Heat conduction argon gas sensor

Abstract

The utility model discloses a heat conduction argon gas sensor which comprises a shell, a sensor probe, a circuit board and a driving circuit, and the sensor probe is a silicon micromechanical gas heat conduction sensor probe; the driving circuit comprises a positive feedback amplification circuit which amplifies a detection signal of the sensor probe and then outputs a first amplification signal; a first negative feedback amplification circuit which further amplifies the first amplification signal of the positive feedback amplification circuit and outputs a second amplification signal; a second negative feedback amplification circuit which further amplifies the second amplification signal of the first negative feedback amplification circuit and outputs a third amplification signal; the temperature compensation circuit outputs a temperature compensation signal; and the signal processing circuit obtains a detection result according to the third amplification signal output by the second negative feedback amplification circuit and the temperature compensation signal. The device is small in size and high in precision.

Description

Technical Field

[0001] The utility model relates to a gas sensor, and more precisely, to a thermal conductivity argon gas sensor. Background Art

[0002] Argon is a colorless, odorless monoatomic gas. The density of argon is 1.4 times that of air and 10 times that of helium. Argon is an inert gas that does not react chemically with other substances at room temperature and is also insoluble in liquid metals at high temperatures. It shows its superiority especially in the arc welding of non-ferrous metals and can be used for filling bulbs and arc welding of stainless steel, magnesium, aluminum, etc., namely "argon arc welding".

[0003] The common detection methods of argon mainly include infrared spectroscopy, mass spectrometry, conductivity method and gas chromatography. Among them:

[0004] 1. Infrared Spectroscopy

[0005] Advantages: Infrared spectroscopy is fast and accurate and is very effective for gas analysis.

[0006] Disadvantages: Although argon does not have absorption in the infrared band, it can interact with the analyte to form reaction products, thus changing the optical properties of the analyte.

[0007] 2. Mass Spectrometry

[0008] Advantages: Mass spectrometry is very effective for gas analysis with high sensitivity and high resolution.

[0009] Disadvantages: Expensive, complex instrument structure, requiring professional maintenance; high environmental requirements.

[0010] 3. Conductivity Method

[0011] Advantages: The conductivity method is simple and fast and is suitable for some occasions of real-time monitoring.

[0012] Disadvantages: The conductivity of argon is relatively low and is not much different from that of air. It is difficult to test by the conductivity method and the accuracy is low.

[0013] 4. Gas Chromatography

[0014] Advantages: Gas chromatography is very effective for the separation of gas components and is characterized by being fast and accurate.

[0015] Disadvantages: It cannot directly analyze unknown substances, cannot directly determine the nature, has low accuracy for high-content analysis, and the machine requires a large cabinet.

[0016] The heat conduction argon sensor uses the conductivity method for detection. However, the existing heat conduction argon detectors are relatively large in size, inconvenient to carry, consume a large amount of electricity, are expensive, and have low measurement accuracy. Summary of the Invention

[0017] The present invention provides a heat conduction argon sensor to solve the technical problems of the existing heat conduction argon sensor, such as large size, inconvenient to carry, and low measurement accuracy.

[0018] To solve the above technical problems, the technical solution adopted by the present invention is to design a heat conduction argon sensor, which includes 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. The sensor probe is a silicon micromachined gas heat conduction sensor probe; the sensor probe includes a first thin film resistor sensitive to gas, a second thin film resistor sensitive to gas, a first thermistor sensitive to temperature, and a second thermistor sensitive to temperature;

[0019] The drive circuit includes:

[0020] A positive feedback amplifier circuit, which is connected to the sensor probe and outputs a first amplified signal after amplifying the detection signal of the sensor probe; the first thermistor is connected to the positive feedback amplifier circuit;

[0021] A first negative feedback amplifier circuit, which is connected to the positive feedback amplifier circuit and outputs a second amplified signal after further amplifying the first amplified signal of the positive feedback amplifier circuit; the second thermistor is connected to the first negative feedback amplifier circuit;

[0022] A second negative feedback amplifier circuit, which is connected to the first negative feedback amplifier circuit and outputs a third amplified signal after further amplifying the second amplified signal of the first negative feedback amplifier circuit;

[0023] A temperature compensation circuit, which outputs a temperature compensation signal;

[0024] A signal processing circuit, which is connected to the second negative feedback amplifier circuit and the temperature compensation circuit, and obtains a detection result according to the third amplified signal output by the second negative feedback amplifier circuit and the temperature compensation signal.

[0025] The model of the sensor probe is TCS208F.

[0026] The positive feedback amplifier circuit includes:

[0027] A first amplifier, whose non-inverting input terminal is grounded, and the inverting input terminal is connected to one end of the first thermistor;

[0028] The first diode, whose negative electrode is connected to the output terminal of the first amplifier and positive electrode is connected to the other end of the first thermistor; One end of the first thin-film resistor is connected to the positive electrode of the first diode, and the other end is connected to one end of the second thin-film resistor;

[0029] The twenty-first capacitor, whose two ends are respectively connected to the positive and negative electrodes of the first diode;

[0030] The second amplifier, whose non-inverting input terminal is grounded and inverting input terminal is connected to the other end of the second thin-film resistor;

[0031] The seventh resistor, whose one end is connected to the inverting input terminal of the first amplifier and the other end is connected to the output terminal of the second amplifier;

[0032] The eighth resistor, whose one end is connected to the output terminal of the second amplifier and the other end is connected to the inverting input terminal of the second amplifier;

[0033] The ninth resistor, whose one end is connected to the output terminal of the second amplifier and the other end is grounded;

[0034] The output terminal of the second amplifier is connected to the first negative feedback amplifier circuit.

