S4.

[0081] In this design, the pump operates at a constant speed or constant suction capacity to maintain a stable suction state in the sampling channel. The total carrier gas flow rate is output by a mass flow controller and used as the primary regulation object in closed-loop control. A baseline value is introduced when calculating the response characteristic values ​​to eliminate the effects of baseline drift.

[0082] The control module pre-sets multiple consecutive sampling time windows (e.g., divided by fixed time intervals or a certain sampling period). Within each sampling time window, it processes the response signals from the six gas sensors and extracts the comprehensive response characteristic value R. When R < R L If the current response signal is considered weak, the output flow rate of the mass flow controller is increased, i.e., the output flow rate of the mass flow controller is adjusted to Q. set =Q set +ΔQ; when R>R U If the current response signal is considered to be at risk of saturation, the output flow rate of the mass flow controller is reduced, i.e., the output flow rate of the mass flow controller is adjusted to Q. set =Q set -ΔQ; when R L ≤R≤R U At that time, the output flow rate of the mass flow controller remains constant.

[0083] Through the above comparison and adjustment process, the carrier gas flow rate can be adaptively adjusted according to the actual response of the gas sensor during a single detection process, thereby reducing the risk of sensor saturation and overload while ensuring signal strength.

[0084] Preferably, the sampling pump's suction capacity should meet or exceed Q. max The corresponding maximum throughput requirement is set to avoid situations where the actual flow rate cannot follow the set value due to insufficient suction.

[0085] The system and method described in this invention are not only applicable to the odor and quality detection of agricultural products (such as fresh fruits and dried fruits), but also to the quality evaluation and classification of samples containing volatile organic compounds, such as Chinese medicinal materials. They also have good applicability in fields such as environmental monitoring and food safety testing.

Claims

1. A thermostatic electronic nose system with adaptive flow control, characterized in that, The system includes a gas source conditioning module, a constant temperature gas chamber, a gas delivery module, a gas detection module, and a control module. The gas source conditioning module includes a filter (1) and a mass flow controller (2). The constant temperature gas chamber includes an insulation shell (4). The insulation shell (4) is equipped with a sample container (5) for containing the sample to be tested, a heater (6) for heating, and a temperature sensor (7) for detecting the internal temperature of the insulation shell (4). The inlet of the filter (1) is connected to a first external carrier gas source, and the outlet of the filter (1) is connected to the inlet of the mass flow controller (2). The outlet of the mass flow controller (2) is connected to the inlet (33) at the top of the sample container (5) via a first connecting pipe. The outlet (34) at the top of the sample container (5) is connected to the inlet of the gas delivery module via a second connecting pipe. The first connecting pipe and the second connecting pipe pass through the insulation shell (4) respectively. The outlet of the gas delivery module is connected to the inlet of the gas detection module (12). The control module is electrically connected to the mass flow controller (2), the heater (6), the temperature sensor (7), the gas delivery module, and the gas detection module (12) respectively.

2. The thermostatic electronic nose system with adaptive flow control according to claim 1, characterized in that, The first connecting pipe is equipped with a flow sensor (3) for detecting the gas flow rate in the first connecting pipe, and the flow sensor (3) is electrically connected to the control module.

3. The thermostatic electronic nose system with adaptive flow control according to claim 1, characterized in that, The insulation shell (4) is also equipped with a circulating fan (8) for making the temperature field inside the insulation shell (4) uniform. The circulating fan (8) is electrically connected to the control module.

4. The thermostatic electronic nose system with adaptive flow control according to claim 1, characterized in that, The gas delivery module includes a solenoid valve (9), a sampling pump (10), and a cleaning pump (11). The gas outlet (34) at the top of the sample container (5) is connected to the first gas inlet of the solenoid valve (9) through a second connecting pipe. The second gas inlet of the solenoid valve (9) is connected to a second external carrier gas source. The first gas outlet of the solenoid valve (9) is connected to the gas inlet of the gas detection module (12) through the sampling pump (10). The second gas outlet of the solenoid valve (9) is connected to the gas inlet of the gas detection module (12) through the cleaning pump (11). The solenoid valve (9), the sampling pump (10), and the cleaning pump (11) are electrically connected to the control module.

