Temperature measurement device based on fluorescence lifetime and thermal radiation type optical fiber temperature sensors

Abstract

The present invention relates to a temperature measurement device based on a fluorescence lifetime type and a thermal radiation type optical fiber temperature sensor, comprising an optical probe, a fluorescence lifetime temperature measurement module, an optical power meter and a data processing unit; the optical probe is respectively connected to the fluorescence lifetime temperature measurement module and the optical power meter through a high temperature resistant transmission optical fiber; the data processing unit is respectively connected to the fluorescence lifetime temperature measurement module and the optical power meter. The present invention overcomes the problem that the fluorescence lifetime type optical fiber sensor can only be used for temperature measurement in a low temperature section due to fluorescence quenching at high temperatures, and the problem that the radiation type optical fiber temperature sensor has a weak radiation signal in a low temperature section, is greatly affected by environmental factors, and cannot accurately measure temperature, solves the problem of real-time temperature monitoring in industries such as metallurgy, and meets the current real-time temperature monitoring needs of medium frequency smelting furnaces, aluminum smelting processes, and electrolysis processes.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a temperature measuring device based on fluorescence lifetime type and thermal radiation type optical fiber temperature sensors. Background Art

[0002] Fiber optic temperature sensors have high sensitivity, electrical insulation, anti-electromagnetic properties, good flexibility, can enter the narrow space inside the object to measure temperature, and can be used for long-distance continuous temperature measurement. They can measure temperature in harsh environments such as high temperature, strong electromagnetic, and chemical corrosion. The current fiber optic temperature sensors include: fluorescence type, optical interference type, Raman distribution type, blackbody radiation type, ultrasonic wave guide type, etc. Among them, the radiation type is mainly a type of sensor developed based on the principle of blackbody radiation; the fluorescence temperature measurement type is mainly based on the fluorescence lifetime or luminescence intensity of rare earth ion-doped luminescent materials. A type of sensor developed with the corresponding relationship between temperature. At present, sapphire fiber technology is relatively mature and can be used for high-temperature measurement, but it is expensive and not conducive to market promotion. Fluorescence fiber optic sensors can only be used for low-temperature measurements due to problems such as fluorescence quenching at high temperatures. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a temperature measuring device based on fluorescence lifetime type and thermal radiation type optical fiber temperature sensors, aiming to solve the above problems.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A temperature measurement device based on fluorescence lifetime and thermal radiation type optical fiber temperature sensors comprises an optical probe, a fluorescence lifetime temperature measurement module, an optical power meter and a data processing unit; the optical probe is respectively connected to the fluorescence lifetime temperature measurement module and the optical power meter through high temperature resistant transmission optical fiber; the data processing unit is respectively connected to the fluorescence lifetime temperature measurement module and the optical power meter.

[0006] Furthermore, the optical probe includes fluorescent material, a quartz rod, a ceramic tube, a transmission optical fiber and high-temperature resistant glue; fluorescent powder is provided at the bottom of the ceramic tube; both ends of the quartz rod are cut flat, ground and polished, and inserted into the ceramic tube, one end is in full contact with the fluorescent powder, and the other end is connected to the optical fiber, and the quartz rod is bonded to the ceramic tube by high-temperature resistant glue.

[0007] Furthermore, the exterior of the ceramic tube is coated with a thin layer of high-temperature resistant black glue.

[0008] A temperature measurement method based on a temperature measurement device of a fluorescence lifetime type and a thermal radiation type optical fiber temperature sensor comprises the following steps:

[0009] Step S1: processing the fluorescent material to make a light probe;

[0010] Step S2: determining the relationship between fluorescence lifetime and temperature in a low-temperature refrigerator and a high-temperature oil bath;

[0011] Step S3: measuring the temperature of the low temperature section according to the temperature determined by the fluorescence lifetime;

[0012] Step S4: using the fluorescence temperature measurement value in the temperature measurement overlap area of ​​the fluorescence lifetime temperature measurement and the thermal radiation power temperature measurement, and determining the constant term of the relationship between the thermal radiation power and the temperature;

[0013] Step S5: measuring the temperature of the high temperature section according to the determined fourth-order polynomial between the thermal radiation power and the temperature.

