CN113176032B - Pressure measurement device and method based on orthogonal phase rapid demodulation and intensity compensation - Google Patents
Pressure measurement device and method based on orthogonal phase rapid demodulation and intensity compensation Download PDFInfo
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- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
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Abstract
The invention discloses a pressure measuring device and method based on orthogonal phase rapid demodulation and intensity compensation, which comprises a wide spectrum light source (1), an optical fiber circulator (2), a Fabry-Perot (F-P) pressure sensor (3), an optical fiber 1 x 3 coupler (4), a low coherence interferometer (5), an intensity compensator (6), a photoelectric detector (13), a data acquisition card (7) and a signal processing unit (8); during measurement, an F-P pressure sensor (3) is used for pressure sensing, an orthogonal phase signal is constructed, the influence of external interference factors on a demodulation result is reduced by using real-time intensity compensation, the phase is quickly calculated in a reverse manner by a four-quadrant arc tangent algorithm subjected to level compensation, and the pressure value is converted into a pressure value in real time by calibration-fitting. Compared with the prior art, the invention can demodulate the signal of the F-P pressure sensor (3) with a plurality of cavities, greatly reduce the influence of signal intensity fluctuation on the demodulation result and obviously improve the stability and the accuracy of the demodulation system.
Description
Technical Field
The invention relates to an optical non-contact pressure real-time measuring device, in particular to a pressure real-time measuring device and a pressure real-time measuring method based on orthogonal phase rapid demodulation and intensity compensation.
Background
Real-time pressure measurement is one of the necessary means to detect the operation of the device, and is challenging in pressure measurement for aircraft engines or shock waves. Due to their small size, light weight, high sensitivity, and electromagnetic interference resistance, the F-P sensor is considered to be one of the potential sensors for pressure detection under harsh conditions. While for signals that require real-time measurements (e.g., pressure signals), fast demodulation of the F-P sensor is critical.
The existing fast demodulation method comprises the following steps: (1) an intensity demodulation method, which realizes fast demodulation of the F-P sensor, but the demodulation result is influenced by the selection of a linear working interval and a Q point, which severely limits the working range and stability of a demodulation system; on the other hand, it is difficult to keep the sensor accurately in the linear range and the light intensity is easily disturbed by other factors. (2) The phase demodulation method is not limited by the working point and has high sensitivity. (3) The multi-wavelength phase demodulation method, which is only applicable to single-cavity F-P sensors, cannot eliminate the influence of multiple cavities on the demodulation, such as F-P sensors based on micro-electro-mechanical systems (MEMS) technology. (4) And (3) a spectral analysis method, which uses a spectrum analyzer (OSA) to analyze the reflection spectrum of the F-P sensor and obtains the corresponding relation between the cavity length and the pressure through subsequent data processing. However, for real-time measurement of pressure, the scan frequency of the OSA must be high and fast demodulation is difficult to achieve.
The current quadrature phase demodulation device is generally affected by the signal intensity caused by the factors such as the power fluctuation of the light source, the change of the optical path loss or the change of the polarization state. Since the quadrature phase demodulation extracts the phase based on the variation of the signal strength, the strength interference has an influence on the accuracy of the demodulation result, which greatly limits the practical application of the quadrature phase demodulation apparatus. In addition, it is necessary to compensate the signal intensity of the quadrature phase demodulating apparatus in real time, considering that the diaphragm of the F-P sensor is bent when it is subjected to a signal such as a pressure, or that the entire signal is changed due to a misalignment between the geometric centers of the optical fiber core and the sensor diaphragm caused by manufacturing and processing.
Disclosure of Invention
Based on the prior art, the invention provides a pressure measuring device and a pressure measuring method based on orthogonal phase rapid demodulation and intensity compensation, and the pressure (gas pressure) is measured in real time by utilizing the rapid demodulation of an F-P pressure sensor.
