CN108519065A - Differential optical fiber Bragg grating tilt angle sensor and application method thereof - Google Patents

Abstract

The invention discloses a differential optical fiber Bragg grating inclination sensor and its use method, a container, a base, a liquid, a hollow floating ball, a transmission rod, an equal-strength cantilever beam, an optical fiber Bragg grating, and a leading optical fiber; the container is fixedly installed on On the base, the inside of the container is filled with liquid, and the middle position of the top of the container is installed with an equal-strength cantilever beam through screws, and an optical fiber Bragg grating is attached to the equal-strength cantilever beam. The free end is connected with the top end of the transmission rod. The invention is simple in structure and easy to operate, and converts the inclination detection of the measured object into the modulation of the wavelength of the fiber Bragg grating, and the wavelength shift of the fiber Bragg grating has a linear relationship with the inclination angle of the measured object; Corrosion resistance and anti-electromagnetic interference (EMI); without any electrical signal, it is suitable for temperature measurement in high-risk environments such as strong electromagnetic, flammable, and explosive.

Description

A kind of differential optical fiber Bragg grating inclination sensor and its application method

technical field

The invention belongs to the technical field of optoelectronic measurement, in particular to a differential optical fiber Bragg grating inclination sensor and a method for using the same.

Background technique

Angle measurement is an important part of geometric measurement. Inclinometers, also known as inclinometers, inclinometers, levels, and inclinometers, are often used to measure the horizontal angle change of the system. The level has changed from the simple water bubble level in the past to the current electronic level. It is the result of the development of automation and electronic measurement technology. As a detection tool, it has become an indispensable and important measurement tool in bridge erection, railway laying, civil engineering, oil drilling, aviation and navigation, industrial automation, intelligent platform, machining and other fields. Specific applications include high-precision laser instrument leveling, construction machinery equipment leveling, long-distance ranging instruments, high-altitude platform safety protection, pitch angle measurement of directional satellite communication antennas, ship navigation attitude measurement, shield pipe jacking applications, dam detection, Geological equipment tilt monitoring, artillery barrel initial shot angle measurement, radar vehicle platform detection, satellite communication vehicle attitude detection, etc.

In recent years, fiber optic sensors have been widely used in the field of measurement technology due to their advantages of high precision, low cost and strong anti-interference ability. Compared with traditional inclination sensors, optical fiber inclination sensing has many advantages, such as high sensitivity, small size, corrosion resistance, anti-electromagnetic radiation, bendable optical path, and convenient telemetry, etc., especially for strong electromagnetic, flammable, explosive, etc. When measuring the environment, the optical fiber Bragg grating temperature sensor uses optical fiber materials, and optical signals are used in signal transmission and sensing, which realizes on-site non-electrical measurement and provides an intrinsically safe online measurement method.

Under the above background, a differential fiber Bragg grating inclination sensor is designed. The sensor has simple structure, easy operation and strong anti-interference ability, and can be used for inclination measurement in various environments.

Contents of the invention

The technical problem to be solved by the present invention is to provide a differential optical fiber Bragg grating inclination sensor and its use method; it can measure the inclination angle of an object; it is an angle measurement for various application environments.

In order to solve the problems referred to above, the technology and method adopted in the present invention are as follows:

A differential optical fiber Bragg grating inclination sensor, comprising a container, a base, liquid, a hollow floating ball, a transmission rod, an equal-intensity cantilever beam, an optical fiber Bragg grating, and an output optical fiber; the container is fixedly mounted on the base, and the inside of the container Equipped with liquid, the middle position of the top of the container is installed with an equal-strength cantilever beam by screws, and an optical fiber Bragg grating is attached to the equal-strength cantilever beam. The free end of the equal-strength cantilever beam is connected to the top of the transmission rod Cooperate with the connection, the lower end of the transmission rod is connected with a hollow floating ball, the hollow floating ball is suspended on the liquid surface, the optical fiber Bragg grating is provided with a leading optical fiber, and the leading optical fiber passes through the optical fiber outlet arranged on the top of the container Lead out and connect with the external optical cable.

Further, there are two fiber Bragg gratings, and the fiber Bragg gratings are respectively pasted on the upper and lower walls of the equal-strength cantilever beam.

