Heat conduction gas sensor

Abstract

The utility model discloses a heat conduction gas sensor which comprises a shell, a sensor probe, a circuit board and a driving circuit, the sensor probe is a silicon micromechanical gas heat conduction sensor probe, and the shell is provided with a hollow containing cavity. The circuit board comprises a first circuit board, a second circuit board and a third circuit board which are sequentially arranged from top to bottom, the sensor probe is provided with an electric connector connected with the driving circuit, and the sensor probe is arranged at the upper end of the first circuit board. The sensor probe is accommodated in the accommodating cavity and is communicated with the outside of the shell, and the heat conduction gas sensor further comprises an electric contact pin which is arranged on the third circuit board and extends out of the lower end of the third circuit board; the electric contact pin is electrically connected with the driving circuit; and the sealant is filled between the first circuit board and the third circuit board and seals the driving circuit in the sealant. The utility model has the advantages of small volume and long service life.

Description

Technical Field

[0001] The utility model relates to a gas sensor, more specifically a heat conduction gas sensor. Background Art

[0002] Helium is a colorless, odorless, non-toxic gas with very small molecules. It is one of the lightest gases on earth and can penetrate through tiny cracks and gaps in most solid and liquid substances. Due to its low density and chemical stability, helium is widely used in various fields, such as meteorology, medicine, industry, etc. Since helium is widely used, it is very important to detect helium leaks.

[0003] The general methods for detecting helium concentration are: thermal conduction, semiconductor, etc. Semiconductor sensors have the advantages of small size and high sensitivity, but also have the disadvantages of low measurement accuracy and slow response speed.

[0004] Thermal conductivity sensors have the advantages of high measurement accuracy and fast response speed, but they also have the following disadvantages:

[0005] 1. Low sensitivity and insufficient response;

[0006] 2. It is large in size and not suitable for use in some small-sized devices.

[0007] Therefore, the helium detectors currently sold on the market all consume large power, are bulky, have low measurement accuracy, and are expensive. Imported helium detectors generally cost hundreds of thousands, and domestic ones cost around 10,000 yuan.

[0008] In addition, due to the uncertainty of the test environment, the existing thermal conductivity sensor cannot protect the electronic circuit part from the harm of corrosive gas, and the life of the sensor is easily affected by the corrosive gas. Utility Model Content

[0009] The utility model provides a heat conduction gas sensor to solve the technical problems that the service life of the prior art sensor is easily affected by corrosive gas and the volume is large.

[0010] In order to solve the above technical problems, the technical solution adopted by the utility model is to design a thermal conduction gas sensor, including a shell, a sensor probe arranged in the shell, a circuit board arranged in the shell and connected to the sensor probe, and a drive circuit arranged on the circuit board. The sensor probe is a silicon micromechanical gas thermal conduction sensor probe. The shell is provided with a hollow accommodating cavity. The circuit board includes a first circuit board, a second circuit board and a third circuit board arranged in sequence from top to bottom. The sensor probe is provided with an electrical connector connected to the drive circuit. The sensor probe is arranged at the upper end of the first circuit board. The sensor probe is accommodated in the accommodating cavity and communicates with the outside of the shell. The thermal conduction gas sensor also includes:

[0011] An electrical pin, which is disposed on the third circuit board and extends out of the lower end of the third circuit board; the electrical pin is electrically connected to the driving circuit;

[0012] A sealant is filled between the first circuit board and the third circuit board, and seals the driving circuit in the sealant.

[0013] The driving circuit is arranged on the second circuit board.

[0014] An air window communicating with the accommodating cavity is disposed at the upper end of the shell, and the thermal conduction gas sensor further comprises a dustproof filter sealing the air window, and the dustproof filter is provided with a plurality of dustproof filter holes communicating with the accommodating cavity.

[0015] A spacing column is arranged between the first circuit board and the second circuit board to space the first circuit board and the second circuit board, and an electric column electrically connecting the first circuit board and the second circuit board is arranged at the center of the spacing column.

[0016] The upper side of the electrical pin is provided with a support platform protruding outward, the second circuit board and the third circuit board are respectively arranged at the upper end and the lower end of the support platform and the second circuit board and the third circuit board clamp the support platform, and the side of the support platform is provided with a groove recessed inward.

[0017] The sealant is epoxy resin sealant.

