A high-precision quantification method for weakly absorbing liquids

Abstract

The present invention provides a high-precision optical quantification method for weakly absorbing liquids, and the steps are as follows: Turn on the photoelectric liquid level switch, and the peristaltic pump extracts the weakly absorbing liquid to be quantified at a certain pump speed V0. Calculate the difference △A between the latest signal and the previous signal, and determine whether |△A|≥0.01V is satisfied. If not, continue to extract at the pump speed V0. If satisfied, the peristaltic pump extracts at the pump speed V1, and determine whether |△A|≤nV is satisfied. If not, extract at the pump speed V1. If satisfied, the peristaltic pump extracts at the pump speed V2, and collect N signals within the time base unit △t1. When the difference △A≥nV, the peristaltic pump extracts at the pump speed V3, and determine again whether |△A|≤0.01V is satisfied. If not, repeat. If satisfied, the peristaltic pump stops, calculate the average value uA of the values of the N signals in the step, and set the average value uA as the quantification judgment threshold. Start the peristaltic pump to discharge the liquid in the reverse direction at the pump speed V3, collect the real-time signal A based on the time base unit △t0, and determine whether A - uA≤0.01V is satisfied. If not, repeat. If satisfied, the peristaltic pump stops, and the quantification ends. The present invention is applicable to the quantification of different light source systems and weakly absorbing liquids with different properties, and has high accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of optical quantification, and in particular to a high-precision optical quantification method for weakly absorbing liquids. Background Art

[0002] Currently, some water quality analysis equipment on the market uses a peristaltic pump / syringe pump combined with a photoelectric level switch to quantitatively extract liquids such as water samples or reagents. This method generally meets the requirements in practical engineering applications, but using optical detection for liquid level determination inherently has certain drawbacks. Liquids of different colors have different absorption capacities for the same optical quantitative device. For example, the ORMON EE-SPX613 uses a 940nm near-infrared light source, and pure water, red transparent liquids, and green transparent liquids have significantly different absorption capacities for this wavelength. Existing photoelectric level switches on the market, whether with analog or digital output, typically use a fixed transmitted light voltage as a threshold signal and output a signal. This works well for liquids with similar compositional properties, but the accuracy of quantitative determination for liquids with significantly different properties can often be inconsistent. This can lead to problems such as no color development, unstable absorbance after color development, or a substandard linear range if the volume ratios of the different liquids involved in the reaction are not strictly in accordance with the set requirements.

[0003] The principle of optical quantification is based on the Lambert-Beer law. Under the same light source and optical path conditions, different substances have different absorption abilities for light sources of the same intensity, that is, the transmitted light intensities are different, and the photovoltage signals obtained after conversion are also different. By setting a reasonable transmission voltage as the threshold to determine whether there is liquid in the quantitative tube, the purpose of liquid quantification can be achieved.

[0004] The so-called weak absorption liquid is relative to the wavelength of the light source of the optical quantitative device. Its essence is that for a single light source or a composite light source with a specific wavelength or a narrow wavelength range, the molar absorption coefficient of the liquid to be quantified is of a small magnitude. According to the Lambert-Beer law, when the molar absorption coefficient is greater than 10 4 L / mol·cm is strong absorption, less than 10 2 L / mol·cm is weak absorption, and those between the two are moderate absorption.

[0005] The optical quantitative method used by water quality analysis equipment on the market currently includes single threshold judgment and double threshold judgment, but it is basically based on Figure 6The signal change curve of the strongly absorbing liquid described in is used to set the same threshold for all liquids to be quantified. The single threshold judgment method is that when the liquid is extracted to the optical path position of the photoelectric liquid level switch, the detected light signal will undergo a large change and be compared with the set threshold. If it is lower than this threshold, the liquid quantification is completed. The problem with this method is that when there are bubbles mixed in the quantitative tube, it is often easy to cause misjudgment, resulting in abnormal values in the analysis equipment. The double threshold judgment is to continue to extract the liquid for a period of time when the liquid position reaches the set threshold level, and then slowly reverse the liquid in the metering tube until the detected signal reaches the set threshold level again to complete the liquid quantification. These two quantitative judgment methods have the problem of different quantitative liquid level positions for liquids with large differences or the same liquid.

