A self-regulating thermal conductivity gas sensor and a gas detection device
By using a two-stage op-amp circuit in a thermally conductive gas sensor, the problem of poor detection accuracy and temperature drift is solved, and high-precision and low-cost gas detection is achieved.
Patent Information
- Application Number
- CN201711486390.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2017-12-30
- Publication Date
- 2024-12-31
- Estimated Expiration
- 2037-12-30
AI Technical Summary
Thermal conductive gas sensor has defects such as poor detection accuracy and large temperature drift in gas detection, resulting in complex structure and high cost.
The two-stage operational amplifier circuit is used to place the thermistor in it so that it maintains the same resistance value before and after detection. The temperature and resistance value are adjusted by the op amp circuit to avoid temperature drifting, and there is no need for a current and voltage acquisition device or control circuit. , simple structure and low cost.
It improves the accuracy and stability of gas detection, simplifies the structure, reduces costs, and realizes the automatic adjustment function of the thermistor value.
Smart Images
Figure CN109991265B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a thermal conductivity gas sensor and a gas detection device, in particular to a self-regulating thermal conductivity gas sensor and a gas detection device. Background Art
[0002] In recent years, with the development of semiconductor technology, thermal conductivity-based gas sensors have been increasingly used. Thermal conductivity gas sensors are devices that measure gas concentrations based on the difference in thermal conductivity of different gases. They can convert information related to gas types and concentrations into electrical signals, and have the following advantages: large detection range, good working stability, long service life, no catalyst aging problems, high stability and reliability, and can detect almost all gases. Moreover, gas concentrations can be detected in the presence or absence of oxygen in the measured environment. These excellent properties are not available in many other gas sensors. However, thermal conductivity gas sensors also have defects such as poor detection accuracy and large temperature drift in gas detection applications, which limits the widespread application of thermal conductivity gas sensors.
[0003] In the document "A New Method for Detecting Gas Concentration Using Thermal Conductivity Sensor" (Journal of Sensor Technology, 2006. Huang Weiyong et al.), a detection method for keeping the sensor working temperature unchanged during the detection process is proposed to solve the defect of low accuracy of thermal conductivity gas sensors due to temperature drift of the semiconductor structure sensor itself. This scheme uses three bridge arm resistors and thermal conductivity sensors to form a bridge, and uses a regulator, a servo circuit, a variable current source and the bridge to form a closed-loop control circuit. When the gas concentration is zero, the bridge arm resistor is adjusted to make the bridge in a balanced state; when the gas to be detected passes through the sensor, the sensor temperature changes, and then the sensor resistance changes, causing the bridge to lose balance. The output unbalanced voltage is amplified and sent to the control servo circuit, and then the current source is controlled to change the output current value to restore the sensor resistance to the initial state, thereby restoring the bridge to a balanced state. By detecting the bridge arm voltage, the concentration of the gas to be measured can be detected. In this way, the defect caused by the change of sensor temperature with the concentration of the gas to be measured in the traditional detection method is overcome. However, this solution requires real-time acquisition of unbalanced voltage and the use of a variable current source. It also requires a special control circuit to control the current output by the current source. This structure is relatively complex, and its final effect is heavily dependent on the accuracy of the acquisition device and the control device, and the cost is relatively high. Summary of the invention
[0004] The purpose of the present invention is to provide a self-regulating thermal conductivity gas sensor to solve the problem of complex structure of current thermal conductivity gas sensors, and also to provide a gas detection device using the sensor.
[0005] In order to solve the above technical problems, the present invention provides a first solution: a self-regulating thermal conductivity gas sensor of the present invention, the sensor comprises a thermistor, a first resistor, a second resistor, a third resistor, a first operational amplifier and a second operational amplifier, the non-inverting input terminals of the first operational amplifier and the second operational amplifier are grounded, the inverting input terminal of the first operational amplifier is connected to its output terminal through the third resistor, the inverting input terminal of the second operational amplifier is connected to its output terminal through the first resistor, the inverting input terminal of the first operational amplifier is connected to the output terminal of the second operational amplifier through the second resistor, and the output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier through the thermistor.
[0006] This solution places the thermistor of the sensor in a two-stage operational amplifier circuit. When the operational amplifier circuit is stable, the thermistor can maintain the set operating temperature and working resistance. When the measured gas is introduced, the measured gas will change the operating temperature of the thermistor, thereby changing the resistance of the temperature sensor module. However, the temperature sensor module can reach a fixed resistance value through the self-adjustment function of the operational amplifier circuit. When the entire circuit regains stability, the temperature and resistance of the thermistor return to the set value. At this time, the voltage value output by the operational amplifier circuit can reflect the thermal conductivity of the introduced gas, and then the concentration value of the introduced gas can be obtained. Since the thermistor maintains the same resistance before and after detection, its own temperature drift is avoided and the measurement accuracy is improved. This solution does not include a current and voltage acquisition device and does not require a control circuit. Therefore, it has a simple structure and low cost. At the same time, it also realizes the automatic adjustment function of the thermistor resistance.
