CN107560780B - Temperature compensation method of optical fiber F-P cavity type pressure sensor - Google Patents
Temperature compensation method of optical fiber F-P cavity type pressure sensor Download PDFInfo
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Abstract
The invention belongs to the technical field of micro-electro-mechanical systems (MEMS) high-temperature pressure sensing, and relates to a temperature compensation method of an optical fiber F-P cavity (Fabry-Perot interferometer) type pressure sensor. The invention aims at the temperature drift causing the measurement error of the optical fiber F-P cavity type pressure sensor, eliminates the temperature factor in the measurement process by utilizing the structure which is not utilized and the signal which exists in the measurement process but is used as the interference processing all the time through the subsequent temperature compensation algorithm, and the temperature compensation method can achieve the purposes of reducing the structural complexity of the sensor to a certain extent and achieving the temperature compensation by using the simplest and most efficient method.
Description
(I) technical field
The invention belongs to the technical field of micro-electro-mechanical systems (MEMS) high-temperature pressure sensing, and relates to a temperature compensation method of an optical fiber F-P cavity (Fabry-Perot interferometer) type pressure sensor.
(II) background of the invention
The output signal of the high-temperature pressure sensor can change along with the change of the temperature of a measured medium (gas or liquid), namely zero temperature drift and sensitivity temperature drift are generated, and the main factors causing pressure measurement errors in a high-temperature environment. Therefore, after the pressure sensor is manufactured, the change of the output signal along with the temperature of the measured medium (gas or liquid) must be measured, and the zero temperature drift and the sensitivity temperature drift are compensated in a proper mode.
The theoretical design temperature of the existing optical fiber F-P cavity type pressure sensor reaches over 1000 ℃, and the temperature difference between the temperature and the room temperature environment is large in actual measurement, so that the sensor has large temperature drift. However, there is no effective temperature compensation method for the use of fiber F-P cavity pressure sensor in different environmental temperatures. Patent 201310606330.0 mentions that the grating is used as a temperature compensation method, however, the wiring difficulty of the sensor itself is too large, and the grating structure on the surface of the optical fiber has poor high temperature resistance, which can theoretically be used as a temperature compensation method, but cannot meet the practical requirement. Patent 201310606168.2 adopts vacuum coating as a temperature compensation method, however, the coating affects the accuracy of the pressure measurement of the sensor, and the thermal expansion coefficient of the coated layer is difficult to match with that of the pressure sensitive diaphragm below under different environmental temperatures, and it is difficult to realize continuous measurement under different environmental temperatures.
Disclosure of the invention
In order to solve the problem that the existing optical fiber F-P cavity type pressure sensor is influenced by temperature, the invention aims to provide a simple and efficient temperature compensation method for the optical fiber F-P cavity type pressure sensor without changing the original structure of the sensor or adding extra sensing parts, so that the optical fiber F-P cavity type pressure sensor can accurately measure pressure in different temperature environments.
The invention provides a temperature compensation method of an optical fiber F-P cavity type pressure sensor, which firstly briefly describes the design structure of the pressure sensor: an optical fiber F-P cavity type pressure sensor is provided with a sensitive diaphragm positioned on a first layer, a blind hole structure positioned on a second layer and a subsequent optical part. The method for measuring the pressure by the sensor is characterized in that a first layer of pressure sensitive membrane is adopted to sense the external pressure, the length of an F-P cavity can be changed after the sensitive membrane is deformed by pressure, and then the correlation coefficient of the variation of the F-P cavity and the pressure value is determined by a rear-end optical demodulation system, so that the purpose of pressure measurement is achieved.
The method of the invention is based on the sensing measurement method of the sensor, adopts the base part of the F-P cavity as a temperature compensation structure, adjusts the thickness parameter of the pressure sensitive diaphragm and the cavity length parameter of the F-P cavity according to the environmental temperature information, and then measures the pressure according to the pressure measurement method, thereby realizing the purpose of temperature compensation.
