CN114608719A - A laser temperature measurement device for high temperature objects - Google Patents

Abstract

The invention discloses a laser temperature measurement device for a high-temperature object, belonging to the technical field of temperature measurement, comprising a photoelectric phase-locked loop, a temperature detection unit, a photoelectric detector and a signal processing unit. The spherical mirror and the F-P etalon set on the object to be measured, the linear frequency modulated light output by the photoelectric phase-locked loop passes through the optical fiber circulator, transmits the optical fiber light, and the aspheric mirror to the F-P etalon, and then transmits back to the optical fiber circulator after reflection , and then processed by the photodetector to the signal processing unit, and the temperature of the object to be measured is calculated by collecting the time of the two adjacent strongest light intensities of the reflected light and combining the relationship between the frequency of the linear frequency modulated light and the time change. The invention also proposes a photoelectric phase-locked loop for realizing nonlinear correction. The invention realizes the temperature measurement of high-temperature objects, and performs frequency sweep measurement on the longitudinal mode interval, thereby improving the test accuracy.

Description

A laser temperature measurement device for high temperature objects

technical field

The invention belongs to the technical field of temperature measurement, in particular to a laser temperature measurement device for a high-temperature object.

Background technique

In industrial production, the scientific control of temperature has always been a very important work content, especially when the product works in a high temperature environment, the temperature determines the quality of the produced product, and is closely related to the production efficiency, which may affect the to the overall process and situation of production. Therefore, the measurement of temperature is of great significance in industrial production.

Temperature is a physical quantity that characterizes the degree of heat and cold of an object. According to the measurement method, temperature testing can be divided into two categories: contact type and non-contact type. The contact temperature measuring instrument measures the temperature by fully contacting the sensitive element with the object to be measured for heat exchange. The method is simple, intuitive and reliable, and the measurement accuracy is high.

Contact temperature measuring instruments can be divided into four categories according to different temperature measuring principles: expansion thermometers, thermal resistance thermometers, thermocouple thermometers and PN junction integrated temperature sensors. The thermal resistance thermometer converts the measurement of temperature into the measurement of resistance. The principle of temperature measurement is that the resistance of the conductor or semiconductor changes with the change of temperature. Thermocouple temperature sensor converts the measured temperature into thermoelectromotive force signal output, and realizes temperature measurement by connecting the wire with the display instrument to form a temperature measurement system. Thermal resistance has the characteristics of high measurement accuracy and wide measurement range. In general, thermocouples are used to measure higher temperatures above 500°C, and thermal resistance measurements are used for ambient temperatures below 500°C. This is because the thermoelectric potential output by thermocouples is very small in the mid-low temperature region below 500°C. The anti-interference measures of the secondary instrument are very demanding, and it is usually difficult for thermocouples to achieve accurate measurement. And in the lower temperature area, considering that the relative error caused by the temperature change of the cold junction is also very prominent, it is generally more appropriate to use a thermal resistance temperature measuring instrument.

The most common non-contact temperature measurement is infrared temperature measurement that is measured by thermal radiation. Its advantages are: the measurement does not interfere with the measured temperature field and does not affect the temperature field distribution, so it has high measurement accuracy; the temperature measurement range is wide, theoretically there is no upper limit of measurement, and a relatively high temperature can be measured; the response of the detector The time is short, the response speed is fast, and it is easy to quickly and dynamically measure; it is not necessary to touch the measured object, and the operation is convenient; the temperature of the tiny target can be determined.

Despite this, there are still many shortcomings in the existing temperature measurement technology. The size of the temperature sensing part of the thermal resistance is large, and the temperature measurement response is slow; the thermocouple temperature measurement needs compensation wires, and the solder and high-frequency magnetic field environment will also affect the temperature measurement. Large errors; more importantly, RTDs and thermocouples limit the upper temperature range due to their physical properties. Infrared temperature measurement is greatly affected by external environmental factors. The spectral radiance of a black body has an extreme value, and the change of the extreme value changes slowly with temperature, so the measurement error is large.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a laser temperature measuring device for a high temperature object in view of the above-mentioned problems in the prior art.