[0035] The first negative feedback amplifier circuit includes:

[0036] The seventh operational amplifier, which has a non-inverting input terminal, an inverting input terminal, an output terminal, a positive voltage input terminal, and a negative voltage input terminal; The inverting input terminal of the seventh operational amplifier is grounded; One end of the second thermistor is connected to the non-inverting input terminal of the seventh operational amplifier;

[0037] The tenth resistor, whose one end is connected to the output terminal of the second amplifier;

[0038] The twenty-second capacitor, whose one end is grounded and the other end is connected to the other end of the tenth resistor;

[0039] The eleventh resistor, whose one end is connected to the other end of the tenth resistor and the other end is connected to the inverting input terminal of the seventh operational amplifier;

[0040] The twenty-third capacitor, whose one end is connected to the other end of the eleventh resistor and the other end is grounded;

[0041] The thirteenth resistor, whose one end is connected to the other end of the eleventh resistor and the other end is grounded;

[0042] The fifteenth resistor, whose one end is connected to the inverting input terminal of the seventh operational amplifier and the other end is connected to the output terminal of the seventh operational amplifier;

[0043] The twelfth resistor, one end of which is connected to the other end of the second thermistor and the other end is grounded;

[0044] The twenty-fourth capacitor, one end of which is connected to one end of the second thermistor and the other end is grounded;

[0045] The fourteenth resistor, one end of which is connected to one end of the second thermistor and the other end is connected to the positive voltage input terminal of the seventh operational amplifier;

[0046] The twenty-fifth capacitor, one end of which is connected to the positive voltage input terminal of the seventh operational amplifier and the other end is grounded;

[0047] The twenty-sixth capacitor, one end of which is connected to the positive voltage input terminal of the seventh operational amplifier and the other end is grounded;

[0048] The sixteenth resistor, one end of which is connected to the output terminal of the seventh operational amplifier;

[0049] The twenty-seventh capacitor, one end of which is connected to the other end of the sixteenth resistor and the other end is grounded;

[0050] The twenty-eighth capacitor, one end of which is connected to the other end of the sixteenth resistor and the other end is grounded;

[0051] The seventeenth resistor, one end of which is connected to the other end of the sixteenth resistor and the other end is grounded;

[0052] The eighteenth resistor, one end of which is connected to the other end of the sixteenth resistor and the other end is connected to the second negative feedback amplification circuit.

[0053] The second negative feedback amplification circuit includes:

[0054] An instrumentation amplifier having a positive input terminal, a negative input terminal, a positive voltage input terminal, a negative voltage input terminal, an output terminal, a first gain setting terminal, a second gain setting terminal, and a reference input terminal; the negative input terminal of the instrumentation amplifier is connected to the other end of the eighteenth resistor; the reference input terminal and the negative voltage input terminal of the instrumentation amplifier are grounded;

[0055] The nineteenth resistor, one end of which is connected to the first gain setting terminal of the instrumentation amplifier and the other end is connected to the second gain setting terminal of the instrumentation amplifier;

[0056] The thirty-second capacitor, one end of which is connected to the positive voltage input terminal of the instrumentation amplifier and the other end is grounded;

[0057] The thirty-third capacitor, one end of which is connected to the positive voltage input terminal of the instrumentation amplifier and the other end is grounded;

[0058] The twenty-fourth resistor, one end of which is connected to the positive input terminal of the instrumentation amplifier and the other end is grounded;

[0059] The forty-third capacitor, one end of which is connected to the positive input terminal of the instrumentation amplifier and the other end is grounded;

[0060] The forty-second capacitor, one end of which is connected to the positive input terminal of the instrumentation amplifier and the other end is grounded;

[0061] The twenty-third resistor, one end of which is connected to the positive input terminal of the instrumentation amplifier;

[0062] The fourth inductor, one end of which is connected to the other end of the twenty-third resistor;

[0063] The thirty-ninth capacitor, one end of which is connected to the other end of the fourth inductor and the other end is grounded;

[0064] The fortieth capacitor, one end of which is connected to the other end of the fourth inductor and the other end is grounded;

[0065] The forty-first capacitor, one end of which is connected to the other end of the twenty-third resistor and the other end is grounded;

[0066] The twenty-fifth resistor, one end of which is connected to the output terminal of the instrumentation amplifier; the other end is connected to the signal processing circuit;

[0067] The twenty-sixth resistor, one end of which is connected to the other end of the twenty-fifth resistor and the other end is grounded;

[0068] The forty-fourth capacitor, one end of which is connected to the other end of the twenty-fifth resistor and the other end is grounded.

[0069] The drive circuit further includes:

[0070] A standard voltage conversion circuit, which converts the input power supply voltage into a standard 5V voltage for output;

[0071] The first power conversion circuit is connected to the standard voltage conversion circuit, the second negative feedback amplification circuit, the temperature compensation circuit, and the signal processing circuit and supplies power to the second negative feedback amplification circuit, the temperature compensation circuit, and the signal processing circuit;

[0072] The second power conversion circuit is connected to the standard voltage conversion circuit, the positive feedback amplification circuit, and the first negative feedback amplification circuit and supplies power to the positive feedback amplification circuit and the first negative feedback amplification circuit;

[0073] The third power conversion circuit, which is connected to the standard voltage conversion circuit and the positive feedback amplification circuit and supplies power to the positive feedback amplification circuit.

[0074] The first amplifier and the second amplifier are implemented by using a dual-channel amplifier with the model number ADA4077-2.

[0075] The model number of the seventh operational amplifier is OPA735AIDBVR.

[0076] The model number of the instrumentation amplifier is INA333AIDRGR.