[0014] Furthermore, the relationship between the fluorescence lifetime and temperature is determined as follows:

[0015] Assume that the fluorophore is excited by a delta function light pulse, and the number of initial excited state particles of the fluorophore in the excited state is n 0 , the decay rate of the excited state population is Γ+k nr , so we have:

[0016]

[0017] Where Г represents the emission rate, and k nr is the non-radiative decay rate;

[0018] The number of particles in the excited state changes exponentially:

[0019] n(t)=n 0 exp(-τ / t) (2)

[0020] The observable fluorescence intensity is proportional to n(t); therefore, formula (1) is expressed in terms of the time-dependent fluorescence intensity I(t), yielding an expression for the number of excited state particles with a single exponential decay:

[0021] I(t)=I 0 exp(-τ / t) (3)

[0022] Among them I 0 is the intensity at time 0, and the lifetime τ is the inverse of the total decay rate, i.e.

[0023] τ=1 / (Γ+k nr )

[0024] Fluorescent materials emit fluorescence after being stimulated, and the intensity decays over time:

[0025]

[0026] Where, I is the fluorescence intensity at time t; I0 is the initial fluorescence intensity of the fluorescent material after being excited; the fluorescence intensity decreases in the form of an exponential function, and τ is called the fluorescence lifetime, which refers to the fluorescence intensity of the material from I 0 Attenuation I 0 / e to the required time.

[0027] Furthermore, the thermal radiation power temperature measurement is specifically:

[0028] Assuming that the detection wavelength is λ, the bandwidth of the measuring instrument is Δλ, and the detection power is P(T), then P(T) is expressed as:

[0029]

[0030] When Δλ is less than a certain value, the above formula can be rewritten as:

[0031]

[0032] Among them, ε(λ 0 , T) can be regarded as a constant, and the bandwidth Δλ is a fixed constant;

[0033] When 0 <1um,T<1500K,exp(C 2 / λ 0 T)>>1, the above formula is written as:

[0034]

[0035] Therefore, the value of P(T) is only related to temperature T, and P(T) is an exponential function of temperature T;

[0036] When an optical power meter is used to measure the temperature corresponding to the radiation power, its temperature measurement sensitivity S(T) is:

[0037]

[0038] Furthermore, the constant term of the relationship between the thermal radiation power and the temperature is determined as follows:

[0039] (1): Directly connect the transmission optical fiber to the optical power meter.

[0040] (2): Select the preset band and conduct experiments based on the temperature displayed by the high-temperature resistance furnace;

[0041] (3): Within the preset range, record the power value measured by the optical power meter every time the temperature rises by 10°C;

[0042] (4): Plot and fit the measurement results. The fitting expression is:

[0043] P(T)=A0 +A 1 T+A 2 T 2 +A 3 T 3 +A 4 T 4 (9)

[0044] Among them, A 0 , A 1 , A 2 , A 3 , A 4 is a constant term;

[0045] (5): Carry out five measurements under the same experimental conditions and take A 0 , A 1 , A 2 , A 3 , A 4 The respective means are used as coefficients of a fourth-order polynomial.

[0046] Furthermore, in the temperature overlap area of ​​250℃-300℃ where the fluorescence lifetime temperature measurement and the thermal radiation power temperature measurement are measured, the temperature measured by the fluorescence temperature measurement is used as the standard, and the corresponding power value measured by the optical power meter is read at the same time.

[0047] The constant term A0 in the PT relationship is calibrated by the power P value and the T value of the fluorescence temperature measurement, wherein the coefficients of the first to fourth order of the fourth-order polynomial remain unchanged;

[0048] The constant value A obtained by multiple calculations in the range of 250℃-300℃ 0 The average is taken and re-determined to obtain a PT relationship in the temperature measurement process, and the dependence between P and T in this formula is used to realize thermal radiation temperature measurement above 300°C.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. The optical probe made of quartz rods used in the present invention can meet the needs of fluorescence lifetime temperature measurement in low temperature section and thermal radiation temperature measurement in high temperature section, and realize a wide range of temperature detection from -200℃ to 850℃;

[0051] 2. The two optical fiber signal channels used in the present invention are respectively used for fluorescence lifetime detection and thermal radiation intensity signal detection, which can avoid the influence of fluorescence and pump light on thermal radiation power detection during fluorescence temperature measurement; secondly, the optical power meter is directly connected to the transmission optical fiber without passing through other optical coupling modules, so that the measured signal intensity is sufficient and no additional signal amplification circuit is required for power amplification;