Further, the hollow floating ball is raised and lowered by the liquid level of the liquid inside the container, which drives the transmission rod to rise and fall, so that the cantilever beam of equal strength is deformed.

Further, the specific steps of the method are as follows:

S1. Place the sensor base on the object to be measured. The container and the base are inclined at the same angle as the object to be measured. The liquid in the container is still in a horizontal state. At this time, the hollow floating ball rises and falls with the liquid level, and the transmission rod rises and falls. , convert the buoyancy force into the pressure of the free end of the equal-strength cantilever beam, and then drive the fiber Bragg grating pasted on the upper and lower walls of the equal-strength cantilever beam to stretch and compress, so that according to the analysis of the fiber-optic Bragg grating demodulator, the The central wavelength difference Δλ _B of the fiber Bragg gratings on the upper and lower walls;

S2. According to the relationship between the central wavelength difference Δλ _B of the fiber Bragg grating pasted on the upper and lower walls of the equal-strength cantilever beam and the inclination angle of the object Calculate the inclination angle of the measured object;

In the formula: l is the working length of the equal strength cantilever beam, h is the thickness of the equal strength cantilever beam, B is the width of the fixed end of the equal strength cantilever beam, E is the elastic modulus of the equal strength cantilever beam, S _ε is the fiber Bragg grating Strain sensitivity coefficient, λ _B is the center wavelength of the fiber Bragg grating, ρ is the density of the liquid, g is the gravity coefficient, and s is the cross-sectional area of the transmission rod.

The working principle of the present invention: in the initial state of the sensor, the liquid is in a horizontal state relative to the container, and the cantilever beam of equal strength does not deform. If the sensor base is placed on the object to be measured, the container and the base are at the same inclination angle as the object to be measured. However, according to the physical principle, the liquid in the container is still in a horizontal state. At this time, the hollow floating ball rises and falls with the liquid level, and causes the transmission rod to rise and fall, and converts the buoyancy into the pressure of the free end of the cantilever beam of equal strength, and then drives the sticking on the other side. Strength The fiber Bragg gratings on the upper and lower walls of the cantilever beam are stretched and compressed (the fiber Bragg gratings on the upper and lower walls are stretched and compressed just the opposite), and the differential bonding of the fiber Bragg gratings helps to offset the influence of the ambient temperature. The leading-out optical fiber is drawn out through the container mouth and connected with the external optical cable. Therefore, the detection of the inclination angle of the object is transformed into the modulation of the wavelength of the fiber Bragg grating to realize the measurement of the inclination angle of the object.

Mathematical model analysis of the present invention is as follows:

The formula for calculating the force F at the free end of a cantilever beam with equal strength is:

F=ρgsΔH (1)

In the formula, ρ is the density of the measured liquid 3 in the container 1, g is the gravity coefficient, s is the cross-sectional area of the transmission rod 5, and ΔH is the change in the liquid level of the container.

The strain at each point of the equal-strength cantilever beam 6 is:

ε＝6·F·l/(Bh ² E) (2)

In the formula, l is the working length of the constant-strength cantilever beam 6, h is the thickness of the constant-strength cantilever beam 6, B is the width of the fixed end of the constant-strength cantilever beam 6, and E is the elastic modulus of the constant-strength cantilever beam 6.

Substitute (1) into (2) to get:

The upper surface is subjected to tensile strain ε, while the lower surface is subjected to compressive strain -ε. If the two gratings are in the same temperature field, the strain signal ε can be expressed as:

In the formula, _SE is the strain sensitivity coefficient of the fiber Bragg grating, and λ _B is the initial center wavelength of the fiber Bragg grating.

The central wavelength difference Δλ _B of the fiber Bragg grating 7 pasted on the upper and lower walls of the equal-strength cantilever beam 6 is:

Δλ _B =λ _B (ε,T)-λ _B (-ε,T) (5)

but:

And because the tangent of the inclination angle θ is:

Substitute formula (6) into formula (7):

This gives the angle of inclination:

Equation (9) shows the mathematical relationship between the tilt angle θ of the measured object and the wavelength shift Δλ _B of the fiber Bragg grating. The tilt angle of the measured object can be calculated by measuring the wavelength shift of the fiber Bragg grating. to measure the inclination.