[0077] The housing is provided with a hollow accommodation cavity, and an air window communicating with the accommodation cavity is provided at the upper end of the housing; 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 arranged at the upper end of the first circuit board. The sensor probe is received in the accommodation cavity and communicates with the outside of the housing, and the drive circuit is arranged on the second circuit board;

[0078] The thermal conduction argon sensor further includes:

[0079] An electrical pin, which is arranged 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 drive circuit;

[0080] Sealant, which is filled between the first circuit board and the third circuit board, and seals the drive circuit in the sealant;

[0081] A dust-proof filter screen, which seals the air window, and a plurality of dust-proof filter holes communicating with the accommodation cavity are arranged on the dust-proof filter screen.

[0082] In the utility model, by arranging a sensor probe in the housing, a circuit board arranged in the housing and connected to the sensor probe, and a drive circuit arranged on the circuit board, and setting the sensor probe as a silicon micromachined gas thermal conduction sensor probe, the volume of the thermal conduction argon sensor can be very small, so as to adapt to the use in many narrow spaces and be convenient to carry. In addition, by adopting a positive feedback amplifier circuit, a first negative feedback amplifier circuit, a second negative feedback amplifier circuit, a temperature compensation circuit and a signal processing circuit, the signal collected by the sensor probe is amplified three times through the positive feedback amplifier circuit, the first negative feedback amplifier circuit and the second negative feedback amplifier circuit, effectively solving the problem that the detection signal of the sensor probe is very weak because the conductivity of argon is relatively small and is not much different from that of air, the signal sent to the signal processing circuit is relatively weak, and the accuracy is relatively low. In addition, further connecting the first thermistor of the sensor probe to the positive feedback amplifier circuit to perform the first-stage temperature compensation on the detection, connecting the second thermistor of the sensor probe to the first negative feedback circuit to perform the second-stage temperature compensation on the detection, and setting a temperature compensation circuit to perform the third-stage temperature compensation on the detection. Through the three-stage temperature compensation, the accuracy problem caused by temperature difference can be effectively solved, and the detection accuracy is further improved. Brief Description of the Drawings

[0083] The present utility model will be described in detail below in conjunction with embodiments and the drawings, where:

[0084] Figure 1 is a structural diagram of the thermal conduction argon gas sensor of the present utility model;

[0085] Figure 2 is a sectional view of the thermal conduction argon gas sensor of the present utility model;

[0086] Figure 3 is a schematic diagram of the drive circuit of the thermal conduction argon gas sensor of the present utility model;

[0087] Figure 4 is a circuit diagram of the positive feedback amplifier circuit of the thermal conduction argon gas sensor of the present utility model;

[0088] Figure 5 is Figure 4 a circuit diagram of the power supply connection angle of the dual-channel amplifier in

[0089] Figure 6 is a circuit diagram of the first negative feedback amplifier circuit of the thermal conduction argon gas sensor of the present utility model;

[0090] Figure 7 is a circuit diagram of the second negative feedback amplifier circuit of the thermal conduction argon gas sensor of the present utility model;

[0091] Figure 8 is a circuit diagram of the signal processing circuit of the thermal conduction argon gas sensor of the present utility model;

[0092] Figure 9 is a circuit diagram of the temperature compensation circuit of the thermal conduction argon gas sensor of the present utility model;

[0093] Figure 10 is a circuit diagram of the standard voltage conversion circuit and the first power supply conversion circuit of the thermal conduction argon gas sensor of the present utility model;

[0094] Figure 11 is a circuit diagram of the second power supply conversion circuit of the thermal conduction argon gas sensor of the present utility model;

[0095] Figure 12 is a circuit diagram of the digital-to-analog conversion circuit of the thermal conduction argon gas sensor of the present utility model. Detailed Embodiments

[0096] The following further elaborates on the detailed embodiments of the present utility model in conjunction with the drawings:

[0097] Please also refer to Figures 1 to 11。The thermal conduction argon gas sensor of the present utility model includes a housing 1, a sensor probe 2, a circuit board 3, a driving circuit, an electrical pin 4, and a sealant. Among them:

[0098] The housing 1 is provided with a hollow accommodation cavity 11. In this specific embodiment, the housing has a structure with openings at both the upper and lower ends, that is, the accommodation cavity penetrates through the upper and lower ends of the housing. In this specific embodiment, the housing 1 is generally cylindrical.

[0099] The sensor probe 2 is arranged inside the housing. The sensor probe is a silicon micro-machined gas thermal conduction sensor probe. Since the volume of the silicon micro-machined gas thermal conduction sensor probe is small, the volume of the thermal conduction argon gas sensor can be made small, so as to adapt to the use in many narrow spaces and is convenient to carry.

[0100] In this specific embodiment, the model of the sensor probe is TCS208F. The TCS208F gas thermal conductivity sensor probe is produced by using advanced MEMS (Micro Electro Mechanical System, micro-electromechanical system) processing technology. It is a concentration-type sensor probe that responds based on the different thermal conductivity coefficients of the measured components. The product has advantages such as a large detection range, high reliability, convenient installation, and simple maintenance. The TCS208F probe is very sensitive to argon, has low power consumption, and high sampling accuracy.

[0101] TCS208F has the following characteristics: 1. Low power consumption and extremely low heating temperature; 2. Very small size, short time constant, and faster response; 3. Can measure very small gas volumes; 4. The diffusion exchange between the sensitive device probe and the measured gas is independent of gas flow; 5. Integrated with an internal temperature compensation resistor, making the measurement result more accurate.

[0102] The circuit board 3 is arranged inside the housing and is 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.

[0103] The driving circuit is arranged on the circuit board. The driving circuit is used to drive the sensor probe and process the detection signal of the sensor probe.

[0104] The sensor probe 2 is arranged at the upper end of the first circuit board. The sensor probe is accommodated in the accommodation cavity and communicates with the outside of the housing.

[0105] The electrical pin 4 is arranged 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.