The technical scheme adopted in the present invention is as follows:

A laser temperature measurement device for high-temperature objects, characterized in that it includes a photoelectric phase-locked loop, a temperature detection unit, a photodetector and a signal processing unit; the temperature detection unit includes a fiber circulator, a transmission fiber, an aspheric mirror and an F-P (Fabry-Perot) etalon, the F-P etalon is set on the object to be measured;

The photoelectric phase-locked loop is used to output linear frequency modulated light, and its output port is optically connected to the laser input port of the fiber circulator; The optical output port of the optical fiber circulator is optically connected to the F-P etalon; the signal light output port of the optical fiber circulator is optically connected to the input end of the photodetector, and the output end of the photodetector is electrically connected to the signal processing unit.

Further, the optoelectronic phase-locked loop includes a broadband tunable laser, a micro-optical lens, a first coupler, an MZ (Mach-Zehnder) interferometer, a second coupler, a balanced photodetector, a Phaser, loop filter, up/down switch control circuit and integrator;

The broadband tunable laser outputs frequency-modulated light, which is coupled to the first coupler through a micro-optical lens, and outputs two beams, one of which is used as the output of the photoelectric phase-locked loop, and the other beam is input to the input of the MZ interferometer. port; the output port of the MZ interferometer is optically connected to the input port of the balanced photodetector through the second coupler, and the output port of the balanced photodetector is electrically connected to the input port of the phase detector; the phase detector combines the input signal with the sine The reference frequency signal is mixed to obtain the frequency error signal, which is transmitted to the loop filter through the output port of the phase detector to obtain the frequency control signal, and then passes through the up/down switch control circuit and the integrator in turn to output the triangular wave signal, which is fed back to The broadband tunable laser realizes nonlinear correction of the broadband tunable laser, so that the photoelectric phase-locked loop outputs chirp light.

Further, the crystal material of the F-P etalon is aluminum oxide or YAG (yttrium aluminum garnet).

Further, the linear frequency modulated light output by the photoelectric phase-locked loop is converged into parallel light by the aspherical mirror, and transmitted to the F-P etalon. The F-P etalon emits reflected light, which is sequentially transmitted back to the duplex port of the optical fiber circulator, and then output from the signal light. The output of the port is converted into an electrical signal into the photodetector, and the temperature T of the measured object is obtained after being processed by the signal processing unit.

Further, the ratio of the reflected light intensity emitted by the F-P etalon to the received incident light intensity is:

Among them, I _r is the reflected light intensity; I _i is the incident light intensity; R ₁ and R ₂ are the reflectances of the front and rear reflective surfaces of the FP etalon, respectively; :

Among them, n is the refractive index of the FP etalon crystal material; L is the distance between the front and rear reflection surfaces of the FP etalon; c is the speed of light propagating in vacuum (3×10 ⁸ m/s);

The longitudinal mode interval of the reflected light (that is, the frequency difference between two adjacent strongest light intensities) Δv is:

Since n and L in formula (3) are related to the temperature T, the temperature on both sides of formula (3) can be derived from:

Then, the relationship between the longitudinal mode interval Δν and the temperature T of the object to be measured is obtained as:

Among them, T ₀ is room temperature; β is the thermo-optic coefficient of the FP etalon crystal material; α is the linear thermal expansion coefficient of the FP etalon crystal material; α and β are both constants; Δv ₀ is the reflected light of the FP etalon before temperature measurement The initial longitudinal mode interval of ;

The signal processing unit obtains the frequency sweep frequency value corresponding to the two adjacent strongest light intensities of the reflected light according to the relationship between the frequency of the linear frequency modulated light and the time change by collecting the time of the two adjacent strongest light intensities of the reflected light. The frequency difference is the longitudinal mode interval Δν, so that the temperature T of the measured object can be calculated.

Further, the initial longitudinal mode interval Δv ₀ of the reflected light of the FP etalon before temperature measurement is set to not be lower than 5 GHz.

Further, when the crystal material of the F-P etalon is Al2O3, the refractive index n=1.53; when the crystal material of the F-P etalon is YAG, the refractive index n=1.82.

Further, the frequency modulation bandwidth of the broadband tunable laser is greater than twice the initial longitudinal mode interval Δν _0. At this time, the longitudinal mode interval Δν of multiple reflected lights is obtained within one frequency modulation bandwidth, and the temperature of the object to be measured is obtained by calculating the average value. T, in order to improve the test accuracy of the laser temperature measurement device.