[0018] The model of the sensor probe is TCS208F.

[0019] The driving circuit comprises:

[0020] A positive feedback amplifier circuit is connected to the sensor probe and amplifies the detection signal of the sensor probe and then outputs it;

[0021] A negative feedback amplifier circuit, which is connected to the positive feedback amplifier circuit and further amplifies the output of the positive feedback amplifier circuit and then outputs it;

[0022] a temperature compensation circuit connected to the second power conversion circuit and the single chip microcomputer, wherein the temperature compensation circuit outputs a temperature compensation signal;

[0023] A single chip microcomputer connected to the negative feedback amplifier circuit, receiving the output of the negative feedback amplifier circuit, and detecting a result according to the output of the negative feedback amplifier circuit and the temperature compensation signal;

[0024] A first power conversion circuit, which is connected to the positive feedback amplifier circuit and provides power for the positive feedback amplifier circuit;

[0025] A second power conversion circuit, which is connected to the negative feedback amplifier circuit and the temperature compensation circuit and provides power for the negative feedback amplifier circuit and the temperature compensation circuit;

[0026] The third power conversion circuit is connected to the single chip microcomputer and provides power for the single chip microcomputer.

[0027] The electrical connectors include a first electrical connector, a second electrical connector, a third electrical connector, a fourth electrical connector, a fifth electrical connector, a sixth electrical connector, a seventh electrical connector and an eighth electrical connector;

[0028] The positive feedback amplifier circuit comprises:

[0029] A first operational amplifier, a non-inverting input terminal of which is grounded, and an inverting input terminal of which is connected to the first electrical connector;

[0030] A second operational amplifier, a non-inverting input terminal of which is grounded, and an inverting input terminal of which is connected to the sixth electrical connector;

[0031] A first resistor, two ends of which are respectively connected to the inverting input terminal of the first operational amplifier and the output terminal of the second operational amplifier;

[0032] a fourth resistor, two ends of which are respectively connected to the inverting input terminal and the output terminal of the second operational amplifier;

[0033] a second diode, an anode of which is connected to the fourth electrical connector, and a cathode of which is connected to the output terminal of the first operational amplifier;

[0034] an eighth capacitor, two ends of which are respectively connected to the output end of the first operational amplifier and the anode of the second diode;

[0035] The second electrical connector is connected to the fourth electrical connector; the fifth electrical connector is connected to the third electrical connector; the seventh electrical connector and the eighth electrical connector are left vacant;

[0036] The input end of the negative feedback amplifier circuit is connected to the output end of the second operational amplifier.

[0037] The model of the single chip microcomputer is ADUC7061, and the temperature compensation circuit includes a temperature sensor TMP116.

[0038] The utility model sets the sensor probe as a silicon micromechanical gas thermal conduction sensor probe by setting a sensor probe in a shell, a circuit board arranged in the shell and connected to the sensor probe, and a drive circuit arranged on the circuit board, so that the volume of the thermal conduction gas sensor can be very small, so as to adapt to the use of many narrow spaces and be convenient to carry. In addition, the shell is provided with a hollow accommodating cavity, the circuit board includes a first circuit board, a second circuit board and a third circuit board arranged in sequence from top to bottom, the sensor probe is provided with an electrical connector connected to the drive circuit, the sensor probe is arranged at the upper end of the first circuit board, the sensor probe is accommodated in the accommodating cavity and communicates with the outside of the shell, and an electrical pin and a sealant are provided, the sealant is filled between the first circuit board and the third circuit board, and the drive circuit is sealed in the sealant. Since the drive circuit is sealed by the sealant, it will not be affected by corrosive gases and has a long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention is described in detail below with reference to the embodiments and drawings, wherein:

[0040] Figure 1 It is a structural diagram of the thermal conduction gas sensor of the utility model;

[0041] Figure 2 This is a cross-sectional view of the thermal conduction gas sensor of the utility model;

[0042] Figure 3 It is a structural diagram of the electrical pin of the thermal conduction gas sensor of the utility model;

[0043] Figure 4 This is a schematic diagram of the driving circuit of the thermal conduction gas sensor of the utility model;

[0044] Figure 5 It is a circuit diagram of a positive feedback amplifier circuit of a thermal conduction gas sensor of the utility model;

