Thermal conductivity cell temperature control device

Abstract

The utility model discloses a thermal conductivity cell temperature control device, which comprises a circuit structure, a heating block and a sleeve, the circuit structure is composed of a temperature measuring module, a main control module, a heating module and a power supply module, the temperature measuring module monitors the temperature change of the heating block, and the main control module outputs a control signal to the heating module after receiving a voltage signal of the temperature measuring module. The heating module heats the heating block, and the heating circuit receives a control signal of the main control module and adjusts a voltage signal applied to the heating element; the heating block is arranged at the upper end of the thermal conductivity cell body, the temperature measuring element and the heating element are respectively arranged in blind holes of the heating block, a cell groove is formed in the top of the thermal conductivity cell body, the sleeve is arranged in a through hole of the heating block, and the tail end area of the sleeve extends into the cell groove to form a detection air chamber for placing a thermosensitive element of the thermal conductivity cell; the utility model provides a temperature control device for a thermal conductivity cell, which realizes real-time high-precision temperature control of a thermal conductivity cell thermosensitive element detection environment and keeps the temperature of the detection environment stable.

Description

Technical Field

[0001] The utility model relates to the field of gas analysis based on the thermal conductivity principle, in particular to a thermal conductivity cell temperature control device. Background Art

[0002] Thermal conductivity gas analyzer is a machine that analyzes gas composition by measuring the change in thermal conductivity of mixed gas according to the different thermal conductivity properties of various substances. The basic principle of thermal conductivity gas analyzer is that since the thermal conductivity of gas is very small, its change is even smaller and it is difficult to measure it by direct method, but the thermal conductivity cell can use indirect method to convert the change in thermal conductivity of mixed gas into the change in resistance value of thermistor, and the change in resistance value is relatively easy to measure accurately. Therefore, thermal conductivity cell is one of the key components in thermal conductivity gas analyzer. It is usually a small heat transfer element used to dissipate heat and conduct heat. When the test gas molecules come into contact with the thermal conductivity cell, the gas molecules will cause the temperature of the thermal conductivity cell to change. This temperature change is the basis for thermal conductivity gas analyzer to detect gas concentration. The temperature control device is a device used to keep the thermal conductivity cell within a specific temperature range. It ensures that the working temperature of the thermal conductivity cell is constant. The precise temperature of the thermal conductivity cell is crucial for measuring gas concentration. The thermal conductivity cell includes a cell body and a thermistor (also called a thermal conductivity element). The thermistor is the core part of the thermal conductivity cell, usually a small sensor that can sense the change in thermal conductivity of the gas.

[0003] From the principle, it can be seen that the temperature fluctuation of the detection environment of the thermistor of the thermal conductivity cell will directly affect the heat exchange results between the test gas and the wall of the thermal conductivity cell, thereby obtaining inaccurate measurement results. Therefore, this test method has extremely high requirements on the temperature stability of the detection environment of the thermistor. The temperature of the detection environment of the thermistor is directly related to the measurement results of thermal conductivity gas analysis, so it needs to be precisely controlled. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a thermal conductivity cell temperature control device to achieve real-time high-precision temperature control of the detection environment of the thermal conductivity cell thermistor element and keep the temperature of the detection environment stable.

[0005] In order to solve the above problems, the technical solution adopted by the utility model is: a thermal conductivity cell temperature control device, including a circuit structure, a heating block and a sleeve with a hollow structure, the circuit structure is composed of a temperature measuring module, a main control module, a heating module and a power supply module; the main control module is electrically connected to the temperature measuring module and the heating module respectively, and the power supply module is electrically connected to the temperature measuring module, the main control module and the heating module respectively; the temperature measuring module includes a temperature measuring element and a constant current circuit, the output end of the constant current circuit is connected to the input end of the temperature measuring element, the constant current circuit provides a stable current for the temperature measuring element, the temperature measuring module is used to monitor the temperature change of the heating block, the main control module receives the voltage signal of the temperature measuring module and then outputs a control signal to the heating module, the heating module includes a heating element and a heating circuit, the output end of the heating circuit is electrically connected to the heating rod, the heating circuit receives the control signal of the main control module, and adjusts the voltage signal applied to the heating rod to adjust the heating power of the heating rod; the power supply module is used to supply power to various components of the circuit;

[0006] The heating block is arranged at the upper end of the thermal conductivity cell body. The heating block has a through hole and a blind hole. The temperature measuring element and the heating element are respectively arranged in the blind hole of the heating block. The sleeve is arranged in the through hole of the heating block. The heating block is tightly fitted with the temperature measuring element, the heating element and the sleeve. A pool groove is opened on the top of the thermal conductivity cell body. The shape of the pool groove matches the sleeve. A partition is arranged in the sleeve to separate the bottom area of ​​the sleeve into an upper unit and a lower unit. The thermistor is arranged in the lower unit. The lead of the thermistor passes through the partition and is led out from the top of the sleeve. The lead of the thermistor is sealed and connected to the partition. The lower unit of the sleeve extends into the pool groove to form a detection air chamber, and heat transfer is formed between the heating block and the detection air chamber.

