An in-situ calibration device for a temperature sensor

Abstract

This invention belongs to the field of optical sensing technology and relates to an in-situ calibration device for a temperature sensor based on laser frequency sweeping technology. The main structure includes a laser, an optical attenuator, an optical beam splitter, a first circulator, a second circulator, a gas molecule absorption cell, a sensing probe, a calibration probe, a photodetector, a data acquisition box, an industrial computer, a voltage output module, an analog-to-digital converter, a current controller, and a temperature controller. It uses a laser frequency sweeping system as the sensor demodulation system and a π-PSFBG as the temperature sensing probe. A gas molecule line, unaffected by ambient temperature, is introduced as a frequency standard to compensate for frequency drift caused by environmental noise in real time. A gallium dot bottle is introduced as an absolute temperature reference to provide an absolutely stable temperature environment for the calibration probe, thus calibrating the system frequency drift caused by the π-PSFBG. In-situ calibration technology achieves long-term stability of the temperature sensor. Its structure is simple and can achieve high-resolution and long-term stable measurement.

Description

Technical fields:

[0001] This invention belongs to the field of optical sensing technology, specifically relating to an in-situ calibration device for a temperature sensor based on laser frequency sweeping technology, so as to enable the temperature sensor to achieve high-resolution and long-term stable measurement. Background technology:

[0002] In recent years, ocean research has gradually shifted from near-shore and shallow waters to the deep ocean. The deep ocean experiences greater pressure and a relatively stable environment. Hydrological observations show that the bottom waters of the North Pacific are warming at a rate of approximately 2 mK per decade, while the Southern Ocean, closer to deep-water sources, is warming at approximately 30 mK per decade. To achieve accurate long-term in-situ observations, temperature sensors need to possess high resolution and good long-term stability. However, traditional electrical temperature sensors exhibit significant drift, and their stability cannot meet these requirements. Furthermore, their complex structure and high cost have pushed their sensing performance to its limits. Optical sensors, particularly fiber optic temperature sensors, offer advantages such as low cost, small size, high sensitivity, resistance to electromagnetic interference, and remote multi-channel sensing capabilities. Through laser frequency scanning demodulation, resolution can reach the mK level. However, the drift problem of fiber optic temperature sensors cannot be ignored.For example, Chinese Patent 202221546953 discloses an ultra-high precision fiber optic temperature sensor, including a housing, an enhanced sensitivity outer tube inside the housing, and a desensitizing core rod inside the enhanced sensitivity outer tube; both the right end of the enhanced sensitivity outer tube and the right end of the desensitizing core rod are fixed; the left end of the desensitizing core rod is located inside the enhanced sensitivity outer tube, and a fiber optic grating is connected between the left end of the enhanced sensitivity outer tube and the left end of the desensitizing core rod; the housing, the enhanced sensitivity outer tube, and the desensitizing core rod all have through holes for the fiber optic cable to pass through; the linear expansion coefficient K of the enhanced sensitivity outer tube and the linear expansion coefficient T of the desensitizing core rod satisfy K / T≥8; Chinese Patent 202221225361 discloses a fiber optic measurement sensor for motor rotors. The temperature control system includes: a wireless power supply device, a fiber optic temperature demodulator, a fiber optic temperature sensor, a wireless data transmission device, and a data control center. The wireless power supply device provides power to the fiber optic temperature demodulator. The fiber optic temperature sensor is connected to the fiber optic temperature demodulator and transmits temperature information to the demodulator for demodulation. The demodulated temperature information is then transmitted to the data control center via the wireless data transmission device. The wireless data transmission device includes a static data transmission device and a dynamic data transmission device; the demodulated temperature information is transmitted via the dynamic data transmission device. The data is transmitted to the static data wireless transmission device, and then from the static data wireless transmission device to the data control center; the data control center displays, analyzes, and / or stores the temperature information; Chinese Patent 202210525331 discloses a bismuth-erbium co-doped fiber-optic distributed temperature sensor based on the rare earth ion fluorescence intensity detection principle, which consists of a pump laser, an N-branch planar waveguide optical splitter, an N-channel parallel multi-channel detection unit, a monitoring center, 2N photodetectors (PDs), a multi-channel data acquisition card, and a computer; the pump light passes through the planar waveguide optical splitter at a ratio of 1: N is divided into N pump beams, each connected to a parallel multiplexer detection unit. Within the parallel multiplexer detection unit, the pump beam passes through an optical isolator and enters an extended single-mode fiber to pump a specially designed bismuth-erbium co-doped fiber, generating fluorescence. A circulator and a fiber grating with a reflection wavelength of λ1 select the fluorescence output at wavelength λ1 to the PD. A circulator and a fiber grating with a reflection wavelength of λ2 select the fluorescence output at wavelength λ2 to the PD. The PD connects to a multi-channel data acquisition card, transmitting the information from the data acquisition card to a computer. A dedicated program processes the data and performs multi-point temperature measurement and system function self-testing.

