Fiber optic sensor

 

(57) Abstract:

Use: a measure of the micrometric movements for pressure, flow rates of liquid and gaseous media and sensors. Fiber optic sensor micrometric movements provides support and information reflecting surfaces are placed opposite ends respectively of the reference and information of optical fibers optically coupled to each channel with asymmetric shoulders V-shaped fiber optic splitters, symmetrical shoulders each of which is optically connected with the emitters and photodetectors that convert optical signals into electrical that are processed and measured. Reference and information surface in the form of two reflecting surfaces, which are rigidly mounted on a controlled object and oriented in opposite directions parallel to each other, and the ends of the reference and information of the optical fibers are located at the same distance from, respectively, the reference and information surfaces and are oriented oppositely to each other, and the output electrical signal produced by the mutual analog subtraction of the electrical signals of the reference and information channel is pricheski measuring instruments. The invention can be used to control the movements of material objects in the environment.

Known single-channel WATERS of the linear displacement of the reflective type, consisting of an emitter, sensor, information of the optical fiber, coupled with the shoulder optical divider, which can be used in fiber-optic V-shaped divisor (the "divisor"), which has two symmetrical shoulder and one unbalanced [1]

During the measurements, the end information of the light guide is located opposite the surface, the magnitude of the displacement which is measured (reference surface). The divergent luminous flux from the side information of the light guide is emitted in the direction of the information surface and is reflected from it. Part of the reflected light flux P1=P0in(x) through the same end of the returned information in the light and spreading it in the opposite direction, through the divider falls on the photodetector. The magnitude of the electrical signal at the output of the photodetector is equal to:

Uo=qk2kcknF0(x) (1)

where q is the transformation ratio of the luminous flux into an electrical signal; k2times the passage of luminous flux in forward and reverse (when reflected) directions; - reflectance of the test surface; kwithand Knthe loss coefficients in symmetric shoulders divider; hin(x) the input efficiency of the reflected light flux through the end information of the fiber, defined as the ratio of the magnitude of the light flux coming through the end of the information light guide P1the value of the luminous flux radiated from the end face of P0:

(x)=P1/P0, 0< 1 (2)

the dimensionless function that depends only on the distance x of the end face of the fiber to the surface. The coefficients q, k, and P0in [2] does not depend on the magnitude of the displacement x and define a constant amplitude output signal Uo,oin equation (1) so that

Uo=Uo,0(x).

If we know the initial distance x0between the butt of the information light guide and the testing surface and the explicit form of the function (x) is the known initial value of the output signal, which is then measured output signal: Uo(x0)=Uo,0(x0). Any linear displacement of the test surface relative to the end face on the magnitude of x will lead to a change of the output signal by the value of U, which can be represented in the form of what the situations, appearing in the elements of the optical path (the optical fibers, splitters) under the influence of the changing external environment parameters (such as pressure, temperature, mechanical action), their dependence on the reflection properties of the surface, and the nonlinear dependence of the output signal from the magnitude of the displacement of the test surface.

The effect of changing parameters of the environment can be significantly reduced by introducing a scheme of measurements of the second (reference) channel [2] includes in the General case, the reference fiber, a fixed reference surface, emitter and photodetector. The distance between the end of the reference fiber and the supporting surface is fixed in the measurement process. Components of the signals in the reference and information channels, caused by external impacts, proportional. The impact of external influences on the measurement results can then be eliminated by comparing the values of the reference and information signals.

For a fixed position of the support surface relative to the end of the reference optical fiber, the input efficiency of the reflected beam with constant accurate to fluctuations due to external influences, so constant € of linear displacement information of the surface. In addition, in this scheme there is dependence of the output signal from the reflective properties of the surface.

The closest analogue to the invention by the technical nature of a fiber optic sensor, containing the first reflecting surface, the first and second optic fibers, the first fiber optic splitter, asymmetrical shoulder which is associated with the butt-end of the first fiber-optic waveguides, a first emitter and a photodetector, optically coupled with symmetrical shoulders fiber optic splitter, modulator, the processing unit and the signal change [3] an Output signal of the nonlinear depending on the magnitude of the displacement of the controlled object, get in this circuit by the analog signal processing of the first and second fibers.

The disadvantage of this scheme is the effect on the amount of signal reflection properties of different parts of the surface of the test object due to their differences in the absence of special processing (grinding, polishing, etc.). In addition, in this scheme, the signals in the first and second optical fibers change in phase, which does not contribute to reducing the non-linearity of the output signal.

Neli is inu reflective properties of the parts of the surface may reduce the accuracy of measurements and reduce the functionality of this sensor.

The objective of the invention is to increase the measurement accuracy and increased functionality of the sensor.

This technical result is achieved by the fiber optic sensor micrometric movements, containing the first reflecting surface, the first and second optic fibers, the first fiber optic splitter, asymmetrical shoulder which is associated with the butt-end of the first fiber-optic waveguides, the first emitter and the photodetector, optically coupled with symmetrical shoulders fiber optic splitter, modulator, the processing unit and the measuring signals entered a differential amplifier, the second optical divider, a second emitter and a photodetector, optically coupled with symmetrical shoulders of the second fiber optic splitter, asymmetrical shoulder which is optically associated with the second face of the fibre, reflector, mounted with the possibility of anchoring the controlled object and the first reflecting surface on one side and from the second reflecting surface on the side opposite to the first, the surfaces are identical and parallel, the end of the second fiber is the same distance from the respective reflecting surfaces.

