JPS62151744A - Measuring instrument for mixing ratio of liquid - Google Patents

Abstract

PURPOSE:To measure the mixing ratio of fluids in real time by flowing two kinds of mixed fluids which differ in refractive index between a projection-side optical fiber and a photodetection-side optical fiber and measuring the power of light photodetected by the photodetection-side optical fiber. CONSTITUTION:A fluid tube 10 is provided with a projection-side optical fiber tube 11 and a photodetection-side optical fiber tube 12 opposite each other. The optical fibers 1 and 2 are provided in the tubes 11 and 12 and two kinds of mixed fluids L which differ in refractive index are made to flow between their end surfaces 18 and 19. Light emitted from the projection-side end surface 18 is diffused in a light cone Q and part of it strike on the photodetection-side end surface 19. The light cone Q is wider and wider as the refractive index of the fluid L is lower and lower, and the quantity of light incident on the photodetection-side end surface 19 is less and less. Further, the refractive index is determined by the mixing ratio of fluids, so variation in the quantity of light incident on the photodetection-side end surface 19 with refractive index is measured by a photodetecting element 14, whose output is used to find the mixing ratio of fluids. Thus, the mixing ratio of fluids is found from the output of the photodetecting element, so the mixing ratio is detected in real time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a device for measuring the mixing ratio of mixed liquids by using optical fibers.

Here, the mixed liquid is a mixture of two types of transparent liquids having different refractive indexes.

B) Prior art and its problems Chemical quantitative analysis methods using reagents are known for measuring the mixing ratio of liquids.

Also known is a physical quantitative analysis method in which the specific gravity and refractive index of a mixed liquid are measured and the mixing ratio is calculated from these values.

These methods involve taking a portion of the mixed liquid, sampling it, and measuring it with a dedicated measuring device. There is a time delay between sampling the liquid and measuring and calculating.

In recent years, there has been an increasing desire to sample physical information about liquids in real time on operating lines.

Various measuring devices have been developed for measuring physical quantity information such as liquid temperature, pressure, and flow rate.

However, there is no simple device that can measure the mixing ratio of liquids online.

If the liquid to be mixed is colorless and transparent, the mixing ratio cannot be determined by measuring light transmittance or the like. If the specific gravities of the liquids to be mixed are close, it is difficult to convert the mixing ratio by measuring the specific gravity.

It is believed that methods using refractive index differences are promising for mixture ratio measurements. However, even when refractive index measurement is used, a portion of the liquid is sampled and exposed to light to measure the refractive index.

There is no device that can easily measure the mixing ratio of liquids online. This is because until now there has been no method that allows continuous measurement of refractive index.

(i) Purpose It is an object of the present invention to provide a device capable of measuring the mixing ratio of liquids in real time.

A second object of the present invention is to provide an apparatus that can easily measure the mixing ratio of liquids both online and offline.

A third object of the present invention is to provide an apparatus that can continuously measure the mixing ratio of liquids without using human hands.

B) Method of the Invention The present invention utilizes changes in the spread of light emitted from the tip of an optical fiber in a liquid to detect the refractive index of the liquid.

When light is emitted into space from an optical fiber consisting of a core and a cladding, the light spreads out into a conical shape.

The extent of the cone depends on the numerical aperture of the optical fiber divided by the refractive index of the space.

Light emitted into a space with a high refractive index forms a narrow full cone. Light emitted into a space with a low refractive index forms a wide full cone.

Another optical fiber for detection will be provided opposite the optical fiber that emits light.

When spread out into a wide filled cone, the amount of light that enters the optical fiber for detection is small. When confined in a narrow filled cone, the amount of light that enters the optical fiber for detection is large.

After all, when optical fibers are installed in a liquid with their ends facing each other, if the refractive index is low, the amount of light that enters the detection optical fiber is small, and if the refractive index is high, the amount of light that enters the detection optical fiber is large.

The present invention utilizes such a principle. The present inventor believes that there has never been a device that measures the refractive index using changes in the spread of light emitted from an optical fiber.