[0003] The drift of fiber optic temperature sensors consists of two parts: one part is the drift of the demodulation system, which mainly comes from the fluctuation of the laser frequency with the environment. The frequency drift of the laser frequency sweep system caused by environmental noise can be compensated in real time using HCN gas absorption lines as the frequency standard. The other part is the drift of the sensor probe, which mainly comes from photothermal effects, etc. Placing the calibration π-PSFBG in a gallium triple point bottle with an absolutely stable temperature environment can calibrate the effects caused by the drift of the temperature sensing π-PSFBG and achieve good long-term stability. Summary of the Invention:

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and to develop and design an in-situ calibration device for temperature sensors that can ensure long-term stability for application in various fiber optic sensor demodulation systems.

[0005] To achieve the above objectives, the main structure of the in-situ calibration device for a temperature sensor according to the present invention includes a laser, an optical attenuator, an optical beam splitter, a first circulator, a second circulator, a gas molecule absorption cell, a sensing probe, a calibration probe, a photodetector, a data acquisition box, an industrial control computer, a voltage output module, an analog-to-digital converter module, a current controller, and a temperature controller. The laser is connected to the optical beam splitter through the optical attenuator. The optical beam splitter is connected to the first circulator, the second circulator, and the gas molecule absorption cell, respectively. The first circulator is connected to the sensing probe, the second circulator is connected to the calibration probe, and the first circulator, the second circulator, and the gas molecule absorption cell are all connected to the photodetector. The photodetector is connected to the industrial control computer through the data acquisition box. The data acquisition box contains a voltage output module and an analog-to-digital converter module. The analog-to-digital converter module is connected to the laser through the current controller. The laser is also connected to the temperature controller.

[0006] The laser involved in this invention is a DFB laser (distributed feedback laser), which provides a light source; the sensing probe is a sensing π-PSFBG (phase-shifted fiber Bragg grating), and the calibration probe is a calibration π-PSFBG, both of which are phase-shifted fiber grating probes; the voltage output module is used to tune the injection current of the laser; the analog-to-digital conversion module processes the transmitted light signal and the reflected light signal received by the photodetector into an error signal by performing first-order derivative processing; the current controller and temperature controller are used to control the current and temperature of the laser.

[0007] The present invention relates to an in-situ calibration device for a temperature sensor. In use, the calibration probe is placed in a gallium dot bottle providing an absolutely stable temperature environment to calibrate the frequency drift caused by π-PSFBG. The laser output from the laser is attenuated by an optical attenuator and then split into three paths by an optical beam splitter: two paths enter the sensing probe and calibration probe respectively through a first circulator and a second circulator; one path enters a gas molecule absorption cell, serving as the sensing optical path, calibration optical path, and reference optical path. A photodetector receives the transmitted light signal from the gas molecule absorption cell and the reflected light signals from the sensing and calibration probes, and transmits them to an industrial control computer via a data acquisition box. The LabVIEW program built into the industrial control computer uses the gas molecule absorption line of the gas molecule absorption cell as a reference frequency, and performs cross-correlation calculations on its error signal with the error signals of the sensing and calibration probes respectively to obtain the center frequency difference between the gas molecule absorption line and the center frequency difference between the sensing and calibration probes. The temperature information is demodulated through the frequency difference, and the horizontal axis of the maximum cross-correlation value represents the time delay of the latter two relative to the gas molecule absorption cell.