The invention relates to a pressure real-time measuring device based on orthogonal phase rapid demodulation and intensity compensation, which sequentially comprises a wide-spectrum light source 1, an optical fiber circulator 2, an F-P pressure sensor 3, an optical fiber 1 multiplied by 3 coupler 4, a low coherence interferometer 5, an intensity compensator 6, a data acquisition card 7, a signal processing unit 8, an optical fiber collimator, a polarizer, a birefringent crystal block, an analyzer and a photoelectric detector from the input end to the output end; the low coherence interferometer 5 specifically comprises two optical paths formed by sequentially connecting an optical fiber collimator, a polarizer, a birefringent crystal block, an analyzer and a photoelectric detector; the intensity compensator 6 specifically comprises a third fiber collimator 93, a polarizer 103, and a third photodetector 133; wherein:
light emitted by the wide-spectrum light source 1 enters the F-P pressure sensor 3 through the optical fiber circulator 2, and Fabry-Perot interference occurs in the F-P pressure sensor 3, so that the light is modulated by external pressure to be measured; the reflected interference light enters the optical fiber 1 × 3 coupler 4 through the optical fiber circulator 2, and is split by the optical fiber 1 × 3 coupler 4, wherein two split light beams of the optical fiber 1 × 3 coupler 4 enter the low coherence interferometer 5, and the other split light beam enters the intensity compensator 6 as a compensation light path;
in the low coherence interferometer 5, the first optical fiber collimator 91 and the second optical fiber collimator 92 collimate the two beams of light split by the optical fiber 1 × 3 coupler 4 and convert the two beams of light into two paths of space light; the two paths of spatial light respectively sequentially pass through a first polarizer 101, a second polarizer 102, a first birefringent crystal block 111, a second birefringent crystal block 112, a first polarization analyzer 121 and a second polarization analyzer 122, the polarization directions of which are 45 degrees to the optical axis of the birefringent crystal, and finally enter a first photoelectric detector 131 and a second photoelectric detector 132, the first photoelectric detector 131 and the second photoelectric detector 132 convert the two paths of spatial light into electric signals, and the two paths of spatial light have an orthogonal relation;
in the intensity compensator 6, the third fiber collimator 93 collimates the light from the fiber 1 × 3 coupler 4 and converts the light into spatial light. The spatial light passes through the third polarizer 103 and is incident on the third photodetector 133 as intensity compensation light, and is converted into an electric signal. The data acquisition card 7 performs analog-to-digital conversion on the electrical signals from the third photodetectors 133 of the low coherence interferometer 5 and the intensity compensator 6 according to a set sampling frequency, and finally, the signal processing unit 8 processes the signal data sampled by the data acquisition card 7, extracts the phase value and the real-time compensation coefficient of the F-P pressure sensor 3 from the signal data, and determines the pressure information to be measured according to the relationship among the phase, the cavity length and the pressure.
The invention discloses a pressure real-time measuring method based on orthogonal phase rapid demodulation and intensity compensation, which comprises the following steps:
first, light emitted from a broad spectrum light source 1 is introduced into an F-P pressure sensor 3 by a fiber circulator 2, and interference light reflected by the F-P pressure sensor 3 is led out into a fiber 1 × 3 coupler 4. Dividing light returned by the F-P pressure sensor 3 into three parts by using an optical fiber 1 x 3 coupler 4, respectively introducing two parts of light into a low coherence interferometer 5, and introducing the other part of light into an intensity compensator 6 as a compensation light path;
then, in the low coherence interferometer 5, two paths of light split by the optical fiber 1 × 3 coupler 4 are collimated by using an optical fiber collimator and converted into space light; the polarizer polarizes light emitted by the optical fiber collimator, and converts the space light into linearly polarized space light; two paths of linearly polarized light polarized by the polarizer are incident to the birefringent crystal block; the birefringent crystal block regenerates the linearly polarized light generated by the polarizer into two orthogonal linearly polarized lights, and due to a birefringent effect, an optical path difference is generated between the ordinary light (o light) and the extraordinary light (e light), wherein the optical path difference between the o light and the e light in the birefringent crystal block is matched with the optical path difference generated by the F-P pressure sensor 3, so that low-coherence interference is generated; meanwhile, because the two paths of birefringent crystal blocks have different thicknesses, the two paths of signals form an orthogonal relation according to a low coherence interference principle; projecting the two linearly polarized light beams passing through the birefringent crystal block by using an analyzer to generate interference; finally, the photoelectric detector is used for converting the optical signal passing through the analyzer into an electric signal through a photoelectric conversion effect;