[0106] 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.

[0107] The drive circuit is arranged on the second circuit board. Thus, the drive circuit is completely sealed between the first circuit board and the third circuit board, which not only facilitates the perfusion of the sealant but also has a better sealing effect.

[0108] An air window 12 communicating with the accommodation cavity is provided at the upper end of the housing 1. The heat conduction argon gas sensor further includes a dust-proof filter net 13 that seals the air window, and a plurality of dust-proof filter holes communicating with the accommodation cavity are provided on the dust-proof filter net. By providing the dust-proof filter net, dust in the gas can be filtered out to prevent dust from entering the accommodation cavity and affecting the detection of the sensor probe.

[0109] 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 apart. An electric column 51 electrically connecting the first circuit board and the second circuit board is provided at the center of the spacer column. By providing the spacer column, the installation of the first circuit board and the second circuit board can be facilitated, and the electric column can cleverly and conveniently and quickly electrically connect the first circuit board and the second circuit board.

[0110] In this specific embodiment, a support platform 41 protruding outward is provided on the upper side of the upper part of the electric pin 4. The second circuit board 32 and the third circuit board 33 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. A groove 42 recessed inward is provided on the side surface of the support platform 41. The support platform can facilitate the installation of the second circuit board and the third circuit board. At the same time, the setting of the groove can make the connection more firm after the sealant is perfused and better seal the drive circuit.

[0111] Please refer to Figures 3 to 11 . The sensor probe includes a first thin film resistor Rm1 sensitive to gas, a second thin film resistor Rm2 sensitive to gas, a first thermistor Rt1 sensitive to temperature, and a second thermistor Rt2 sensitive to temperature. The first thin film resistor Rm1 and the second thin film resistor Rm2 are used to detect argon gas and convert it into different resistance values. The first thermistor Rt1 and the second thermistor Rt2 are used for temperature compensation.

[0112] The drive circuit includes a positive feedback amplifier circuit, a first negative feedback amplifier circuit, a second negative feedback amplifier circuit, a temperature compensation circuit, a standard voltage conversion circuit, a first power conversion circuit, a second power conversion circuit, and a third power conversion circuit.

[0113] Wherein:

[0114] The positive feedback amplifier circuit is connected to the sensor probe and amplifies the detection signal of the sensor probe and then outputs a first amplified signal; the first thermistor is connected to the positive feedback amplifier circuit. The first thermistor is connected to the positive feedback amplifier circuit, so that the first-stage temperature compensation can be performed on the detection, which is beneficial to improving the detection accuracy.

[0115] The model of the sensor probe is TCS208F. The positive feedback amplifier circuit serves as the first-stage amplification and amplifies the detection signal of the sensor probe for the first time.

[0116] The first negative feedback amplifier circuit is connected to the positive feedback amplifier circuit and further amplifies the first amplified signal of the positive feedback amplifier circuit and then outputs a second amplified signal; the second thermistor is connected to the first negative feedback amplifier circuit. The second thermistor is connected to the first negative feedback amplifier circuit, so that the second-stage temperature compensation can be performed on the detection. The first negative feedback amplifier circuit serves as the second-stage amplification and amplifies the first signal of the positive feedback amplifier circuit for the second time.

[0117] In the case where the conductivity of the measured gas is relatively low, the changes of the first thin-film resistor Rm1 and the second thin-film resistor Rm2 caused by the gas change are relatively small. However, the changes of the first thermistor Rt1 and the second thermistor Rt2 caused by the temperature are relatively large, which will cause the high and low temperature characteristics to differ greatly from the normal temperature characteristics. Therefore, in this specific embodiment, the second thermistor Rt2 is placed in the first negative feedback amplifier circuit for further temperature compensation, so as to further improve the detection accuracy.

[0118] The second negative feedback amplifier circuit is connected to the first negative feedback amplifier circuit and further amplifies the second amplified signal of the first negative feedback amplifier circuit and then outputs a third amplified signal. The second negative feedback amplifier circuit serves as the third-stage amplification and outputs the amplified signal to the signal processing circuit.

[0119] The temperature compensation circuit outputs a temperature compensation signal. The temperature compensation circuit is used to compensate for the change of the detection signal of the sensor probe caused by the temperature difference. The temperature compensation circuit performs the third-stage temperature compensation on the detection, so as to further improve the detection accuracy. The specific circuit diagram of the temperature compensation circuit is as Figure 9 shown. In this specific embodiment, the temperature compensation circuit is implemented by using the temperature sensing chip U4 and its peripheral circuits. In this specific embodiment, the model of the temperature sensing chip is TMP116.

[0120] The signal processing circuit is connected to the second negative feedback amplifier circuit and the temperature compensation circuit, and obtains a detection result based on the third amplified signal output by the second negative feedback amplifier circuit and the temperature compensation signal. The signal processing circuit is connected to an external main controller through a serial port. The main controller communicates with the signal processing circuit according to the serial port protocol, and displays information such as the composition, concentration, and range of the gas on the screen of the main controller. The present utility model has no special requirements for the externally connected main controller and can work properly without additional software injection. The serial port of the main controller supports signals with a common 5V level and can perform serial communication with the signal processing circuit according to the serial port protocol, making it suitable for more externally connected main controllers. It is simple to operate and has a wider application range.

[0121] The specific circuit diagram of the signal processing circuit is as Figure 8 shown. In this specific embodiment, the signal processing circuit is implemented by using a single-chip microcomputer U5 and its peripheral circuits. The model of the single-chip microcomputer U5 is STM32F070F6.