[0007] Solution 2: Based on Solution 1, the thermistor is a platinum resistor or a thermocouple.
[0008] Solution 3: A self-regulating thermal conductivity gas detection device of the present invention comprises a housing and a detection gas path therein, and also comprises a self-regulating thermal conductivity gas sensor for detecting gas in the detection gas path, wherein an air inlet and an air outlet are provided on the housing, and the air inlet and the air outlet are connected through the detection gas path; the self-regulating thermal conductivity gas sensor comprises a thermistor, a first resistor, a second resistor, a third resistor, a first operational amplifier and a second operational amplifier, wherein the non-inverting input terminals of the first operational amplifier and the second operational amplifier are grounded, the inverting input terminal of the first operational amplifier is connected to the output terminal thereof through the third resistor, the inverting input terminal of the second operational amplifier is connected to the output terminal thereof through the first resistor, the inverting input terminal of the first operational amplifier is connected to the output terminal thereof through the second resistor, and the output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier through the thermistor.
[0009] This solution uses a measuring sensor that can self-regulate the working temperature and resistance of the thermistor to reduce the defects of the gas detection device in the prior art, which is complex in structure, high in cost and cannot achieve self-regulation. The thermistor of the sensor is placed in a two-stage operational amplifier circuit. When the operational amplifier circuit is stable, the thermistor can maintain the set working temperature and working resistance. When the measured gas is introduced, the measured gas will change the working temperature of the thermistor, thereby changing the resistance of the temperature sensor module. However, the temperature sensor module can reach a fixed resistance value through the self-regulation function of the operational amplifier circuit. When the entire circuit is restored to stability, the temperature and resistance of the thermistor are restored to the set value. At this time, according to the voltage value output by the operational amplifier circuit, the thermal conductivity of the introduced gas can be reflected, and then the concentration value of the introduced gas can be obtained. Since the thermistor maintains the same resistance before and after detection, its own temperature drift is avoided and the measurement accuracy is improved. This solution does not include a current and voltage acquisition device, and does not need to set a control circuit, so it has a simple structure and low cost, and also realizes the automatic adjustment function of the thermistor resistance.
[0010] Solution 4: Based on Solution 3, the thermistor is a platinum resistor or a thermocouple.
[0011] Option 5: Based on Option 3 or 4, the device also includes a constant temperature module and a temperature control module for adjusting the temperature of the constant temperature module. The constant temperature module is a heat conductive block with a groove structure or a through hole structure, and the detection gas path is placed in the groove structure or through hole structure of the constant temperature module.
[0012] This solution sets a constant temperature heat conduction block in the gas detection device, and places the detection gas path inside or on the surface of the heat conduction block to heat and keep the measured gas in the gas path warm, so that the measured gas maintains a constant temperature during the detection process. Since the thermal conductivity of the measured gas is different at different temperatures, this solution maintains the temperature of the measured gas at a constant value, avoiding the error caused by the temperature difference of the measured gas during detection, and improving the measurement accuracy of the gas detection device.
[0013] Solution 6: Based on Solution 5, the device also includes a signal processing module for receiving and processing the signal of the self-regulating thermal conductivity gas sensor, and the signal processing module is placed inside or around the constant temperature module.
[0014] This solution sets the signal processing module inside or around the constant temperature module to keep the signal processing module at a constant operating temperature, avoids temperature drift errors caused by different operating temperatures of the signal processing module, and ensures the measurement accuracy of the gas detection device.
[0015] Solution 7: Based on Solution 6, the temperature control module includes a temperature sensing unit, a temperature adjustment unit and a computing processing unit. The temperature sensing unit is placed inside or around the constant temperature module. The temperature sensing unit is connected to the computing processing unit for sampling, and the temperature adjustment unit is connected to the computing processing unit for control.
[0016] Solution 8: Based on Solution 5, the groove structure is a U-shaped groove, or the through hole structure is a U-shaped through hole.
[0017] This solution adopts a U-shaped groove or through hole, which can facilitate the setting of the air inlet and outlet of the air path and simplify the volume of the entire device.
[0018] Solution nine: Based on Solution seven, the temperature regulating unit is a semiconductor temperature control block, a heating plate, a heating film or a resistance wire. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 It is a schematic structural diagram of a first embodiment of a gas detection device of the present invention;
[0020] Among them, 1 is the housing, 2 is the semiconductor temperature control block, 3 is the temperature sensor, 4 is the air inlet, 5 is the air outlet, 6 is the constant temperature pool, 7 is the measurement sensor, 8 is the signal processing board, and 9 is the detection gas path;
[0021] Figure 2 The figure is a circuit diagram of the self-regulating thermal conductivity gas sensor of the present invention. DETAILED DESCRIPTION
[0022] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.
