CN103149955B - Temperature accurate control device used for integrated cavity spectrum technology isotope analysis - Google Patents

Abstract

A precise temperature control device for isotope analysis of integral cavity spectroscopy comprises: a primary seal with an optical path system and a secondary seal system with stable and precise temperature control. The optical path system is installed inside the primary sealed housing, which is characterized in that the optical path system integrates a laser, a DFB laser light source, a beam converging collimator lens group, a laser optical path, an optical cavity, a laser beam converging lens, an InGaAs detector, and the above components All were in a nitrogen atmosphere to avoid the interference of external gases. The secondary sealing system with stable and precise temperature control includes a secondary sealing shell, a platinum resistance temperature sensor, a rigid support, a semiconductor refrigeration stack, a mesh heat exchanger, a fan, shock-absorbing foam, and a temperature placed outside the secondary sealing shell The controller, drive circuit module, various control commands and electrical signals are all sealed and connected through cables. The invention has the advantages of simple structure, convenient operation, fast response, good shock resistance, high temperature control precision and good stability.

Description

A Precise Temperature Control Device for Isotope Analysis Using Integrating Cavity Spectroscopy

technical field

The invention relates to a precise temperature control device, in particular to a precise temperature control device applied in the field of gas isotope analysis of integrating cavity spectroscopy technology.

Background technique

In recent years, the application of stable isotope analysis in the field of environmental science and environmental protection has been paid more and more attention, especially in the study of atmosphere, soil, water quality and ecological environment. For example, the use of stable isotope abundance changes to study and indicate environmental pollution sources and pollution levels; the use of stable isotope tracers can identify the source of greenhouse gas emissions and analyze human activities such as fossil fuel combustion, cement production, animal husbandry and agricultural production The contribution to greenhouse gas emissions can not only accurately estimate the total emissions of each emission source, but also has certain guiding significance for the implementation of "energy saving and emission reduction" in factories and cities; the determination of methane isotopes helps to understand the relationship between methane sources and sinks in the atmosphere Physical and chemical change mechanism, used for quantitative research on methane emission mechanism and oxidation rate of rice fields, wetlands, etc. In addition, stable isotope analysis has also been widely used in many disciplines such as geology, nuclear industry, archaeology, ecological and environmental science research, biology and chemistry research, water resources development, agricultural production, food safety, and clinical medicine.

Integrating cavity spectroscopy technology calculates the gas concentration to be measured by measuring the difference between the time-integrated light intensity passing through the optical cavity and the incident light intensity. This method is closer to the traditional direct absorption spectrum and more in line with the Beer-Lambert law. This technology has extremely high measurement frequency, spectral resolution and measurement sensitivity. The structure of the measurement equipment is simple and the results do not require complicated calibration. It can also be made miniaturized and portable, assisting other physical means. The same laser isotope analyzer can realize gas and liquid analysis. Therefore, it has many advantages over isotope analyzers based on mass spectrometry.

In the isotope measurement and analysis process of the integral cavity spectroscopy technology, in order to maximize the performance of the instrument system itself, in addition to selecting an independent laser light source, it is also essential to maintain a single, constant temperature and minimum environmental vibration. The speed of temperature regulation is the main influencing factor of all electrical systems, laser light source, instrument size, sound velocity, etc. Usually, these parameters will vary by 10 ^-4 ~10 ^-5 per Kelvin. If the measurement target is solid or liquid, the temperature change will cause a large drift of the system and even a great inaccuracy of the measurement results. When using integrating cavity spectroscopy to measure gas isotope analysis, such as: C ¹⁴ O ₂ , C ¹³ O ₂ , C ¹² O ₂ , temperature changes will affect the Boltzman distribution of different isotopes, and even aggravate the measurement of known fixed components. The inaccuracy of the isotope ratio of the situation. Moreover, the measurement of the true concentration of gas isotopes and the stability of the ultra-precise optical path depend to a large extent on temperature stability, otherwise accurate measurement results cannot be obtained, and accurate, fast and stable temperature control is exactly what makes the instrument One of the important indicators with the smallest zero drift. Therefore, an accurate temperature control device is of great significance for expanding the applicable environment of the isotope analyzer of integrating cavity spectroscopy and improving the effectiveness and accuracy of detection.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies of the prior art, and provide a precise temperature control device for isotope analysis of the integral cavity spectroscopy technique, so as to solve the problem that the isotope analysis of the existing integral cavity spectroscopy technique is affected by temperature during the measurement process Accuracy, stability and zero drift issues.