Further, the temperature tested by the laser temperature measuring device is higher than 1200°C.

Further, the laser temperature measurement device includes a plurality of temperature detection units, and also includes a first optical switch array and a second optical switch array, so as to realize the temperature measurement of a plurality of objects to be measured; the output of the photoelectric phase-locked loop is The ports are respectively optically connected to the laser input ports of the optical fiber circulators in each temperature detection unit through the first optical switch array, and the signal light output ports of the optical fiber circulators in each temperature detection unit are optically connected to the photodetector through the second optical switch array, The F-P etalon of each temperature detection unit is arranged on the corresponding object to be measured.

The beneficial effects of the present invention are:

1. The present invention proposes a laser temperature measurement device for high-temperature objects, which utilizes the temperature-sensitive characteristics of the F-P etalon to measure the light intensity change period of the reflected light by incident chirp light, thereby obtaining the frequency sweep frequency value corresponding to the cycle time, That is, the size of the longitudinal mode interval, and then the temperature of the object can be obtained, and since the F-P etalon is not coated, the temperature of the high-temperature object can be measured;

2. The present invention realizes the frequency sweep measurement of the longitudinal mode interval by setting the frequency modulation bandwidth of the broadband tunable laser, so as to improve the test accuracy;

3. Preferably, the present invention proposes an optoelectronic phase-locked loop, which realizes the nonlinear correction of the broadband tunable laser through closed-loop control, so as to output chirp light and ensure the measurement accuracy;

4. Preferably, a transmission optical fiber is used to transmit the reflected light, combined with the optical switch technology (multi-channel optical switching), to realize multi-object measurement.

Description of drawings

1 is a schematic structural diagram of a laser temperature measurement device for a high-temperature object provided in Embodiment 1 of the present invention;

Fig. 2 is the structural representation of F-P etalon in the embodiment of the present invention 1;

3 is a schematic diagram of the port structure of the optical fiber circulator in Embodiment 1 of the present invention;

Fig. 4 is the relational diagram of the chirp optical frequency outputted by the optical phase-locked loop in the embodiment 1 of the present invention as a function of time;

Fig. 5 is the reflection spectrogram that F-P etalon sends out in the embodiment of the present invention 1;

Fig. 6 is the relation diagram of longitudinal mode interval Δv and temperature T in the embodiment 1 of the present invention;

7 is a schematic structural diagram of a laser temperature measurement device for a high-temperature object provided in Embodiment 2 of the present invention;

The descriptions of the marks in the accompanying drawings are as follows:

1. Broadband tunable laser; 2. Optical fiber circulator; 3. Transmission fiber; 4. Aspheric mirror; 5. F-P etalon; 6. Photodetector; 7. Signal processing unit; 8. Micro-optical lens; 9-1 1. The first coupler; 9-2. The second coupler; 10. MZ interferometer; 11. Balanced photodetector; 12. Phase detector; 13. Loop filter; 14. Up/down switch control circuit; 15. Integrator; 16. First optical switch array; 17. Second optical switch array.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

This embodiment provides a laser temperature measurement device for a high-temperature object. The structure is shown in FIG. 1 and includes a photoelectric phase-locked loop, a temperature detection unit, a photodetector 6 and a signal processing unit 7; the temperature detection unit sequentially includes The optical fiber circulator 2, the transmission fiber 3, the aspheric mirror 4 and the F-P etalon 5, the F-P etalon 5 is arranged on the object to be measured; the photoelectric phase-locked loop comprises a broadband tunable laser 1 and a micro-optical lens connected end-to-end in sequence 8. First coupler 9-1, MZ interferometer 10, second coupler 9-2, balanced photodetector 11, phase detector 12, loop filter 13, up/down switch control circuit 14 and integrator 15.