Distinctions of the invention are the first and second reflecting surfaces in the form of a double-sided reflector, oppositely oriented reflecting surface which is subjected to the same treatment to align their reflective characteristics, as well as a hard link between them in the measurement process. These differences result in the fact that when you move the controlled fiber changes of signal values in the first and second optical fibers occur in antiphase, which allows through their mutual subtraction substantially linearize the sensor characteristics. It should be noted that since the first and second channels are identical, the difference between them is conditional, and Fig.1, which presents the scheme of realization of the sensor, the numbering of the positions of the first channel adopted an"odd" channel), and for the second channel-even ("even" channel).

In the circuit of Fig.1 the following notation: 1 a controlled object; 2 reflector; 3,4 ends of the first /3/ and the second /4/ optical fibers 5 and 6, respectively; 7 and 8 optical connectors (OS) asymmetrical shoulder splitters; 9, 10, 11, 12 symmetric shoulders splitters; 13, 14-photodetectors; 15, 16 emitters; 17 differential , 12, an asymmetrical shoulder with the optical connector 8 falls on the end face 4 of the light guide 6. From the end face 4 a divergent luminous flux extends in the direction of the surface 2 and is reflected from it back in the direction of the end face 4. Part of the reflected light flux enters back into the end face 4 and through the light guide 6, a symmetrical shoulder of the coupler with an optical connector 8 and the second symmetrical shoulder 10 of the coupler fall on the photodetector 14. The other part of the reflected flow through symmetric shoulder 12 goes back to the emitter and is lost. Similarly for the odd channel.

The magnitude of the signals at the output of the photodetectors in the even and odd channels, respectively:

< / BR>
where q14and q13the photoelectric conversion coefficients (sensitivity) of the photodetectors in the even and odd channels, respectively; k5, k6, k7, k8, k9, k10, k11, k12losses in the optical fibers 5, 6 and the shoulders 7, 8, 9, 10, 11 and 12 splitters;handnefficiency input of reflected light fluxes through faces 4 and 3, respectively, defined as /2/; P15and P16light streams at the output of the emitters 15 and 16.

By analogy with the single-channel datchik changes of signals at the input of the differential amplifier when the movement of the controlled object by the value of Delta X opposite, you can obtain the expression for odd U(Xhand odd U(Xn) channels, respectively:

< / BR>
The signal at the output of the differential amplifier is equal to the difference of the signals at the outputs of the channels.

In the specific case of fibers were used with stepped profile index core refractive diameter of 50 μm; the aperture of the fiber NA of 0.23. Therefore, with an error of less than 0.1% of nh(x)=n(x)=(x). In Fig.2 presents the dependence of (x) in graphical form, taken from [4] and restated in the case of pairing the mirror surface with the butt-end of the fiber with the above parameters. To determine the nature of the dependence of the magnitude of the output signal Urezthe magnitude of the linear displacement x of the measured surface must be set to a certain initial position of the ends of the optical fibers 3 and 4 (Fig.2) that the proposed device are the same: xn,0= xh,0= x0. Adjusting independently currents pumping emitters, it is possible to receive equal signals on the differential control inputs such that Uh,0=Un,0=U0. Then in the initial position, if x x0the output signal DN in accordance with the expressions (6) and (7) equal to zero C is e DN becomes equal to Urez=U0[(x0)x(x0)(x)3/3+ ...] and in a first approximation, linear with respect to x.

In practice, however, in relations (6) and (7) to improve the precision, it is necessary to take into account terms of higher order. This leads to a linear dependence of the output signal occurs in a limited range of linear motion.

In Fig. 2 shows the calculated graphs of the normalized values of the output signal Urez/U0[(x) for single-channel sensor, curve 1 and for dual channel, curves 2 5] distance between the butt of the left light guide (Fig.2) and the controlled object (x x0+ Dx) for different values of x0calculated by numerical interpolation using the results from [4] Curves 2, 3, 4, 5, built a prototype (corresponding dependencies /1/); 2 x0175 microns; 3 for x0125 μm, 4 for x0100 μm, 5 for x0= 175 microns.

The calculations are performed assuming uniform distribution of radiation on the fiber end faces with stepped profile of the refractive index of /4/. It is evident from Fig. 2 shows that in the region x0100 μm dependence of the output signal depends almost linearly on the magnitude of the move kontroliste constant in this range.

In Fig.3 presents curves of the sensitivity of x for different values of x0in a neighborhood of x0100 μm. The figure shows that in the range x0from 110 to 120 microns relative change of magnitude the sensitivity does not exceed 5%

It should be noted that the maximum value of the normalized output signals, the proposed device is always less than the absolute value of the output signal in a single channel sensor.

In the proposed device can be used fiber optic cables with different parameters depending on the requirements device requirements, but in any case, we need to know the dependence of (x).

Fiber optic sensor micrometric movements, containing the first reflecting surface, the first and second optic fibers, the first fiber optic splitter, asymmetrical shoulder which is associated with the end of the first fiber-optic waveguides, the first emitter and the photodetector, optically coupled with symmetrical shoulders of the first fiber optic splitter, modulator, the processing unit and the measurement signal, characterized in that it introduced a differential amplifier, the second optical divider, the second suc, asimmetrichnoe shoulder which is connected with the second end of the fiber light guide, reflector, mounted with the possibility of anchoring the controlled object and the first reflecting surface on one side and a second reflecting surface on the side opposite the first, the surfaces are identical and parallel, the end of the second fiber-optic waveguides optically coupled with the second reflecting surface, the end faces of optical fibers are located at the same distance from the respective reflecting surfaces.

 

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