Optical fiber sensor for measuring concentration of trace NaCl solution
By designing an optical fiber sensor that utilizes optical fiber and signal detection systems, the existing NaCl solution concentration micro-monitoring methods are solved, and low-cost and high-precision NaCl solution concentration monitoring is achieved to meet the monitoring needs of clinical medical-level monitoring.
Patent Information
- Application Number
- CN202510344235.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-21
- Publication Date
- 2025-06-20
AI Technical Summary
The existing micro-monitoring methods for NaCl solution concentration are costly, complex in operation and poor stability, making it difficult to meet the low-cost and high-precision monitoring needs in the medical and health field.
An optical fiber sensor is designed, using a special fiber and signal detection system, and a 650nm laser and a photoresistor sensor module are used to perform signal processing and human-computer interaction with the STM32 microcontroller to achieve high-precision measurement of NaCl solution concentration.
Low-cost and high-precision NaCl solution concentration monitoring is achieved, with the average relative error being controlled at 0.9255%, meeting the clinical medical-level trace NaCl solution concentration monitoring needs.
Smart Images
Figure CN120177419A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of fiber optic sensing, and particularly relates to an optical fiber sensor for measuring the concentration of trace NaCl solution, which is applicable to the field of medical health. Background Art
[0002] The trace monitoring of the concentration of NaCl solution is very important in the field of medical health, especially in the quality control during the preparation of physiological saline, which can avoid the situation of adverse reactions in patients caused by excessive deviation of the concentration of physiological saline.
[0003] Existing methods for realizing the trace monitoring of the concentration of NaCl solution (such as gravimetric method, titration method, Raman spectroscopy method, etc.) have problems such as complex operation, high cost, and poor stability. Therefore, there is an urgent need for a low-cost and high-precision trace monitoring scheme. Summary of the Invention
[0004] The purpose of the present invention is to overcome the problems of high cost and complex operation in the above-mentioned means for trace monitoring of the concentration of NaCl solution, and to provide an optical fiber sensor for measuring the concentration of trace NaCl solution. To achieve the above purpose, the present invention provides the following technical solutions.
[0005] An optical fiber sensor for measuring the concentration of trace NaCl solution, characterized in that: it includes a signal source, a sensing element and a signal detection system; the signal source is driven by 220V alternating current; the rear end of the rear optical fiber of the sensing element and the photosensitive resistor sensing part in the signal detection system are adhesively fixed by ultraviolet glue and encapsulated by a self-made paper black box to prevent the influence of external light sources on the measurement.
[0006] Further defined, the sensing element includes a front fixing device, a front optical fiber, a plastic container, a rear optical fiber, and a rear fixing device. The two ends of the front optical fiber are respectively connected and fixed to the front fixing device and the plastic container, and the two ends of the rear optical fiber are respectively connected and fixed to the rear fixing device and the plastic container. By adjusting the distance between the front and rear optical fibers (2mm), the beam coupling efficiency is optimized. The entire sensing element is fixed on the breadboard by screws arranged on the front fixing device and the rear fixing device.
[0007] Further defined, the front optical fiber and the rear optical fiber are special optical fibers with a PMMA material, a core diameter of 1mm, and strong bending resistance after processing.
[0008] Further defined, the plastic container is made of high-pressure polyethylene, has hydrophobicity, and is easy to handle the residual NaCl solution.
[0009] Further defined, the signal detection system includes a patch panel, an STM32C8T6 core board, a photoresistor sensor module, an OLED display, and a mobile phone power bank. The STM32C8T6 core board, the photoresistor sensor module, and the OLED display are all connected to the patch panel through DuPont wires. The STM32C8T6 core board is then connected to the ST-LINK STM32 debugger through DuPont wires. The ST-LINK STM32 is connected to the mobile phone power bank through a USB interface to supply power to the entire signal detection system.