The broadband tunable laser 1 outputs frequency-modulated light, which is coupled to the first coupler 9-1 through the micro-optical lens 8, and outputs two beams, one of which is used as the output of the photoelectric phase-locked loop, and the other beam is input to the The input port of the MZ interferometer 10; the output port of the MZ interferometer 10 is optically connected to the input port of the balanced photodetector 11 through the second coupler 9-2, and the output port of the balanced photodetector 11 is electrically connected to the phase detector 12 The phase detector 12 mixes the input signal with the sinusoidal reference frequency signal with the same frequency to obtain a frequency error signal, which is transmitted to the loop filter 13 through the output port of the phase detector 12 to obtain the frequency control signal, Then, through the up/down switch control circuit 14 and the integrator 15 in turn, the triangular wave signal is output, which is fed back to the broadband tunable laser 1 to realize nonlinear correction of the broadband tunable laser 1, so that the photoelectric phase-locked loop outputs chirp light. The relationship between the frequency of the output linear frequency modulated light in this embodiment changes with time as shown in FIG. 4 , and the frequency modulation bandwidth is 60 GHz.

The linear frequency modulated light output by the photoelectric phase-locked loop is transmitted to the laser input port of the optical fiber circulator 2 through its output port; the duplex port of the optical fiber circulator 2 is optically connected to the optical input port of the aspheric mirror 4 through the transmission fiber 3, The light output port of the aspheric mirror 4 is optically connected to the F-P etalon 5 ; the signal light output port of the optical fiber circulator 2 is optically connected to the input end of the photodetector 6 , and the output end of the photodetector 6 is electrically connected to the signal processing unit 7 .

Specifically, the linear frequency modulated light output by the photoelectric phase-locked loop is converged into parallel light by the aspherical mirror 4, and transmitted to the F-P etalon 5, and the F-P etalon 5 emits reflected light (parallel light), which is converged by the aspherical mirror 4 and coupled to the transmission fiber The optical fiber end face of 3 is transmitted back to the duplex port of the optical fiber circulator 2, and then output from the signal light output port to the photodetector 6 and converted into an electrical signal, and processed by the signal processing unit 7 to obtain the temperature change of the object to be measured. .

The broadband tunable laser 1 adopts a DBR (Distributed Bragg Reflection) semiconductor laser chip, which has an independent frequency modulation port, and performs linear frequency modulation by injecting triangular waves.

The frequency change of the photoelectric signal output by the output port of the balanced photodetector 11 reflects the frequency modulation linearity.

The phase detector 12 is a laser frequency error measurement circuit designed based on the frequency mixing principle, and the output frequency error signal is a measure of the phase error between the input signal and the sinusoidal reference frequency signal, which can improve the circuit bandwidth and reduce the circuit delay; The frequency measurement error caused by laser amplitude modulation is reduced by digitization, and the signal quality is improved.

The loop filter 13 is used to filter and shape the frequency error signal, not only to filter out the high frequency waveform, but also to establish the dynamic characteristics of the feedback loop and provide a suitable frequency control signal.

The up/down switch control circuit 14 periodically integrates and resets the integrator 15 under the control of the frequency control signal, and continuously makes the triangular wave signal output after the integration drive the broadband tunable laser 1 until the output signal of the phase-locked loop reaches the maximum value. The frequency and phase are stabilized.

The port structure of the optical fiber circulator 2 is shown in Figure 3, including a laser input port, a duplex port and a signal light output port, with good isolation, so that the input optical signal and the reflected signal light do not crosstalk , and the reflected light is received and output.

The transmission optical fiber 3 is used to transmit light, and can flexibly change the distance between the object to be measured and the measuring device.

The F-P etalon 5 is a block crystal, the structure is shown in Figure 2, it is a YAG material, the linear frequency modulated light is injected from the front reflection surface, and is reflected by the front reflection surface and the rear reflection surface and then exits; the F-P etalon 5 emits The ratio of the reflected light intensity to the received incident light intensity is:

Among them, I _r is the reflected light intensity; I _i is the incident light intensity; R ₁ and R ₂ are the reflectances of the front and rear reflection surfaces of the FP etalon 5, respectively; The relation of the optical frequency ν is:

Among them, n=1.82, which is the refractive index of YAG of the FP etalon 5; L is the distance between the front reflection surface and the rear reflection surface of the FP etalon 5; c is the speed of light propagation in vacuum (3×10 ⁸ m/s);

The longitudinal mode interval of the reflected light (that is, the frequency difference between two adjacent strongest light intensities) Δv is:

Actually, the distance L and the refractive index n between the front reflection surface and the rear reflection surface of the FP etalon 5 can be set to adjust the initial longitudinal mode interval Δν ₀ of the reflected light of the FP etalon 5 before temperature measurement. The initial longitudinal mode interval Δv ₀ of the reflected light of the FP etalon 5 before temperature measurement is set to 10 GHz, and the free spectrum of the reflected light is shown in Figure 5 .