The technical scheme of the present invention is as follows: a precise temperature control device for isotope analysis of integral cavity spectroscopy, which is characterized in that it includes: an optical path system 1, a primary sealing shell 2, four platinum resistance temperature sensors 3, a secondary sealing Housing 5, two thermal control devices, nitrogen 9 atmosphere, temperature controller 10, drive circuit module 11, rigid bracket 13 and shock-absorbing foam 14; the two thermal control devices are respectively installed in the secondary sealed housing 5 symmetrically At both ends of the housing, each thermal control device is composed of a semiconductor refrigeration stack 6, a mesh heat exchanger 7 and a fan 8, and 1/3 of the mesh heat exchanger 7 is installed inside the semiconductor refrigeration stack 6 and connected to the semiconductor refrigeration stack. The refrigeration stack 6 is closely and seamlessly connected, so that the heat exchange between the mesh heat exchanger 7 and the semiconductor refrigeration stack 6 can reach the most sufficient situation, and the fan 8 is installed on the same side of the mesh heat exchanger 7, and the installation position should be consistent The same as the left or the right, so that the heat exchange air flow under the action of the fan 8 forms a clockwise or counterclockwise laminar flow 4 direction; Isolation and vibration damping, and then fixed inside the secondary sealed casing 5 through a rigid bracket 13; the inside of the primary sealed casing 2 and the inside of the secondary sealed casing 5 need to be filled with nitrogen 9 atmosphere; four platinum resistance temperature sensors The two platinum resistance temperature sensors in 3 are respectively installed and embedded in the housings at both ends of the primary sealed housing 2, and the other two platinum resistance temperature sensors are respectively installed at the end of the mesh heat exchanger 7 away from the fan 8; all Platinum resistance temperature sensors 3 are all connected to each other with the temperature controller 10 installed on the outside of the secondary sealed casing 5, and obtain the temperature conditions inside the primary sealed casing 2 and the inside of the secondary sealed casing 5 in real time; The feedback information of the platinum resistance temperature sensor 3 is controlled by the PID control output to control the drive circuit module 11 installed outside the secondary sealed casing 5 to perform precise temperature control work. When the PID control of the temperature controller 3 issues a temperature control command, the drive The circuit module 11 starts to work normally, drives the semiconductor refrigeration stack 6 for heating or cooling control, and starts the fan 8 to accelerate the heat cycle, which greatly shortens the time for temperature control and improves the efficiency of heat exchange, thereby ensuring temperature stability. In addition, the driving circuit module 11 performs cyclic control in real time according to the received temperature controller 10 instruction until reaching the specified temperature during operation; meanwhile, it processes temperature changes in real time during the working process and performs cyclic control until reaching the specified temperature.

The optical path system 1 includes a DFB laser 301 , a beam converging collimating lens group 302 , a collimated beam 303 , an optical cavity 304 , a laser beam converging lens 306 , and an InGaAs detector 307 . The DFB laser 301 is driven by the laser driving source 308 installed outside the primary sealed casing 2 and the secondary sealed casing 5 to generate modulated laser light, and the laser beam passes through the beam converging collimating lens group 302 to form a collimated beam 303 (spot diameter ≤ 1mm) After the collimated beam 303 is absorbed by the gas to be measured 305 inside the optical cavity 304, it is converged to the photosensitive surface of the InGaAs detector 307 by the laser beam converging lens 306, and the converging spot size is ≤1mm ² . Then the signal after the photoelectric conversion is sent to the signal follow-up processing unit 309 installed outside the primary sealed casing 2 and the secondary sealed casing 5 through the cable 12 for subsequent signal processing and inversion of gas isotope abundance. The parts were all in a nitrogen 9 atmosphere.

The laser driving source 308 is installed outside the primary sealed casing 2 and the secondary sealed casing 5, including: a temperature controller driven by the laser, a current controller, and a signal generator unit that generates triangular wave scanning signals and sine wave modulation signals ; The temperature controller and the current controller drive the DFB laser (301) to work normally, and the signal generator unit makes the DFB laser 301 generate modulated laser light.