[0010] After the plastic container is filled with the NaCl solution to be measured, the 650nm laser is turned on with a 220V AC power supply. The 650nm laser emits laser light. The front end of the front optical fiber captures the optical signal emitted by the 650nm laser. The optical signal propagates forward in the front optical fiber and exits at the rear end of the front optical fiber. The rear end of the front optical fiber is aligned with the front end of the rear optical fiber, and the spacing is set to 2mm. The difference in the converging effect of the NaCl solutions with different concentrations in the plastic container on the light beam exiting the rear end of the front optical fiber causes different light intensities to be received at the front end of the rear optical fiber. The optical signal then propagates in the rear optical fiber to the rear end of the rear optical fiber and finally acts on the photoresistor sensing part to generate different light signal intensities. The light signal intensity is measured by the magnitude of the light intensity analog value on the OLED display. By conducting multiple experiments to measure the light intensity analog values corresponding to different concentrations of NaCl solutions and then using Origin software for numerical fitting between the NaCl solution concentration and the light intensity analog value to obtain a fitting formula, and finally using the assembly language in Keil5 software to write the fitting formula and the human-computer interaction scheme into the STM32C8T6 core board. After analog photoelectric conversion, the concentration of the measured NaCl solution can be read according to the NaCl solution concentration value on the OLED display.
[0011] The difference in the converging effect of the NaCl solutions with different concentrations on the light beam exiting the rear end of the front PMMA optical fiber is a conclusion drawn based on geometric optical approximation, Snell's law, and the empirical formula between the NaCl solution concentration and the refractive index. And the prerequisite is that the rear end of the front optical fiber and the front end of the rear PMMA optical fiber must be fully immersed in the NaCl solutions with different concentrations to ensure the validity of Snell's law. The origin of the conclusion is further explained below.
[0012] The characteristics of light propagation in an optical fiber can be studied using the ray - optics approximation method. The following approximations can be made using ray - optics: If a light source irradiates one end of the optical fiber, there will be an infinite number of light beams propagating inside the optical fiber. That is, the light emitted from the light source is approximated as a collection of an infinite number of light beams. Analyzing the propagation behavior of light in the optical fiber in this way will make the calculation very simple. The prerequisite for using the ray - optics method is that the wavelength of the incident light wave is much smaller than the core size of the optical fiber. The core diameters of the pre - placed optical fiber and the post - placed optical fiber are both 1 mm, and the wavelength of the light source is 650 nm. Therefore, the conditions for using the ray - optics method for research are met. According to the ray - optics method, if a light beam exits from the rear end of the pre - placed optical fiber, the relationship between its incident angle and exit angle will satisfy Snell's law (Equation 1): n1sinθ1=n2sinθ2 Where n1 is the refractive index of the core of the pre - placed optical fiber, θ1 is the incident angle of this light beam, n2 is the refractive index of the measured NaCl solution, and θ2 is the exit angle of this light beam. From this, Equation 2 can be easily obtained: The relationship between the concentration of the NaCl solution and the refractive index conforms to the empirical formula: n2=1.33254+0.00187c Where c is the concentration of the NaCl solution. Combining Equation 2 and Equation 3, it can be found that the size of the exit angle of the light beam is inversely proportional to the concentration of the NaCl solution. Thus, if a laser source irradiates the front end of the pre - placed optical fiber (the front end of the pre - placed optical fiber is always placed in the air), there will be an infinite number of light beams propagating inside the pre - placed optical fiber. Immerse the rear end of the pre - placed optical fiber in the NaCl solution and continuously increase its concentration, and finally the range of the exit light beam will become smaller and smaller, that is, it plays a role in converging the light beam.
[0013] The alignment of the rear end of the pre - placed optical fiber and the front end of the post - placed optical fiber is judged according to the magnitude of the simulated light intensity value when no NaCl solution is injected into the plastic container. The magnitude of the simulated light intensity value is inversely proportional to the light intensity received by the photosensitive - resistor sensing part. By adjusting the relative positions of the pre - placed optical fiber and the post - placed optical fiber multiple times, it can be obtained that there is a minimum simulated light intensity value at a certain position. At this time, it is considered that the rear end of the pre - placed optical fiber and the front end of the post - placed optical fiber are already aligned.
