CN103017972B - Bragg grating pressure cell and test method based on lever principle - Google Patents

Abstract

The invention discloses a Bragg grating pressure cell and a test method based on lever principle. The Bragg grating pressure cell mainly comprises a flat diaphragm, a shell, two strain transmitting devices, an optical fiber grating and two optical fiber leadout holes, wherein the flat diaphragm is arranged at the upper end of the shell; the two optical fiber leadout holes are formed in the lower end of the shell; the optical fiber grating is led in from one optical leadout hole and is led out from the other optical fiber leadout hole; the flat diaphragm is connected to the optical fiber grating by the strain transmitting devices; the two strain transmitting devices are symmetrically arranged below the flat diaphragm; and the upper surface of the strain transmitting devices are contacted with the flat diaphragm, and the lower surfaces of the strain transmitting devices are contacted with the optical fiber grating. The Bragg grating pressure cell and the test method based on the lever principle have the beneficial effects that the manufacturing technique is simple; the complete external manufacturing can be implemented; the product cost is reduced; the good expansibility is achieved; the measurement with different norms and ranges and different precisions can be realized by changing the arm lengths of the strain transmitting devices; and the high reliability and the good repeatability are achieved.

Description

Based on Bragg grating pressure cell and the method for testing of lever principle

Technical field

The present invention relates to engineering measurer, particularly a kind of for small-range, the highly sensitive Bragg grating pressure cell based on lever principle and method of testing.

Background technology

Unique advantages such as fiber grating is strong with its antijamming capability, electrical insulation capability good, corrosion-resistant, volume is little, loss is little more and more come into one's own.But the pressure sensitivity coefficient of naked grating is only 3pm/Mpa, this can not meet the requirement of the sensitivity that usual pressure is measured.

Patent (CN101206150A) discloses a kind of optical fiber pressure sensor based on membrane deflection, comprising: a support tube, and the lower end of this support tube is the diaphragm for experiencing pressure, and its sidewall has two circular holes; One fiber grating, this fiber grating is installed in support tube, and two circular holes of support tube sidewall are passed at its two ends, for measuring pressure; One end cap, this end cap is arranged on the upper end of support tube, to seal this support tube; One lever, this lever is general, and like a L shape, this lever is parallel to by an axle centre that fiber grating is installed on support tube inside, and one end of this lever contacts with the central point of diaphragm, and the other end of this lever has a projection, and this lever is for transmitting pressure.But in the strain transfer structure of the lever in its sensor construction and spring composition, spring is connected with sensor outer housing inwall, which increases sensor difficulty of processing, also likely increases sensor production cost.Sensor manufacturing process involved in the present invention is simple, can realize complete outside and make, reduce cost of products.

Summary of the invention

The present invention is directed to the problem that naked grating pressure sensitivity coefficient is low, propose a kind of Bragg grating pressure cell based on lever principle and method of testing in conjunction with planar diaphragm and lever construction two kinds of grating enhanced sensitivities.

The scheme that the present invention adopts for achieving the above object is:

Based on the Bragg grating pressure cell of lever principle, mainly comprise flat diaphragm, shell, strain transfer device, fiber grating and optical fiber fairlead; The upper end of described shell is provided with flat diaphragm, and the lower end of shell is provided with two optical fiber fairleads, and described fiber grating enters from an optical fiber fairlead, and go out from another optical fiber fairlead, described flat diaphragm is connected to fiber grating by strain transfer device; Described strain transfer device has two, is symmetricly set in the below of flat diaphragm, contacts above with flat diaphragm, contact below with fiber grating.

A spring is provided with between two described strain transfer devices.

Two described strain transfer devices are two hinged general levers like L-type.

Described strain transfer device is connected with shell by support.

Flat diaphragm and the main function of strain transfer device are the increases realizing fiber grating pressure sensitivity coefficient.The Main Function of optical fiber fairlead is realize the extraction of optical fiber and the networking of pressure cell.

The measuring method of the described Bragg grating pressure cell based on lever principle, is characterized in that, comprise the steps:

Step 1: by fiber grating demodulation device, the variation delta λ of detection fiber raster center wavelength _b..

Step 2: push over Δ λ _bwith fiber grating axial strain ε _λbetween mathematical relation, relational expression is:

Δλ _B＝λ _B(1-P _e)ε _λ

P in formula _efor the valid elastic-optic constants of fiber grating, λ _bfor fiber bragg grating center wavelength.