The DFB laser 301 is a tunable semiconductor laser.

Described follow-up processing unit 309 is installed on the outside of primary sealed housing 2 and secondary sealed housing 5, comprising: photoelectric signal amplifying circuit, lock-in amplifier, data acquisition card and computer; The output signal of InGaAs detector 308 is sent into photoelectric signal Amplifying circuit, the signal amplified by the amplifying circuit is sent to the lock-in amplifier for demodulation to obtain the corresponding harmonic signal, the harmonic signal is collected by the data acquisition card installed in the computer, and then the subsequent signal processing and gas isotope abundance inversion.

The optical cavity 304 is an off-axis integrating cavity, the side of the cavity is connected to the gas inlet and outlet, and at the same time, the laser beam 303 incident into the cavity is reflected back and forth multiple times, which greatly increases the absorption optical path length of the measured gas, thereby improving the detection of the gas. sensitivity.

The PID control adopts a fuzzy self-adaptive PID control algorithm, and the work content includes temperature setting, data acquisition, and PID control output. By comparing the difference between the real-time temperature and the set temperature, the PID output is used to control the semiconductor refrigeration stack 6 to refrigerate or Heat is applied to keep the optical path system 1 stable at a certain temperature.

All power supplies of the system are powered by DC-24V.

The advantage of the present invention compared with prior art is:

(1) The general requirements of the current integrating cavity spectroscopic isotope analysis technology are high sensitivity and high precision, and the device itself should be strong, portable and widely used. For example, when the instrument is exposed to an environment where the temperature of the external environment changes frequently and there is vibration, the precise temperature control device for the spectroscopic isotope analysis of the integrating cavity must not be disturbed by the thermal environment and the vibration environment, and maintain a high degree of stability and accuracy. However, the present invention solves the problem of temperature stability in the measurement process of the existing integrating cavity spectroscopy technology isotope analysis, improves the accuracy and stability of the measurement, and can reduce the influence of external factors and improve the advantages of zero drift of the system.

(2) The present invention seals the optical path system composed of lasers, lenses, optical cavities and InGaAs detectors together for primary sealing, and then puts them into the secondary sealing shell for re-sealing, and carries out temperature accuracy for the entire secondary sealing shell. control. The purpose of precise temperature control is not to precisely control the temperature at a certain temperature, but to pursue the stability of the system optical path at a certain temperature, at least ±0.01K, preferably ±0.001K.

(3) Each part of the present invention is separately integrated and packaged, adopts a multi-point temperature measurement and control system, and adopts a closed-loop control PID algorithm to achieve real-time temperature detection and real-time accurate and stable control.

(4) The present invention greatly shortens the time of temperature control and improves the efficiency of heat exchange by adopting components such as semiconductor refrigeration stacks, mesh heat exchangers, and fans, and realizes precise temperature control in a very short period of time and long-term The temperature is precise and stable.

(5) The present invention adopts a fan with less vibration, a rigid support and an anti-seismic material to ensure the anti-seismicity and structural stability of the system while ensuring the temperature control accuracy and stability.

(6) Both the primary sealed casing and the secondary sealed casing of the present invention are strictly sealed, and the inside is filled with nitrogen atmosphere, so the influence of other interfering gases is eliminated during the isotope measurement process.

Description of drawings

Fig. 1 is the top plan view of integral temperature precise control system of the present invention;

Fig. 2 is a side plan view of the overall precise temperature control system of the present invention;

Fig. 3 is an optical path system diagram of the primary sealed housing of the present invention.

Detailed ways

As shown in Fig. 1, Fig. 2 and Fig. 3, the device of the present invention includes two parts: one is the optical path system 1; the other is a secondary sealing system for precise temperature control; the secondary sealing system for precise temperature control includes: optical The path system 1 is sealed for the first time through the primary sealing shell 2, the platinum resistance temperature sensor 3, the gas laminar flow 4, the secondary sealing shell 5, the semiconductor refrigeration stack 6, the mesh heat exchanger 7, the fan 8, and the nitrogen gas 9 Atmosphere, temperature controller 10, drive circuit module 11, cable 12, rigid bracket 13, shock-absorbing foam 14.