[0007] Furthermore, the lead wire of the thermosensitive element passes through the partition and is led out from the top of the sleeve, and the connection between the lead wire of the thermosensitive element and the partition is a sealed connection.

[0008] Furthermore, the temperature measuring element adopts the thermocouple PT1000, the main control module adopts the STC12C5A60S2 single-chip microcomputer, and the temperature measuring module also includes an electrically connected AD acquisition module and a voltage conversion module. The input end of the AD acquisition module is connected to the output end of the temperature measuring element, and the output end of the voltage conversion module is connected to the input end of the main control module. The analog voltage signal output by the temperature measuring element is converted into a digital voltage signal through the AD acquisition module, and then converted into a digital voltage signal suitable for the operation of the main control module through the voltage conversion module and transmitted to the main control module.

[0009] Furthermore, the constant current circuit in the temperature measurement module includes an operational amplifier U4A, an operational amplifier U4B, an operational amplifier U5B, a fifth resistor, a sixth resistor, a seventh resistor, a ninth resistor and a tenth resistor, and the operational amplifiers are all LM258 models;

[0010] The non-inverting input terminal of the operational amplifier U5B is connected to the reference voltage, the output terminal of the operational amplifier U5B is connected to the first terminal of the sixth resistor, the inverting input terminal of the operational amplifier U5B is connected to its output terminal, the node between the second terminal of the sixth resistor and the first terminal of the fifth resistor is connected to the non-inverting input terminal of the operational amplifier U4A, the node between the first terminal of the seventh resistor and the first terminal of the tenth resistor is connected to the output terminal of the operational amplifier U4A, the node between the first terminal of the ninth resistor and the second terminal of the tenth resistor is connected to the inverting input terminal of the operational amplifier U4A, the second terminal of the ninth resistor is grounded, the node between the first terminal of the tenth resistor and the first terminal of the seventh resistor is connected to the output terminal of the operational amplifier U4A, the positive power supply input terminal of the operational amplifier U4A is connected to the power supply module, the negative power supply input terminal of the operational amplifier U4A is grounded, the output terminal of the operational amplifier U4B is connected to the second terminal of the fifth resistor, the inverting input terminal of the operational amplifier U4B is connected to its output terminal, and the node between the second terminal of the seventh resistor and the thermocouple PT1000 is connected to the non-inverting input terminal of the operational amplifier U4B.

[0011] Furthermore, the heating element is a heating rod, and the heating circuit includes a first MOS tube, a tenth capacitor and an eighth resistor;

[0012] The tenth capacitor and the eighth resistor are connected in parallel, the gate of the first MOS tube is connected to the second end of the eighth resistor, the source of the first MOS tube is grounded, and the drain of the first MOS tube is connected to the heating rod as the output end of the heating circuit.

[0013] Further, the power module includes a power circuit and a voltage reference chip MAX6070AAUT30+T, and the voltage reference chip is used to provide a 3V voltage reference;

[0014] The power supply circuit includes a first diode, a first voltage regulator diode, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, linear regulators LM7812, LM7805 and AMS1117-3.3, and the power supply circuit is used to provide +24V, +12V, +5V, +3.3V power supply voltages;

[0015] The anode of the first diode is connected to the external power supply +24V, the anode of the first voltage regulator diode is grounded, the second capacitor, the eighth capacitor and the first voltage regulator diode are connected in parallel and then connected in series with the first diode, the cathode of the first diode is connected to pin 1 of LM7812, the fifth capacitor and the sixth capacitor are connected in parallel between pin 3 of LM7812 and ground, the fifth capacitor and the sixth capacitor are also connected in parallel between pin 3 of LM7805 and ground, pin 3 of LM7812 is connected to pin 1 of LM7805, pin 2 of LM7812 is grounded, the third capacitor and the fourth capacitor are connected in parallel between pin 3 of LM7805 and ground, the third capacitor and the fourth capacitor are also connected in parallel between pin 3 of AMS1117-3.3 and ground, Pin 3 of LM7805 is connected to pin 3 of AMS1117-3.3, pin 2 of LM7805 is grounded, the first capacitor and the seventh capacitor are connected in parallel between pin 2 of AMS1117-3.3 and ground, pin 1 of AMS1117-3.3 is grounded, and pin 2 of AMS1117-3.3 outputs power supply +3.3V.

[0016] Furthermore, a sealing ring is provided between the sleeve and the pool slot to increase the sealing performance of the detection air chamber.