[0023] like Figure 1An embodiment of a self-regulating thermal conductivity gas detection device, the device includes a housing and a detection gas circuit therein, a signal processing module (such as a signal processing board), an air inlet pipeline and an air outlet pipeline, the air inlet pipeline and the air outlet pipeline are connected to form a detection gas circuit, and also includes a self-regulating thermal conductivity gas sensor for detecting the gas in the detection gas circuit, ensuring that the sensitive element (such as a thermistor) of the sensor can contact the gas to be detected (for example, the sensitive element is set in the detection gas circuit or a chamber for placing the sensitive element connected to the detection gas circuit is set), or The device ensures that the sensitive element contacts the wall of the detection gas path to indirectly obtain the temperature of the gas being measured; an air inlet and an air outlet are provided on the shell, and the air inlet and the air outlet are connected through the detection gas path; the self-regulating thermal conductivity gas sensor includes a thermistor Rm, and the air inlet pipeline is connected to the air outlet pipeline through the measuring sensor to form a detection gas path. The device also includes a constant temperature module for providing a constant temperature environment and a temperature control module for adjusting the temperature of the constant temperature module. The temperature control module is used to adjust the temperature of the constant temperature module to keep the temperature of the constant temperature module at a set constant temperature. The constant temperature module is a heat-conducting block with a groove structure or a through-hole structure. The detection gas path is placed in the groove structure or the through-hole structure of the constant temperature module, so as to keep the measured gas at a constant temperature during the detection process, so as to avoid measurement errors caused by different gas temperatures; the signal processing module is also placed inside the constant temperature module (of course, it can also be set on the surface or around the constant temperature module), so that the signal processing module also maintains a constant operating temperature, thereby avoiding temperature drift errors caused by different operating temperatures; the temperature control module includes a temperature sensing unit for detecting the temperature of the constant temperature module, a temperature adjustment unit (such as a semiconductor temperature control block) for adjusting the temperature of the constant temperature module, and a computing processing module (such as a processor) for receiving temperature feedback from the temperature sensor and issuing temperature control instructions to the temperature adjustment module.
[0024] The schematic diagram of the measuring sensor circuit is as follows Figure 2 As shown, including thermistor R m , a first operational amplifier A and a second operational amplifier B, wherein the non-inverting input terminals of the first operational amplifier A and the second operational amplifier B are grounded, the inverting input terminal of the first operational amplifier A is connected to the output terminal thereof through a third resistor R3, the inverting input terminal of the second operational amplifier B is connected to the output terminal thereof through a first resistor R1, the inverting input terminal of the first operational amplifier A is connected to the output terminal of the second operational amplifier B through a second resistor R2, and the output terminal of the first operational amplifier A is connected to the output terminal of the second operational amplifier B through a thermistor R m Connect the inverting input terminal of the second operational amplifier B.
[0025] The specific circuit of the measuring sensor uses the positive feedback system of the operational amplifier to stabilize the gain to 1 and the thermistor of the sensor measuring resistor to keep the temperature of the measuring resistor constant. Among them, R1, R2, and R3 are fixed value resistors, R mis the thermistor with positive temperature coefficient, and is also the measuring resistance of the sensor, I m For the flow through R m The current, U1 is the voltage of pin 1 of the op amp, U o It is the voltage of pin 7 of the op amp and can also be used as an output signal.
[0026] Then, according to the circuit analysis, the following equation can be obtained:
[0027]
[0028]
[0029] From (1) and (2), we can conclude that:
[0030] From formula (3), we can get that when the op amp is balanced, R m The resistance value of is also a fixed value (this fixed value is related to the resistance values of R1, R2, and R3 and can be set manually through adjustment). m The thermal characteristics of the resistance is constant when R m The temperature of the semiconductor structure is also a constant value. At this time, the temperature drift of the sensor itself is successfully avoided.
[0031] While avoiding the error source, the output signal U o It is in a certain proportional relationship with the thermal conductivity of the gas being measured.
[0032] In the first case, when the thermal conductivity λ of the gas increases, the thermistor R m Temperature T m Reduce the resistance of thermistor R m The operational amplifier circuit self-regulates the current I in equation (1) m Increase, the thermistor T m Increase, the resistance value of the thermistor R m The resistance is increased to the set value again, so that the circuit is balanced again. o The thermal conductivity of the measured gas can be obtained, and then the concentration of the gas can be obtained.