[0045] Figure 6 It is a circuit diagram of a negative feedback amplifier circuit of a thermal conduction gas sensor of the utility model;

[0046] Figure 7 The utility model is a circuit diagram of a single chip microcomputer of a heat conduction gas sensor. DETAILED DESCRIPTION

[0047] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings:

[0048] Please also see Figures 1 to 3 The utility model thermal conduction gas sensor comprises a housing 1, a sensor probe 2, a circuit board 3, a drive circuit, an electrical pin 4 and a sealant. Among them:

[0049] The housing 1 is provided with a hollow accommodating cavity 11. In this specific embodiment, the housing is a structure with upper and lower ends opened, that is, the accommodating cavity penetrates the upper and lower ends of the housing. In this specific embodiment, the housing 1 is cylindrical as a whole.

[0050] The sensor probe 2 is arranged in the housing. The sensor probe is a silicon micromachined gas thermal conductivity sensor probe. Since the silicon micromachined gas thermal conductivity sensor probe is small in size, the thermal conductivity gas sensor can be small in size to adapt to many narrow spaces and be easy to carry. In this specific embodiment, the sensor probe model is TCS208F. The TCS208F probe is very sensitive to helium, has low power consumption, and high sampling accuracy.

[0051] TCS208F has the following features: 1. Low power consumption and extremely low heat generation temperature; 2. Small size, short time constant and faster response; 3. It can measure very small gas volumes; 4. The sensitive device probe and the measured gas are diffusely exchanged and have nothing to do with gas flow; 5. It integrates a built-in temperature compensation resistor to make the measurement results more accurate.

[0052] The circuit board 3 is arranged in the housing and connected to the sensor probe. The circuit board 3 includes a first circuit board 31, a second circuit board 32 and a third circuit board 33 arranged in sequence from top to bottom.

[0053] The driving circuit is arranged on the circuit board and is used to drive the sensor probe and process the detection signal of the sensor probe.

[0054] The sensor probe 2 is provided with an electrical connector 21 connected to the driving circuit. The sensor probe is arranged at the upper end of the first circuit board. The sensor probe is accommodated in the accommodating cavity and communicates with the outside of the housing.

[0055] The electrical pin 4 is disposed on the third circuit board and extends out of the lower end of the third circuit board; the electrical pin is electrically connected to the driving circuit.

[0056] The sealant is filled between the first circuit board and the third circuit board, and the drive circuit is sealed in the sealant. In this specific embodiment, the sealant is an epoxy resin sealant. Since the drive circuit is sealed by the sealant, it will not be affected by corrosive gases and has a long service life.

[0057] The utility model sets the sensor probe as a silicon micromechanical gas thermal conduction sensor probe by setting a sensor probe in a shell, a circuit board arranged in the shell and connected to the sensor probe, and a drive circuit arranged on the circuit board, so that the volume of the thermal conduction gas sensor can be very small, so as to adapt to the use of many narrow spaces and be convenient to carry. In addition, the shell is provided with a hollow accommodating cavity, the circuit board includes a first circuit board, a second circuit board and a third circuit board arranged in sequence from top to bottom, the sensor probe is provided with an electrical connector connected to the drive circuit, the sensor probe is arranged at the upper end of the first circuit board, the sensor probe is accommodated in the accommodating cavity and communicates with the outside of the shell, and an electrical pin and a sealant are provided, the sealant is filled between the first circuit board and the third circuit board, and the drive circuit is sealed in the sealant. Since the drive circuit is sealed by the sealant, it will not be affected by corrosive gases and has a long service life.

[0058] In this specific embodiment, the driving circuit is arranged on the second circuit board, so that the driving circuit is completely sealed between the first circuit board and the third circuit board, which not only facilitates the injection of the sealant but also has a better sealing effect.

[0059] In this specific embodiment, the upper end of the housing 1 is provided with an air window 12 communicating with the accommodating chamber, and the thermal conduction gas sensor further includes a dustproof filter 13 sealing the air window, and the dustproof filter is provided with a plurality of dustproof filter holes communicating with the accommodating chamber. By providing the dustproof filter, dust in the gas can be filtered out to prevent dust from entering the accommodating chamber and affecting the detection of the sensor probe.