[0122] The single-chip microcomputer U5 communicates with the digital-to-analog conversion circuit through the I2C bus and outputs a corresponding analog signal through the digital-to-analog conversion circuit for users in need. In this specific embodiment, the digital-to-analog conversion circuit is implemented by using a digital-to-analog conversion chip U3 and its peripheral circuits. The model of the digital-to-analog conversion chip U3 is DAC5571 IDBVR.

[0123] In this specific embodiment, the positive feedback amplifier circuit includes a first amplifier U6-A, a first diode D1, a twenty-first capacitor C21, a second amplifier U6-B, a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9. Among them:

[0124] The non-inverting input terminal of the first amplifier U6-A is grounded, and the inverting input terminal is connected to one end of the first thermistor Rt1.

[0125] The negative electrode of the first diode D1 is connected to the output terminal of the first amplifier U6-A, and the positive electrode is connected to the other end of the first thermistor Rt1; one end of the first thin film resistor Rm1 is connected to the positive electrode of the first diode D1, and the other end is connected to one end of the second thin film resistor Rm2.

[0126] Both ends of the twenty-first capacitor C21 are respectively connected to the positive and negative electrodes of the first diode D1;

[0127] The non-inverting input terminal of the second amplifier U6-B is grounded, and the inverting input terminal is connected to the other end of the second thin film resistor Rm2. In this specific embodiment, the first amplifier and the second amplifier are implemented by a dual-channel amplifier ADA4077-2. U6-A and U6-B are respectively two amplification channels of the dual-channel amplifier, and U6-C is the power supply part of the dual-channel amplifier. The circuit of the power supply pin of the dual-channel amplifier ADA4077-2 is as Figure 5 shown. Its positive power supply pin V+ is connected to +8.5V voltage, and its negative power supply pin V- is connected to -5V voltage.

[0128] One end of the seventh resistor R7 is connected to the inverting input terminal of the first amplifier U6-A, and the other end is connected to the output terminal of the second amplifier U6-B.

[0129] One end of the eighth resistor R8 is connected to the output terminal of the second amplifier U6-B, and the other end is connected to the inverting input terminal of the second amplifier U6-B.

[0130] One end of the ninth resistor R9 is connected to the output terminal of the second amplifier, and the other end is grounded.

[0131] The output terminal of the second amplifier is connected to the first negative feedback amplifier circuit.

[0132] In this specific embodiment, the first negative feedback amplifier circuit includes a seventh operational amplifier U7, a tenth resistor R10, a twenty-second capacitor C22, an eleventh resistor R11, a twenty-third capacitor C23, a thirteenth resistor R13, a fifteenth resistor R15, a twelfth resistor R12, a twenty-fourth capacitor C24, a fourteenth resistor R14, a twenty-fifth capacitor C25, a twenty-sixth capacitor C26, a sixteenth resistor R16, a twenty-seventh capacitor C27, a twenty-eighth capacitor C28, a seventeenth resistor R17, and an eighteenth resistor R18.

[0133] Wherein:

[0134] The seventh operational amplifier U7 has a non-inverting input terminal IN+, an inverting input terminal IN-, an output terminal OUT, a positive voltage input terminal V+, and a negative voltage input terminal V-; the inverting input terminal IN- of the seventh operational amplifier U7 is grounded; one end of the second thermistor Rt2 is connected to the non-inverting input terminal IN+ of the seventh operational amplifier U7. In this specific embodiment, the model of the seventh operational amplifier is OPA735AIDBVR.

[0135] One end of the tenth resistor R10 is connected to the output terminal OUT of the second amplifier U7.

[0136] One end of the twenty-second capacitor C22 is grounded, and the other end is connected to the other end of the tenth resistor.

[0137] One end of the eleventh resistor R11 is connected to the other end of the tenth resistor, and the other end is connected to the negative input terminal IN- of the seventh operational amplifier U7.

[0138] One end of the twenty-third capacitor C23 is connected to the other end of the eleventh resistor, and the other end is grounded.

[0139] One end of the thirteenth resistor R13 is connected to the other end of the eleventh resistor, and the other end is grounded.

[0140] One end of the fifteenth resistor R15 is connected to the negative input terminal IN- of the seventh operational amplifier U7, and the other end is connected to the output terminal OUT of the seventh operational amplifier U7.

[0141] One end of the twelfth resistor R12 is connected to the other end of the second thermistor Rt2, and the other end is grounded.

[0142] One end of the twenty-fourth capacitor C24 is connected to one end of the second thermistor Rt2, and the other end is grounded. The second thermistor Rt2 is placed in the first negative feedback amplifier circuit for further temperature compensation, thereby further improving the detection accuracy.

[0143] One end of the fourteenth resistor R14 is connected to one end of the second thermistor Rt2, and the other end is connected to the positive voltage input terminal of the seventh operational amplifier.

[0144] One end of the twenty-fifth capacitor C25 is connected to the positive voltage input terminal V+ of the seventh operational amplifier U7, and the other end is grounded.

[0145] One end of the twenty-sixth capacitor C26 is connected to the positive voltage input terminal V+ of the seventh operational amplifier U7, and the other end is grounded.

[0146] One end of the sixteenth resistor R16 is connected to the output terminal OUT of the seventh operational amplifier U7.

[0147] One end of the twenty-seventh capacitor C27 is connected to the other end of the sixteenth resistor, and the other end is grounded.

[0148] One end of the twenty-eighth capacitor C28 is connected to the other end of the sixteenth resistor, and the other end is grounded.

[0149] One end of the seventeenth resistor R17 is connected to the other end of the sixteenth resistor, and the other end is grounded.

[0150] One end of the eighteenth resistor R18 is connected to the other end of the sixteenth resistor, and the other end is connected to the second negative feedback amplifier circuit.