Since n and L in formula (3) are related to temperature T, derivation of both sides of formula (3) can be obtained:

Therefore, the relationship between the longitudinal mode interval Δv and the temperature T is obtained as:

Among them, T ₀ is room temperature, take T ₀ =27℃; β=7.3×10 ^-6 ℃ ^-1 , is the thermo-optic coefficient of YAG of FP etalon 5; α=7.8×10 ^-6 ℃ ^-1 , is FP The linear thermal expansion coefficient of the YAG of the etalon 5; α and β are both constants; the relationship between the longitudinal mode interval Δν and the temperature T in this embodiment is shown in FIG. 6 , which is basically a linear relationship. In the case of high temperature, the relationship between the longitudinal mode interval Δν and the temperature T needs to be further calibrated according to the working environment.

The reflected light emitted by the F-P etalon 5 is sequentially transmitted to the photodetector 6 through the aspheric mirror 4, the transmission fiber 3, and the fiber circulator 2, and is converted into an electrical signal, and then sent to the signal processing unit 7; the signal processing unit 7 passes through the oscilloscope. Collect the time of the two adjacent strongest light intensities of the reflected light, and obtain the frequency sweep frequency corresponding to the two adjacent strongest light intensities of the reflected light according to the relationship between the frequency of the chirp light and time as shown in Figure 4. The frequency difference is the longitudinal mode interval Δν; the 6 longitudinal mode intervals Δν of the reflected light of the F-P etalon 5 in the 60GHz frequency modulation bandwidth are measured and obtained, and the temperature value corresponding to each longitudinal mode interval Δν is obtained by calculating the average value. the temperature of the object.

Example 2

This embodiment provides a laser temperature measurement device for a high-temperature object. The structure is shown in FIG. 7, including a photoelectric phase-locked loop, three temperature detection units, a photodetector 6, a signal processing unit 7, and a first optical switching array. 16 and a second optical switch array 17.

The temperature detection unit sequentially includes an optical fiber circulator 2, a transmission optical fiber 3, an aspheric mirror 4, and an F-P etalon 5. The F-P etalon 5 is arranged on the corresponding object to be measured. The working principle of the temperature detection unit is the same as that of Embodiment 1.

The optoelectronic phase-locked loop includes a broadband tunable laser 1, a micro-optical lens 8, a first coupler 9-1, an MZ interferometer 10, a second coupler 9-2, a balanced photodetector 11, The phase detector 12 , the loop filter 13 , the up/down switch control circuit 14 and the integrator 15 , and the working principle of the photoelectric phase-locked loop is the same as that of the first embodiment.

The output ports of the photoelectric phase-locked loop are respectively optically connected to the laser input ports of the optical fiber circulators 2 in each temperature detection unit through the first optical switching array 16, and the signal light output ports of the optical fiber circulators 2 in each temperature detection unit are connected to each other through the optical fiber circulator. The second optical switch array 17 is optically connected to the photodetector 6 , which in turn is connected to the signal processing unit 7 . By controlling the first optical switch array 16 and the second optical switch array 17 to select the temperature measurement of the corresponding object to be measured, the temperature measurement of multiple objects to be measured is realized.

The above embodiment is only an example of the measurement of a high-temperature object proposed by the present invention, and its internal optical path and circuit structure are not used to limit the present invention, but only to help understand the principle of the present invention, and the protection scope of the present invention is not limited to the above-mentioned configurations and embodiments. , those skilled in the art can make other various specific deformations and combinations without departing from the essence of the present invention according to the disclosed technology, but still fall within the protection scope of the present invention.