[0060] In this specific embodiment, a spacer column 5 is provided between the first circuit board 31 and the second circuit board 32 to space the first circuit board and the second circuit board, and an electric post 51 is provided in the center of the spacer column to electrically connect the first circuit board and the second circuit board. The spacer column can facilitate the installation of the first circuit board and the second circuit board, and the provision of the electric post can ingeniously conveniently and quickly electrically connect the first circuit board and the second circuit board.

[0061] In this specific embodiment, a support platform 41 protruding outward is provided on the upper side of the electrical pin 4, the second circuit board 32 and the third circuit board 33 are respectively provided at the upper and lower ends of the support platform, and the second circuit board and the third circuit board clamp the support platform, and a groove 42 recessed inward is provided on the side of the support platform 41. The support platform can facilitate the installation of the second circuit board and the third circuit board, and at the same time, the provision of the groove can make the connection more firm after the sealant is poured, and the drive circuit is better sealed.

[0062] Please also see Figures 4 to 7The driving circuit includes a positive feedback amplifier circuit, a negative feedback amplifier circuit, a temperature compensation circuit, a single chip microcomputer, a first power conversion circuit, a second power conversion circuit and a third power conversion circuit. Wherein:

[0063] The positive feedback amplifier circuit is connected to the sensor probe and amplifies the detection signal of the sensor probe and then outputs it.

[0064] The negative feedback amplifier circuit is connected to the positive feedback amplifier circuit and further amplifies the output of the positive feedback amplifier circuit and then outputs it. The positive feedback amplifier circuit and the negative feedback amplifier circuit are used to amplify the detection signal of the sensor probe.

[0065] The temperature compensation circuit is connected to the second power conversion circuit and the single chip microcomputer, and the temperature compensation circuit outputs a temperature compensation signal. The temperature compensation circuit is used to compensate for the error caused by the temperature in the sensor probe detection.

[0066] The single chip microcomputer is connected to the negative feedback amplifier circuit, receives the output of the negative feedback amplifier circuit, and detects the result according to the output of the negative feedback amplifier circuit and the temperature compensation signal. The single chip microcomputer can be connected to other hosts, so that the data can be further processed and displayed on the hosts.

[0067] The first power conversion circuit is connected to the positive feedback amplifier circuit and provides power for the positive feedback amplifier circuit.

[0068] The second power conversion circuit is connected to the negative feedback amplifier circuit and the temperature compensation circuit and provides power to the negative feedback amplifier circuit and the temperature compensation circuit.

[0069] The third power conversion circuit is connected to the single chip microcomputer and provides power for the single chip microcomputer.

[0070] The utility model adopts a low power supply voltage design, and the standard input power supply voltage is 5 V. The 5 V voltage is converted into +8.5 V and -5 V by the first power supply conversion circuit to supply power to the positive feedback amplifier circuit. Although this part of the voltage is a little higher, the current is very small.

[0071] The 5V voltage is converted into a +3.3V voltage by the second power conversion circuit to supply power to the negative feedback amplifier circuit and the temperature compensation circuit.

[0072] The 5V voltage is converted into a +2.5V voltage by the third power conversion circuit to power the microcontroller.

[0073] Due to the precise design of positive feedback amplifier circuit and negative feedback amplifier circuit and the use of low power supply voltage, the power consumption is very small. The power consumption of the whole machine can be reduced to 0.18 watts. Currently, all domestic thermal conduction helium sensors cannot meet this indicator.

[0074] In this specific embodiment, the model of the sensor probe UP1 is TCS208F, and the electrical connectors include a first electrical connector a1, a second electrical connector a2, a third electrical connector a3, a fourth electrical connector a4, a fifth electrical connector a5, a sixth electrical connector a6, a seventh electrical connector and an eighth electrical connector.

[0075] The positive feedback amplifier circuit includes a first operational amplifier U4-A, a second operational amplifier U4-B, a first resistor R1, a fourth resistor R4, a second diode D2 and an eighth capacitor C8. Wherein:

[0076] The non-inverting input terminal of the first operational amplifier U4-A is grounded, and the inverting input terminal is connected to the first electrical connector a1.

[0077] The non-inverting input terminal of the second operational amplifier U4-B is grounded, and the inverting input terminal is connected to the sixth electrical connector a6. The first operational amplifier and the second operational amplifier are implemented by ADA4077-2.