polarizing light emitted by the optical fiber collimator by using a polarizer in the intensity compensator 6 to serve as intensity compensation light, wherein the polarizing direction of the intensity compensation light is consistent with that of the low coherence interferometer 5; converting the optical signal of the intensity compensation light passing through the polarizer into an electric signal by utilizing a photoelectric detector in the intensity compensator 6 through a photoelectric effect;
finally, the data acquisition card 7 is used for carrying out analog-to-digital conversion on the electric signals output by the photoelectric detectors in the low coherence interferometer 5 and the intensity compensator 6 according to the set sampling frequency; the cavity length information and the real-time compensation coefficient of the F-P pressure sensor 3 are quickly extracted from the signals of the data acquisition card 7 based on the signal processing unit 8, and the detected pressure information is obtained in real time through the corresponding relation among the phase, the cavity length and the pressure, so that the real-time measurement of the pressure is realized.
Compared with the prior art, the method is superior to the prior method in the aspects of demodulating the signal of the F-P pressure sensor (3) with a plurality of cavities, reducing the influence of signal intensity fluctuation on the demodulation result, and the stability and the accuracy of the demodulation system.
Drawings
FIG. 1 is a schematic diagram of a pressure measurement device based on quadrature phase fast demodulation and intensity compensation;
FIG. 2 is a graph comparing an intensity compensated signal to an uncompensated signal;
FIG. 3 is a calibration fitting curve graph of pressure-phase within a measurement range of 0-3 MPa;
FIG. 4 is a graph showing the results of pressure measurement of 0 to 3 MPa.
Reference numerals:
1. the optical fiber interferometer comprises a wide spectrum (ASE or SLED) light source, a 2 optical fiber circulator, a 3 Fabry-Perot (F-P) pressure sensor, a 4 optical fiber 1 x 3 coupler, a 5 low coherence interferometer, a 6 intensity compensator, a 7 data acquisition card, a 8 signal processing unit, 91, 92, 93, first to third optical fiber collimators, 101, 102, 103, first to third polarizers, 111, 112, first and second birefringent crystal blocks, 121, 122, first and second analyzers, 131, 132 and first to third photodetectors.
Detailed Description
The wide spectrum light source 1 is an SLED light source or ASE light source which takes 1550nm as the center wavelength and has the spectrum width of 70-80 nm. Embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. The description of the embodiments is merely exemplary in nature and is in no way intended to limit the invention.
Fig. 1 is a schematic diagram of a pressure real-time measuring device based on quadrature phase fast demodulation and intensity compensation. The device includes: the system comprises a wide spectrum (ASE or SLED) light source 1, an optical fiber circulator 2, a Fabry-Perot (F-P) pressure sensor 3, an optical fiber 1 multiplied by 3 coupler 4, a low coherence interferometer 5, an intensity compensator 6, a data acquisition card 7, a signal processing unit 8, an optical fiber collimator, a polarizer, a birefringent crystal block, an analyzer and a photoelectric detector. The low coherence interferometer 5 specifically comprises two optical paths formed by sequentially connecting an optical fiber collimator, a polarizer, a birefringent crystal block, an analyzer and a photoelectric detector; the intensity compensator 6 specifically includes a third fiber collimator 93, a polarizer 103, and a third photodetector 133.
Light emitted by the wide-spectrum light source 1 enters the F-P pressure sensor 3 through the optical fiber circulator 2, and Fabry-Perot interference occurs in the F-P pressure sensor 3, so that the light is modulated by external pressure to be measured; the reflected interference light enters the optical fiber 1 × 3 coupler 4 through the optical fiber circulator 2, and is split by the optical fiber 1 × 3 coupler 4, wherein two split light beams of the optical fiber 1 × 3 coupler 4 enter the low coherence interferometer 5, and the other split light beam enters the intensity compensator 6 as a compensation light path.