Step 3: push over its center place strain stress and fiber grating axial strain ε _λbetween mathematical relation be:

${\mathrm{\ϵ}}_{\mathrm{\λ}}=\frac{L1}{L2}\·\frac{\mathrm{\ϵ}}{\cos \mathrm{\θ}}$

θ its center place's strain stress and strain transfer device rotational strain ε in formula ₁between angle, L1 is strain transfer device upper arm lengths, and L2 is arm lengths under strain transfer device.

Step 4: the corresponding relation pushed between its center place strain stress and outside pressure P is:

$\mathrm{\ϵ}={\mathrm{\ϵ}}_t{|}_{r=0}=\frac{3p}{8E{h}^2}(1-{\mathrm{\υ}}^2)(R^2-r^2)=\frac{3p{R}^2(1-{\mathrm{\υ}}^2)}{8E{h}^2}$

In formula: p is ambient pressure suffered by diaphragm, E is the elastic modulus of diaphragm, and U is Poisson ratio, and h is thickness, and R is diaphragm radius, and r is distance its center distance.

Step 5: be according to the mathematical relation expression formula that 1-4 obtains between fiber bragg grating center wavelength variable quantity and outside pressure P:

$\mathrm{\Δ}{\mathrm{\λ}}_B={\mathrm{\λ}}_B(1-P_e)\·\frac{L1}{L2}\·\frac{1}{\cos \mathrm{\θ}}\·\frac{3R^2(1-{\mathrm{\υ}}^2)}{8E{h}^2}\·P=K_P\·P$

K in formula _pfor the pressure sensitivity coefficient of this pressure cell.

Step 6: repeat above-mentioned steps, the real time value of outside pressure P can be obtained.

The invention has the beneficial effects as follows: manufacture craft is simple, complete outside can be realized and make, reduce cost of products; Expansion is good, realizes the measurement of different size range, different accuracy by changing strain transfer device brachium; Reliability is high, reproducible.

Accompanying drawing explanation

Fig. 1 is the cut-open view of this pressure cell;

Fig. 2 is the vertical view of support 3;

Fig. 3 is the principle of work schematic diagram of strain transfer device.

In figure: 1-flat diaphragm, 2-shell, 3-support, 4-strain transfer device, 5-spring, 6-fiber grating, 7-optical fiber fairlead.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in detail:

The present invention mainly comprises flat diaphragm 1, shell 2, strain transfer device 4, fiber grating 6 and optical fiber fairlead 4; The upper end of described shell 2 is provided with flat diaphragm 1, the lower end of shell 1 is provided with two optical fiber fairleads 7, described fiber grating 6 enters from an optical fiber fairlead 7, goes out from another optical fiber fairlead 7, and described flat diaphragm 1 is connected to fiber grating 6 by strain transfer device 4; Described strain transfer device 4 has two, is symmetricly set in the below of flat diaphragm, contacts above with flat diaphragm 1, contacts below with fiber grating 6.A spring 5 is provided with between two strain transfer devices 4.Two strain transfer devices 4 are general like L-type.Strain transfer device 4 is connected with shell 2 by support 3.

The present invention is the strain value ε by flat diaphragm 1, outside pressure P being converted to its center place.And then after being amplified by membrane strains value ε by strain conversion equipment, be converted to the strain stress of fiber grating _λ.The changes delta λ of the centre wavelength of detection fiber grating _b, the size of outside pressure P after suitably calculating, can be drawn.Concrete steps are as follows:

Step 1: by fiber grating demodulation device, the variation delta λ of detection fiber raster center wavelength _b..

Step 2: obtain Δ λ by fiber grating rudimentary knowledge _bwith fiber grating axial strain ε _λbetween mathematical relation be:

Δλ _B＝λ _B(1-P _e)ε _λ

P in formula _efor the valid elastic-optic constants of fiber grating, λ _bfor fiber bragg grating center wavelength.