[0078] Two ends of the first resistor R1 are connected to the inverting input terminal of the first operational amplifier and the output terminal of the second operational amplifier respectively.

[0079] Two ends of the fourth resistor R4 are respectively connected to the inverting input terminal and the output terminal of the second operational amplifier.

[0080] The anode of the second diode D2 is connected to the fourth electrical connector a4, and the cathode is connected to the output end of the first operational amplifier.

[0081] Two ends of the eighth capacitor C8 are connected to the output end of the first operational amplifier and the anode of the second diode respectively.

[0082] The second electrical connector is connected to the fourth electrical connector a4; the fifth electrical connector a5 is connected to the third electrical connector a3; and the seventh electrical connector and the eighth electrical connector are left vacant.

[0083] The input end of the negative feedback amplifier circuit is connected to the output end Vout1 of the second operational amplifier.

[0084] The negative feedback amplifier circuit is composed of the chip INA333AIDRGR and peripheral circuits. The output end ADC of the negative feedback amplifier circuit is connected to the ADC2 interface of the microcontroller U2, and is provided to the microcontroller U2 for analog-to-digital conversion.

[0085] In this specific embodiment, the model of the single chip microcomputer is ADUC7061, and the temperature compensation circuit includes a temperature sensor TMP116.

[0086] The single-chip microcomputer U2 is connected to an external host computer through a serial port. The host computer communicates with the single-chip microcomputer U2 according to the serial port protocol, and displays information such as the composition, concentration, and range of the gas on the screen of the host computer.

[0087] The utility model has no special requirements for the external host computer and can work normally without additional software injection. As long as the serial port of the host computer can meet the level requirements of the single-chip computer U2 (the serial port high level is between 2V-3.6V), it can communicate with the single-chip computer U2 according to the serial port protocol, which is simple to operate and has a wide range of applications.

[0088] The single chip microcomputer U2 also outputs the corresponding analog signal at DAC0 for use by users in need.

[0089] The utility model sets the sensor probe as a silicon micromechanical gas thermal conduction sensor probe by setting a sensor probe in a shell, a circuit board arranged in the shell and connected to the sensor probe, and a drive circuit arranged on the circuit board, so that the volume of the thermal conduction gas sensor can be very small, so as to adapt to the use of many narrow spaces and be convenient to carry. In addition, the shell is provided with a hollow accommodating cavity, the circuit board includes a first circuit board, a second circuit board and a third circuit board arranged in sequence from top to bottom, the sensor probe is provided with an electrical connector connected to the drive circuit, the sensor probe is arranged at the upper end of the first circuit board, the sensor probe is accommodated in the accommodating cavity and communicates with the outside of the shell, and an electrical pin and a sealant are provided, the sealant is filled between the first circuit board and the third circuit board, and the drive circuit is sealed in the sealant. Since the drive circuit is sealed by the sealant, it will not be affected by corrosive gases and has a long service life.

[0090] The utility model has the following features:

[0091] 1. Adopt TCS208F probe, which is very sensitive to helium, has low power consumption and high sampling accuracy.

[0092] 2. Sealant is used to seal the entire electronic circuit to protect it from the harm of corrosive gases and extend the life of the machine.

[0093] 3. Due to the precise design of the operational amplifier and the use of low power supply voltage, the power consumption is very small. The power consumption of the whole machine can be as low as 0.18 watts. All domestic thermal conduction helium sensors cannot reach this indicator.

[0094] 4. It is very small, only the size of a finger, can fit into many small spaces, and is easy to carry.

[0095] 5. The size and definition of the output interface are suitable for many host control interfaces, with stronger versatility, can adapt to more host control and display test results, and is easy to replace.

[0096] The utility model thermal conduction gas sensor can be widely used in natural gas, CH4, H2, CO2, CO, SF6, Xe, He, NH3 and other gas component detection, and can also be used to measure very small gas volume changes.