The optical path system 1 is shown in Fig. 3, and mainly includes: a DFB laser 301 installed outside the primary sealed casing 2 and the secondary sealed casing 5, a beam converging collimating lens group 302, a collimated beam 303, an optical cavity 304, The gas to be measured 305 inside the optical cavity 304 , the laser beam converging lens 306 , and the InGaAs detector 307 . The DFB laser 302 is driven by the laser drive source 308 installed outside the primary sealed casing 2 and the secondary sealed casing 5 to generate modulated laser light. The straight beam 303 and the collimated beam 303 are absorbed by the gas to be measured 305 inside the optical cavity 304, and then converged to the photosensitive surface of the InGaAs detector ³⁰⁷ by the laser beam converging lens 306. The final signal is sent to the signal follow-up processing unit 309 installed outside the primary sealed housing 2 and the secondary sealed housing 5 through the cable 12 for subsequent signal processing and inversion of gas isotope abundance. All components of the system are in the primary In the nitrogen atmosphere 9 inside the sealed case 2 .

The specific process of implementing the present invention is as follows: firstly, the optical path system 1 is sealed for the first time by being installed inside the primary sealing casing 2, and the primary sealing casing 2 is made of a metal material with a large thermal conductivity and is easy to process. Then, the optical path system 1 and the primary sealing case 2 are jointly sealed inside the secondary sealing case 5 for resealing. The purpose of this design is to ensure complete thermal isolation of the external environment. The material of the secondary sealing case 5 Rigid plastics with better thermal insulation properties can be used as materials. The primary sealed casing 2 is thermally isolated and damped by shock-absorbing foam 14, such as polyurethane foam, vinyl copolymer foam, etc., and then fixed to the secondary sealed casing 5 by a rigid bracket 13. Inside, the shock-absorbing foam 14 is also used between the rigid support 13 and the secondary sealing shell 5 for further vibration reduction. All the platinum resistance temperature sensors 3 are connected with the temperature controller 10 installed outside the secondary sealed casing 5 for obtaining the temperature inside the primary sealed casing 2 and the secondary sealed casing 5 in real time. The temperature controller 10 performs temperature comparison between each temperature measurement point and temperature control point through the fuzzy adaptive PID control algorithm according to the temperature information fed back by the platinum resistance temperature sensor 3 at different parts, and sends different control signals through the cable 12 according to the comparison results. The command is given to the drive circuit module 11 installed outside the secondary sealed casing 5, and the drive circuit module 11 controls the operation of the semiconductor refrigeration stack 6 and the fan 8 to precisely control the temperature according to the received PID control command. In order to make the temperature of the optical path system 1 change evenly, a set of thermal control devices are installed on the opposite sides of the secondary sealing shell 5, mainly composed of a semiconductor refrigeration stack 6, a mesh heat exchanger 7, and a fan 8. The installation situation is: about 1/3 of the mesh heat exchanger 7 is installed inside the semiconductor refrigeration stack 6 and is closely and seamlessly connected with the semiconductor refrigeration stack 6, so that the heat exchange can reach the most sufficient situation. Two fans 8 are installed on the On the same side of the two mesh heat exchangers 7, the installation positions should be consistent with the left