CN116297003A - F-P cavity interference type density sensing device - Google Patents
F-P cavity interference type density sensing device Download PDFInfo
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- CN116297003A CN116297003A CN202310131043.2A CN202310131043A CN116297003A CN 116297003 A CN116297003 A CN 116297003A CN 202310131043 A CN202310131043 A CN 202310131043A CN 116297003 A CN116297003 A CN 116297003A
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- 230000003287 optical effect Effects 0.000 claims abstract description 22
- 239000000523 sample Substances 0.000 claims abstract description 20
- 239000007788 liquid Substances 0.000 claims abstract description 19
- 239000002131 composite material Substances 0.000 claims description 7
- 230000005540 biological transmission Effects 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 17
- 238000000034 method Methods 0.000 abstract description 11
- 230000035945 sensitivity Effects 0.000 abstract description 7
- 230000008859 change Effects 0.000 abstract description 5
- 238000001739 density measurement Methods 0.000 abstract description 5
- 238000001514 detection method Methods 0.000 abstract description 5
- 230000008569 process Effects 0.000 abstract description 2
- 239000013307 optical fiber Substances 0.000 description 18
- 239000013535 sea water Substances 0.000 description 4
- 239000000835 fiber Substances 0.000 description 3
- 230000003068 static effect Effects 0.000 description 3
- 238000005303 weighing Methods 0.000 description 3
- 239000008280 blood Substances 0.000 description 2
- 210000004369 blood Anatomy 0.000 description 2
- 239000000306 component Substances 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000007917 intracranial administration Methods 0.000 description 2
- 238000011545 laboratory measurement Methods 0.000 description 2
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- 238000010586 diagram Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000005305 interferometry Methods 0.000 description 1
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
- G01N9/24—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity by observing the transmission of wave or particle radiation through the material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
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Abstract
The invention belongs to the technical field of density sensing, and relates to an F-P cavity interference type density sensing device, which comprises a main structure including a laser, a circulator, an F-P cavity sensing probe, a photodetector, an electronic control module, a collimator and an operational amplifier, wherein the measuring principle is as follows: when the density of the liquid sample to be measured changes, the refractive index changes caused by the change of the density of the liquid sample to be measured so as to enable the center wavelength of the reflected light to drift, thereby realizing the detection of a density signal and obtaining a density-voltage relation curve; the measuring process is as follows: the optical signal is output to the F-P cavity sensing probe after entering the circulator from the laser, reflected and re-enters the circulator and then is input to the photoelectric detector, converted into an electric signal, processed by the electronic control module, input to the laser controller and output in two paths: one path of input laser carries out feedback control to realize laser frequency locking, and the other path of input laser records and outputs by a data acquisition card to realize density measurement; the device has the advantages of simple structure and high measurement accuracy, sensitivity and signal to noise ratio.
Description
Technical field:
the invention belongs to the technical field of density sensing, and particularly relates to an F-P cavity interference type density sensing device which is based on a laser frequency tracking and locking technology and is used for sensing and measuring density by taking an F-P cavity (Fabry-Perot resonant cavity) as a measuring unit.
The background technology is as follows:
the density measurement mode of the liquid comprises laboratory measurement and on-line measurement. Commercially available densitometers mainly use a static weighing method and a vibrating tube measuring method: the static weighing method is a measuring method for measuring the buoyancy of an object immersed in standard liquid by using an Archimedes principle through a balance, so that the fluid density is obtained, the device of the static weighing measuring system is most widely applied under laboratory conditions, a large number of samples are required to be obtained during measurement, and online measurement cannot be realized; the vibrating tube measuring method is a measuring method for measuring the density of fluid by utilizing the relation between the vibration of an object and the density of the object, is used for laboratory measurement and online measurement, and is free from a sampling system when the online measurement is adopted, but is easy to be interfered by electromagnetic signals in marine measuring environments and geological measuring environments, so that the measuring result is inaccurate.
In recent years, a technical scheme for online measurement of sea water density based on an optical method is proposed: in 2012, marc Le Menn et al in france designed a seawater densitometer based on the optical refraction principle, and calculated the density of the liquid by measuring the refractive angle transformation of light by utilizing the lorentz relationship between the refractive index and the density of the liquid, which is the earliest technical scheme for realizing the measurement of the density of the liquid by using an optical method, however, in a high-pressure environment, the refractive densitometer has poor stability; in 2019, hiroshi Uchida et al in the national metrology institute of japan proposed an ultra-high resolution seawater density sensor based on a spectral interferometry, the measurement resolution and range of density were dependent on a core component, a laser shifter, which is required to have extremely high sensitivity in order to achieve high resolution measurement.