Now, the relationship between the liquid mixture ratio and the refractive index will be described. There are two liquids, let them be S and T. Let the refractive index be Ns and Nj. Assume that these are different values. Mixtures of these liquids often contain Ns,
The refractive index is determined by the mixing ratio. Although not necessarily linear, there is a unique relationship between the mixing ratio and the refractive index.

Therefore, if the refractive index is known, the mixing ratio of the liquid can be determined.

With reference to FIG. 1, the principle underlying the invention will be explained in more detail.

In the liquid reservoir, an output side optical fiber 1 and a light receiving side optical fiber 2 are provided facing each other with a common axis.

The optical fiber consists of a core 3 and a cladding 4.

The angle θ between the light ray propagating in the optical fiber and the axis is tentatively designated as the path angle θ.

For multimode step-index optical fibers,
The path angle θ is an arbitrary angle less than or equal to the total reflection angle θC. Assuming that the mode is uniformly excited, the distribution with respect to θ is uniform when θC≧θ. However, the assumption of uniform mode excitation is not necessary for the present invention. The total reflection angle is defined by cosθC=−(1)nl. nl is the core refractive index, and n2 is the cladding refractive index.

At the end of the optical fiber, light is emitted from the core into the liquid. Since the path angle θ of the light propagating through the core was less than or equal to θC, the emitted light is included in a full cone Q having a half-vertical angle of θ. When the light propagating at the total reflection angle θC is emitted at the end of the core, this becomes the generatrix of the full cone Q. According to Snell's law, the relationship between the apex angle θ and the total reflection angle θC is as follows. Ml is the refractive index of the liquid. From this formula, the half apex angle θ of the full cone formed by the emitted light can be determined by the liquid refractive index N7B
It can be found as a function of

An optical fiber has a numerical aperture NA (numerical Ap
erture) is defined.

NA=f-m--n22 (3). (1
), this is equal to n1sinθC. Equation (2) can be written as NA s1nθ=−(4) Ml after all.

The half apex angle θ of the full cone Q formed by the emitted light is determined by: NA is a constant determined by the optical fiber. The refractive index Nl of the liquid is the only variable. It's a simple relationship.

The half apex angle θ of the full cone Q will be referred to as the maximum exit angle.

For example, assume that an optical fiber with NA=0.35 is used.

Glycerin (Nt = 1.478) and x ta/-
/l/ (Hs=1.370.), the maximum output angle θ is θ(Griseri:/ ) = 5in-1(0,85/
1.478 ) = 1 & 7° (6) e (x-tanol) = SL + 1 (0,35/IJ
70)=148° (7) In this way, even if the refractive index difference is about 0.1, there is a difference of about 1°.

Consider a plane parallel to the end face (a plane perpendicular to the axis) that is a distance q away from the output end face. Suppose that the emitted light is projected onto this projection surface. The projected light should be circular. If the radius of this circle is Rq, then Rq==R(-1-qtanθ
(8) becomes. Rc is the core radius.

The area A of the projected circle is A = M (Rc+q tanθ) 2
It is given by (9). The projection circle is called a spot. Assuming that the radii Rc, q, NA, etc. of the optical fiber core are known, there is a unique relationship between the spot area A and the liquid refractive index N4. If N6 is large, A is small and NI
If I is small, A is large.

For example, if we compare the cases of glycerin (Nt: 1.473) and ethanol (N, = 1.370) with R(==Q, 4m%q=l Q*x), A(glycerin)=25 .3ff2 A (ethanol) = 29.1u2.

FIG. 2 shows the use of the maximum output angles θS and θt and the difference in spot radius Rq for liquids with different refractive indexes.

This holds true no matter what value the distance q is.

In fact, if the liquid is not completely transparent, there is absorption of the liquid. Even if there is absorption, the point remains that if the distance q is the same, the spots will be as shown in FIGS. 2(a) and 2(b). Strength decreases due to absorption, but the degree of decrease is q
If it is small and highly transparent, it will not occupy much space.

If the amount of light that enters and propagates into the output optical fiber 1 is kept constant, the wider the spot area A, the lower the energy density of the output light. The narrower A, the greater the energy density of the emitted light.