[0052] 3. The present invention adopts the method of fluorescence lifetime temperature measurement in the low temperature section to automatically calibrate and calibrate the thermal radiation temperature measurement relationship in the high temperature area within the range of 250℃-300℃, which can avoid the influence of the use loss of optical fiber materials and changes in environmental factors on the transmission thermal radiation power of optical fiber, and can greatly extend the life and temperature measurement accuracy of optical fiber temperature sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a schematic diagram of the structure of an optical probe in one embodiment of the present invention;

[0054] Figure 2 This is a schematic diagram of the optical path structure of fluorescence lifetime temperature measurement in one embodiment of the present invention;

[0055] Figure 3 is an assembly diagram for determining the relationship between fluorescence lifetime and temperature in one embodiment of the present invention;

[0056] Figure 4 Schematic diagram of an optical fiber temperature sensor device combining fluorescence lifetime and thermal radiation temperature measurement in one embodiment of the present invention;

[0057] In the figure, 1 is a fluorescent material, 2 is a quartz rod, 3 is a ceramic tube, 4 is an optical fiber, 5 is a high temperature resistant glue, 6 is a fluorescence lifetime temperature measurement module, 7 is an optical power meter, 8 is a data processing unit, 9 is an LED, 10 is a black sleeve, 11 is an excitation light, 12 is a fluorescence, 13 is a silicon PIN tube, 14 is a filter (2), 15 is a filter (1), 16 is a convex lens, 17 is a fluorescence lifetime detection probe, 18 is a PT100 temperature measurement probe, 19 is a metal block, and 20 is a second-stage cold head of a refrigerator. DETAILED DESCRIPTION

[0058] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0059] Please refer to Figure 1-4 The present invention provides a temperature measurement device based on fluorescence lifetime and thermal radiation type optical fiber temperature sensors, comprising an optical probe, a fluorescence lifetime temperature measurement module, an optical power meter and a data processing unit; the optical probe is connected to the fluorescence lifetime temperature measurement module and the optical power meter respectively through a high temperature resistant transmission optical fiber; the data processing unit is connected to the fluorescence lifetime temperature measurement module and the optical power meter respectively.

[0060] In this embodiment, the optical probe includes fluorescent material, a quartz rod, a ceramic tube, a transmission optical fiber and high-temperature resistant glue; fluorescent powder is provided at the bottom of the ceramic tube; both ends of the quartz rod are cut flat, ground and polished, and inserted into the ceramic tube, one end is in full contact with the fluorescent powder, and the other end is connected to the optical fiber, and the quartz rod is bonded to the ceramic tube by high-temperature resistant glue.

[0061] refer to Figure 2In this embodiment, the low temperature section temperature measurement optical path based on the device includes a silicon PIN tube, a filter (2), a filter, a convex lens, an optical fiber, a quartz rod, a fluorescent material, an LED, and a black sleeve (the black sleeve is used to absorb the scattered light emitted by the LED to prevent it from entering the PIN tube and interfering with the PIN tube measurement). Among them, the filter (1) and the filter (2) are high-pass filters that are highly reflective of light in the band below 500nm and highly transparent to light in the band above 500nm. The filter (1) is incident at a 45-degree angle, while the filter (2) is incident at a 90-degree angle.

[0062] Step 1: LED is used as a pump source to emit excitation light with a wavelength of 395nm.

[0063] Step 2: The excitation light is incident on the filter (1) at an angle of 45 degrees to the filter (1), and is reflected, thereby being incident in parallel on a convex lens on the same horizontal line for focusing.

[0064] Step 3: After being converged by the convex lens, the excitation light is incident on the optical fiber end face again and coupled into the transmission optical fiber.

[0065] Step 4: The excitation light is transmitted through the optical fiber and the quartz rod, and is vertically incident on the fluorescent material to excite the fluorescent material.

[0066] Step 5: After being excited, the phosphor emits fluorescence, which is then transmitted through reflection to one end face of the convex lens, and then passes through filters (1) and (2) again, and the signal is received by the PIN tube.

[0067] In this embodiment, in the optical path application, the optical fiber end face can be approximately regarded as a point light source, and the fluorescence emitted from the optical fiber end face will be approximately parallel after being focused by the convex lens. The filters (1) and (2) will filter out the reflected excitation light contained in the fluorescence transmission process, and the PIN tube will generate an electrical signal corresponding to the fluorescence intensity after receiving the fluorescence signal.

