A tilted fiber grating concentration measuring instrument and concentration measuring method

Abstract

The invention discloses a tilted fiber grating concentration measuring instrument and a concentration measuring method. By adopting a tilted fiber grating sensor made of plastic optical fiber and encapsulating it in a reaction chamber, the interference effect of the pressure generated by a solution to be measured on the tilted fiber grating sensor is reduced, and the measurement accuracy and reliability are improved. In addition, since the manufacturing process of plastic optical fiber is mature, the price is lower than that of glass optical fiber, and the cost is relatively low. Moreover, the plastic optical fiber as a sensor also has the characteristics of high elastic strain limit, high fracture toughness, high bending flexibility, and high sensitivity to strain and temperature.

Description

Technical Field

[0001] The invention relates to the field of optical fiber sensing, and in particular to an inclined optical fiber grating concentration measuring instrument and a concentration measuring method. Background Art

[0002] Solution concentration is an important physical quantity in daily life. It is one of the main parameters to characterize solution characteristics. It is also an important measurement parameter in industrial and agricultural production and scientific research experiments. Many physical and chemical properties of substances are easily affected by concentration. Too high or too low concentration will affect the quality of the product. Therefore, the measurement and control of solution concentration is widely used in chemical, metallurgical, papermaking, food, sugar, pharmaceutical and other industries, and is an important technical means to ensure product quality.

[0003] There are many methods and instruments for measuring solution concentration. In chemistry, the concentration can be measured by chemical reaction method, and in physics, it can be measured by optical or electrical methods. Since the concentration of a solution is dependent on many physical quantities, such as density, conductivity, refractive index, etc., in principle, the change in one of the physical quantities can be used to characterize the change in concentration. Using the refractive index of a solution to measure concentration is a relatively common method. Compared with chemical methods, the refractive index method does not need to consider various reaction conditions and has a wider range of applications. Compared with electrical measurement methods, it is simple, cheap, and has high measurement accuracy. In addition, the optical refractive index sensing method is simple, fast, and not subject to electromagnetic interference.

[0004] According to the principle of optical measurement, the refractive index measurement methods can be roughly classified into three categories: geometric optics, wave optics and fiber optic sensing. Fiber optic sensing provides a more practical test method for measuring and controlling the refractive index of solutions. Fiber grating concentration sensor is a solution concentration test system based on fiber optic sensing. This measurement method is not only free from electromagnetic interference, high sensitivity, light weight, small size, high temperature and high pressure corrosion resistance, and can be remotely monitored, but has become one of the mainstream directions of sensor technology development.

[0005] At present, there are three main methods for concentration measurement using fiber grating sensors: coated fiber grating concentration measurement method, long period fiber grating (Long Period Fiber Grating, LPFG) concentration measurement method and tilted fiber grating (Tilted Fiber Bragg Grating, TFBG) concentration measurement method. Among them, coated fiber grating reduces the mechanical strength of the grating itself, and long period fiber grating has an inherent temperature cross-sensitivity effect, which reduces its wide application in environments that are easily affected by external temperature. Therefore, its application range is limited to a certain extent. Tilted fiber grating avoids the disadvantages of both and has the advantages of both.

[0006] At present, most of the tilted fiber Bragg gratings are FBG optical sensors made of silicon dioxide, namely fiber Bragg grating sensors, such as the Chinese patent No. 200910228965.5, whose invention name is "A tilted fiber Bragg grating liquid level change measuring instrument". The tilted fiber Bragg grating in the measuring instrument is made by using phase mask side radiation technology, tilting the template during the writing process and writing it into a hydrogen-carrying single-mode optical fiber through excimer laser ultraviolet; the tilted fiber Bragg grating is located at the liquid surface of the container to be measured and the upper end of the tilted fiber Bragg grating must extend out of the liquid surface of the container to be measured.

[0007] However, as is known to all, silica optical fiber is relatively expensive, and since the fiber grating is located at the liquid surface of the container to be measured, the pressure generated by the solution to be measured will cause certain interference to its measurement accuracy and reliability, thereby reducing its measurement accuracy and reliability. Summary of the invention

[0008] In view of the above-mentioned technical problems, the present invention provides a tilted fiber grating concentration measuring instrument.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A tilted fiber grating concentration measuring instrument comprises a light source generator, a reaction tank and a spectrum analyzer, and also comprises a reaction cavity which can be arranged in the reaction tank, wherein a TFBG sensor is built in the reaction cavity, and the two ends of the TFBG sensor are respectively connected to the light source generator and the spectrum analyzer through an input optical fiber and an output optical fiber, wherein the TFBG sensor is made of plastic optical fiber.

[0011] Furthermore, two ends of the TFBG sensor extend out of the reaction chamber.