The amount of light incident on the end face of the receiving optical fiber is proportional to the energy density. Therefore, it is inversely proportional to the spot area A.

The intensity of the light incident on the light-receiving optical fiber 2 is detected by a light-receiving element provided at the end of this optical fiber. The photocurrent of the light receiving element is amplified and becomes a voltage, and the voltage signal V has a value inversely proportional to A.

In other words, (1) (ethanol) A (glycerin). In this way, the refractive index of the liquid can be determined based on the difference in the energy of the light incident on the receiving optical fiber.

FIG. 3 is a graph showing the measurement results of the mixing ratio X and the amplified voltage V of the detector provided at the end of the light-receiving optical fiber in a mixed solution of ethanol and glycerin.

The left end is 100% ethanol, the right end is 100% glycerin.
is the limit of At one point on the left end, the voltage is about 100 mV, and at point S on the right end, the voltage is about 60 mV. Between ST, the mixture ratio X changes continuously, but the voltage also changes continuously. It's pretty linear.

Although it cannot be said that such a linear relationship holds true for any mixture of liquids, there is a unique relationship between the mixing ratio and the refractive index. If this relationship is known in advance,
The mixing ratio can be determined from the refractive index.

In FIG. 1, the core diameter of the receiving optical fiber is the same as the core diameter of the emitting optical fiber. However, the core diameter of the light-receiving optical fiber may be larger or smaller. If it is small, the amount of incident light will decrease, so
The amount of light entering the photodetector is also reduced, reducing sensitivity. However, this can be covered by improving the performance of the photodetector.

If the core diameter of the receiving optical fiber is made too large,
All the light rays emitted from the output side optical fiber enter the light receiving side optical fiber, and there is no change in the amount of light.

If Dt is the diameter of a spot formed at a distance q by a liquid having the highest refractive index among the liquids to be measured, then the spot diameter of the emitted light is always larger than Dt.

In this case, if the light-receiving side optical fiber core diameter is made smaller than Dt, the change in refractive index can be detected correctly.

In other words, the core diameter is D≦Rc+qtan(sin' (NA/Nt))
The upper limit is limited by Ql. The lower limit is limited by the performance of the photodetector.

The above explanation assumes that the output energy distribution normalized at the maximum output angle θ is the same whether the liquid has a high refractive index or a liquid has a low refractive index. When the output angle is φ (φ≦θ), the output energy distribution I (φ
) is constant regardless of φ I(φ) = cons
t is not necessary, and the above explanation assumes that I(φ/θ) can exist as a distribution function.

In reality, it depends on the refractive index distribution within the core of the optical fiber and the excitation conditions of the incident light! (φ/θ) represents various distribution functions.

Since the refractive index is different between the end face of the optical fiber and the liquid, Fresnel reflection occurs. This decreases as the difference in refractive index between the core and the liquid decreases.

Due to reflection, etc., the distribution of emitted light may not be easily expressed by the value (φ/θ) obtained by normalizing the output angle φ with the maximum output angle θ. For example, as shown in FIG. 4, it is possible that there is no difference in the optical power distribution near φ=0.

The horizontal axis is the output angle φ. The upper graph shows the optical power pattern in a liquid with a high refractive index Nt.

The lower graph shows the optical power pattern of the liquid S having a low refractive index Ns.

The power of liquid T is included in ±θt. The power of liquid S is included in ±θS. Although the power distribution of S is wider, in the vicinity of φ=O, it is possible that S and T are of the same degree. In such a special case, the angle φ=φ1 at which the difference in optical power becomes significant is determined in advance.

Then, as shown in FIG. 5, the axis of the receiving optical fiber is shifted by Δ from the axis of the emitting optical fiber. Naturally, Δ=q−φ1(II). φ1<θt.

(3) Configuration The present invention will be explained in detail with reference to FIG.

A joint part 1 is installed in the middle of the fluid pipe 10 through which the fluid flows.
5 will be provided. That is, it is perpendicular to the fluid pipe 10,
Two fiber tubes 11 and 12 are provided on the same straight line. These pipes may be arbitrary, such as stainless steel pipes, steel pipes, or brass pipes. It may also be a PVC pipe. FIG. 7 is a sectional view.