The density measurement method can not meet the requirements of high sensitivity and accurate measurement of the density of the liquid under the conditions of high pressure and on line.
The PDH (quasi-synchronous digital hierarchy) laser frequency locking technology can be applied to a sensing measurement scene with ultra-high sensitivity, and during measurement, firstly, an F-P cavity is locked on a stable frequency reference source, so that the stability of the F-P cavity is realized; then, the laser with the required stable frequency is locked on the F-P cavity, so that the purpose of transmitting the stability of the reference frequency source to the laser frequency stability is realized. Because the PDH laser frequency locking technology is adopted, the response time is faster than that of a frequency stabilization system adopting a scanning transmission cavity mode, and the frequency fluctuation faster than the F-P cavity response time can be measured and restrained.
The F-P cavity interference sensing technology has the advantages of high sensitivity, high accuracy and the like as a sensing technology adopting light waves as an information carrier, and meanwhile, the F-P cavity mirror made of microcrystalline glass material is not easy to deform under high pressure due to the fact that the microcrystalline glass has a low thermal expansion coefficient, has excellent mechanical properties and is stable in structure, so that the F-P cavity sensing technology is widely applied to various detection environments with high sensitivity and high pressure. For example, chinese patent 202110420173.9 discloses a human invasive pressure temperature multi-parameter real-time optical fiber detection system, comprising: the micro-bubble optical fiber F-P pressure sensor is used for detecting the pressure of human blood or intracranial; the demodulator is connected with the micro-bubble optical fiber F-P pressure sensor and is used for receiving the optical signal output by the micro-bubble optical fiber F-P pressure sensor, demodulating the optical signal and converting the optical signal into an electric signal; the upper computer is connected with the demodulator and is used for receiving the electric signal output by the demodulator and displaying the pressure condition of human blood or intracranial; the micro-bubble optical fiber F-P pressure sensor comprises a single-mode optical fiber and a multi-mode optical fiber which are connected with each other, wherein the single-mode optical fiber is connected with the demodulator through an optical fiber jumper wire and is provided with an optical fiber grating FBG; one end of the multimode fiber is connected with a single mode fiber, and the other end of the multimode fiber is provided with a microbubble F-P cavity; the optical fiber structure formed by the single-mode optical fiber and the multimode optical fiber is fixed in the inner tube; the inner tube is fixed in the outer tube; when the microbubble optical fiber F-P pressure sensor is placed in a human body, the cavity length of a microbubble F-P cavity changes due to the influence of pressure, delta P is the pressure difference between the pressure born by the outside of the microbubble optical fiber F-P pressure sensor and the pressure in the microbubble F-P cavity in the relation between the external pressure of the microbubble optical fiber F-P pressure sensor and the cavity length of the microbubble F-P cavity, delta L is the cavity length change quantity of the microbubble F-P cavity, R is the inner diameter of the microbubble F-P cavity, t is the cavity wall thickness of the microbubble F-P cavity, theta is the acute angle clamped between the external pressure direction and the cross section of the microbubble F-P cavity, E is the Young modulus of the multimode optical fiber, and v is the Poisson ratio of the multimode optical fiber; a liquid refractive index in situ sensor disclosed in chinese patent 202110187634.2, comprising: the device is provided with a V-shaped groove prism, and the V-shaped groove is used for accommodating liquid to be tested; the laser device emits laser signals which are refracted through the liquid to be tested in the V-shaped groove; the FP cavity is used for receiving the laser signals after the liquid to be measured in the V-shaped groove is refracted; the light intensity detection device is used for measuring the light intensity of the laser signal emitted by the FP cavity and sending the light intensity to the controller; a controller for calculating the refractive index of the liquid to be measured according to the light intensity; the change of the refractive index of the liquid to be measured can lead to the change of the incident angle of the laser signal which is incident into the F-P cavity from the V-shaped groove, so that the light intensity of the laser signal emitted from the F-P cavity is changed.
Therefore, the F-P cavity interference type density sensing device based on the laser frequency locking technology is developed and designed, and has important significance for measurement under strong electromagnetic interference and deep sea high pressure conditions.
The invention comprises the following steps:
the invention aims to overcome the defects of the prior art, and develops and designs an F-P cavity interference type density sensing device with low cost, sensitive measurement and high precision and signal to noise ratio so as to realize accurate measurement of sea water density.