Step 3: draw its center strain stress and fiber grating axial strain ε by accompanying drawing 3 _λbetween mathematical relation be:

${\mathrm{\ϵ}}_{\mathrm{\λ}}=\frac{L1}{L2}\·\frac{\mathrm{\ϵ}}{\cos \mathrm{\θ}}$

In formula, the implication of parameters is shown in shown in accompanying drawing 3;

Step 4: show that the corresponding relation between its center strain stress and outside pressure P is by components and parts design basis:

$\mathrm{\ϵ}={\mathrm{\ϵ}}_t{|}_{r=0}=\frac{3p}{8E{h}^2}(1-{\mathrm{\υ}}^2)(R^2-r^2)=\frac{3p{R}^2(1-{\mathrm{\υ}}^2)}{8E{h}^2}$

In formula: p is ambient pressure suffered by diaphragm, E is the elastic modulus of diaphragm, and U is Poisson ratio, and h is thickness, and R is diaphragm radius, and r is distance its center distance.

Step 5: the mathematical relation expression formula that arrangement above-mentioned steps 1-4 can obtain between fiber bragg grating center wavelength variable quantity and outside pressure P is:

$\mathrm{\Δ}{\mathrm{\λ}}_B={\mathrm{\λ}}_B(1-P_e)\·\frac{L1}{L2}\·\frac{1}{\cos \mathrm{\θ}}\·\frac{3R^2(1-{\mathrm{\υ}}^2)}{8E{h}^2}\·P=K_P\·P$

K in formula _pfor the pressure sensitivity coefficient of this pressure cell.As can be seen from the above equation, this pressure cell is at the variation delta λ of fiber bragg grating center wavelength _bwith outside pressure P, there is good linear relationship.

Step 6 repeats above-mentioned steps, can obtain the real time value of outside pressure P.

Claims (1)

1., based on the measuring method of the Bragg grating pressure cell of lever principle, described Bragg grating pressure cell, comprises flat diaphragm, shell, strain transfer device, fiber grating and optical fiber fairlead; The upper end of described shell is provided with flat diaphragm, and the lower end of shell is provided with two optical fiber fairleads, and described fiber grating enters from an optical fiber fairlead, and go out from another optical fiber fairlead, described flat diaphragm is connected to fiber grating by strain transfer device; Described strain transfer device has two, is symmetricly set in the below of flat diaphragm, contacts above with flat diaphragm, contact below with fiber grating; Be provided with a spring between two described strain transfer devices, two described strain transfer devices are the lever of two hinged L-types, it is characterized in that, comprise the steps:

Step 1: by fiber grating demodulation device, the variation delta λ of detection fiber raster center wavelength _b.;

Step 2: push over Δ λ _bwith fiber grating axial strain ε _λbetween mathematical relation, relational expression is:

Δλ _B＝λ _B(1-P _e)ε _λ

P in formula _efor the valid elastic-optic constants of fiber grating, λ _bfor fiber bragg grating center wavelength;

Step 3: push over its center place strain stress and fiber grating axial strain ε _λbetween mathematical relation be:

${\mathrm{\ϵ}}_{\mathrm{\λ}}=\frac{L1}{L2}\·\frac{\mathrm{\ϵ}}{\cos \mathrm{\θ}}$

θ its center place's strain stress and strain transfer device rotational strain ε in formula ₁between angle, L1 is strain transfer device upper arm lengths, and L2 is arm lengths under strain transfer device;

Step 4: the corresponding relation pushed between its center place strain stress and outside pressure P is:

$\mathrm{\ϵ}={\mathrm{\ϵ}}_t{|}_{r=0}=\frac{3p}{8{\mathrm{Eh}}^2}(1-{\mathrm{\υ}}^2)(R^2-r^2)=\frac{3p{R}^2(1-{\mathrm{\υ}}^2)}{8{\mathrm{Eh}}^2}$

In formula: p is ambient pressure suffered by diaphragm, E is the elastic modulus of diaphragm, and υ is Poisson ratio, and h is thickness, and R is diaphragm radius, and r is distance its center distance;

Step 5: be according to the mathematical relation expression formula that 1-4 obtains between fiber bragg grating center wavelength variable quantity and outside pressure P:

$\mathrm{\Δ}{\mathrm{\λ}}_B={\mathrm{\λ}}_B(1-P_e)\·\frac{L1}{L2}\·\frac{1}{\cos \mathrm{\θ}}\·\frac{3R^2(1-{\mathrm{\υ}}^2)}{8{\mathrm{Eh}}^2}\·P=K_P\·P$

K in formula _pfor the pressure sensitivity coefficient of this pressure cell;

Step 6: repeat above-mentioned steps, the real time value of outside pressure P can be obtained.