or right. When the PID control of the temperature controller 10 sends a temperature control command, the drive circuit module 11 starts to work normally, driving the semiconductor refrigeration stack 6 based on the Peltier effect, and the semiconductor refrigeration stack 6 can perform heating or cooling operations under the control of the current direction . When the temperature of the semiconductor refrigeration stack 6 changes slightly, the fan 8 is started and the rotating speed is controlled, and the mesh heat exchanger 7 inside the semiconductor refrigeration pile 6 can be sensed very quickly and heat is conducted to parts other than the semiconductor refrigeration pile 6, and passed through the fan. 8 quickly transfer heat to the atmosphere of nitrogen 9 (or other pure gases with small thermal conductivity), and flexibly control the cycle of accelerating the heat atmosphere. The material of the mesh heat exchanger 7 is generally a metal material, which has excellent thermal conductivity and can quickly perform heat exchange. Under the action of the above thermal control device, the heat exchange gas forms a gas laminar flow 4 in a clockwise or counterclockwise direction, and the clockwise or counterclockwise gas laminar flow 4 is affected by the secondary sealing shell 5, which is characterized by the center The speed is high and the edge flow velocity is small, so a heat exchange airflow is formed on the outer casing of the primary sealed casing 2 of the optical path system 1, which greatly promotes the temperature control time and heat exchange efficiency, and nitrogen 9 is also a heat exchange Substances with very small conductivities, so the heat exchange between the optical path system 1 and the flowing nitrogen gas 9 is very small, thereby ensuring temperature stability. At the same time, during the working process, the temperature controller 10 processes temperature changes in real time, sends instructions to the drive circuit module 11 in real time, and the drive circuit module 11 performs cycle control in real time according to the received instructions to achieve thermal isolation and temperature uniformity. In the case of ensuring the precise control and stability of the above temperature, the isotope analysis of the integrating cavity spectroscopy technology is in an accurate working state, that is, the optical system is in a normal and stable working process, that is: the DFB laser 302 is installed in the primary sealed shell 2 and the secondary The laser driving source 308 outside the sealed casing 5 drives to generate modulated laser light. The modulated laser beam passes through the beam converging collimating lens group 302 to form a collimated beam 303 (spot diameter ≤ 1mm), and the collimated beam 303 passes through the optical cavity 304 inside. After the gas to be measured 305 is absorbed, it is converged to the photosensitive surface of the InGaAs detector 307 through the laser beam converging lens 306, and the converging spot size is ≤1mm ² , and then the signal after the photoelectric conversion is sent into the primary sealed casing through the cable 12 2 and the signal subsequent processing unit 309 outside the secondary sealed housing 5 performs subsequent signal processing and inversion of gas isotope abundance. All the components mentioned above are in the nitrogen 9 atmosphere inside the primary sealed casing 2 and the secondary sealed casing 5 to ensure that there is no interfering gas. Finally, it is ensured that the accuracy, stability and zero drift of the isotope analysis affected by the temperature during the measurement process of the integral cavity spectroscopy are reduced to the minimum. The power used in the above-mentioned integrating cavity spectroscopy isotope analysis system is provided by a DC-24V power supply.