The technical scheme adopted by the invention is as follows: a temperature compensation method of an optical fiber F-P cavity type pressure sensor is characterized by comprising the following steps:
1) before the high-temperature pressure measurement is started, the output of the pressure sensor is set to zero, and the rear-end optical demodulation system records the phase difference delta of light beams reflected by the upper surface and the lower surface of the F-P cavity and the upper surface and the lower surface of the substrate structure at the lower end of the F-P cavity at the moment0And delta1。
2) The ambient temperature rises to TxThe optical demodulation system at the back end records delta1And changing, and obtaining the thickness of the substrate structure at the lower end of the F-P cavity according to the relation between the phase and the film thickness: h is1And calculating the value of the environment temperature at the moment according to the thickness change and the thermal expansion coefficient of the material forming the F-P cavity of the sensor: t isx. The F-P cavity length is mainly influenced by the thickness change of the sensitive diaphragm and the substrate structure according to the known ambient temperature TxThen the thickness of the sensitive membrane can be calculated as h2', then according to h1′、h2' and the initial F-P cavity length value can be calculated at TxAt ambient temperature, further obtaining the change in cavity length at TxThe cavity length h 'of the F-P cavity under the environment temperature without applying the pressure is the cavity length obtained by considering the change of the environment temperature to the cavity length, the subsequent calculation process is calculated on the basis of h', so that the influence factor of the temperature does not exist in the subsequent calculation process, and only the influence of the pressure change to the F-P cavity length exists, so that the temperature influence factor is eliminated by the temperature compensation method, and the purpose of temperature compensation is achieved.
3) At TxApplying a pressure to the sensitive membrane at a temperature of (a) and recording as: pxThe length of the F-P chamber changes due to the application of pressure, and is noted as h ". The change in the degree of flexure of the sensitive membrane, which can be obtained from h "and h', is noted as: and deltax, calculating the pressure value to be measured by the sensor according to the relation between the flexibility and the applied pressure of the sensitive membrane: px。
Compared with the prior art, the invention has the beneficial effects that: aiming at the temperature drift causing the measurement error of the optical fiber F-P cavity type pressure sensor, the invention skillfully utilizes the structure of the sensor and the signal which really exists but is always taken as interference and filtered in the pressure measurement process, and eliminates the temperature influence factor in the measurement process through a subsequent temperature compensation algorithm.
(IV) description of the drawings:
fig. 1 is a schematic view of the structure of a sensor on which the present invention is based.
FIG. 2 is a flow chart of a method for temperature compensation of a fiber F-P cavity pressure sensor.
The pressure sensor comprises a pressure sensitive membrane 1, a 2-F-P cavity, a 3-substrate material, a 4-F-P cavity upper surface, a 5-F-P cavity lower surface and a 6-substrate lower surface.
(V) specific embodiment:
the invention is described in further detail below with reference to the drawings.
The temperature compensation method of the pressure sensor is based on a temperature compensation algorithm of the pressure sensor, and the structure of the sensor is shown in figure 1.
The calculation method of the invention is as follows:
1) before the temperature compensation starts, the initial phase and the interference spectrum are recorded all over the sensor, taking the phase difference between the F-P cavity surface 4 and the surface 5 as delta0And the F-P cavity surface 5 and the substrate surface 6 have a phase difference of delta1. The calculation formula of the initial phase difference can be obtained by the following formula:
wherein λ is0Is the initial wavelength of the light, n is the refractive index of the medium in the F-P cavity, h is the length of the F-P cavity, and theta is the reflection angle of the light in the F-P cavity. n' is the refractive index of the substrate material medium, h1θ' is the reflection angle of the light in the substrate, which is the thickness of the substrate material.
2) Applying a temperature, placing the sensor at a temperature TxIn the environment of (1), when T takes into account the actual measurement situationxIs an unknown quantity. Firstly, considering the cavity length change of the substrate material, the phase difference delta of the substrate material can be obtained according to the obtained interference spectrum of the substrate material1', taking into account that the thermal expansion of the sensor is mainly verticalThe expansion in the vertical direction can be approximated by no change in the reflection angle of the light, and the thickness of the base material at that time can be obtained according to equation 2 and is denoted as h1'. and the coefficient of thermal expansion of the sensor, i.e., the rate of change of axial strain of the material with temperature αTIs known, then according to
h1′＝h1+α2h1(Tx-T0) ③
(T0At an initial temperature of α2Coefficient of thermal expansion for the base material) to obtain TxThe size of (2). So far, the magnitude of the ambient temperature is known and is denoted as T1。
Also, considering that the thermal expansion of the sensor is primarily vertical, the change in F-P cavity length can be approximated as being caused by thermal expansion of the pressure sensitive diaphragm and the base material2The initial thickness of the sensitive membrane is h2Then, the change in F-P cavity length at this time is recorded as Δ h:
Δh＝(h1α1-h2α2)×(T1-T0) ④
then, at this time, the cavity length h of the F-P cavity is,
h′＝h-Δh ⑤
h 'is the cavity length obtained by considering the change of the environment temperature to the cavity length, and the subsequent calculation process is carried out on the basis of h', so that the subsequent calculation process has no influence factors of the temperature, and only the influence of the pressure change to the F-P cavity length exists, so that the temperature influence factors are eliminated by the temperature compensation method, and the purpose of temperature compensation is achieved.