In order to achieve the above purpose, the main structure of the F-P cavity interferometric density sensing device comprises a circulator which is respectively connected with a laser, an F-P cavity sensing probe and a photoelectric detector, wherein the photoelectric detector is connected with the input end of a laser controller through an electronic control module, and two output ends of the laser controller are connected with the laser and a data acquisition card.
The laser related by the invention is an ultra-narrow linewidth adjustable laser with a center wavelength of 633 nm; the circulator can control the optical signal to transmit along the annular direction and is provided with three ports, wherein the optical signal input from the first port is output only at the second port, and the optical signal input from the second port is output only at the third port; the F-P cavity sensing probe adopts an F-P cavity (Fabry-PerotCavity) and consists of a front reflecting mirror, a rear reflecting mirror and a liquid sample to be tested, wherein the liquid sample is positioned between the two reflecting mirrors; the photodetector is capable of detecting the intensity of the optical signal; the electronic control module consists of a multiplier, a low-pass filter, a PID controller, an adder and a signal generator, and can control modulation, demodulation, mixing, phase discrimination and automatic gain of signals; the voltage signal output by the laser controller can control the laser 1 to output optical signals with different wavelengths; the data acquisition card is capable of recording voltage signals.
When the F-P cavity interference type density sensing device is used, light enters the circulator from the laser and is output to the F-P cavity sensing probe, the light is reflected and returns to the circulator and is received by the photoelectric detector, the photoelectric detector converts an optical signal into an electric signal, the electric signal is transmitted to the electronic control module and is processed into a composite signal, and the composite signal is input to the laser controller and is output in two ways: one path of input laser performs feedback control to realize laser frequency locking; and the other route is recorded and output by the data acquisition card to obtain a density-voltage relation curve, so that the density is obtained.
Compared with the prior art, the main structure of the invention comprises a laser, a circulator, an F-P cavity sensing probe, a light detector, an electronic control module, a collimator and an operational amplifier, wherein the electronic control module is internally provided with a multiplier, a low-pass filter, a PID controller, an adder and a signal generator, and the measuring principle is as follows: when the density of the liquid sample to be measured changes, the refractive index changes caused by the change of the density of the liquid sample to be measured so as to enable the center wavelength of the reflected light to drift, thereby realizing the detection of a density signal and obtaining a density-voltage relation curve; the measuring process is as follows: the optical signal is output to the F-P cavity sensing probe after entering the circulator from the laser, reflected and re-enters the circulator and then is input to the photoelectric detector, converted into an electric signal, processed by the electronic control module, input to the laser controller and output in two paths: one path of input laser carries out feedback control to realize laser frequency locking, and the other path of input laser records and outputs by a data acquisition card to realize density measurement; the density meter has the advantages of simple structure, high measurement accuracy, high sensitivity and high signal to noise ratio, and low cost, and is particularly suitable for density measurement under strong electromagnetic interference and deep sea high pressure conditions.
Description of the drawings:
fig. 1 is a schematic diagram of the main structure of the present invention.
The specific embodiment is as follows:
the invention is further illustrated by the following examples in conjunction with the accompanying drawings.
Example 1:
the main structure of the F-P cavity interference type density sensing device comprises a circulator 2, a laser 1, an F-P cavity sensing probe 3, a photoelectric detector 4, an electronic control module 5, a collimator 6 and an operational amplifier 7; the first port, the second port and the third port of the circulator 2 are respectively connected with the laser 1, the F-P cavity sensing probe 3 and the photoelectric detector 4, the photoelectric detector 4 is connected with the input end of the laser controller 6 through the electronic control module 5, and the two output ends of the laser controller 6 are connected with the laser 1 and the operational amplifier 7; the electronic control module 5 is internally provided with a multiplier 51, a low-pass filter 52, a PID controller 53, an adder 54 and a signal generator 55, wherein the multiplier 51 is respectively connected with the photodetector 4 and the low-pass filter 52, the low-pass filter 52 is connected with the PID controller 53, the PID controller 53 is connected with the adder 54, the adder 54 is connected with the laser controller 6, and the signal generator 55 is respectively connected with the multiplier 51 and the adder 54.
The signal output by the low-pass filter 52 according to the present embodiment is input to the PID controller 53 as an error signal for feedback control by the PID controller 53, and the laser frequency is tracked and locked by adjusting the parameters of the PID controller 53; the PID controller 53 adopts a proportional-integral-derivative control circuit constructed by a basic operational amplifier circuit, and performs feedback control by adjusting resistance and capacitance values in the circuit; the signal generator 55 is capable of generating a sine wave signal having a maximum frequency of 30 MHz.