In the seven fiber tubes 11 and 12, an output side optical fiber and a light receiving side optical fiber 2 are provided. A light emitting source 13 is provided at the starting end of the output side optical fiber.

At the end of the light-receiving side optical fiber 2, a light-receiving element 14 (PDl
APD, etc.) is provided.

The axes of the two fibers may coincide, or, as described above, may be offset by Δ.

The fluid stream also passes between the end face 18 of the output side optical fiber and the end face 19 of the light receiving side optical fiber. Inside the fluid pipe 10,
It is preferable to fill it with fluid, but a small portion of air above is also acceptable.

However, there must be no air or air bubbles present in the opposing parts of the end faces 18,19.

The light emitted from the optical fiber end face 18 on the output side is diffused along the full cone Q, and only a part of it is transmitted to the end face 19 of the optical fiber on the receiving side.
to go into.

If the refractive index of the liquid is low, the full cone Q becomes wider, so the amount of light incident on the light-receiving optical fiber decreases.

When the mixing ratio of liquid S1 to liquid T is tx, the refractive index is determined by the mixing ratio X. The amount of light incident on the receiving optical fiber changes depending on the refractive index. The amount of light can be measured by the light receiving element 14.

If the relationship '/(X) between the liquid mixture ratio X and the output V of the light receiving element is determined in advance, the mixture ratio X can be found from the measured output V.

A fluid can be flowing or stationary.

When the refractive index of the liquid is small or the refractive index difference (Nt-Ns)
If is small, the noise will be large and the SN characteristics will be poor.

In such a case, a reference fiber 20 is provided as shown in FIG. The output side optical fiber 1 is also opposed to this. The same amount of light is input from the same light source into the two output side optical fibers 1.1'. The reference fiber and the output side optical fiber 1' are made of a low refractive index liquid (S
) or a high refractive index liquid (with η being 100%) is provided facing a certain space. A mixed liquid exists between the light receiving side optical fiber 2 for detection and the output side optical fiber 1.

By taking the difference in the outputs of the light receiving elements, it is possible to obtain a signal that is less affected by noise and the like. Actually, the detection fiber 2,
Reference fiber 20 and output side optical fiber 1.1
' fill with the same liquid S or T, adjust the offset 7 so that the differential electrical output becomes O, then fill with a different liquid and calibrate the differential electrical output to a certain constant value, Let us measure fluids with arbitrary mixing ratios.

Prevention) Example I Using the apparatus shown in Figures 6 and 7, ethanol (refractive index 1.370) and olive oil (refractive index 1.476) were used.
) The relationship between the mixing ratio of the mixed liquid and the output of the light receiving element was determined.

The fluid tube is a stainless steel tube with an inner diameter of 6 mm. Two pieces of stainless steel pipe are connected with a spherical joint.

To the spherical joint, 30 optical fibers having a core diameter of 0.8 mm were fixed facing each other so as to be perpendicular to the stainless steel tube. The end face pressure m(q) was set to 4.

A Norogen lamp was attached to the starting end of the output optical fiber as a light source. A photodiode was installed as a light-receiving element at the end of the light-receiving optical fiber.

The temperature of the liquid was 20°C. The refractive index of ethanol at 20°C is 1.370, and the refractive index of olive oil is 1.476.

The dynamic range when using 100% ethanol and when using 100% olive oil was 0.89 dB.

The level of 100% olive oil is increased to 110m using an amplifier circuit.
'/ was amplified. A graph of the measurement results of the mixture ratio and output voltage thus obtained is shown in FIG.

The mixing ratio of ethanol and olive oil is appropriately selected within the range of 0:1 to 1:1 to 1:0. The mixing ratio and voltage are not linear, but are monotonic functions.

((1) Example ■ Two sets of the same apparatus as in Example I were prepared. One set had gasoline (n = 1.405) and methanol) L' (n = 1
．． 331) was mixed between 1:0 and 1:1 to 0:1.

The other was for the beam reference and only allowed methanol to pass through.