5. The thermostatic electronic nose system with adaptive flow control according to claim 1, characterized in that, The gas detection module (12) includes a housing (16), and a detection gas chamber is provided inside the housing (16). The detection gas chamber includes a first gas guide chamber (17), an upper gas chamber (18), a second gas guide chamber (19), a middle gas chamber (20), a third gas guide chamber (21), and a lower gas chamber (22) arranged sequentially from top to bottom. An air inlet (23) is provided at the top of the housing (16), and the air inlet (23) is connected to the first gas guide chamber (17). The first gas guide chamber (17) is inverted funnel shape. The upper gas chamber (18), the middle gas chamber (20), and the lower gas chamber (22) are all cylindrical. The diameter of the upper gas chamber (18) and the lower gas chamber (22) is D, and the diameter of the middle gas chamber (20) is E, where D > E. The cross-section of the second gas guide chamber (19) is circular and the diameter is... The cross-section of the third air chamber (21) is circular and the diameter gradually increases from top to bottom. The bottom of the housing (16) is provided with an air outlet (24) that communicates with the lower air chamber (22). The upper air chamber (18) is provided with a first horizontal partition (25). The top of the lower air chamber (22) is provided with a second horizontal partition (26). The first horizontal partition (25) is evenly distributed with a plurality of first vent holes. The second horizontal partition (26) is evenly distributed with a plurality of second vent holes. The diameter of the first vent hole is larger than the diameter of the second vent hole. The side wall of the middle air chamber (20) is provided with three gas sensors (27) at equal intervals. The bottom surface of the lower air chamber (22) is provided with three gas sensors (27). The gas sensors (27) are electrically connected to the control module.

6. The thermostatic electronic nose system with adaptive flow control according to claim 5, characterized in that, The three gas sensors (27) in the lower gas chamber (22) are located directly below the three gas sensors (27) in the middle gas chamber (20).

7. The thermostatic electronic nose system with adaptive flow control according to claim 5, characterized in that, The air inlet (23) and air outlet (24) are both straight pipes and coaxial with the detection chamber.

8. The thermostatic electronic nose system with adaptive flow control according to claim 1, characterized in that, The sample container (5) includes a cup body (28), a sealing film, and a membrane-breaking sampling cap (29). The sealing film is used to seal the top opening of the cup body (28). The membrane-breaking sampling cap (29) includes a cap body (30) and an annular clamping mechanism (31). The annular clamping mechanism (31) is used to fit around the top of the cup body (28) and lock it in place. The annular clamping mechanism (31) is located below the cap body (30). The annular clamping mechanism (31) and the cap body (30) are connected in an annular shape. The flexible connecting membrane (32) is sealed and connected. The cover (30) can rotate relative to the annular clamping mechanism (31). The cover (30) is provided with an air inlet (33) and an air outlet (34) that penetrate the cover (30). The air inlet (33) and the air outlet (34) are symmetrically arranged on the left and right sides of the cover (30). The bottom surface of the cover (30) is provided with a membrane breaking structure for piercing the sealing membrane. The membrane breaking structure includes a plurality of conical thorns (35) arranged at equal intervals along the circumference.

9. A control method for an adaptive flow control thermostatic electronic nose system, used in the adaptive flow control thermostatic electronic nose system of claim 1, characterized in that, Includes the following steps: S1: Place the sample to be tested in the sample container, seal the sample container, and control the heater to heat the constant temperature chamber to the set temperature range and maintain it within the set temperature range. Let it stand for T minutes. S2: The first external carrier gas source outputs carrier gas to the mass flow controller. The control module controls the mass flow controller to deliver carrier gas to the sample container at the initially set output flow rate. The gas delivery module delivers the volatile gas generated by the sample to be tested at the top of the sample container to the gas detection module. The gas sensor in the gas detection module detects the volatile gas and sends the generated response signal to the control module. S3: The control module calculates the comprehensive response characteristic value based on the response signals generated by all gas sensors, compares the comprehensive response characteristic value with the preset target response characteristic value range, and adjusts the output flow rate of the mass flow controller according to the comparison result until the comprehensive response characteristic value is within the preset target response characteristic value range. S4: Within the preset detection time, the gas sensor in the gas detection module detects the volatile gas and sends the generated response signal to the control module. The control module processes the response signal to obtain the detection result.

10. The control method for an adaptive flow control thermostatic electronic nose system according to claim 9, characterized in that, Step S3 The process includes the following steps: S31: The control module acquires the response signal generated by each gas sensor in the current sampling window and calculates the response characteristic value corresponding to each gas sensor in the current sampling window; the response characteristic value r of the i-th gas sensor in the k-th sampling window. i,k The calculation formula is as follows: x i，k (t)=(s i (t)-b i,k ) / b i,k , Among them, t k Let T be the starting time of the k-th sampling window. w s is the sampling window length. i (t) represents the response signal of the i-th gas sensor at time t, b i,k Let [t] be the baseline value of the i-th gas sensor in the k-th sampling window. k -T b , t k ] represents the baseline sub-window before the start of the k-th sampling window, T b S32: The control module calculates the comprehensive response characteristic value R corresponding to the current sampling window based on the response characteristic values ​​of all gas sensors in the current sampling window; the comprehensive response characteristic value R corresponding to the kth sampling window. k The calculation formula is as follows: Among them, w i S33: The control module compares the comprehensive response feature value R corresponding to the current sampling window with the preset target response feature value interval, where the target response feature value interval is [R]. L R U If R < R L If the output flow rate of the mass flow controller is increased by the preset value ΔQ, then proceed to step S31; if R > R U If the output flow rate of the mass flow controller is reduced by a preset value ΔQ, then proceed to step S31; if R L ≤R≤R U Then proceed to step S4.

Images