[0012] Furthermore, the reaction chamber is provided with an electromagnetic valve. When the electromagnetic valve is opened, the solution to be tested in the reaction tank enters the reaction chamber. When the solution to be tested fills the reaction chamber, the electromagnetic valve is closed.

[0013] Furthermore, it also includes a bidirectional pump, a controller for controlling the bidirectional pump, a liquid reservoir for holding a constant temperature cleaning agent, and a waste liquid collection device, wherein the controller is electrically connected to the bidirectional pump, one end of the bidirectional pump is connected to the reaction chamber through a first connecting pipe, and the other end of the bidirectional pump is connected to the liquid reservoir and the waste liquid collection device through a second connecting pipe and a third connecting pipe, respectively.

[0014] Furthermore, the angle θ between the grating plane of the TFBG sensor and the core cross section is 6°-45°.

[0015] Furthermore, the length of the TFBG sensor is 4 mm-10 mm.

[0016] Based on the above-mentioned tilted fiber Bragg grating concentration measuring instrument, the present invention also provides a method for using the tilted fiber Bragg grating to perform concentration measurement, comprising the following steps:

[0017] Step 1: adding a solution to be tested into a reaction tank of the tilted fiber Bragg grating concentration measuring instrument;

[0018] Step 2: Place the reaction chamber with the built-in TFBG sensor into the reaction tank, and allow the solution to be tested in step 1 to submerge the reaction chamber, and let it stand for a period of time;

[0019] Step 3: Open the electromagnetic valve to allow the solution to be tested to enter the reaction chamber and fill the reaction chamber, close the electromagnetic valve, and let it stand for a while;

[0020] Step 4: Turn on the light source generator in the tilted fiber Bragg grating concentration measuring instrument, and the light source is incident on the spectrum analyzer in the tilted fiber Bragg grating concentration measuring instrument through the input optical fiber, the TFBG sensor and the output optical fiber in sequence, thereby obtaining a first spectrum graph;

[0021] Step 5: The controller in the tilted fiber grating concentration measuring instrument controls the bidirectional pump to extract the detected solution in the reaction chamber and discharge it to the waste liquid collection device in the tilted fiber grating concentration measuring instrument; and when the solution in the reaction chamber is completely discharged, the controller controls the bidirectional pump to reverse and pump the detergent in the liquid reservoir into the reaction chamber to clean the reaction chamber; then, the controller controls the bidirectional pump to extract the sewage in the reaction chamber and discharge it to the waste liquid collection device; this is repeated several times to clean the reaction chamber;

[0022] Step 6: Open the solenoid valve again and repeat steps 3-5;

[0023] Step 7: Compare the spectrum waveform data and calculate the concentration of the solution to be tested.

[0024] The beneficial effects of the present invention are as follows: by adopting a tilted fiber Bragg grating sensor made of plastic optical fiber and encapsulating it in a reaction chamber, the interference effect of the pressure generated by the solution to be measured on the tilted fiber Bragg grating sensor is reduced, and the measurement accuracy and reliability are improved. In addition, since the manufacturing process of plastic optical fiber is mature, the price is lower than that of glass optical fiber, and the cost is relatively low. In addition, the plastic optical fiber as a sensor also has the characteristics of high elastic strain limit, high fracture toughness, high bending flexibility, and high sensitivity to strain and temperature.

[0025] Furthermore, the present invention controls the bidirectional pump through the controller to pump the tested solution in the reaction chamber to the waste liquid collection device, and pumps the constant temperature detergent in the liquid reservoir into the reaction chamber, so as to repeatedly clean the inside of the reaction chamber, thereby realizing automatic cleaning of the reaction chamber, without taking out the reaction chamber separately and then taking out the TFBG sensor for cleaning; on the other hand, when the test solution is injected into the reaction chamber again for testing, the interference of the residual test solution is avoided, thereby greatly improving the accuracy of solution concentration measurement and the reliability of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0027] Figure 1 It is a structural schematic diagram of a tilted fiber Bragg grating concentration measuring instrument of the present invention;

[0028] Figure 2 The present invention is a schematic diagram of the structure of a reaction tank of a tilted fiber grating concentration measuring instrument. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] See also Figure 1A tilted fiber Bragg grating concentration measuring instrument includes a light source generator 1, a reaction tank 2 and a spectrum analyzer 3, and also includes a reaction cavity 21 that can be set in the reaction tank 2, and the reaction cavity 21 has a built-in TFBG sensor 22. Both ends of the TFBG sensor 22 extend out of the reaction cavity 21 and are connected to the light source generator 1 and the spectrum analyzer 3 through an input optical fiber 11 and an output optical fiber 12, respectively, wherein the TFBG sensor 22 is made of plastic optical fiber.