[0008] Compared with existing technologies, this invention uses a laser frequency sweeping system as the sensor demodulation system, a π-PSFBG as the temperature sensing probe, and introduces gas molecule lines unaffected by ambient temperature as the frequency standard to compensate for frequency drift of the laser frequency sweeping system caused by environmental noise in real time. It also introduces a gallium dot bottle as an absolute temperature reference to provide an absolutely stable temperature environment for calibrating the probe, thereby calibrating the system frequency drift caused by the π-PSFBG. In-situ calibration technology is used to achieve long-term stability of the temperature sensor. Its structure is simple, with fast response speed, high signal-to-noise ratio, multi-channel sensing, high resolution, and strong versatility. It can achieve high-resolution and long-term stable measurements and can be used in fields such as marine exploration, underwater and surface safety monitoring, submarine landslide monitoring, and earthquake monitoring. Attached image description:

[0009] Figure 1 This is a schematic diagram of the main structure of the present invention.

[0010] Figure 2 This is a schematic diagram showing the time delay drift of the sensing probe and calibration probe under the same constant temperature environment as described in this invention within 10 minutes. The horizontal axis represents time in seconds, and the vertical axis represents time delay in seconds.

[0011] Figure 3 This is a schematic diagram showing the relationship between the time delay and temperature of the sensing probe involved in this invention, where the horizontal axis represents temperature in °C and the vertical axis represents time delay in seconds.

[0012] Figure 4 This is a schematic diagram illustrating the time delay drift trend of the sensing probe and calibration probe under stable temperature conditions over a 4-hour period, where the horizontal axis represents time in seconds and the vertical axis represents time delay in seconds.

[0013] Figure 5 This is a schematic diagram illustrating the time delay stability of the calibrated sensing probe after temperature stabilization over a period of 4 hours, as per the present invention. The horizontal axis represents time in seconds, and the vertical axis represents time delay in seconds.

[0014] Figure 6 This is a schematic diagram illustrating the temperature stability of the sensor probe after calibration and noise reduction within 4 hours when the temperature is stable, as per the present invention. The horizontal axis represents time in seconds, and the vertical axis represents temperature in degrees Celsius. Detailed implementation method:

[0015] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0016] Example 1:

[0017] The main structure of the in-situ calibration device for a temperature sensor involved in this embodiment includes a laser 1, an optical attenuator 2, an optical beam splitter 3, a first circulator 4, a second circulator 5, a gas molecule absorption cell 6, a sensing probe 7, a calibration probe 8, a photodetector 9, a data acquisition box 10, an industrial computer 11, a voltage output module 12, an analog-to-digital converter module 13, a current controller 14, and a temperature controller 15. The outlet of the laser 1 is connected to the inlet of the optical beam splitter 3 through the optical attenuator 2. The outlet of the optical beam splitter 3 is connected to one port of the first circulator 4, one port of the second circulator 5, and the inlet of the gas molecule absorption cell 6, respectively. The first circulator 4 has two ports connected to the sensing probe 7, the second circulator 5 has two ports connected to the calibration probe 8, the first circulator 4 has three ports, the second circulator 5 has three ports and the outlet of the gas molecule absorption cell 6 are all connected to the inlet of the photodetector 9, the outlet of the photodetector 9 is connected to the inlet of the data acquisition box 10, the outlet of the data acquisition box 10 is connected to the industrial control computer 11, the data acquisition box 10 has a built-in voltage output module 12 and an analog-to-digital converter module 13, the analog-to-digital converter module 13 is connected to the inlet of the laser 1 through the current controller 14, and the inlet of the laser 1 is also connected to the temperature controller 15.

[0018] The calibration steps for an in-situ calibration device for a temperature sensor involved in this embodiment are as follows:

[0019] First, the sensing probe 7 and calibration probe 8 were subjected to measurements for 10 minutes in a relatively stable environment. The results are as follows: Figure 2 As shown, their respective drift coefficients a0 and a1 are obtained, and the calibration coefficient is calculated.