[0097] The above description is only a preferred embodiment of the present invention and is 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 thermal conduction gas sensor, comprising a housing, a sensor probe disposed in the housing, a circuit board disposed in the housing and connected to the sensor probe, and a drive circuit disposed on the circuit board, characterized in that: The sensor probe is a silicon micromechanical gas thermal conduction sensor probe, the shell is provided with a hollow accommodating cavity, the circuit board includes a first circuit board, a second circuit board and a third circuit board arranged in sequence from top to bottom, the sensor probe is provided with an electrical connector connected to the drive circuit, the sensor probe is arranged at the upper end of the first circuit board, the sensor probe is accommodated in the accommodating cavity and communicates with the outside of the shell, and the thermal conduction gas sensor also includes: An electrical pin, which is disposed on the third circuit board and extends out of the lower end of the third circuit board; the electrical pin is electrically connected to the driving circuit; A sealant is filled between the first circuit board and the third circuit board, and seals the driving circuit in the sealant.

2. The thermal conduction gas sensor according to claim 1, characterized in that: The driving circuit is arranged on the second circuit board.

3. The thermal conduction gas sensor according to claim 1, characterized in that: An air window communicating with the accommodating cavity is disposed at the upper end of the shell, and the thermal conduction gas sensor further comprises a dustproof filter sealing the air window, and the dustproof filter is provided with a plurality of dustproof filter holes communicating with the accommodating cavity.

4. The thermal conduction gas sensor according to claim 1, wherein: A spacing column is arranged between the first circuit board and the second circuit board to space the first circuit board and the second circuit board, and an electric column electrically connecting the first circuit board and the second circuit board is arranged at the center of the spacing column.

5. The thermal conduction gas sensor according to claim 4, characterized in that: The upper side of the electrical pin is provided with a support platform protruding outward, the second circuit board and the third circuit board are respectively arranged at the upper end and the lower end of the support platform and the second circuit board and the third circuit board clamp the support platform, and the side of the support platform is provided with a groove recessed inward.

6. The thermal conduction gas sensor according to claim 1, wherein: The sealant is epoxy resin sealant.

7. The thermal conduction gas sensor according to claim 1, characterized in that: The model of the sensor probe is TCS208F.

8. The thermal conduction gas sensor according to claim 7, characterized in that: The driving circuit comprises: A positive feedback amplifier circuit is connected to the sensor probe and amplifies the detection signal of the sensor probe and then outputs it; A negative feedback amplifier circuit, which is connected to the positive feedback amplifier circuit and further amplifies the output of the positive feedback amplifier circuit and then outputs it; a temperature compensation circuit, wherein the temperature compensation circuit outputs a temperature compensation signal; A single chip microcomputer, which is connected to the negative feedback amplifier circuit and the temperature compensation circuit, receives the output of the negative feedback amplifier circuit, and detects the result according to the output of the negative feedback amplifier circuit and the temperature compensation signal; A first power conversion circuit, which is connected to the positive feedback amplifier circuit and provides power for the positive feedback amplifier circuit; A second power conversion circuit, which is connected to the negative feedback amplifier circuit and the temperature compensation circuit and provides power for the negative feedback amplifier circuit and the temperature compensation circuit; The third power conversion circuit is connected to the single chip microcomputer and provides power for the single chip microcomputer.

9. The thermal conduction gas sensor according to claim 8, characterized in that: The electrical connectors include a first electrical connector, a second electrical connector, a third electrical connector, a fourth electrical connector, a fifth electrical connector, a sixth electrical connector, a seventh electrical connector and an eighth electrical connector; The positive feedback amplifier circuit comprises: A first operational amplifier, a non-inverting input terminal of which is grounded, and an inverting input terminal of which is connected to the first electrical connector; A second operational amplifier, a non-inverting input terminal of which is grounded, and an inverting input terminal of which is connected to the sixth electrical connector; A first resistor, two ends of which are respectively connected to the inverting input terminal of the first operational amplifier and the output terminal of the second operational amplifier; a fourth resistor, two ends of which are respectively connected to the inverting input terminal and the output terminal of the second operational amplifier; a second diode, an anode of which is connected to the fourth electrical connector, and a cathode of which is connected to the output terminal of the first operational amplifier; an eighth capacitor, two ends of which are respectively connected to the output end of the first operational amplifier and the anode of the second diode; The second electrical connector is connected to the fourth electrical connector; the fifth electrical connector is connected to the third electrical connector; the seventh electrical connector and the eighth electrical connector are left vacant; The input end of the negative feedback amplifier circuit is connected to the output end of the second operational amplifier.

10. The thermal conduction gas sensor according to claim 9, characterized in that: The model of the single chip microcomputer is ADUC7061, and the temperature compensation circuit includes a temperature sensor TMP116.

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