[0017] According to the above solution, the temperature control device also includes a heat preservation ring, which is sleeved on the periphery of the heating block.

[0018] Furthermore, the number of sleeves is set to two, and the structures of the two sleeves are exactly the same. An air inlet is opened at the bottom of the pool groove into which one sleeve extends, and the lower unit at the bottom of the sleeve serves as a detection air chamber of the thermistor of the thermal conductivity cell, and the lower unit at the bottom of the other sleeve serves as a reference air chamber.

[0019] Preferably, the heat conduction cell body, the heating block and the sleeve are all made of stainless steel, and the insulation ring is made of CPVC.

[0020] Compared with the prior art, the beneficial effects of the utility model are:

[0021] 1. The utility model detects the temperature of the heating block in real time through the temperature measuring module. The main control module outputs a control signal in real time according to the measured temperature, controls the heating module to adjust the voltage signal applied to the heating element to adjust the power of the heating element, and can quickly reach the target temperature, realize real-time high-precision temperature control of the detection environment of the thermal conductivity cell thermistor element, and keep the temperature of the detection environment stable.

[0022] 2. A constant current circuit is added to the temperature measurement module of the utility model to provide a stable working environment for the temperature measurement element, so that its output signal is linearly related to the ambient temperature, thereby improving the measurement accuracy of the temperature measurement element.

[0023] 3. The structure of the heating block of the utility model is closely fitted with the temperature measuring element, the heating element and the sleeve, which improves the heat conduction efficiency and makes the temperature more evenly distributed on the contact surface, so that the temperature control effect finally achieved is more accurate.

[0024] 4. The utility model adds a sleeve for placing the thermal element of the thermal conductivity cell, which can reduce the environmental impact on the thermal element and improve its accuracy and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a circuit structure diagram of the utility model;

[0026] Figure 2 It is an exploded view of the utility model;

[0027] Figure 3 It is a structural diagram of the utility model;

[0028] Figure 4 It is a top view of the utility model;

[0029] Figure 5 The cross section of the utility model Figure 1 ;

[0030] Figure 6 The cross section of the utility model Figure 2 ;

[0031] In the figure, 1, thermal conductivity cell body, 2, insulation ring, 3, heating block, 4, sleeve, 5, heating element, 6, temperature measuring element, 7, cell tank, 8, detection air chamber, 9, sealing ring, 10, partition, 11, lead wire, 12, air path;

[0032] Figure 7 This is the principle diagram of the main control module of the utility model;

[0033] Figure 8 This is a schematic diagram of a constant current circuit in a temperature measurement module of the utility model;

[0034] Fig. 9 This is a circuit diagram of a 24-bit AD acquisition module in the temperature measurement module of the utility model;

[0035] Fig.10 This is a circuit diagram of a voltage conversion module in a temperature measurement module of the utility model;

[0036] Fig.11 This is a schematic diagram of a heating circuit in a heating module of the utility model;

[0037] FIG12 is a schematic diagram of a power module circuit of the utility model, FIG12(a) is a power circuit diagram, FIG12(b) is an LED indicator circuit diagram, and FIG12(c) is a voltage reference circuit diagram;

[0038] FIG13 is a schematic diagram of a circuit interface circuit of Embodiment 2 of the present utility model, FIG13(a) is a schematic diagram of a power interface circuit, FIG13(b) is a schematic diagram of a heating rod interface circuit, and FIG13(c) is a schematic diagram of a PT1000 interface circuit;

[0039] Fig.14 This is a temperature control effect curve diagram of the utility model. DETAILED DESCRIPTION

[0040] To make the content of the utility model clearer, the specific implementation of the utility model is further described in detail below in conjunction with the accompanying drawings. It should be noted that for the purpose of clarity, the representation and description of components that are not related to the utility model and are known to ordinary technicians in the field are omitted in the drawings and descriptions.

[0041] refer to Figure 1 The circuit structure of the utility model is composed of a temperature measuring module, a main control module, a heating module and a power module; the main control module is electrically connected to the temperature measuring module and the heating module respectively, and the power module is electrically connected to the temperature measuring module, the main control module and the heating module respectively; the temperature measuring module is composed of a constant current circuit, a temperature measuring element 6, an AD acquisition module and a voltage conversion module connected in sequence, the constant current circuit is used to provide a stable current for the temperature measuring element 6, provide a stable working environment for the temperature measuring element, so that its output signal is linearly related to the ambient temperature, and improve the measurement accuracy of the temperature measuring element. The analog voltage signal output by the temperature measuring element 6 is converted into a digital voltage signal by the AD acquisition module, and then converted into a digital voltage signal adapted to the operation of the main control module by the voltage conversion module and then transmitted to the main control module for monitoring the temperature change of the heating block 3; the main control module receives the voltage signal of the temperature measuring module and outputs a control signal to the heating module, the heating module includes a heating element 5 and a heating circuit, the output end of the heating circuit is electrically connected to the heating rod, the heating circuit receives the control signal of the main control module, and adjusts the voltage signal applied to the heating element 5 to adjust the heating power of the heating element; the power module is used to power each device of the circuit.