The beneficial effects of the present invention are:

1. The inclination detection of the measured object is transformed into the modulation of the wavelength of the fiber Bragg grating, and the wavelength shift of the fiber Bragg grating has a linear relationship with the inclination angle of the measured object.

2. The fiber Bragg grating used has strong corrosion resistance and anti-electromagnetic interference (EMI).

3. Without any electrical signal, it is suitable for temperature measurement in high-risk environments such as strong electromagnetic, flammable, and explosive.

4. Simple structure and easy operation.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without creative work;

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the partial top view schematic diagram of the inventive medium-strength cantilever beam;

Fig. 3 is a partial side view schematic diagram of the inventive medium-strength cantilever beam;

Each label in the figure: 1 is a container, 2 is a base, 3 is a liquid, 4 is a hollow floating ball, 5 is a transmission rod, 6 is an equal-strength cantilever beam, 7 is an optical fiber Bragg grating, and 8 is an output optical fiber.

Detailed ways

Preferred embodiments of the present invention will be described in detail below in conjunction with accompanying drawings, so that advantages and features of the present invention can be more easily understood by those skilled in the art, so that the protection scope of the present invention is defined more clearly;

As shown in Figures 1-3, the technical solution of the present invention is a differential optical fiber Bragg grating inclination sensor, including a container 1, a base 2, a liquid 3, a hollow floating ball 4, a transmission rod 5, an equal-strength cantilever beam 6, an optical fiber Bragg Grating 7 and exporting optical fiber 8; the container 1 is fixedly installed on the base 2, the liquid 3 is housed inside the container 1, and an equal-strength cantilever beam 6 is installed on the middle position of the top of the container 1 by screws. An optical fiber Bragg grating 7 is visibly arranged on the equal-intensity cantilever beam 6, and the free end of the equal-intensity cantilever beam 6 is connected with the top end of the transmission rod 5, and the lower end of the transmission rod 5 is connected with a hollow floating ball 4, and the hollow floating ball 4 The floating ball 4 is suspended on the surface of the liquid 3 , and the optical fiber Bragg grating 7 is provided with a leading optical fiber 8 , which is led out through an optical fiber outlet arranged on the top of the container 1 and connected with an external optical cable.

Described fiber Bragg grating 7 is provided with two, and described fiber Bragg grating 7 is pasted on the upper and lower walls of equal intensity cantilever beam 6 respectively.

The hollow floating ball 4 rises and falls through the liquid level of the liquid 3 inside the container 1, and drives the transmission rod 5 to rise and fall, so that the cantilever beam 6 of equal strength is deformed.

A kind of using method of differential fiber Bragg grating inclination sensor, the concrete steps of described method are as follows:

S1. Place the sensor base 2 on the object to be measured. The container 1 and the base 2 are inclined at the same angle as the object to be measured. The liquid 3 in the container 1 is still in a horizontal state. At this time, the hollow float 4 rises and falls with the liquid level of the liquid 3. , and make the transmission rod 5 go up and down, transform the buoyancy into the pressure of the free end of the equal-strength cantilever beam 6, and then drive the fiber Bragg grating 7 pasted on the upper and lower walls of the equal-strength cantilever beam 6 to stretch and compress, so that according to the fiber Bragg grating The demodulator analyzes and obtains the center wavelength difference Δλ _B of the fiber Bragg grating 7 pasted on the upper and lower walls of the equal-strength cantilever beam 6;

S2, according to the relationship between the central wavelength difference Δλ _B of the fiber Bragg grating 7 pasted on the upper and lower walls of the equal-strength cantilever beam 6 and the oblique angle of the object Calculate the inclination angle of the measured object;

In the formula: l is the working length of the equal-strength cantilever beam 6, h is the thickness of the equal-strength cantilever beam 6, B is the width of the fixed end of the equal-strength cantilever beam 6, E is the elastic modulus of the equal-strength cantilever beam 6, S _ε is The strain sensitivity coefficient of the fiber Bragg grating 7, λ _B is the central wavelength of the fiber Bragg grating 7, ρ is the density of the liquid 3, g is the gravity coefficient, and s is the cross-sectional area of the transmission rod 5.