In particular, the thickness of the pressure-sensitive membrane is then denoted h2′。
Alternatively, the cavity length h' of the F-P cavity at this time may also be based on the interference pattern and the initial phase difference δ obtained at this time0To obtain the phase change amount delta1According to Δ δ1Obtained by the formula 1.
3) A pressure is applied to the sensor and,is denoted by Px. Then, the pressure sensitive diaphragm will generate a deflection change after receiving the pressure, which is recorded as: Δ x. Based on the interference pattern and the initial phase difference delta obtained after applying pressure0To obtain the phase change amount delta2According to Δ δ2The cavity length of the F-P cavity at this time, denoted as h ", is obtained by equation 1. Then, the change in the deflection Δ x ═ h ″ -h' of the pressure sensitive diaphragm can be obtained.
The formula for the deflection of a circular pressure sensitive diaphragm:
wherein E is the Young modulus of the material, mu is the Poisson's ratio of the material, a is the radius of the pressure sensitive membrane, and r is the distance between the measuring point and the center of the membrane. The pressure value P to be measured can be obtained according to the above formulax。
Example (b):
a temperature compensation method for a silicon glass-based F-P cavity pressure sensor. Firstly, the concrete parameters of the silicon glass-based F-P cavity pressure sensor are briefly explained, the length of the F-P cavity is 21 mu m, the thickness of the circular sensitive membrane is 46 mu m, the diameters of the membrane and the F-P cavity are 1300 mu m, and the thickness of the lower layer glass sheet is 500 mu m.
The method comprises the following steps:
the sensor is zeroed and the initial phase difference is recorded. For simple calculation, the initial room temperature is set to 25 ℃, and lambda is selected0Light in the infrared band at a wavelength of 1500 nm. θ is normal incidence, i.e., θ equals 90 ° and cos θ equals 1. If the middle of the F-P cavity is an air medium with a refractive index n of 1 and the refractive index n' of glass of 1.5, the phase difference δ of the F-P cavity layer can be calculated by using the above 1,2 equations0＝56π，δ1＝2000π。
Step two:
and eliminating the related calculation of the temperature factor. Applying a certain temperature, and recording the change of the phase difference of the substrate at the moment by the infrared spectrometer, wherein delta is1When the thickness of the glass substrate was calculated to be 500.12375 μm from equation 2, 2000.5 pi. Since the thickness of the glass before the temperature application was 500 μm, (this type of sensor)The glass used is BF33 glass with thermal expansion coefficient α2＝3.3×10-6K), the amount of change in temperature can be calculated to be 75 ℃, and the ambient temperature at that time can be found to be 100 ℃, the coefficient of thermal expansion of silicon is α at ambient temperature of 100 ℃1＝2.5×10-6The variation of F-P cavity length at this time was 0.115125 μm from equation 4. Then, the cavity length h' of the F-P cavity at this time is 21.115125 μm, and the thickness h of the silicon-based pressure sensitive diaphragm at this time can be calculated by equation 32′＝46.008625μm
Step three:
pressure is applied and the magnitude of the applied pressure is calculated by equation 6. The cavity length of the F-P cavity is changed by 0.1 mu m according to the phase recorded by the infrared spectrometer and the relationship between the phase and the cavity length of the F-P cavity. Then, the young's modulus of silicon is 190GPa, the poisson's ratio is 0.278, and a is 650 μm, and r is 0, and P is 60kPa can be calculated according to equation 6.
While the embodiments of the present patent have been described in detail, the present patent is not limited to the above-described embodiments of the circular silicon glass-based pressure membrane, and various changes can be made without departing from the spirit and scope of the present patent within the knowledge of those skilled in the art.