[0042] Combination Figure 2-6The utility model also includes a heating block 3 and a sleeve 4 with a hollow structure. In order to reduce the influence of bridge current fluctuations or changes in external conditions and further improve the measurement accuracy, the number of sleeves 4 is set to 2. The structures of the two sleeves 4 are exactly the same. Thermistors of thermal conductivity cells are placed in the two sleeves 4. An air inlet is provided at the bottom of a pool groove 8 into which one sleeve 4 extends, and the lower unit at the bottom of the sleeve 4 serves as a detection air chamber 8 of the thermistor of the thermal conductivity cell. The bottom of the pool groove 8 into which the other sleeve 4 extends has no air inlet, and the lower unit at the bottom of the sleeve 4 is not ventilated and serves as a reference air chamber. The heating block 3 is arranged at the upper end of the thermal conductivity cell body 1. The heating block 3 has two through holes and two blind holes. The temperature measuring element 6 and the heating element 5 are respectively arranged in the blind holes of the heating block 3. The two sleeves 4 are arranged in the through holes of the heating block 3. The heating block 3 is tightly fitted with the temperature measuring element 6, the heating element 5 and the sleeve 4. The top of the thermal conductivity cell body 1 is provided with a pool groove 7. The shape of the pool groove 7 matches the sleeve 4. The two sleeves 4 are provided with a partition 10, so that the bottom area of ​​the sleeve 4 is divided into an upper unit and a lower unit. The lower unit at the bottom of the sleeve 4 The entire area of ​​the unit extends into the pool tank 7 to form a detection air chamber 8, and the thermistor is arranged in the detection air chamber 8. The lead 11 of the thermistor is sealed and connected to the partition 10. The lead 11 of the thermistor passes through the partition 10 and is led out from the top 4 of the sleeve. A sealing ring 9 is provided between the sleeve 4 and the pool tank 7 to increase the sealing of the detection air chamber, and heat transfer is formed between the heating block 3, the sleeve 4 and the detection air chamber 8; an air inlet is opened at the bottom of the detection air chamber 8, that is, the bottom of the pool tank 7, and the air inlet is connected to the air path for connecting external gas.

[0043] The heating block 3 is arranged at the upper end of the thermal conductivity cell body 1. The heating block 3 has two through holes and two blind holes. The temperature measuring element 6 and the heating element 5 are respectively arranged in the blind holes of the heating block 3. Two sleeves with a hollow structure are arranged in the through holes of the heating block 3. The heating block 3 is tightly fitted with the temperature measuring element 6, the heating element 5 and the sleeve 4. The top of the thermal conductivity cell body 1 is provided with a pool groove 7. The shape of the pool groove 7 matches the sleeve 4. The two sleeves 4 are provided with a partition 10 to separate the bottom area of ​​the sleeve 4 into an upper unit and a lower unit. The bottom of the sleeve 4 The entire area of ​​the lower unit of the part extends into the pool tank 7 to form a detection air chamber 8, and the thermistor is arranged in the detection air chamber 8. The lead 11 of the thermistor is sealed and connected with the partition 10. The lead 11 of the thermistor passes through the partition 10 and is led out from the top 4 of the sleeve. A sealing ring 9 is provided between the sleeve 4 and the pool tank 7 to increase the sealing of the detection air chamber, and heat transfer is formed between the heating block 3, the sleeve 4 and the detection air chamber 8; an air inlet is provided at the bottom of the detection air chamber 8, that is, the bottom of the pool tank 7, and the air inlet is connected to the air path for connecting external gas.

[0044] The present embodiment adds a sleeve 4 for placing the thermistor of the thermal conductivity cell, which can reduce the environmental impact on the thermistor to improve its accuracy and stability. The thermocouple PT1000 is used as the temperature measuring element 6, and a four-wire model is specifically selected to reduce the impact of the change in wire resistance on the measurement result; the heating element 5 selects a heating rod with stable power and small size, specifically a rod-shaped heating rod, and a structural component with a suitable size is designed for it. The structure of the heating block 3 is tightly fitted with the thermocouple PT1000, the heating rod and the sleeve 4, which improves the heating conduction efficiency, and the temperature is more evenly distributed on the contact surface, so that the temperature control effect finally achieved is more accurate, ensuring that the temperature measurement result is accurate and the heating output is stable.