[0033] In the second case, when the thermal conductivity λ of the gas decreases, the temperature T of the thermistor m Increase, the resistance value of the thermistor R m Increase, the operational amplifier circuit self-adjusts so that the current I in equation (1) m Reduce the thermistor T m Reduce the resistance of thermistor R m Reduce the resistance back to the set value to restore the circuit to balance.
[0034] From the above two cases, we can see that thermal conductivity λ and Im In a certain proportional relationship. o =-I m R1, so U o It is also proportional to the thermal conductivity λ. Therefore, by measuring the output U of the circuit when it is rebalanced o The thermal conductivity of the measured gas can be obtained, and then the concentration of the gas can be obtained.
[0035] In the above embodiments, a thermistor is used as a sensitive element of the measuring sensor, and the thermistor includes a thermocouple or a platinum resistor.
[0036] In the above embodiment, the air inlet pipeline, the measuring sensor and the air outlet pipeline form a detection air circuit, and a U-shaped groove or through hole for accommodating the detection air circuit is set on the constant temperature heat conductive block. Of course, in the specific implementation, the shape of the groove and the through hole can be set to a straight line, L-shape or other shapes that are convenient for implementation.
[0037] In the above embodiment, a semiconductor temperature control block is used as the temperature adjustment unit of the constant temperature module, and a heating plate, a heating film or a resistance wire may also be used as other implementations.
[0038] The above is a specific implementation mode, but the present invention is not limited to the described implementation mode. The basic idea of the present invention lies in the above basic scheme. Changes, modifications, substitutions and variations of the implementation mode without departing from the principle and spirit of the present invention still fall within the protection scope of the present invention.
Claims
1. A self-regulating thermal conductivity gas sensor, characterized in that: The sensor includes a thermistor, a first resistor, a second resistor, a third resistor, a first operational amplifier and a second operational amplifier, wherein the non-inverting input terminals of the first operational amplifier and the second operational amplifier are grounded, the inverting input terminal of the first operational amplifier is connected to the output terminal thereof through the third resistor, the inverting input terminal of the second operational amplifier is connected to the output terminal thereof through the first resistor, the inverting input terminal of the first operational amplifier is connected to the output terminal of the second operational amplifier through the second resistor, and the output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier through the thermistor.
2. The self-regulating thermal conductivity gas sensor according to claim 1, characterized in that: The thermistor is a platinum resistor or a thermocouple.
3. A self-regulating thermal conductivity gas detection device, comprising a housing and a detection gas path therein, and also comprising a self-regulating thermal conductivity gas sensor for detecting gas in the detection gas path, wherein the housing is provided with an air inlet and an air outlet, and the air inlet and the air outlet are connected through the detection gas path; characterized in that: The self-regulating thermal conductivity gas sensor includes a thermistor, a first resistor, a second resistor, a third resistor, a first operational amplifier and a second operational amplifier, wherein the non-inverting input terminals of the first operational amplifier and the second operational amplifier are grounded, the inverting input terminal of the first operational amplifier is connected to the output terminal thereof through the third resistor, the inverting input terminal of the second operational amplifier is connected to the output terminal thereof through the first resistor, the inverting input terminal of the first operational amplifier is connected to the output terminal of the second operational amplifier through the second resistor, and the output terminal of the first operational amplifier is connected to the inverting input terminal of the second operational amplifier through the thermistor.
4. The self-regulating thermal conductivity gas detection device according to claim 3, characterized in that: The thermistor is a platinum resistor or a thermocouple.
5. The self-regulating thermal conductivity gas detection device according to claim 3 or 4, characterized in that: The device also includes a constant temperature module and a temperature control module for adjusting the temperature of the constant temperature module. The constant temperature module is a heat-conducting block with a groove structure or a through-hole structure, and the detection gas path is placed in the groove structure or the through-hole structure of the constant temperature module.
6. The self-adjusting thermal conductivity gas detection device according to claim 5, characterized in that: The device also includes a signal processing module for receiving and processing the signal of the self-regulating thermal conductivity gas sensor, and the signal processing module is arranged inside or around the constant temperature module.
7. The self-regulating thermal conductivity gas detection device according to claim 6, characterized in that: The temperature control module includes a temperature sensing unit, a temperature regulating unit and a computing unit. The temperature sensing unit is placed inside or around the constant temperature module. The temperature sensing unit is connected to the computing unit for sampling, and the temperature regulating unit is connected to the computing unit for control.
8. The self-adjusting thermal conductivity gas detection device according to claim 5, characterized in that: The groove structure is a U-shaped groove, or the through hole structure is a U-shaped through hole.
9. The self-adjusting thermal conductivity gas detection device according to claim 7, characterized in that: The temperature regulating unit is a semiconductor temperature control block, a heating plate, a heating film or a resistance wire.