[0014] The distance between the rear end of the front optical fiber and the front end of the rear optical fiber is set to 2 mm, which is the result of comprehensively considering the loss of light in the NaCl solution and the change threshold of the outgoing light beam range. When the distance is too small, the front end of the rear optical fiber can always receive most of the optical signals emitted from the rear end of the front optical fiber, and the change in the outgoing light beam range does not significantly change the final simulated light intensity value, reducing the sensitivity of the fiber optic sensor. When the distance is too large, there are various forms of losses when light propagates in the NaCl solution, such as medium light absorption, Rayleigh scattering, and Mie scattering, etc., resulting in a relatively weak light intensity detected by the photosensitive resistor sensing part at the end, and the change in the simulated light intensity value is not obvious, also reducing the sensitivity of the fiber optic sensor, and the measurable NaCl solution concentration range will also be shortened accordingly. Through multiple experiments, it is found that when the distance between the two optical fiber heads is 2 mm, the change in the NaCl solution concentration can cause a relatively obvious change in the simulated value, and the sensitivity of the fiber optic concentration sensor is better. Therefore, 2 mm is selected as the distance between the two optical fiber heads.
[0015] Verified by the calibration experiment, when the NaCl solution concentration is in the range of 0.2 - 1%, the fitting curve between the concentration and the simulated light intensity value is approximately a linear relationship, and the fitting degree is as high as 0.99161, that is, the fitting formula is: c = -0.0251A + 20.08 Where c represents the NaCl solution concentration and A represents the simulated light intensity value.
[0016] The human-computer interaction scheme and digital-to-analog conversion refer to using the assembly language in Keil5 to convert the current of the photosensitive resistor sensing part transmitted to the STM32C8T6 core board, that is, the digital signal is converted into an analog light intensity value, and the simulated light intensity value is substituted into the fitting formula to be converted into the corresponding NaCl solution concentration, and the words "Simulated light intensity value:" and "NaCl solution concentration value:" are output on the OLED display screen, and the corresponding digital-to-analog conversion results are output after the colon of each section of words, which is convenient for users to read the data.
[0017] To further measure the measurement accuracy of this fiber optic sensor, several portions of NaCl solutions with different concentrations are randomly configured within the range of the fiber optic concentration sensor's range, and the corresponding simulated light intensity values when containing different concentrations of NaCl solutions are read out in sequence. The simulated light intensity values are substituted into the fitting formula to obtain the measured concentration and a relative error analysis is made with the actual concentration. The final results are shown in Table 1. Table 1 Invention Error Analysis
[0018] As can be seen from Table 1, the average relative error of this fiber optic sensor is controlled within 0.9255%. According to the standards of the Chinese Pharmacopoeia / USP and the WHO medical supplies specifications, the NaCl solution monitored by the present invention can meet the error requirements (<1%) for intravenous infusion / injection and wound irrigation / external use in the clinical medical level.
[0019] Considering the influence of the external temperature on the refractive index of the NaCl solution, through calibration experiments, it is verified that the ideal working environment temperature of the present invention is 15 - 28 °C. In this temperature range, the influence of temperature on the measurement accuracy of the present invention can be ignored, and the accuracy of the measurement results cannot be guaranteed beyond this temperature range.
[0020] Compared with the prior art, the innovation points and advantages of the present invention are as follows: 1. Based on the discovery of the difference in the converging effect of the outgoing light beam at the rear end of the pre - placed PMMA fiber by NaCl solutions with different concentrations, the fiber optic sensor is designed. The final measurement error and measurement range can achieve the monitoring of trace NaCl solution concentration at the clinical medical level, and the measurement operation is relatively simple; 2. The STM32 microcontroller is used to complete signal processing and human - machine interaction, significantly reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 are the three - view drawings of the present invention; Figure 2 is the top - view drawing of the present invention; Figure 3 is the circuit connection diagram in the signal detection system of the present invention. Reference numerals in the figures: 1 - 650nm laser, 2 - optical stainless steel support rod, 3 - pre - placed fixer, 4 - pre - placed optical fiber, 5 - plastic container, 6 - post - placed optical fiber, 7 - breadboard, 8 - post - placed fixer, 9 - wiring board, 10 - STM32C8T6 core board, 11 - photoresistor sensor module, 12 - OLED display screen, 13 - ST - LINK STM32 debugger, 14 - mobile phone power bank. DETAILED DESCRIPTION OF THE INVENTION
[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.