[0045] Preferably, it also includes a heat preservation ring 2, which is sleeved on the periphery of the heating block 3. The heat preservation ring reduces heat loss, improves heating efficiency, and improves energy utilization.

[0046] Preferably, the heat conduction cell body 1, the heating block 3 and the sleeve 4 are all made of stainless steel, and the insulation ring 2 is made of CPVC material, which has extremely low thermal conductivity and good thermal insulation performance, plays a good role in heat preservation, and reduces the interference of external environmental factors.

[0047] refer to Figure 7 The main control module uses the STC12C5A60S2 microcontroller produced by STC, which is based on the ACS-51 series, has low cost and low power consumption, has a sufficient number of IO pins and communication interfaces, and has an operating voltage of 5V. The PAC module of the STC12C5A60S2 microcontroller is set by the program of the microcontroller to work in 8-bit PWM mode. The main control module is connected to the temperature measurement module and the heating module to calculate the collected temperature values. The PAC module of the STC12C5A60S2 microcontroller adjusts the duty cycle of the PWM signal output to the heating circuit to adjust the power of the heating module and realize temperature control.

[0048] refer to Figure 8 The constant current circuit in the temperature measurement module includes an operational amplifier U4A, an operational amplifier U4B, an operational amplifier U5B, a fifth resistor, a sixth resistor, a seventh resistor, a ninth resistor and a tenth resistor, and the operational amplifiers are all LM258 models;

[0049] The non-inverting input terminal of the operational amplifier U5B is connected to the reference voltage, the output terminal of the operational amplifier U5B is connected to the first terminal of the sixth resistor, the inverting input terminal of the operational amplifier U5B is connected to its output terminal, the node between the second terminal of the sixth resistor and the first terminal of the fifth resistor is connected to the non-inverting input terminal of the operational amplifier U4A, the node between the first terminal of the seventh resistor and the first terminal of the tenth resistor is connected to the output terminal of the operational amplifier U4A, the node between the first terminal of the ninth resistor and the second terminal of the tenth resistor is connected to the inverting input terminal of the operational amplifier U4A, the second terminal of the ninth resistor is grounded, the node between the first terminal of the tenth resistor and the first terminal of the seventh resistor is connected to the output terminal of the operational amplifier U4A, the positive power supply input terminal of the operational amplifier U4A is connected to the power supply module, the negative power supply input terminal of the operational amplifier U4A is grounded, the output terminal of the operational amplifier U4B is connected to the second terminal of the fifth resistor, the inverting input terminal of the operational amplifier U4B is connected to its output terminal, and the node between the second terminal of the seventh resistor and the thermocouple PT1000 is connected to the non-inverting input terminal of the operational amplifier U4B.

[0050] Among them, the first operational amplifier is used as a voltage follower, which plays the role of buffering, isolation, and improving load capacity. The second operational amplifier is used as a common-phase proportional operational amplifier. After analysis, it can be obtained that the voltage value of its output terminal and the voltage difference of the common-phase input terminal of the third operational amplifier are exactly the voltage value of the common-phase input terminal of the first operational amplifier, that is, the given reference voltage value +3V, so the current output by this circuit is 3V / 1500Ω=2mA. The constant current circuit provides a stable constant current of 2mA for PT1000. PT1000 is a thermistor. With the change of temperature, the resistance changes basically linearly. After the 2mA constant current source, a voltage signal linearly related to the temperature is formed, thereby obtaining the real-time temperature. In addition, PT1000 uses a four-wire system to avoid the influence of the change of the resistance of the connecting wire on the measurement result, and improve the accuracy of the measurement result.

[0051] refer to Figure 9-10 The 24-bit AD acquisition module uses the MAX11201 chip, and the power supply is provided by the linear regulator AMS1117-3.3 of the power module. The reference is provided by the voltage reference chip MAX6070AAUT30+T of the power module. The AD acquisition part has 24-bit acquisition accuracy, converts the analog signal output by PT1000 into a digital signal, and communicates with the microcontroller through I2C; the voltage conversion module uses the TXS0108E chip produced by TI, which converts the 3.3V signal output by the AD acquisition part into a 5V signal with the same working voltage as the microcontroller, helping the microcontroller to communicate with the AD acquisition part.

[0052] refer to Fig.11The heating circuit of the heating module includes a first MOS tube, a tenth capacitor and an eighth resistor; the tenth capacitor and the eighth resistor are connected in parallel, the gate of the first MOS tube is connected to the second end of the eighth resistor, the drain of the first MOS tube is connected to the power module +24V through the HT2 heating rod, and the source of the first MOS tube is grounded. The heating circuit receives a PWM signal output from the single-chip microcomputer. When the level is high, the MOS tube is turned on, the drain of the first MOS tube is connected to the power module +24V through the HT2 heating rod, forming a loop, and the heating rod works; when the level is low, the MOS tube is turned off, and the heating rod does not work, thereby controlling the heating power of the heating rod.