In the low coherence interferometer 5, the first and second optical fiber collimators 91 and 92 collimate the two beams of light split by the optical fiber 1 × 3 coupler 4 and convert the two beams of light into two paths of spatial light; the two paths of spatial light respectively pass through a first polarizer 101, a second polarizer 102, a first birefringent crystal block 111, a second birefringent crystal block 112, a first analyzer 121, a second analyzer 122, a polarization direction of which is perpendicular to the polarizers, of which the polarization direction is 45 degrees to the optical axis in sequence, and finally enter a first photoelectric detector 131, a second photoelectric detector 132, and the first photoelectric detector 131, the second photoelectric detector 132 convert the two paths of spatial light into electric signals. According to the principle of low coherence interference, two paths of space light have an orthogonal relation because the birefringent crystal blocks are respectively provided with specific thicknesses. Wherein, the thicknesses of the first and second birefringent crystal blocks 111 and 112 in the two paths are different. According to the low coherence interference principle, the thicknesses of the first birefringent crystal block (111) and the second birefringent crystal block (112) are set so that the two signals are in orthogonal relation.
In the intensity compensator 6, the third fiber collimator 93 collimates the light from the fiber 1 × 3 coupler 4 and converts the light into spatial light. The spatial light passes through the third polarizer 103 and is incident on the third photodetector 133 as intensity compensation light, and is converted into an electric signal. The data acquisition card 7 performs analog-to-digital conversion on the electrical signals from the third photodetectors 133 of the low coherence interferometer 5 and the intensity compensator 6 according to a set sampling frequency, and finally, the signal processing unit 8 processes the signal data sampled by the data acquisition card 7, extracts the phase value and the real-time compensation coefficient of the F-P pressure sensor 3 from the signal data, and determines the pressure information to be measured according to the relationship among the phase, the cavity length and the pressure.
The invention relates to a measuring method of a pressure real-time measuring device based on orthogonal phase rapid demodulation and intensity compensation, which comprises the following concrete implementation steps:
first, light emitted from a broad spectrum light source 1 is introduced into an F-P pressure sensor 3 by a fiber circulator 2, and interference light reflected by the F-P pressure sensor 3 is led out into a fiber 1 × 3 coupler 4. Dividing light returned by the F-P pressure sensor 3 into three parts by using an optical fiber 1 x 3 coupler 4, respectively introducing two parts of light into a low coherence interferometer 5, and introducing the other part of light into an intensity compensator 6 as a compensation light path;
then, in the low coherence interferometer 5, two paths of light split by the optical fiber 1 × 3 coupler 4 are collimated by using an optical fiber collimator and converted into space light; the polarizer polarizes light emitted by the optical fiber collimator, and converts the space light into linearly polarized space light; two paths of linearly polarized light polarized by the polarizer are incident to the birefringent crystal block; the birefringent crystal block regenerates the linearly polarized light generated by the polarizer into two orthogonal linearly polarized lights, and due to a birefringent effect, an optical path difference is generated between the ordinary light (o light) and the extraordinary light (e light), wherein the optical path difference between the o light and the e light in the birefringent crystal block is matched with the optical path difference generated by the F-P pressure sensor 3, so that low-coherence interference is generated; meanwhile, because the two paths of birefringent crystal blocks have different thicknesses, the two paths of signals form an orthogonal relation according to a low coherence interference principle; projecting the two linearly polarized light beams passing through the birefringent crystal block by using an analyzer to generate interference; and finally, converting the optical signal passing through the analyzer into an electric signal by using a photoelectric conversion effect by using a photoelectric detector.