[0151] In this specific embodiment, the second negative feedback amplifier circuit includes an instrumentation amplifier U9, a nineteenth resistor R19, a thirty-second capacitor C32, a thirty-third capacitor C33, a twenty-fourth resistor R24, a forty-third capacitor C43, a forty-second capacitor C42, a twenty-third resistor R23, a fourth inductor L4, a thirty-ninth capacitor C39, a fortieth capacitor C40, a forty-first capacitor C41, a twenty-fifth resistor R25, a twenty-sixth resistor R26, and a forty-fourth capacitor C44. Among them:

[0152] The instrumentation amplifier U9 has a positive input terminal VIN+, a negative input terminal VIN-, a positive voltage input terminal V+, a negative voltage input terminal V-, an output terminal VOUT, a first gain setting terminal RG, a second gain setting terminal RG_1, and a reference input terminal REF; the negative input terminal VIN- of the instrumentation amplifier U9 is connected to the other end of the eighteenth resistor; the reference input terminal REF and the negative voltage input terminal V- of the instrumentation amplifier are grounded. In this specific embodiment, the model of the instrumentation amplifier is INA333AIDRGR.

[0153] One end of the nineteenth resistor R19 is connected to the first gain setting terminal RG of the instrumentation amplifier U9, and the other end is connected to the second gain setting terminal RG_1 of the instrumentation amplifier U9.

[0154] One end of the thirty-second capacitor C32 is connected to the positive voltage input terminal V+ of the instrumentation amplifier U9, and the other end is grounded.

[0155] One end of the thirty-third capacitor C33 is connected to the positive voltage input terminal V+ of the instrumentation amplifier U9, and the other end is grounded.

[0156] One end of the twenty-fourth resistor R24 is connected to the positive input terminal VIN+ of the instrumentation amplifier U9, and the other end is grounded.

[0157] One end of the forty-third capacitor C43 is connected to the positive input terminal VIN+ of the instrumentation amplifier U9, and the other end is grounded.

[0158] One end of the forty-second capacitor C42 is connected to the positive input terminal VIN+ of the instrumentation amplifier U9, and the other end is grounded.

[0159] One end of the twenty-third resistor R23 is connected to the positive input terminal VIN+ of the instrumentation amplifier U9.

[0160] One end of the fourth inductor L4 is connected to the other end of the twenty-third resistor.

[0161] One end of the thirty-ninth capacitor C39 is connected to the other end of the fourth inductor, and the other end is grounded.

[0162] One end of the fortieth capacitor C40 is connected to the other end of the fourth inductor, and the other end is grounded.

[0163] One end of the forty-first capacitor C41 is connected to the other end of the twenty-third resistor, and the other end is grounded.

[0164] One end of the twenty-fifth resistor R25 is connected to the output terminal VOUT of the instrumentation amplifier U9; the other end is connected to the signal processing circuit.

[0165] One end of the twenty-sixth resistor R26 is connected to the other end of the twenty-fifth resistor, and the other end is grounded.

[0166] One end of the forty-fourth capacitor C44 is connected to the other end of the twenty-fifth resistor, and the other end is grounded.

[0167] In order to supply power to the signal processing circuit, the positive feedback amplification circuit, the first negative feedback amplification circuit, and the second negative feedback amplification circuit, the drive circuit further includes a standard voltage conversion circuit, a first power conversion circuit, a second power conversion circuit, and a third power conversion circuit. Among them:

[0168] The standard voltage conversion circuit converts the input power supply voltage into a standard 5V voltage output. The standard voltage conversion circuit is implemented by using a power management chip U1 and its peripheral circuits. In this specific embodiment, the model of the power management chip U1 is TPS610997YFFT. The power supply part adopts a low power supply voltage design, and the input power supply voltage is 0.7V to 5.5V. To ensure that the thermal conduction argon gas sensor adapts to a lower power supply voltage, the present invention uses the power management chip U1 to first adjust the input voltage between 0.7V and 5.5V to a standard 5V voltage, and then supply it to other circuits for use. That is to say: Any single battery, two batteries, three batteries or USB interface can supply power to the thermal conduction argon gas sensor of the present invention normally.

[0169] The first power conversion circuit is connected to the standard voltage conversion circuit, the second negative feedback amplification circuit, the temperature compensation circuit, and the signal processing circuit and supplies power to the second negative feedback amplification circuit, the temperature compensation circuit, and the signal processing circuit.

[0170] The first power conversion circuit is implemented by using a low dropout linear regulator U2 and its peripheral circuits. In this specific embodiment, the model of U2 is LP5907MFX-3.3. The 5V voltage is converted into a +3.3V voltage through the first power conversion circuit. Power is supplied to U3, U4, U5, and U9.

[0171] The second power conversion circuit is connected to the standard voltage conversion circuit, the positive feedback amplification circuit, and the first negative feedback amplification circuit, and supplies power to the positive feedback amplification circuit and the first negative feedback amplification circuit. The second power conversion circuit is implemented by using a low dropout linear regulator U8 and its peripheral circuits. In this specific embodiment, the model of U8 is LMR62014. The 5V voltage is converted into +8.5V voltage through the second power conversion circuit.

[0172] The third power conversion circuit is connected to the standard voltage conversion circuit and the positive feedback amplification circuit and supplies power to the positive feedback amplification circuit. The 5V voltage is converted into -5V voltage through the third power conversion circuit. +8.5V and -5V supply power to the positive feedback amplification circuit in the previous stage. Although this part of the voltage is a bit high, the current is very small. Therefore, the power consumption of the whole machine is not large.

[0173] The utility model utilizes a high-quality, small-sized, and fast-responsive silicon micromachined gas thermal conductivity sensor TCS208F probe to convert the concentration of the measured argon gas into different resistance values. The low-voltage and high-precision operational amplifier converts the changing resistance into a voltage signal, which is provided to the 32-bit MCU for analog-to-digital conversion. The MCU outputs digital signals through the serial port. After communicating with the main control machine, information such as the composition and concentration value of the measured gas is displayed on the screen of the main control machine.