Claims (8)

1. a laser temperature measuring device for a high-temperature object, characterized in that it comprises a photoelectric phase-locked loop, a temperature detection unit, a photodetector and a signal processing unit; the temperature detection unit comprises a fiber circulator, a transmission fiber, an aspheric mirror and the F-P etalon set on the object to be measured; The photoelectric phase-locked loop is used to output linear frequency modulated light, and its output port is optically connected to the laser input port of the fiber circulator; The optical output port of the optical fiber circulator is optically connected to the F-P etalon; the signal light output port of the optical fiber circulator is optically connected to the input end of the photodetector, and the output end of the photodetector is electrically connected to the signal processing unit. 2. The laser temperature measuring device of a high-temperature object according to claim 1, wherein the photoelectric phase-locked loop comprises a broadband tunable laser, a micro-optical lens, a first coupler, an MZ interferometer, which are sequentially connected end to end. a second coupler, a balanced photodetector, a phase detector, a loop filter, an up/down switch control circuit and an integrator; The broadband tunable laser outputs frequency-modulated light, which is coupled to the first coupler through a micro-optical lens, and outputs two beams, one of which is used as the output of the photoelectric phase-locked loop, and the other beam is input to the input of the MZ interferometer. port; the output port of the MZ interferometer is optically connected to the input port of the balanced photodetector through the second coupler, and the output port of the balanced photodetector is electrically connected to the input port of the phase detector; the phase detector combines the input signal with the sine The reference frequency signal is mixed to obtain the frequency error signal, which is transmitted to the loop filter through the output port of the phase detector to obtain the frequency control signal, and then passes through the up/down switch control circuit and the integrator in turn to output the triangular wave signal, which is fed back to Broadband Tunable Lasers. 3 . The laser temperature measuring device for a high-temperature object according to claim 1 , wherein the crystal material of the F-P etalon is Al2O3 or YAG. 4 . 4. The laser temperature measuring device of high temperature object according to claim 1, is characterized in that, the ratio of the reflected light intensity I _r of the FP etalon to the incident light intensity I _i is:

Among them, R ₁ and R ₂ are the reflectances of the front and rear reflection surfaces of the FP etalon, respectively; δ is the round-trip phase delay, and the relationship with the incident light frequency ν is:

Among them, n is the refractive index of the crystal material of the F-P etalon; L is the distance between the front and rear reflection surfaces of the F-P etalon; c is the speed of light propagating in vacuum; The longitudinal mode interval Δν of the reflected light is obtained as:

Taking the derivation of the temperature on both sides of formula (3), we can get:

Then the relationship between the longitudinal mode interval Δν and the temperature T is obtained as:

Among them, T ₀ is room temperature; β is the thermo-optic coefficient of the FP etalon crystal material; α is the linear thermal expansion coefficient of the FP etalon crystal material; α and β are both constants; Δν ₀ is the initial longitudinal mode interval of the reflected light; The signal processing unit obtains the frequency sweep frequency value corresponding to the two adjacent strongest light intensities of the reflected light according to the relationship between the frequency and time of the chirp light by collecting the time of the two adjacent strongest light intensities of the reflected light. The difference is the longitudinal mode interval Δν, so that the temperature T of the measured object can be calculated. 5 . The laser temperature measuring device for a high-temperature object according to claim 4 , wherein the initial longitudinal mode interval Δν ₀ is set to be not lower than 5 GHz. 6 . 6 . The laser temperature measuring device for a high-temperature object according to claim 4 , wherein the frequency modulation bandwidth of the broadband tunable laser is greater than twice the initial longitudinal mode interval Δν ₀ , and multiple reflections are obtained within one frequency modulation bandwidth. 7 . The longitudinal mode interval of light is Δν, and the temperature T of the object to be measured is obtained by calculating the average value. 7 . The laser temperature measuring device for a high-temperature object according to claim 1 , wherein the temperature tested by the laser temperature measuring device is higher than 1200° C. 8 . 8. The laser temperature measuring device for a high-temperature object according to claim 1, characterized in that it comprises a plurality of temperature detection units, a first optical switch array and a second optical switch array, so as to realize the measurement of a plurality of objects to be measured. temperature; the output ports of the photoelectric phase-locked loop are respectively optically connected to the laser input ports of the optical fiber circulators in each temperature detection unit through the first optical switch array, and the signal light output ports of each optical fiber circulator are connected through the second optical switch array. The light is connected to the photodetector, and each F-P etalon is set on the corresponding object to be measured.

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