Claims (5)
1. A temperature compensation method of an optical fiber F-P cavity type pressure sensor is characterized by comprising the following steps:
the method comprises the following steps: before the high-temperature pressure measurement is started, the output of the pressure sensor is set to zero, and the rear-end optical demodulation system records the phase difference delta of light beams reflected by the upper surface and the lower surface of the F-P cavity and the upper surface and the lower surface of the substrate structure at the lower end of the F-P cavity at the moment0And delta1；
Step two: the ambient temperature rises to TxThe optical demodulation system at the back end records delta1And changing, and obtaining the thickness of the substrate structure at the lower end of the F-P cavity according to the relation between the phase and the film thickness: h is1And calculating the value of the environment temperature at the moment according to the thickness change and the thermal expansion coefficient of the material forming the F-P cavity of the sensor: t isx(ii) a According to the achievement ofKnown ambient temperature TxCalculating the thickness h of the sensitive membrane2', then according to h1′、h2' and the initial F-P cavity length value is calculated at TxAt ambient temperature, further obtaining the change in cavity length at TxThe cavity length h' of the F-P cavity at ambient temperature when no pressure is applied;
step three: at TxApplying a pressure to the sensitive membrane at a temperature of (a) and recording as: pxThe length of the F-P cavity is changed due to the application of pressure, the length of the F-P cavity is recorded as h ", the change of the flexibility of the sensitive membrane can be obtained according to h" and h', and the change of the flexibility is recorded as: and deltax, calculating the pressure value to be measured by the sensor according to the relation between the flexibility and the applied pressure of the sensitive membrane: px。
2. The method for compensating temperature of an optical fiber F-P cavity type pressure sensor according to claim 1, wherein the calculation formula of the initial phase difference in the first step is obtained by the following formula:
wherein λ is0Is the initial wavelength of light, n is the refractive index of the medium in the F-P cavity, h is the length of the F-P cavity, theta is the reflection angle of the light in the F-P cavity, n' is the refractive index of the medium of the substrate material, h1θ' is the reflection angle of the light in the substrate, which is the thickness of the substrate material.
3. The method for compensating the temperature of the optical fiber F-P cavity type pressure sensor according to claim 1, wherein the specific process of the second step is as follows:
applying a temperature, placing the sensor at a temperature TxIn the environment of (1), at this time TxFor unknown quantities, first consider the cavity length variation of the substrate material, depending on the resulting substrateThe interference spectrum of the material is obtained by obtaining the phase difference delta of the substrate material1' the thickness of the base material at this time is obtained from the formula 2 and is denoted by h1', based on
h1'＝h1+α1h1(Tx-T0) ③
Calculating to obtain TxSize of (1), wherein T0At an initial temperature of α1Is the coefficient of thermal expansion of the substrate material; so far, the magnitude of the ambient temperature is known and is denoted as T1，
The coefficient of thermal expansion of a known pressure sensitive diaphragm is α2The initial thickness of the sensitive membrane is h2The change in F-P cavity length at this time, is recorded as Δ h:
Δh＝(h1α1-h2α2)×(T1-T0) ④
then, at this time, the cavity length h' of the F-P cavity is,
h′＝h-Δh ⑤
the thickness of the pressure-sensitive membrane at this time is denoted as h2′。
4. The method of temperature compensation for an optical fiber F-P cavity pressure sensor of claim 3, wherein the cavity length h' of the F-P cavity is alternatively based on the interference pattern and the initial phase difference δ obtained at that time0To obtain the phase change amount delta1According to Δ δ1Obtained by the formula 1.
5. The method for compensating the temperature of the optical fiber F-P cavity type pressure sensor according to claim 1, wherein the specific process of the third step is as follows:
applying pressure to the sensor, denoted Px(ii) a The change in deflection of the pressure sensitive diaphragm upon receiving pressure is recorded as: Δ x; based on the interference pattern and the initial phase difference delta obtained after applying pressure0To obtain the phase change amount delta2According to Δ δ2Obtaining the cavity length of the F-P cavity at the moment through a formula 1, and marking the cavity length as h'; deflection change Δ x-h 'of pressure sensitive diaphragm'；
The formula for the deflection of a circular pressure sensitive diaphragm:
wherein E is the Young modulus of the material, mu is the Poisson's ratio of the material, a is the radius of the pressure sensitive membrane, r is the distance between the measuring point and the center of the membrane, and the pressure value P to be measured is obtained according to the formulax。
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| CN2784889Y (en) * | 2004-12-10 | 2006-05-31 | 暨南大学 | Optical fiber Fabry-Perot liquid level sensor |
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| CN2784889Y (en) * | 2004-12-10 | 2006-05-31 | 暨南大学 | Optical fiber Fabry-Perot liquid level sensor |
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