The exact same measurement system was used. To process both output levels, a circuit was used that amplified the output level of the tutanol-only sample by subtracting it from the output level of the gasoline/tutanol mixed sample.

A mixture of liquids with small refractive index differences has a narrow dynamic range of measured values. However, if the output of the mixed sample is subtracted from the output of one liquid at 100%, the dynamic range can be widened. Furthermore, the S/N ratio can be improved.

Figure 9 shows measured data of methanol/gasoline mixture ratio and output voltage.

From the graphs in FIGS. 8 and 9, it can be seen that the change in refractive index and the mixing ratio have good linearity. The mixing ratio of liquids can be determined from the output voltage.

(2) Effects (1) The mixing ratio of two types of liquids can be detected in real time.

(2) Since it can be detected instantly, it can be used both online and offline.

(3) The entire device can be made smaller.

(4) Since it is a small device, it can be attached to moving objects such as cars, airplanes, and ships.

(5) The fluid may be flowing. Changes in mixing ratio can be detected continuously.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of opposing parts of two optical fibers for explaining the present invention in detail. FIG. 2 is a diagram illustrating the spread of light emitted from an optical fiber. (a) is a longitudinal cross-sectional view, and (b) shows a circular pattern drawn by emitted light. FIG. 3 is a graph showing the measurement results of an ethanol/glycerin mixture according to the present invention. The horizontal axis is the mixing ratio, and the vertical axis is the potential of the light receiving element. FIG. 4 is a diagram showing emitted light patterns when there is no similarity between the emitted light patterns of two types of liquids to be mixed. The horizontal axis is the angle that the emitted light makes with the normal line. FIG. 5 is a cross-sectional view showing the axis of the light-receiving optical fiber shifted from the axis of the output-side optical fiber. FIG. 6 is an external perspective view of the device of the present invention. FIG. 7 is a longitudinal sectional view of the device of the present invention. FIG. 8 is a graph showing the results of measuring the output potential of the receiving optical fiber using the apparatus of the present invention for samples with different mixing ratios of ethanol/olive oil. FIG. 9 is a graph showing the difference in output potential between samples with different methanol/gasoline mixing ratios, using a 100% methanol sample as a reference, and the amplified value. Figure 10 shows the fiber for measuring the mixed liquid and either one +
7) A configuration diagram showing a mechanism for amplifying the difference in photodiode output using a reference fiber for measuring a 100% liquid sample. 1... Output side optical fiber 2...
・Receiving side optical fiber 3...Core 4...Clad 5-...Emitted light 6 when liquid S is 100%...
......Emitted light 10 when liquid T is 100%...
...Fluid tube 11, 12...Fiber tube 13...Light emitting source 14... Light receiving element 15...Joint part Inventor: Mogi Masa Haruokamoto Kazuhiro Yoshimura Kozo 1) Hiroo Patent applicant Sumitomo Electric Industries, Ltd. Ethanol 10σ 50%
σ fuetano → ν glycerin 0%
50% 100% glycerin (refractive index 1.473

Claims (3)

[Claims] (1) A step index consisting of a light-emitting element that generates light of a constant intensity, and a core and cladding with a constant refractive index that allows the light of the light-emitting element to pass from one end face and emit the light into the liquid to be measured from the other end face. a light-emitting side optical fiber of the mold, a light-receiving side optical fiber provided opposite to the end face of the light-emitting side optical fiber and receiving a part of the emitted light at this end face, and a light-receiving side optical fiber provided at the other end of the light-receiving side optical fiber. A liquid mixture ratio measuring device comprising a light receiving element that measures the power of light received by a light receiving side optical fiber, and the liquid mixing ratio is determined from the output voltage of the light receiving element. (2) A patent in which the mixed liquid is a mixture of two transparent liquids with different refractive indexes, and the core area of the receiving optical fiber is narrower than the spread of the emitted light in the liquid with the larger refractive index. A liquid mixture ratio measuring device according to claim (1). (3) The position of the end face of the receiving side optical fiber is shifted from the axis of the output side optical fiber by an angle φ_1 smaller than the maximum output angle Θ_t for the high refractive index liquid.
2) The liquid mixture ratio measuring device described in item 2).