[0174] In terms of structure, the present invention adopts an extremely small structural volume. The overall dimensions of the cylinder are: Φ31.5mm x 16.8mm. If the height of the output terminal copper column is added, the maximum dimension is Φ31.5mm x 21.4mm. The maximum volume with the copper column is only 16,677 cubic millimeters = 16.677 cubic centimeters, which is only a little larger than a finger.

[0175] The utility model has the following characteristics:

[0176] 1. The TCS208F probe is adopted. Although the TCS208F probe is not very sensitive to argon gas, it has low power consumption and high sampling accuracy. This solution adopts a multi-stage amplification method to make up for the problem of low sensitivity. Three-stage temperature compensation is adopted to compensate for the high and low temperature error problems.

[0177] 2. Due to the precise design of the operational amplifier and the adoption of a low power supply voltage, the power consumption is very small. The overall power consumption of the machine is: 5V * 32mA = 0.16 watt. Currently, all thermal conduction argon gas sensors cannot reach this index.

[0178] 3. The volume is extremely small, only a little larger than a finger, which can adapt to many narrow spaces for use and is convenient to carry.

[0179] 4. The size and definition of the output interface are suitable for a large number of host interfaces, with stronger versatility, and can adapt to more host controls and display test results, facilitating replacement.

[0180] 5. The input voltage is 0.7V to 5.5V. It can be suitable for using any conventional single battery, two batteries, three batteries or any standard mobile phone charger power supply.

[0181] In this utility model, by arranging a sensor probe inside the housing, a circuit board arranged inside the housing and connected to the sensor probe, and a drive circuit arranged on the circuit board, and setting the sensor probe as a silicon micro-machined gas thermal conductivity sensor probe, the volume of the thermal conductivity argon sensor can be very small, so as to adapt to the use in many narrow spaces and facilitate carrying. In addition, by adopting a positive feedback amplifier circuit, a first negative feedback amplifier circuit, a second negative feedback amplifier circuit, a temperature compensation circuit and a signal processing circuit, the signal collected by the sensor probe is amplified three times through the positive feedback amplifier circuit, the first negative feedback amplifier circuit and the second negative feedback amplifier circuit, effectively solving the problem that due to the relatively small conductivity of argon, which is not much different from the conductivity of air, the detection signal of the sensor probe is very weak, the signal sent to the signal processing circuit is weak, and the accuracy is low. In addition, further connecting the first thermistor of the sensor probe to the positive feedback amplifier circuit for the first-stage temperature compensation of the detection, connecting the second thermistor of the sensor probe to the first negative feedback circuit for the second-stage temperature compensation of the detection, and setting a temperature compensation circuit for the third-stage temperature compensation of the detection. Through the three-stage temperature compensation, the accuracy problem caused by temperature difference can be effectively solved, and the detection accuracy is further improved.

[0182] The above are only the preferred embodiments of the present utility model and are not intended to limit the present utility model. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A thermal conduction argon 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 conductivity sensor probe; the sensor probe comprises a first thin film resistor sensitive to gas, a second thin film resistor sensitive to gas, a first thermistor sensitive to temperature, and a second thermistor sensitive to temperature; The driving circuit comprises: a positive feedback amplifier circuit connected to the sensor probe and outputting a first amplified signal after amplifying the detection signal of the sensor probe; the first thermistor is connected to the positive feedback amplifier circuit; a first negative feedback amplifier circuit connected to the positive feedback amplifier circuit and further amplifying the first amplified signal of the positive feedback amplifier circuit to output a second amplified signal; and the second thermistor is connected to the first negative feedback amplifier circuit; a second negative feedback amplifier circuit, which is connected to the first negative feedback amplifier circuit and further amplifies the second amplified signal of the first negative feedback amplifier circuit to output a third amplified signal; A temperature compensation circuit outputs a temperature compensation signal; The signal processing circuit is connected to the second negative feedback amplifier circuit and the temperature compensation circuit, and obtains a detection result according to the third amplified signal output by the second negative feedback amplifier circuit and the temperature compensation signal.

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

3. The thermal conduction argon sensor according to claim 2, characterized in that: The positive feedback amplifier circuit comprises: A first amplifier, a non-inverting input terminal of which is grounded, and an inverting input terminal of which is connected to one end of the first thermistor; a first diode, whose cathode is connected to the output end of the first amplifier and whose anode is connected to the other end of the first thermistor; one end of the first thin-film resistor is connected to the anode of the first diode and the other end is connected to one end of the second thin-film resistor; A twenty-first capacitor, two ends of which are respectively connected to the positive electrode and the negative electrode of the first diode; A second amplifier, a non-inverting input terminal of which is grounded, and an inverting input terminal of which is connected to the other end of the second thin-film resistor; a seventh resistor, one end of which is connected to the inverting input terminal of the first amplifier, and the other end of which is connected to the output terminal of the second amplifier; an eighth resistor, one end of which is connected to the output end of the second amplifier, and the other end of which is connected to the inverting input end of the second amplifier; a ninth resistor, one end of which is connected to the output end of the second amplifier, and the other end of which is grounded; The output end of the second amplifier is connected to the first negative feedback amplifier circuit.