[0068] refer to Figure 3 , showing the method for determining the relationship between the fluorescence lifetime and temperature of the present invention. The relationship between the fluorescence lifetime and temperature of the fluorescent material under the excitation of the excitation light is determined in a low temperature refrigerator and a high temperature oil tank respectively. It is characterized by comprising the following steps:

[0069] ① Steps for determining the high temperature zone:

[0070] Step 1: Bundle the fluorescent light probe and the standard PT100 sensor head together to form an experimental combined probe. The bundling material is a metal block.

[0071] Step 2: After turning on the oil tank heater, set the final target temperature to 250°C.

[0072] Step 3: Place the combined probe in the oil tank and secure it with wire to ensure that it does not shake during the heating process.

[0073] Step 4: Connect the ST head at the other end of the optical fiber to the ST socket of the optical path, and connect the two wires of the PT100 sensor head to its temperature measurement circuit respectively; use an adapter cable to connect the RS-485 communication circuit to the USB interface on the PC; then turn on the power of the data acquisition device and the host computer interface on the PC in turn.

[0074] Step 5: When the oil tank temperature reaches 250°C, turn off the heating button and then turn on the oil tank circulation pump; at the same time, turn on the "fluorescence lifetime automatic detection system". Use the cooling process temperature-fluorescence lifetime determination method.

[0075] Step 6: Wait for the oil tank to cool to room temperature before stopping the determination process.

[0076] ②The steps to determine the low temperature zone are as follows:

[0077] Step 1: First, you need to pierce a hole on the top of the vacuum cover so that you can insert the combined probe from the top of the vacuum cover into the vacuum cover; use iron wire to fix the combined probe to the diode cold head of the refrigerator.

[0078] Step 2: Tighten the screws of the vacuum cover and seal the small hole on the vacuum cover with glass glue; the optical fiber and PT100 cable need to pass through the small hole on the top of the vacuum cover, and the optical fiber and PT100 need to be processed to ensure the airtightness of the vacuum cover.

[0079] Step 3: Vacuuming: First close the high vacuum valve, turn on the vacuum pump power, and first evacuate the air in the connecting pipe, which takes about one minute, and then open the vacuum valve. During this process, a vacuum gauge is used to monitor the vacuum degree. When the vacuum degree displayed by the vacuum gauge is less than 30Pa, the vacuum valve and vacuum pump power are closed in turn.

[0080] Step 4: Open the "fluorescence lifetime automatic acquisition system" on the PC, open the tap of the cold water circulation system of the refrigerator, and start the refrigerator. Then repeat the data determination process in the high temperature zone.

[0081] Step 5: After the temperature drops to the lowest possible temperature, turn off the refrigerator power switch to stop refrigeration, and disconnect the cooling water of the helium compressor after 5 minutes; after the diode cold head naturally heats up to room temperature, stop the determination process.

[0082] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A temperature measurement method based on a temperature measurement device of a fluorescence lifetime type and a thermal radiation type optical fiber temperature sensor, characterized in that: The temperature measurement device comprises an optical probe, a fluorescence lifetime temperature measurement module, an optical power meter and a data processing unit; the optical probe is connected to the fluorescence lifetime temperature measurement module and the optical power meter respectively through a high temperature resistant transmission optical fiber; the data processing unit is connected to the fluorescence lifetime temperature measurement module and the optical power meter respectively; The temperature measurement method comprises the following steps: Step S1: processing the fluorescent material to make a light probe; Step S2: determining the relationship between fluorescence lifetime and temperature in a low-temperature refrigerator and a high-temperature oil bath; Step S3: measuring the temperature of the low temperature section according to the temperature determined by the fluorescence lifetime; Step S4: using the fluorescence temperature measurement value in the temperature measurement overlap area of ​​the fluorescence lifetime temperature measurement and the thermal radiation power temperature measurement, and determining the constant term of the relationship between the thermal radiation power and the temperature; Step S5: measuring the temperature of the high temperature section according to the determined fourth-order polynomial between the thermal radiation power and the temperature.

2. The temperature measurement method of the temperature measurement device based on the fluorescence lifetime type and thermal radiation type optical fiber temperature sensor according to claim 1 is characterized in that: The optical probe includes fluorescent material, a quartz rod, a ceramic tube, a transmission optical fiber and high-temperature resistant glue; fluorescent powder is arranged at the bottom of the ceramic tube; both ends of the quartz rod are cut flat, ground and polished, and inserted into the ceramic tube, one end is in full contact with the fluorescent powder, and the other end is connected to the optical fiber, and the quartz rod is bonded to the ceramic tube by high-temperature resistant glue.