[0053] Referring to FIG. 12 (a), the power module includes a power circuit and a voltage reference chip MAX6070AAUT30+T, the voltage reference chip is used to provide a 3V voltage reference; the power circuit includes a first diode, a first voltage regulator diode, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, a linear regulator LM7812, LM7805 and AMS1117-3.3, and the power circuit is used to provide +24V, +12V, +5V, +3.3V power supply voltages; the anode of the first diode is connected to an external power supply +24V, the anode of the first voltage regulator diode is grounded, the second capacitor, the eighth capacitor and the first voltage regulator diode are connected in parallel and then connected in series with the first diode, the cathode of the first diode is connected to pin 1 of the LM7812, The fifth capacitor and the sixth capacitor are connected in parallel between pin 3 of LM7812 and ground, the fifth capacitor and the sixth capacitor are also connected in parallel between pin 3 of LM7805 and ground, pin 3 of LM7812 is connected to pin 1 of LM7805, pin 2 of LM7812 is grounded, the third capacitor and the fourth capacitor are connected in parallel between pin 3 of LM7805 and ground, the third capacitor and the fourth capacitor are also connected in parallel between pin 3 of AMS1117-3.3 and ground, pin 3 of LM7805 is connected to pin 3 of AMS1117-3.3, pin 2 of LM7805 is grounded, the first capacitor and the seventh capacitor are connected in parallel between pin 2 of AMS1117-3.3 and ground, Pin 1 of AMS1117-3.3 is grounded, and pin 2 of AMS1117-3.3 outputs power supply +3.3V; it is connected to an external 24VDC signal, D1 plays the role of rectification and reverse connection protection, D2 plays the role of overvoltage protection and protects the back-end circuit, E2, C8, C5, C6, C3, C4, E1, C7 are peripheral capacitor matching devices of LDO, which play the role of filtering. The linear regulator LM7812 has two functions, one is to convert DC24V to DC12V, and the other is to evenly distribute the heat generated by the power conversion. The function of LM7805 is to convert DC12V to DC5V, and the function of AMS1117-3.3 is to convert DC5V to DC3.3V.

[0054] Referring to FIG. 12 (b), the power module further includes 24V, 12V and 5V power LED indicator circuits, wherein the 24V power LED indicator circuit includes a second resistor and a third diode, wherein the anode of the third diode is connected to the 24V power supply, the cathode is connected to the first end of the second resistor, and the second end of the second resistor is grounded, for indicating the working state of the circuit 24V; the 12V power LED indicator circuit includes a first resistor and a first diode, wherein the anode of the first diode is connected to the 12V power supply, the cathode is connected to the first end of the first resistor, and the second end of the first resistor is grounded, for indicating the working state of the circuit 12V; the 5V power LED indicator circuit includes a third resistor and a second diode, wherein the anode of the second diode is connected to the 5V power supply, the cathode is connected to the first end of the third resistor, and the second end of the third resistor is grounded, for indicating the working state of the circuit 5V.

[0055] Referring to FIG. 12 ( c ), a voltage reference chip MAX6070AAUT30+T is used to provide a high-precision 3V voltage reference, and C1 , C2 , and C9 are corresponding filter capacitors.

[0056] Referring to Figures 13 (a)-(c), the integrated circuit board of the temperature control device has P1, P2 and P3 interfaces. The P1 interface is used to connect the circuit to a 24V power supply. The P2 interface is used to connect the temperature measuring element (6) PT100, which is connected to the P2 interface via lead 11. The P3 interface is used to connect the heating element (5) heating rod via lead 11 and the P3 interface.

[0057] The working principle of this embodiment is as follows: the power supply module supplies power to each circuit module, the temperature measuring element PT1000 monitors the temperature of the heating block 3, and transmits the measured real-time temperature data to the main control module. After the main control module receives the temperature data, the PAC module of the STC12C5A60S2 single-chip microcomputer outputs PWM control signals with different duty cycles to the heating module. PWM control signals with different duty cycles correspond to different output powers, so as to accurately adjust the power of the heating rod. The heating rod heats the heating block. By closely fitting the heating rod and the heating block 3, the heat transferred by the heating rod to the heating block 3 can be transferred to the sleeve 4. The lower unit area under the partition 10 of the sleeve 4 extends into the pool tank 7 to form a detection chamber 8, so that the temperature of the detection chamber 8 is equivalent to the temperature of the heating block 3. A thermistor is placed in the detection chamber 8, and finally the temperature control of the thermistor detection environment is achieved.