4. The thermal conduction argon sensor according to claim 3, characterized in that: The first negative feedback amplifier circuit comprises: a seventh operational amplifier, comprising a positive input terminal, a negative input terminal, an output terminal, a positive voltage input terminal, and a negative voltage input terminal; the negative input terminal of the seventh operational amplifier is grounded; one end of the second thermistor is connected to the positive input terminal of the seventh operational amplifier; a tenth resistor, one end of which is connected to the output end of the second amplifier; A twenty-second capacitor, one end of which is grounded, and the other end of which is connected to the other end of the tenth resistor; an eleventh resistor, one end of which is connected to the other end of the tenth resistor, and the other end of which is connected to the negative input terminal of the seventh operational amplifier; A twenty-third capacitor, one end of which is connected to the other end of the eleventh resistor, and the other end of which is grounded; a thirteenth resistor, one end of which is connected to the other end of the eleventh resistor, and the other end of which is grounded; a fifteenth resistor, one end of which is connected to the negative input terminal of the seventh operational amplifier, and the other end of which is connected to the output terminal of the seventh operational amplifier; a twelfth resistor, one end of which is connected to the other end of the second thermistor and the other end of which is grounded; A twenty-fourth capacitor, one end of which is connected to one end of the second thermistor and the other end of which is grounded; a fourteenth resistor, one end of which is connected to one end of the second thermistor, and the other end of which is connected to the positive voltage input terminal of the seventh operational amplifier; A twenty-fifth capacitor, one end of which is connected to the positive voltage input terminal of the seventh operational amplifier, and the other end of which is grounded; A twenty-sixth capacitor, one end of which is connected to the positive voltage input terminal of the seventh operational amplifier, and the other end of which is grounded; a sixteenth resistor, one end of which is connected to the output end of the seventh operational amplifier; A twenty-seventh capacitor, one end of which is connected to the other end of the sixteenth resistor, and the other end of which is grounded; A twenty-eighth capacitor, one end of which is connected to the other end of the sixteenth resistor, and the other end of which is grounded; a seventeenth resistor, one end of which is connected to the other end of the sixteenth resistor and the other end of which is grounded; An eighteenth resistor has one end connected to the other end of the sixteenth resistor, and the other end connected to the second negative feedback amplifier circuit.

5. The thermal conductivity argon sensor according to claim 4, characterized in that: The second negative feedback amplifier circuit comprises: An instrument amplifier, comprising a positive input terminal, a negative input terminal, a positive voltage input terminal, a negative voltage input terminal, an output terminal, a first gain setting terminal, a second gain setting terminal, and a reference input terminal; the negative input terminal of the instrument amplifier is connected to the other end of the eighteenth resistor; the reference input terminal and the negative voltage input terminal of the instrument amplifier are grounded; a nineteenth resistor, one end of which is connected to the first gain setting terminal of the instrument amplifier, and the other end of which is connected to the second gain setting terminal of the instrument amplifier; A thirty-second capacitor, one end of which is connected to the positive voltage input terminal of the instrumentation amplifier, and the other end of which is grounded; A thirty-third capacitor, one end of which is connected to the positive voltage input terminal of the instrumentation amplifier and the other end of which is grounded; A twenty-fourth resistor, one end of which is connected to the positive input terminal of the instrumentation amplifier, and the other end of which is grounded; a forty-third capacitor, one end of which is connected to the positive input terminal of the instrumentation amplifier and the other end of which is grounded; a 42nd capacitor, one end of which is connected to the positive input terminal of the instrumentation amplifier, and the other end of which is grounded; a twenty-third resistor, one end of which is connected to the positive input terminal of the instrumentation amplifier; a fourth inductor, one end of which is connected to the other end of the twenty-third resistor; A thirty-ninth capacitor, one end of which is connected to the other end of the fourth inductor, and the other end of which is grounded; a fortieth capacitor, one end of which is connected to the other end of the fourth inductor and the other end of which is grounded; a forty-first capacitor, one end of which is connected to the other end of the twenty-third resistor, and the other end of which is grounded; A twenty-fifth resistor, one end of which is connected to the output end of the instrumentation amplifier; and the other end of which is connected to the signal processing circuit; A twenty-sixth resistor, one end of which is connected to the other end of the twenty-fifth resistor and the other end of which is grounded; A forty-fourth capacitor has one end connected to the other end of the twenty-fifth resistor and the other end grounded.

6. The thermal conduction argon sensor according to claim 2, characterized in that: The driving circuit further includes: A standard voltage conversion circuit, which converts the input power supply voltage into a standard 5V voltage output; The first power conversion circuit is connected to the standard voltage conversion circuit, the second negative feedback amplifier circuit, the temperature compensation circuit, and the signal processing circuit and provides power for the second negative feedback amplifier circuit, the temperature compensation circuit, and the signal processing circuit; The second power conversion circuit is connected to the standard voltage conversion circuit, the positive feedback amplifier circuit, and the first negative feedback amplifier circuit and provides power for the positive feedback amplifier circuit and the first negative feedback amplifier circuit; The third power conversion circuit is connected to the standard voltage conversion circuit and the positive feedback amplifier circuit and provides power for the positive feedback amplifier circuit.

7. The thermal conduction argon sensor according to claim 3, characterized in that: The first amplifier and the second amplifier are implemented by using a dual-channel amplifier of model ADA4077-2.

8. The thermal conduction argon sensor according to claim 4, characterized in that: The model of the seventh operational amplifier is OPA735AIDBVR.

9. The thermal conductivity argon sensor according to claim 5, characterized in that: The model of the instrument amplifier is INA333AIDRGR.

10. The thermal conductivity argon sensor according to claim 1, characterized in that: The shell is provided with a hollow accommodating cavity, and the upper end of the shell is provided with an air window communicating with the 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 arranged at the upper end of the first circuit board, the sensor probe is accommodated in the accommodating cavity and communicated with the outside of the shell, and the driving circuit is arranged on the second circuit board; The thermal conductivity argon 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; A dustproof filter screen seals the air window, and the dustproof filter screen is provided with a plurality of dustproof filter holes communicated with the accommodating cavity.

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