Its specific parameters are:

1. The technical parameters of the fiber Bragg grating 7 are: central wavelength λ _B = 1550nm;

2. The size parameters of equal strength cantilever beams are: working length l is 120mm, fixed point width B is 68mm, 45# steel Young’s modulus is E=200GPa, cantilever beam thickness h is 2mm;

3. The parameters of the liquid are: density ρ=10×102, gravity coefficient g=9.8;

4. The cross-sectional area of the transmission rod is s=102×πmm2

5. Configure the experiment according to Figure 1;

6. Obtain the shift value Δλ _B of the center wavelength of the fiber Bragg grating 7 with a fiber grating demodulator;

7. According to formula 8, the response sensitivity of the Bragg wavelength shift Δλ _B of the fiber Bragg grating to the inclination angle of the measured object is:

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, and any change or replacement that is not thought of through creative work should be covered within the scope of protection of the present invention. Therefore, The protection scope of the present invention should be determined by the protection scope defined in the claims.

Claims (4)

1. A differential optical fiber Bragg grating inclination sensor is characterized in that it comprises container (1), base (2), liquid (3), hollow float (4), transmission rod (5), equal strength cantilever beam (6), fiber Bragg grating (7) and lead-out optical fiber (8); Described container (1) is fixedly installed on the base (2), and liquid (3) is housed in described container (1), described container ( 1) An equal-strength cantilever beam (6) is installed on the middle position of the inner top by screws, and an optical fiber Bragg grating (7) is glued on the equal-intensity cantilever beam (6), and the equal-intensity cantilever beam (6) The free end of the transmission rod (5) is matched with the top end of the transmission rod (5), and the lower end of the transmission rod (5) is connected with a hollow floating ball (4), and the hollow floating ball (4) is suspended on the surface of the liquid (3). The optical fiber Bragg grating (7) is provided with a lead-out optical fiber (8), and the lead-out optical fiber (8) is led out through an optical fiber outlet arranged on the top of the container (1) and connected with an external optical cable. 2. a kind of differential optical fiber Bragg grating inclination sensor as claimed in claim 1, is characterized in that: described optical fiber Bragg grating (7) is provided with two, and described optical fiber Bragg grating (7) is respectively pasted on equal intensity The upper and lower walls of the cantilever beam (6). 3. A kind of differential optical fiber Bragg grating inclination sensor as claimed in claim 1, characterized in that: the hollow floating ball (4) moves up and down through the liquid level of the liquid (3) inside the container (1) to drive the transmission rod (5) lifting and lowering, so that the cantilever beam of equal strength (6) is deformed. 4. the using method of a kind of differential fiber Bragg grating inclination sensor as claimed in claim 1, is characterized in that: the concrete steps of described method are as follows: S1. Place the sensor base (2) on the object to be measured. The container (1) and the base (2) are inclined at the same angle as the object to be measured. The liquid (3) in the container (1) is still in a horizontal state. At this time, the hollow floating The ball (4) rises and falls with the liquid level of the liquid (3), and causes the transmission rod (5) to rise and fall, and converts the buoyancy force into the pressure on the free end of the cantilever beam (6) of equal strength, and then drives the cantilever beam (6) of equal strength 6) The fiber Bragg grating (7) on the upper and lower walls is stretched and compressed, so that the center wavelength difference of the fiber Bragg grating (7) pasted on the upper and lower walls of the equal-strength cantilever beam (6) is obtained according to the analysis of the fiber Bragg grating demodulator value Δλ _B ; S2, according to the relationship between the central wavelength difference Δλ _B of the fiber Bragg grating (7) pasted on the upper and lower walls of the equal-strength cantilever beam (6) and the object tilt angle Calculate the inclination angle of the measured object; In the formula: l is the working length of the equal-strength cantilever beam (6), h is the thickness of the equal-strength cantilever beam (6), B is the width of the fixed end of the equal-strength cantilever beam (6), and E is the equal-strength cantilever beam (6) The modulus of elasticity, S _ε is the strain sensitivity coefficient of the fiber Bragg grating (7), λ _B is the center wavelength of the fiber Bragg grating (7), ρ is the density of the liquid (3), g is the gravity coefficient, and s is the transmission rod The cross-sectional area of the rod (5).