Meanwhile, in the intensity compensator 6, the polarizer is used for polarizing the light emitted by the optical fiber collimator to be used as intensity compensation light, and the polarizing direction of the intensity compensation light is consistent with that of the low coherence interferometer 5; the photoelectric detector converts the optical signal of the intensity compensation light passing through the polarizer into an electric signal through a photoelectric effect;
finally, the data acquisition card 7 is used for carrying out analog-to-digital conversion on the electric signals output by the photoelectric detectors in the low coherence interferometer 5 and the intensity compensator 6 according to the set sampling frequency; the signal processing unit 8 based on an embedded system or a computer quickly extracts cavity length information and a real-time compensation coefficient of the F-P pressure sensor 3 from signals of the data acquisition card 7, and obtains measured pressure information in real time through corresponding relations among phases, cavity lengths and pressures, so that real-time measurement of the pressures is realized.
The signal processing unit 8 specifically includes the following steps:
firstly, caching three paths of signals including two paths of orthogonal signals and one path of compensation signals acquired by a data acquisition card 7; taking the stabilized signal of the compensation optical path as a reference value isObtaining real-time variation coefficient alpha of integral light intensity on light path in real timetThe formula is as follows:
wherein, IsTo compensate for the real-time light intensity of the light path, t is time.
According to the principle of low coherence interference, the variation coefficient of the overall light intensity of two paths of orthogonal signals and the variation coefficient alpha of a compensation light pathtThe same is true. Therefore, the light intensity I of two orthogonal signals is divided by the variation coefficient alpha of the compensation light path in real timetRealize two paths of orthogonal signalsReal-time intensity compensation of the signal;
two-path orthogonal signal light intensity I after compensation1comp、I2compThe expression of (a) is as follows:
wherein A is1、A2Respectively, the DC quantities of two orthogonal signals, B1、B2Are respectively the AC coefficients of two paths of orthogonal signals, t is time,
is a phase that varies with time;
from a mathematical representation of the signal, orthogonal signal intensity I1compMaximum value of (1)1comp_max＝A1+B1Intensity of quadrature signal I1compMinimum value of (1)1comp_min＝A1-B1，
Calculated to obtain I1compD.c. quantity A of1The formula is as follows:
A1＝(I1comp_max+I1comp_min)/2
calculated to obtain I1compAc coefficient of (B)1The formula is as follows:
B1＝(I1comp_max-I1comp_min)/2
the same way can obtain A2、B2。
The light intensity I of the orthogonal signal1comp、I2compBy subtracting the DC component A respectively1、A2Then divided by the AC coefficient B1、B2Obtaining two paths of normalized orthogonal signals, wherein the expression is as follows:
the value range of the two orthogonal signals is (-1, 1). Where the two orthogonal signals are respectively about the same variable
I.e. orthogonal to each other.
Calculating the phase inversely according to the four-quadrant arc tangent algorithm
The calculation formula of the four-quadrant arc tangent algorithm is as follows:
the phase has a value range (-pi, pi);
after the grade judgment of the phase, if the result of subtracting the former phase value from the latter phase value is larger than 2 pi-delta (delta is a minimum value), the phase jumps, and the latter phase value is added with a compensation value of 2 pi; and similarly, if the result of subtracting the former phase value from the latter phase value is less than-2 pi + delta, subtracting the 2 pi compensation value from the latter phase value.
The quadrant arc tangent principle after the compensation of the order is expressed as
Where m is the compensation factor (an integer) for the phase. Because the central wavelength of the wide-spectrum light source 1 is known, the relation between the phase and the cavity length of the sensor can be obtained; from the sensor parameters, the relationship between cavity length and pressure can be obtained. Through the phase-cavity length relation and the cavity length-pressure relation, a phase-pressure relation can be directly established, and therefore the pressure signal is measured.
As shown in fig. 2, in order to verify the feasibility of the compensation, two-path signal strength interference which may be encountered in practical applications is compensated and compared with the uncompensated original signal. According to the experimental result of fig. 2, the method can effectively eliminate at least 97% of light intensity fluctuation, and proves that the method can effectively reduce the influence of external interference on the signal intensity, thereby ensuring the stability of the signal intensity.