When the F-P cavity interferometric density sensing device according to this embodiment is used, the laser 1 emits laser light with a center wavelength of 633nm, the laser light is input from the first port of the circulator 2, output from the second port, input to the F-P cavity sensing probe 3, circularly reflected between the two reflectors 31 and 33, reflected optical signals return to the second port and are received by the photodetector 4 connected to the third port, and the photodetector 4 converts the optical signals into electrical signals and transmits the electrical signals to the electronic control module 5: the multiplier 51 mixes the electric signal output by the photodetector 4 with the sine modulation signal output by the signal generator 55 to obtain an error signal, the low-pass filter 52 filters the error signal to filter out the high-frequency component in the error signal, the error signal of the low-frequency component is gain-adjusted by the PID controller 53 to obtain a control signal, the adder 54 adds the control signal from the PID controller 53 and the signal output by the signal generator 55 to a composite signal, and then the composite signal is input to the laser controller 6, one path of the composite signal is input to the laser 1 to control the wavelength of the output optical signal, and the other path of the composite signal is input to the data acquisition card 7 to record the voltage signals output by the laser controller 6 at different moments.
Claims (9)
1. The main structure of the F-P cavity interference type density sensing device comprises a circulator which is respectively connected with a laser, an F-P cavity sensing probe and a photoelectric detector, and is characterized in that the photoelectric detector is connected with the input end of a laser controller through an electronic control module, and the two output ends of the laser controller are connected with the laser and a data acquisition card.
2. An F-P cavity interferometric density sensing device according to claim 1, characterized in that the laser is an ultra narrow linewidth tunable laser with a centre wavelength of 633 nm.
3. An F-P cavity interferometric density sensing device as in claim 1, characterized in that the circulator is capable of controlling the transmission of optical signals in an annular direction, having three ports, the optical signals input from the first port being output only at the second port and the optical signals input from the second port being output only at the third port.
4. An F-P cavity interferometric density sensing device according to claim 1, characterized in that the F-P cavity sensing probe employs an F-P cavity consisting of a front mirror 31 and a back mirror and a liquid sample to be measured between the two mirrors.
5. An F-P cavity interferometric density sensing device according to claim 1, characterized in that the photodetector detects the intensity of the optical signal.
6. The F-P cavity interferometric density sensing device of claim 1, characterized in that the electronic control module consists of a multiplier, a low-pass filter, a PID controller, an adder and a signal generator, and controls modulation, demodulation, mixing, phase demodulation and automatic gain of the signals; the signal output by the low-pass filter is input into a PID controller and used as an error signal for feedback control of the PID controller, and the laser frequency is tracked and locked by adjusting parameters of the PID controller; the PID controller adopts a proportional-integral-derivative control circuit constructed by a basic operational amplifier circuit, and performs feedback control by adjusting resistance and capacitance values in the circuit; the signal generator generates a sine wave signal having a maximum frequency of 30 MHz.
7. An F-P cavity interferometric density sensing device according to claim 1, characterized in that the voltage signal output by the laser controller controls the laser to output optical signals of different wavelengths.
8. An F-P cavity interferometric density sensing device according to claim 1, characterized in that the data acquisition card records the voltage signal.
9. An F-P cavity interferometric density sensing device as claimed in any one of claims 1 to 8, in which, in use, light is output from the laser into the circulator and then to the F-P cavity sensing probe, reflected back to the circulator and then received by the photodetector, the photodetector converts the light signal into an electrical signal and is transmitted to the electronic control module for processing into a composite signal for input to the laser controller and then output in two ways: one path of input laser performs feedback control to realize laser frequency locking; and the other route is recorded and output by a data acquisition card to obtain a density-voltage relation curve, so as to obtain the density.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117824724A (en) * | 2024-03-06 | 2024-04-05 | 广东海洋大学 | Fiber Bragg grating signal demodulation system and method based on interference fringe characteristics |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117824724A (en) * | 2024-03-06 | 2024-04-05 | 广东海洋大学 | Fiber Bragg grating signal demodulation system and method based on interference fringe characteristics |
| CN117824724B (en) * | 2024-03-06 | 2024-05-28 | 广东海洋大学 | Fiber Bragg grating signal demodulation system and method based on interference fringe characteristics |
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