[0023] Such as Figure 1 、 Figure 2As shown in the figure, the present invention provides a technical solution: an intensity modulation type fiber optic sensor for measuring the concentration of NaCl solution, comprising a signal source, a sensing element and a signal detection system. The characteristics are as follows: the signal source is a 650 nm laser, which is fixed on a breadboard through an optical stainless steel support rod. The sensing element includes a front fixing device, a front optical fiber, a plastic container, a rear optical fiber and a rear fixing device. The two ends of the front optical fiber are respectively connected and fixed to the front fixing device and the plastic container, and the two ends of the rear optical fiber are respectively connected and fixed to the rear fixing device and the plastic container. The rear end of the front optical fiber and the front end of the rear optical fiber inside the plastic container are 2 mm apart. The whole sensing element is fixed on the breadboard by installing screws on the front fixing device and the rear fixing device. The signal detection system includes a wiring board, an STM32C8T6 core board, a photoresistor sensor module, an OLED display screen and a mobile phone power bank. The STM32C8T6 core board, the photoresistor sensor module and the OLED display screen are all connected to the wiring board through Dupont wires. The STM32C8T6 core board is then connected to an ST-LINKSTM32 debugger through a Dupont wire. The ST-LINKSTM32 is connected to the mobile phone power bank through a USB interface to supply power to the whole signal detection system. The specific circuit connection method is as Figure 3 shown.
[0024] The specific measurement scheme is as follows: after the plastic container is filled with the NaCl solution to be measured, the 650 nm laser is connected to the 220 V AC power supply, and the concentration of the measured NaCl solution can be obtained according to the NaCl solution concentration value on the OLED display screen. A disposable plastic dropper can be used to extract and replace the NaCl solution in the container and record the NaCl solution concentration value correspondingly to achieve multiple measurements.
Claims
1. An optical fiber sensor for measuring the concentration of NaCl solution, characterized in that: The invention comprises a signal source, a sensing element and a signal detection system; the signal source is driven by 220V alternating current; the rear end of the rear optical fiber (6) of the sensing element and the photosensitive sensing part on the photoresistor sensor (10) in the signal detection system are bonded by ultraviolet glue and are packaged by a self-made paper black box (15).
2. The optical fiber sensor for measuring the concentration of NaCl solution according to claim 1, characterized in that: The signal source is a 650nm laser (1), which is fixed on a breadboard (7) via an optical stainless steel support rod (2).
3. The optical fiber sensor for measuring the concentration of NaCl solution according to claim 1, characterized in that: The sensor element comprises a front fixture (3), a front optical fiber (4), a plastic container (5), a rear optical fiber (6), and a rear fixture (8). The front and rear ends of the front optical fiber (4) are respectively connected and fixed to the front fixture (3) and the plastic container (5); the front and rear ends of the rear optical fiber (6) are respectively connected and fixed to the plastic container (5) and the rear fixture (8); the rear end of the front optical fiber (4) in the plastic container (5) is aligned with the front end of the rear optical fiber (6) and is 2 mm apart. The entire sensor element is fixed to a breadboard (7) by screws on the front fixture (4) and the rear fixture (8).
4. The optical fiber sensor for measuring the concentration of NaCl solution according to claim 3, characterized in that: The front optical fiber (4) and the rear optical fiber (6) are special optical fibers made of PMMA after processing, with a core diameter of 1 mm and strong bending resistance.
5. The optical fiber sensor for measuring the concentration of NaCl solution according to claim 3, characterized in that: The plastic container (5) is made of high-pressure polyethylene and is hydrophobic.
6. The optical fiber sensor for measuring the concentration of NaCl solution according to claim 1, characterized in that: The signal detection system comprises a wiring board (9), an STM32C8T6 core board (10), a photoresistor sensor module (11), an OLED display screen (12), an ST-LINK STM32 debugger (13), and a mobile phone power bank (14); the STM32C8T6 core board (10), the photoresistor sensor module (11), and the OLED display screen (12) are all connected to the wiring board (9) via a DuPont line; the STM32C8T6 core board (10) is further connected to the ST-LINK STM32 debugger (13) via a DuPont line; and the ST-LINK STM32 is connected to the mobile phone power bank (14) via a USB interface.