[0058] The working process of the present embodiment applied to the thermal conductivity gas analyzer is as follows: a constant current is given to the thermistor, and the thermal conductivity cell temperature control device heats the detection gas chamber 8. After the thermocouple PT100 detects that the ambient temperature reaches the target value and remains stable, the resistance of the thermistor remains unchanged, and the reference gas is slowly delivered to the detection gas chamber 8 through the gas path 12. The heat in the detection gas chamber 8 is transferred to the cell wall by the gas in the form of heat conduction. After reaching thermal equilibrium, the temperature measured by the thermistor stabilizes at a certain value. This equilibrium temperature determines the initial resistance of the thermistor. After the initial resistance of the thermistor is obtained, the gas to be tested is delivered to the detection gas chamber 8. Because the thermal conductivity of the gas to be tested is different from that of the reference gas, the equilibrium point temperature of the thermal detection environment also changes accordingly, and the resistance of the thermistor also changes with the equilibrium point temperature, thereby realizing the conversion of the change amount between the thermal conductivity of the gas and the resistance of the thermistor, and finally being able to measure the content of the measured component in the mixed gas.

[0059] refer to Fig.14 , the horizontal axis is time, the unit is s, the vertical axis is temperature, the unit is ℃, the utility model was tested at room temperature, the target temperature of the test was 55℃, the serial port of the single-chip microcomputer was connected to the PC, the temperature of the thermistor was controlled, the temperature obtained by the single-chip microcomputer was printed out in real time, and a curve of the equivalent temperature of the thermistor changing with time was obtained. The utility model can achieve a target temperature control of 55℃ in a relatively short time, and the actual test can achieve a control accuracy of ±0.01℃ in more than half an hour, indicating that the temperature control device of the utility model maintains high stability and accuracy during long-term operation, and can be applied to application scenarios with very strict temperature requirements, such as thermal conductivity gas analyzers, to make their measurement results more accurate.

[0060] The above only expresses the implementation mode of the utility model, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A thermal conductivity cell temperature control device, characterized in that : comprising a circuit structure, a heating block (3) and a sleeve (4) having a hollow structure, wherein the circuit structure is composed of a temperature measurement module, a main control module, a heating module, and a power supply module; The main control module is electrically connected to the temperature measurement module and the heating module respectively, and the power supply module is electrically connected to the temperature measurement module, the main control module and the heating module respectively; The temperature measuring module comprises a temperature measuring element (6) and a constant current circuit, wherein the output end of the constant current circuit is connected to the input end of the temperature measuring element (6), and the constant current circuit provides a stable current for the temperature measuring element. The temperature measuring module is used to monitor the temperature change of the heating block (3). The main control module receives the voltage signal of the temperature measuring module and then outputs a control signal to the heating module. The heating module comprises a heating element (5) and a heating circuit, and is used to heat the heating block (3). The output end of the heating circuit is electrically connected to the heating element (5). The heating circuit receives the control signal of the main control module and adjusts the voltage signal applied to the heating element (5) to adjust the heating power of the heating element (5). The power supply module is used to supply power to various components of the circuit. The heating block (3) is arranged at the upper end of the thermal conductivity cell body (1). The heating block (3) has a through hole and a blind hole. The temperature measuring element (6) and the heating element (5) are respectively arranged in the blind hole of the heating block (3). The sleeve (4) is arranged in the through hole of the heating block (3). The heating block (3) is tightly fitted with the temperature measuring element (6), the heating element (5) and the sleeve (4). The top of the thermal conductivity cell body (1) is provided with a cell groove (7). The shape of the cell groove (7) matches that of the sleeve (4). A partition (10) is arranged in the sleeve (4) so ​​that the bottom area of ​​the sleeve (4) is divided into an upper unit and a lower unit. The entire area of ​​the lower unit at the bottom of the sleeve (4) extends into the cell groove (7) to form a detection air chamber (8) for placing the thermosensitive element. Heat transfer is formed between the heating block (3), the sleeve (4) and the detection air chamber (8).

2. The thermal conductivity cell temperature control device according to claim 1, characterized in that : The lead wire (11) of the thermistor passes through the partition (10) and is led out from the top of the sleeve (4). The connection between the lead wire (11) of the thermistor and the partition (10) is a sealed connection.

3. The thermal conductivity cell temperature control device according to claim 1, characterized in that The temperature measuring element (6) adopts a thermocouple PT1000, the main control module adopts a STC12C5A60S2 single chip microcomputer, the temperature measuring module also includes an AD acquisition module and a voltage conversion module which are electrically connected, the input end of the AD acquisition module is connected to the output end of the temperature measuring element (6), the output end of the voltage conversion module is connected to the input end of the main control module, the analog voltage signal output by the temperature measuring element is converted into a digital voltage signal by the AD acquisition module, and then converted into a digital voltage signal suitable for the operation of the main control module by the voltage conversion module and then transmitted to the main control module.