FIG. 3 is a graph of calibration fitting of pressure-phase within the measurement range of 0-3MPa using the present invention, and it can be seen that the linearity of the method of the present invention is very good and the fitting error is very small within the entire measurement range, especially within the local range.
The pressure of 0-3MPa is measured in real time by using the measuring device and the measuring method of the invention, and the measuring result is shown in figure 4. It can be seen that the measuring device and the measuring method of the invention can accurately recover the real-time change of the pressure to be measured in the whole measuring range.
Claims (4)
1. A pressure real-time measuring device based on orthogonal phase rapid demodulation and intensity compensation is characterized by comprising a wide spectrum light source (1), an optical fiber circulator (2), an F-P pressure sensor (3), an optical fiber 1 x 3 coupler (4), a low coherence interferometer (5), an intensity compensator (6), a data acquisition card (7), a signal processing unit (8), an optical fiber collimator, a polarizer, a birefringent crystal block, an analyzer and a photoelectric detector in sequence from an input end to an output end; the low-coherence interferometer (5) specifically comprises two optical paths formed by sequentially connecting an optical fiber collimator, a polarizer, a birefringent crystal block, an analyzer and a photoelectric detector; the intensity compensator (6) specifically comprises a third optical fiber collimator (93), a polarizer (103) and a third photoelectric detector (133); wherein:
light emitted by the wide-spectrum light source (1) enters the F-P pressure sensor (3) through the optical fiber circulator (2), and Fabry-Perot interference occurs in the F-P pressure sensor (3); the reflected interference light enters the optical fiber 1 x 3 coupler (4) through the optical fiber circulator (2) and is split by the optical fiber 1 x 3 coupler (4), wherein two split light beams of the optical fiber 1 x 3 coupler (4) enter the low coherence interferometer 5, and the other split light beam enters the intensity compensator (6) as a compensation light path;
in the low coherence interferometer (5), a first optical fiber collimator (91) and a second optical fiber collimator (92) collimate two beams of light split by an optical fiber 1 multiplied by 3 coupler (4) and convert the two beams of light into two paths of space light; the two paths of spatial light respectively sequentially pass through a first polarizer (101), a second polarizer (102), a first birefringent crystal block (111), a second birefringent crystal block (112), a first polarization analyzer (121) and a second polarization analyzer (122), the polarization directions of which are perpendicular to the polarizers, and the first polarizer (102), the second polarizer (111), the second birefringent crystal block (112), and the first polarization analyzer (121) and the second polarization analyzer (122) respectively, and are incident to a first photoelectric detector (131) and a second photoelectric detector (132), the first photoelectric detector (131) and the second photoelectric detector (132) convert the two paths of spatial light into electric signals, and the two paths of spatial light have an orthogonal relation;
in the intensity compensator (6), a third fiber collimator (93) collimates the light from the fiber 1 × 3 coupler (4) to convert it into spatial light; the spatial light is used as intensity compensation light after passing through a third polarizer (103), enters a third photoelectric detector (133) and is converted into an electric signal;
the data acquisition card (7) performs analog-to-digital conversion on electric signals from a first photoelectric detector (131), a second photoelectric detector (132) and a third photoelectric detector (133) of the intensity compensator (6) of the low coherence interferometer (5) according to a set sampling frequency, and finally, a signal processing unit (8) processes signal data sampled by the data acquisition card (7), extracts a phase value and a real-time compensation coefficient of the F-P pressure sensor (3) from the signal data, and determines pressure information to be measured according to the relation among the phase, the cavity length and the pressure.
2. The pressure real-time measurement device based on orthogonal phase fast demodulation and intensity compensation as claimed in claim 1, wherein the thickness of the first birefringent crystal block (111) and the second birefringent crystal block (112) are set such that the two signals are orthogonal to each other.