[0032] In this embodiment, the light source generator 1 and the TFBG sensor 22 are connected via an input optical fiber 11, the TFBG sensor 22 and the spectrum analyzer 3 are connected via an output optical fiber 12, the TFBG sensor 22 is disposed in a reaction chamber 21, and the reaction chamber 21 is placed in a reaction tank 2 containing a solution to be tested. When working, the light emitted by the light source generator 1 passes through the input optical fiber 11, the TFBG sensor 22 and the output optical fiber 12 in sequence, and then enters the spectrum analyzer 3, thereby obtaining a spectrum graph.

[0033] In this embodiment, the TFBG sensor 22 is made of plastic optical fiber, which is cheaper than glass optical fiber and has relatively low cost. In addition, plastic optical fiber as a sensor also has the advantages of high elastic strain limit, high fracture toughness, high bending flexibility and high sensitivity to strain and temperature.

[0034] In this embodiment, by packaging the TFBG sensor 22 in the reaction chamber 21, the influence of the pressure generated by the solution to be tested on the TFBG sensor 22 is reduced, thereby improving the measurement accuracy and reliability.

[0035] In a specific embodiment, an electromagnetic valve 23 is provided on the reaction chamber 21. When the electromagnetic valve 23 is opened, the solution to be tested in the reaction tank 2 enters the reaction chamber 21. When the solution to be tested fills the reaction chamber 21, the electromagnetic valve 23 is closed. At the same time, the part of the TFBG sensor 22 located in the reaction chamber 21 is completely immersed in the solution to be tested. After standing for a period of time, the test can be carried out.

[0036] In this embodiment, in order to facilitate cleaning and improve detection accuracy, the tilted fiber grating concentration measuring instrument also includes a bidirectional pump 4, a controller 5 for controlling the bidirectional pump 4, a liquid reservoir 6 for containing a constant temperature cleaning agent, and a waste liquid collection device 7, wherein the controller 5 is electrically connected to the bidirectional pump 4, one end of the bidirectional pump 4 is connected to the reaction chamber 21 via a first connecting tube 41, and the other end of the bidirectional pump 4 is connected to the liquid reservoir 6 and the waste liquid collection device 7 via a second connecting tube 42 and a third connecting tube 43, respectively.

[0037] After a test is performed, the tested solution in the reaction chamber 21 needs to be extracted. If the reaction chamber 21 is manually taken out from the reaction tank 2 and then the tested solution is poured out, this method is cumbersome and not conducive to multiple tests and time saving. Therefore, in this embodiment, the two-way pump 4 is used to achieve automatic cleaning, so that after a test is performed, the two-way pump 4 can be started by the controller 5 to discharge the tested solution in the reaction chamber 21 through the first connecting pipe 41, the two-way pump 4 and the third connecting pipe 43 to the waste liquid collection device 7; then, the controller 5 The two-way pump 4 is controlled to reverse, and the constant temperature cleaning agent in the liquid reservoir 6 is pumped into the reaction chamber 21 through the second connecting pipe 42, the two-way pump 4 and the first connecting pipe 41 to clean the reaction chamber 21; then, the controller 5 controls the start of the two-way pump 4 to discharge the cleaning agent after cleaning the reaction chamber 21 through the first connecting pipe 41, the two-way pump 4 and the third connecting pipe 43 to the waste liquid collection device 7. This is repeated several times to clean the reaction chamber 21. At this time, the electromagnetic valve 23 is opened again to allow the solution to be tested to flow into the reaction chamber 21, and the test process is repeated.

[0038] In this embodiment, the controller 5 controls the bidirectional pump 4 to pump the tested solution in the reaction chamber 21 to the waste liquid collection device 7, and pumps the constant temperature detergent in the liquid reservoir 6 into the reaction chamber 21, so as to repeatedly clean the inside of the reaction chamber 21, that is, the reaction chamber 21 is automatically cleaned, and there is no need to take out the reaction chamber 21 separately and then take out the TFBG sensor 22 for cleaning; on the other hand, when the solution to be tested is injected into the reaction chamber 21 again for testing, the interference of the residual solution to be tested is avoided, which greatly improves the accuracy of solution concentration measurement and the reliability of detection.

[0039] In this embodiment, the angle θ between the grating plane of the TFBG sensor 22 and the core cross section is 6°-45°.

[0040] In this embodiment, the length of the TFBG sensor 22 is 4 mm-10 mm.