4. The thermal conductivity cell temperature control device according to claim 1, characterized in that : The constant current circuit in the temperature measurement module includes an operational amplifier U4A, an operational amplifier U4B, an operational amplifier U5B, a fifth resistor, a sixth resistor, a seventh resistor, a ninth resistor and a tenth resistor, and the operational amplifiers are all LM258 models; The non-inverting input terminal of the operational amplifier U5B is connected to the reference voltage, the output terminal of the operational amplifier U5B is connected to the first terminal of the sixth resistor, the inverting input terminal of the operational amplifier U5B is connected to its output terminal, the node between the second terminal of the sixth resistor and the first terminal of the fifth resistor is connected to the non-inverting input terminal of the operational amplifier U4A, the node between the first terminal of the seventh resistor and the first terminal of the tenth resistor is connected to the output terminal of the operational amplifier U4A, the node between the first terminal of the ninth resistor and the second terminal of the tenth resistor is connected to the inverting input terminal of the operational amplifier U4A, the second terminal of the ninth resistor is grounded, the node between the first terminal of the tenth resistor and the first terminal of the seventh resistor is connected to the output terminal of the operational amplifier U4A, the positive power supply input terminal of the operational amplifier U4A is connected to the power supply module, the negative power supply input terminal of the operational amplifier U4A is grounded, the output terminal of the operational amplifier U4B is connected to the second terminal of the fifth resistor, the inverting input terminal of the operational amplifier U4B is connected to its output terminal, and the node between the second terminal of the seventh resistor and the thermocouple PT1000 is connected to the non-inverting input terminal of the operational amplifier U4B.

5. The thermal conductivity cell temperature control device according to claim 1, characterized in that : The heating element (5) adopts a heating rod, and the heating circuit includes a first MOS tube, a tenth capacitor and an eighth resistor; The tenth capacitor and the eighth resistor are connected in parallel, the gate of the first MOS tube is connected to the second end of the eighth resistor, the source of the first MOS tube is grounded, and the drain of the first MOS tube is connected to the heating rod as the output end of the heating circuit.

6. The thermal conductivity cell temperature control device according to claim 1, characterized in that :The power module includes a power circuit and a voltage reference chip MAX6070AAUT30+T, and the voltage reference chip is used to provide a 3V voltage reference; The power supply circuit includes a first diode, a first voltage regulator diode, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, linear regulators LM7812, LM7805 and AMS1117-3.3, and the power supply circuit is used to provide +24V, +12V, +5V, +3.3V power supply voltages; The anode of the first diode is connected to the external power supply +24V, the anode of the first voltage regulator diode is grounded, the second capacitor, the eighth capacitor and the first voltage regulator diode are connected in parallel and then connected in series with the first diode, the cathode of the first diode is connected to pin 1 of LM7812, the fifth capacitor and the sixth capacitor are connected in parallel between pin 3 of LM7812 and ground, the fifth capacitor and the sixth capacitor are also connected in parallel between pin 3 of LM7805 and ground, pin 3 of LM7812 is connected to pin 1 of LM7805, pin 2 of LM7812 is grounded, the third capacitor and the fourth capacitor are connected in parallel between pin 3 of LM7805 and ground, the third capacitor and the fourth capacitor are also connected in parallel between pin 3 of AMS1117-3.3 and ground, Pin 3 of LM7805 is connected to pin 3 of AMS1117-3.3, pin 2 of LM7805 is grounded, the first capacitor and the seventh capacitor are connected in parallel between pin 2 of AMS1117-3.3 and ground, pin 1 of AMS1117-3.3 is grounded, and pin 2 of AMS1117-3.3 outputs power supply +3.3V.

7. The thermal conductivity cell temperature control device according to claim 1, characterized in that : A sealing ring (9) is provided between the sleeve (4) and the tank (7) to increase the sealing performance of the detection air chamber (8).

8. The thermal conductivity cell temperature control device according to claim 1, characterized in that: It also comprises a heat preservation ring (2), which is sleeved on the periphery of the heating block (3).

9. The thermal conductivity cell temperature control device according to claim 1, characterized in that: The number of sleeves (4) is set to two, and the structures of the two sleeves (4) are exactly the same. An air inlet is provided at the bottom of the pool groove (7) into which one of the sleeves (4) extends, and the lower unit at the bottom of the sleeve (4) serves as a detection air chamber (8) of the thermal conductivity cell thermistor element, and the lower unit at the bottom of the other sleeve (4) serves as a reference air chamber.

10. The thermal conductivity cell temperature control device according to claim 8, characterized in that : The heat conduction cell body (1), the heating block (3) and the sleeve (4) are all made of stainless steel, and the insulation ring (2) is made of CPVC.

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