Parts not described in detail in the present invention belong to the well-known technology in the art.

Claims (8)

1. A precise temperature control device for isotope analysis of integral cavity spectroscopy, characterized in that it comprises: an optical path system (1), a primary sealed housing (2), four platinum resistance temperature sensors (3), a secondary sealed housing (5), two thermal control devices, nitrogen (9) atmosphere, temperature controller (10), drive circuit module (11), rigid bracket (13) and shock-absorbing foam (14); the two The thermal control devices are respectively installed at both ends of the symmetrical shell of the secondary sealing shell (5). Each thermal control device is composed of a semiconductor refrigeration stack (6), a mesh heat exchanger (7) and a fan (8). The 1/3 part of the heat exchanger (7) is installed in the inside of the semiconductor refrigeration stack (6) and is closely and seamlessly connected with the semiconductor refrigeration stack (6), so that the mesh heat exchanger (7) and the semiconductor refrigeration stack (6) ) to achieve the most sufficient heat exchange, the fan (8) is installed on the same side of the mesh heat exchanger (7), and the installation position should be consistent with the left or right, so that the heat exchange airflow under the action of the fan (8) A clockwise or counterclockwise laminar flow (4) is formed; the optical path system (1) is installed inside the primary sealed casing (2), and the primary sealed casing (2) is thermally isolated and damped by shock-absorbing foam (14). vibrate, and then fixed inside the secondary sealing shell (5) by a rigid support (13); the inside of the primary sealing shell (2) and the inside of the secondary sealing shell (5) need to be filled with nitrogen (9) atmosphere Two platinum resistance temperature sensors in the four platinum resistance temperature sensors (3) are respectively installed and embedded in the housings at both ends of the primary sealed housing (2), and the other two platinum resistance temperature sensors are respectively installed in the mesh heat The end of the exchanger (7) away from the fan (8); all the platinum resistance temperature sensors (3) are connected with the temperature controller (10) installed outside the secondary sealed casing (5), and obtain the temperature of the primary sealed casing in real time. The temperature inside the body (2) and the inside of the secondary sealing shell (5); the temperature controller (10) is installed in the secondary sealing shell through PID control output control according to the feedback information of different platinum resistance temperature sensors (3) The drive circuit module (11) outside the body (5) performs precise temperature control work. When the PID control of the temperature controller (10) sends out a temperature control command, the drive circuit module (11) starts to work normally and drives the semiconductor refrigeration stack (6 ) for heating or cooling control, and start the fan (8) to accelerate heat circulation, which greatly shortens the time for temperature control and improves the efficiency of heat exchange, thereby ensuring temperature stability, and the drive circuit module (11) is running During the process, real-time cycle control is performed according to the received temperature controller (10) instruction until the specified temperature is reached; at the same time, the temperature change is processed in real time during the working process, and cycle control is performed until the specified temperature is reached. the 2. The precise temperature control device for isotope analysis of integral cavity spectroscopy according to claim 1, characterized in that: the optical path system (1) includes a DFB laser (301), a beam converging collimating lens group ( 302), collimated light beam (303), optical cavity (304), laser beam converging lens (306), InGaAs detector (307); The laser drive source (308) outside the casing (5) drives to generate modulated laser light. The modulated laser beam passes through the beam converging collimator lens group (302) to form a collimated beam (303), and the collimated beam (303) passes through the optical cavity After the gas to be measured (305) inside (304) is absorbed, it is converged to the photosensitive surface of the InGaAs detector (307) through the laser beam converging lens (306); then the signal after photoelectric conversion is sent to the installation through the cable (12). The subsequent signal processing and the inversion of gas isotope abundance are carried out in the signal post-processing unit (309) outside the primary sealed casing (2) and the secondary sealed casing (5), and all components of the system are in nitrogen (9) atmosphere. the 3. The precise temperature control device for isotope analysis of integrated cavity spectroscopy according to claim 2, characterized in that: the laser drive source (308) is installed in the primary sealed casing (2) and the secondary sealed casing The outside of the body (5), including: a laser-driven temperature controller, a current controller, and a signal generator unit that generates triangular wave scanning signals and sine wave modulation signals; the temperature controller and the current controller drive the DFB laser (301) to work normally, The signal generator unit makes the DFB laser (301) generate modulated laser light. the 4. The precise temperature control device for isotope analysis by integrating cavity spectroscopy according to claim 2, characterized in that: the DFB laser (301) is a tunable semiconductor laser. the 5. The precise temperature control device for isotope analysis by integrating cavity spectroscopy according to claim 2, characterized in that: the signal subsequent processing unit (309) is installed in the primary sealed housing (2) and the secondary sealed The outside of the housing (5) includes: a photoelectric signal amplifier circuit, a lock-in amplifier, a data acquisition card and a computer; the output signal of the InGaAs detector (307) is sent into the photoelectric signal amplifier circuit, and the signal amplified by the amplifier circuit is sent into the lock The phase amplifier is demodulated to obtain the corresponding harmonic signal, and the harmonic signal is collected by the data acquisition card installed in the computer, and then the subsequent signal processing and the inversion operation of the gas isotope abundance are carried out by the computer. the 6. The precise temperature control device for isotope analysis of integrating cavity spectroscopy according to claim 2, characterized in that: the optical cavity (304) is an off-axis integrating cavity, and the side of the cavity is connected to the inlet and outlet ports, while the The laser beam (303) incident into the cavity is reflected back and forth multiple times, which greatly increases the absorption optical path length of the gas to be measured, thereby improving the sensitivity of the gas to be detected. the 7. The precise temperature control device for isotope analysis of integrating cavity spectroscopy according to claim 1, characterized in that: the PID control adopts a fuzzy adaptive PID control algorithm, and the work content includes temperature setting, data acquisition, The PID control output controls the cooling or heating of the semiconductor refrigeration stack (6) through the PID output by comparing the difference between the real-time temperature and the set temperature, so as to keep the optical path system (1) stable at a certain temperature. the 8. The precise temperature control device for isotope analysis by integrating cavity spectroscopy according to claim 1, characterized in that: all power supplies of the system are powered by DC-24V. the