3. A pressure real-time measurement method based on quadrature phase fast demodulation and intensity compensation is characterized by comprising the following steps:
firstly, light emitted by a wide-spectrum light source (1) is introduced into an F-P pressure sensor (3) by using an optical fiber circulator (2), and interference light reflected by the F-P pressure sensor (3) is introduced into an optical fiber 1 x 3 coupler (4); dividing light returned by the F-P pressure sensor (3) into three parts by using an optical fiber 1 x 3 coupler (4), respectively introducing two light parts into a low coherence interferometer (5), and introducing the other light part serving as a compensation light path into an intensity compensator (6);
then, in a low coherence interferometer (5), two paths of light split by the optical fiber 1 multiplied by 3 coupler (4) are collimated by an optical fiber collimator and converted into space light; the polarizer polarizes light emitted by the optical fiber collimator, and converts the space light into linearly polarized space light; two paths of linearly polarized light polarized by the polarizer are incident to the birefringent crystal block; the birefringent crystal block regenerates the linearly polarized light generated by the polarizer into two orthogonal linearly polarized light and generates low coherence interference; meanwhile, because the two paths of birefringent crystal blocks have different thicknesses, the two paths of signals form an orthogonal relation according to a low coherence interference principle; projecting the two linearly polarized light beams passing through the birefringent crystal block by using an analyzer to generate interference; finally, the photoelectric detector is used for converting the optical signal passing through the analyzer into an electric signal through a photoelectric conversion effect;
polarizing light emitted by the optical fiber collimator by using a polarizer in the intensity compensator (6) to serve as intensity compensation light, wherein the polarizing direction of the intensity compensation light is consistent with that of the low coherence interferometer (5); converting the optical signal of the intensity compensation light passing through the polarizer into an electric signal by utilizing a photoelectric detector in the intensity compensator (6) through a photoelectric effect;
finally, the data acquisition card (7) is used for carrying out analog-to-digital conversion on the electric signals output by the photodetectors in the low coherence interferometer (5) and the intensity compensator (6) according to the set sampling frequency; the cavity length information and the real-time compensation coefficient of the F-P pressure sensor (3) are quickly extracted from the signals of the data acquisition card (7) based on the signal processing unit (8), and the measured pressure information is obtained in real time through the corresponding relation among the phase, the cavity length and the pressure, so that the real-time measurement of the pressure is realized.
4. A method for real-time measurement of pressure based on fast quadrature phase demodulation and intensity compensation as claimed in claim 3, wherein the signal processing unit (8) comprises in particular the following processing:
firstly, caching three paths of signals including two paths of orthogonal signals and one path of compensation signals acquired by a data acquisition card (7); taking the stabilized signal of the compensation optical path as a reference value isObtaining real-time variation coefficient alpha of integral light intensity on light path in real timetThe formula is as follows:
wherein, IsT is time to compensate the real-time light intensity of the light path;
dividing the light intensity I of two orthogonal signals by the variation coefficient alpha of the compensation light path in real timetReal-time intensity compensation of two paths of orthogonal signals is realized;
two-path orthogonal signal light intensity I after compensation1comp、I2compThe expression of (a) is as follows:
wherein A is1、A2Respectively, the DC quantities of two orthogonal signals, B1、B2Are respectively the alternating current coefficients of two paths of orthogonal signals,
is a phase that varies with time;
calculating to obtain a first path of orthogonal signal I1compD.c. quantity A of1The formula is as follows:
A1＝(I1comp_max+I1comp_min)/2
calculating to obtain a first path of orthogonal signal I1compAc coefficient of (B)1The formula is as follows:
B1＝(I1comp_max-I1comp_min)/2
in the same way, a second path of orthogonal signal I is obtained2compD.c. quantity A of2The second path of orthogonal signal I2compAc coefficient of (B)2；
The light intensity I of the orthogonal signal1comp、I2compBy subtracting the DC component A respectively1、A2Then divided by the AC coefficient B1、B2Obtaining two paths of normalized orthogonal signals, wherein the expression is as follows:
calculating the phase inversely according to the four-quadrant arc tangent algorithm
The calculation formula is as follows:
through the relation of phase-cavity length and the relation of cavity length-pressure, the relation of phase-pressure can be directly established, and thus the measurement of pressure signals is realized.
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