3. The temperature measurement method of the temperature measurement device based on the fluorescence lifetime type and thermal radiation type optical fiber temperature sensor according to claim 2 is characterized in that: The ceramic tube is coated with a thin layer of high-temperature resistant black high-temperature resistant glue on the outside.

4. The temperature measurement method of the temperature measurement device based on the fluorescence lifetime type and thermal radiation type optical fiber temperature sensor according to claim 1, characterized in that: The relationship between the fluorescence lifetime and temperature is determined as follows: Assume that the fluorophore is excited by a delta function light pulse, the initial excited state particle number of the fluorophore in the excited state is n0, and the decay rate of the excited state particle number is Γ+k nr , so we have: Where Г represents the emission rate, and k nr is the non-radiative decay rate; The number of particles in the excited state changes exponentially: n(t)=n0exp(-τ / t) (2) The observable fluorescence intensity is proportional to n(t); therefore, formula (1) is expressed in terms of the time-dependent fluorescence intensity I(t), yielding an expression for the number of excited state particles with a single exponential decay: I(t)=I0exp(-τ / t) (3) where I0 is the intensity at time 0 and the lifetime τ is the inverse of the total decay rate, i.e. τ=1 / (Γ+k nr ) Fluorescent materials emit fluorescence after being stimulated, and the intensity decays over time: Where I is the fluorescence intensity at time t; I0 ​​is the initial fluorescence intensity after the fluorescent material is excited; the fluorescence intensity decreases in the form of an exponential function, and τ is called the fluorescence lifetime, which refers to the time required for the fluorescence intensity of the material to decay from I0 to I0 / e.

5. The temperature measurement method of the temperature measurement device based on the fluorescence lifetime type and thermal radiation type optical fiber temperature sensor according to claim 1, characterized in that: The thermal radiation power temperature measurement is specifically: Assuming that the detection wavelength is λ, the bandwidth of the measuring instrument is Δλ, and the detection power is P(T), then P(T) is expressed as: When Δλ is less than a certain value, the above formula can be rewritten as: Among them, ε(λ0, T) can be regarded as a constant, and the bandwidth Δλ is a fixed constant; When λ0<1um,T<1500K, exp(C2 / λ0T)>>1, the above formula is written as: Therefore, the value of P(T) is only related to temperature T, and P(T) is an exponential function of temperature T; When an optical power meter is used to measure the temperature corresponding to the radiation power, its temperature measurement sensitivity S(T) is:

6. The temperature measurement method based on the temperature measurement device of the fluorescence lifetime type and thermal radiation type optical fiber temperature sensor according to claim 1, characterized in that: The constant term of the relationship between thermal radiation power and temperature is determined as follows: (1): Directly connect the transmission optical fiber to the optical power meter; (2): Select the preset band and conduct experiments based on the temperature displayed by the high-temperature resistance furnace; (3): Within the preset range, record the power value measured by the optical power meter every time the temperature rises by 10°C; (4): Plot and fit the measurement results. The fitting expression is: P(T)=A0+A1T+A2T 2 +A3T 3 +A4T 4 (9) Among them, A0, A1, A2, A3, A4 are constant terms; (5): Carry out five measurements under the same experimental conditions and take the average values ​​of A0, A1, A2, A3, and A4 as the coefficients of the fourth-order polynomial.

7. The temperature measurement method of the temperature measurement device based on the fluorescence lifetime type and thermal radiation type optical fiber temperature sensor according to claim 6, characterized in that: In the temperature overlap area of ​​250℃-300℃ between fluorescence lifetime temperature measurement and thermal radiation power temperature measurement, the temperature measured by fluorescence temperature measurement is used as the standard, and the corresponding power value measured by the optical power meter is read at the same time. The constant term A0 in the PT relationship is calibrated by the power P value and the T value of the fluorescence temperature measurement, wherein the coefficients of the first to fourth order of the fourth-order polynomial remain unchanged; The constant term value A0 obtained by multiple calculations within the range of 250℃-300℃ is averaged and re-determined to obtain a PT relationship in the temperature measurement process. The dependence between P and T in this formula is used to realize thermal radiation temperature measurement above 300℃.

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