[0020] Then, the sensing probe 7 was placed in a relatively stable temperature environment, and the calibration probe was placed in a gallium spot bottle. Measurements were taken for 4 hours, and the results were as follows. Figure 3 and Figure 4 As shown, the time delay TD of sensor probe 7 is obtained. s and the time delay TD of calibration probe 8 c After in-situ calibration, the actual time delay of sensor probe 7 is: TD sct =TD st -a(TD ct -TD c0 ), of which TD st and TD ct The time delays of sensing probe 7 and calibration probe 8 at time t are TD. c0 The time delay for calibrating probe 8 without drift is represented by the average value of one minute at the start of measurement;

[0021] Finally, the time delay is converted into a temperature value to obtain the calibrated temperature stability, as shown in the following results. Figure 5 and Figure 6 As shown, it has good long-term stability, which can reach ±2mk.

Claims

1. A temperature sensor in-situ calibration device, the main structure of which includes a laser, an optical attenuator, an optical beam splitter, a first circulator, a second circulator, a gas molecule absorption cell, a sensing probe, a calibration probe, a photodetector, a data acquisition box, an industrial computer, a voltage output module, an analog-to-digital converter module, a current controller, and a temperature controller; characterized in that, The laser is connected to an optical beamsplitter via an optical attenuator. The beamsplitter is connected to a first circulator, a second circulator, and a gas molecule absorption cell. The first circulator is connected to a sensing probe, and the second circulator is connected to a calibration probe. The first circulator, the second circulator, and the gas molecule absorption cell are all connected to a photodetector. The photodetector is connected to an industrial computer via a data acquisition box, which contains a voltage output module and an analog-to-digital converter (ADC). The ADC is connected to the laser via a current controller. The laser is also connected to a temperature controller. During use, the calibration probe is placed in a gallium dot bottle that provides an absolutely stable temperature environment to calibrate the frequency drift caused by the π-PSFBG. The laser output is attenuated by the optical attenuator and then split into three paths by the optical beamsplitter: two paths are respectively... The light passes through the first and second circulators and enters the sensing and calibration probes. One path leads to the gas molecule absorption cell, serving as the sensing, calibration, and reference optical paths. The photodetector receives the transmitted light signal from the gas molecule absorption cell and the reflected light signals from the sensing and calibration probes. This data is then transmitted to the industrial computer via a data acquisition box. The LabVIEW program built into the industrial computer uses the gas molecule absorption line of the gas molecule absorption cell as the reference frequency. It performs cross-correlation calculations on the error signals of the gas molecule absorption line with the error signals of the sensing and calibration probes, respectively, to obtain the center frequency difference between the gas molecule absorption line and the center frequencies of the sensing and calibration probes. The temperature information is demodulated using the frequency difference. The maximum cross-correlation values ​​on the x-axis represent the time delays of the latter two relative to the gas molecule absorption cell.

2. The in-situ calibration device for a temperature sensor according to claim 1, characterized in that, The calibration steps are as follows: First, the sensing probe and calibration probe are measured in a relatively stable environment for 10 minutes to obtain their respective drift coefficients. and And calculate the calibration coefficient. ; Then, the sensor probe was placed in a relatively stable temperature environment, and the calibration probe was placed in a gallium dot bottle. The measurement was performed for 4 hours to obtain the time delay of the sensor probe. and the delay of the calibration probe After in-situ calibration, the true time delay of the sensor probe is: ,in, and Let be the time delays of the sensing probe and the calibration probe at time t, respectively. The time delay for calibrating the probe before drift is expressed as the average value of the first minute at the start of the measurement; Finally, the time delay is converted into a temperature value to obtain the calibrated temperature stability.

3. A temperature sensor in-situ calibration device according to claim 1 or 2, characterized in that, The laser is a DFB laser, which serves to provide a light source.

4. A temperature sensor in-situ calibration device according to claim 1 or 2, characterized in that, The sensing probe is a sensing π-PSFBG and the calibration probe is a calibration π-PSFBG, both of which are phase-shifted fiber optic grating probes.

5. A temperature sensor in-situ calibration device according to claim 1 or 2, characterized in that, The voltage output module is used to tune the injection current of the laser.

6. A temperature sensor in-situ calibration device according to claim 1 or 2, characterized in that, The analog-to-digital conversion module processes the transmitted and reflected light signals received by the photodetector using the first derivative to generate an error signal.

7. A temperature sensor in-situ calibration device according to claim 1 or 2, characterized in that, Current controllers and temperature controllers are used to control the current and temperature of the laser.

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