[0041] Based on the above-mentioned tilted fiber Bragg grating concentration measuring instrument, the present invention also provides a method for measuring concentration using a tilted fiber Bragg grating, comprising the following steps:

[0042] Step 1: Add the solution to be tested into the reaction tank 2 of the tilted fiber Bragg grating concentration measuring instrument;

[0043] Step 2: Place the reaction chamber 21 with the built-in TFBG sensor 22 into the reaction tank 2, and allow the solution to be tested in step 1 to submerge the reaction chamber 21, and let it stand for a while;

[0044] Step 3: Open the electromagnetic valve 23 to allow the solution to be tested to enter the reaction chamber 21 and fill the reaction chamber 21, close the electromagnetic valve 23, and let it stand for a while;

[0045] Step 4: Turn on the light source generator 1 in the tilted fiber Bragg grating concentration measuring instrument, and the light source is incident on the spectrum analyzer 3 in the tilted fiber Bragg grating concentration measuring instrument through the input fiber 11, the TFBG sensor 22 and the output fiber 12 in sequence, thereby obtaining a first spectrum diagram;

[0046] Step 5: The controller 5 in the tilted fiber Bragg grating concentration measuring instrument controls the bidirectional pump 4 to extract the detected solution in the reaction cavity 21 and discharge it to the waste liquid collection device 7 in the tilted fiber Bragg grating concentration measuring instrument; and when the solution in the reaction cavity 21 is completely discharged, the controller 5 controls the bidirectional pump 4 to reverse and pump the detergent in the liquid reservoir 6 into the reaction cavity 21 to clean the reaction cavity 21; then, the controller 5 controls the bidirectional pump 4 to extract the sewage in the reaction cavity 21 and discharge it to the waste liquid collection device 7; this is repeated several times to clean the reaction cavity 21;

[0047] Step 6: Open the electromagnetic valve 23 again and repeat steps 3-5;

[0048] Step 7: Compare the spectrum waveform data and calculate the concentration of the solution to be tested.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for concentration measurement using tilted fiber Bragg grating, characterized in that: The liquid to be measured is measured using a tilted fiber Bragg grating concentration measuring instrument, which includes a light source generator, a reaction tank and a spectrum analyzer, and also includes a reaction cavity that can be arranged in the reaction tank, wherein the reaction cavity is equipped with a TFBG sensor, and the two ends of the TFBG sensor are respectively connected to the light source generator and the spectrum analyzer through an input optical fiber and an output optical fiber, wherein the TFBG sensor is made of plastic optical fiber; and the following steps are included: Step 1: adding a solution to be tested into a reaction tank of the tilted fiber Bragg grating concentration measuring instrument; Step 2: Place the reaction chamber with the built-in TFBG sensor into the reaction tank, and allow the solution to be tested in step 1 to submerge the reaction chamber, and let it stand for a period of time; Step 3: Open the electromagnetic valve to allow the solution to be tested to enter the reaction chamber and fill the reaction chamber, close the electromagnetic valve, and let it stand for a while; Step 4: Turn on the light source generator in the tilted fiber Bragg grating concentration measuring instrument, and the light source is incident on the spectrum analyzer in the tilted fiber Bragg grating concentration measuring instrument through the input optical fiber, the TFBG sensor and the output optical fiber in sequence, thereby obtaining a first spectrum graph; Step 5: The controller in the tilted fiber grating concentration measuring instrument controls the bidirectional pump to extract the detected solution in the reaction chamber and discharge it to the waste liquid collection device in the tilted fiber grating concentration measuring instrument; and when the solution in the reaction chamber is completely discharged, the controller controls the bidirectional pump to reverse and pump the detergent in the liquid reservoir into the reaction chamber to clean the reaction chamber; then, the controller controls the bidirectional pump to extract the sewage in the reaction chamber and discharge it to the waste liquid collection device; this is repeated several times to clean the reaction chamber; Step 6: Open the solenoid valve again and repeat steps 3-5; Step 7: Compare the spectrum waveform data and calculate the concentration of the solution to be tested.

2. The method according to claim 1, characterized in that: Two ends of the TFBG sensor extend out of the reaction chamber.

3. The method according to claim 1, characterized in that: The reaction chamber is provided with an electromagnetic valve. When the electromagnetic valve is opened, the solution to be tested in the reaction tank enters the reaction chamber. When the solution to be tested fills the reaction chamber, the electromagnetic valve is closed.

4. The method according to claim 1, characterized in that: It also includes a bidirectional pump, a controller for controlling the bidirectional pump, a liquid reservoir for containing a constant temperature cleaning agent, and a waste liquid collection device, wherein the controller is electrically connected to the bidirectional pump, one end of the bidirectional pump is connected to the reaction chamber through a first connecting pipe, and the other end of the bidirectional pump is connected to the liquid reservoir and the waste liquid collection device through a second connecting pipe and a third connecting pipe, respectively.

5. The method according to any one of claims 1 to 4, characterized in that: The angle θ between the grating plane of the TFBG sensor and the core cross section is 6°-45°.

6. The method according to any one of claims 1 to 4, characterized in that: The length of the TFBG sensor is 4 mm-10 mm.

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