[0006] Single threshold judgment method: This method is more applicable when the overall system of the analytical equipment is relatively stable. Once the liquid to be quantified is mixed with bubbles or a drain valve, and other devices that need to be passed through during quantification have a large dead volume, a large air segment will be formed in front of the actual liquid in the metering tube during quantification, which will cause a small segment of liquid to be pressed against the air segment. This will lead to misjudgment, which will cause abnormal values and large fluctuations in the measurement results. In addition, since the wavelength of the light source of the liquid level photoelectric detection switch is usually a fixed monochromatic single wavelength or a narrow range of wavelength composite light, this results in liquids of different viscosities, colors or turbidities having different absorption capacities for the intensity of the light source at the same position in the metering tube. If this single threshold method is used as the basis for judgment, the quantitative accuracy of liquids with different weak absorption capacities will vary greatly, and the larger the internal volume of the quantitative device, the greater the quantitative error.

[0007] Double threshold judgment method: To a certain extent, it can eliminate the interference caused by bubbles that cannot be eliminated by the single threshold method, but there is another problem. Figure 4 The weakly absorbing liquid signal curve shows a parabola-like shape. Therefore, using a double-threshold method can result in different liquid levels for the same liquid when the threshold is used twice. The double-threshold method also suffers from the significant variability in quantitative accuracy for different weakly absorbing liquids compared to the single-threshold method. Summary of the Invention

[0008] In response to the technical problem that the existing optical quantification-based judgment methods have large differences in quantitative accuracy for weakly absorbing liquids with different properties, the present invention proposes a high-precision optical quantification method for weakly absorbing liquids, which can not only eliminate the problem of misjudgment caused by bubbles, but also, for weakly absorbing liquids with different properties, detect the signal changes of the liquid level from continuously approaching the optical path position of the liquid level photoelectric detection switch to exceeding the optical path position of the liquid level switch, find the optimal threshold through algorithm analysis and set it, and then reversely infer the liquid to the liquid level height of the optimal threshold to complete quantification, thereby eliminating to some extent the problem of different liquid level heights when liquids with different properties reach the same threshold. The method is suitable for all analytical equipment for volume quantification of weakly absorbing liquids based on optical quantification.

[0009] In order to achieve the above object, the technical solution of the present invention is implemented as follows: a high-precision optical quantitative method for weakly absorbing liquids, the steps of which are as follows:

[0010] Step 1: Turn on the photoelectric liquid level switch and use the peristaltic pump at a pumping speed of V0 to extract the weakly absorbing liquid to be measured;

[0011] Step 2: Collect signals using the time base unit △t0 and calculate the latest signal A m With the last signal A m-1 The difference △A is obtained, and it is judged whether the difference △A satisfies |△A|≥0.01 V. If not, the pump speed V0 is used to extract, collect signals, and calculate the difference △A. The cycle continues until the requirements are met, and then step 3 is performed.

[0012] Step 3: The peristaltic pump continues to pump the weakly absorbing liquid at a pump speed of V1 and determines whether the difference △A satisfies |△A| ≤ n V. If not, continue pumping and signal acquisition at the pump speed of V1. If satisfied, proceed to step 4; where n is the set threshold signal range.

[0013] Step 4: The peristaltic pump continues to pump at the pump speed V2, and collects N signals within this period of time in the time base unit △t1, while continuing to judge the difference △A;

[0014] Step 5: When the difference △A ≥ n V, the peristaltic pump extracts liquid at a pump speed of V3 and again determines whether the difference △A satisfies |△A| ≤ 0.01 V. If not, repeat this step; if so, proceed to step 6.

[0015] Step 6: The peristaltic pump stops, and the average value uA of the N collected signals is calculated, and the average value uA is set as the quantitative judgment threshold;

[0016] Step 7: Start the peristaltic pump to discharge the weakly absorbing liquid in the reverse direction at a pump speed of V3, collect the real-time signal A based on the time base unit △t0, and determine whether A-uA≤0.01V. If not, repeat this step. If satisfied, proceed to step 8.

[0017] Step 8: The peristaltic pump stops and the light source of the liquid level photoelectric detection switch is turned off; the quantification is completed.

[0018] Preferably, the signal change during the whole process of detecting the weak absorption liquid to be quantified from the start of entering the metering tube to a certain distance where the concave liquid level completely exceeds the optical path of the liquid level photoelectric detection switch is completely reversible with the signal curve change detected when the weak absorption liquid is discharged from the inside of the metering tube again. For each different weak absorption liquid, the height position of the concave liquid level in the metering tube corresponding to the minimum signal value detected by the liquid level photoelectric detection switch is the same.

[0019] Preferably, the ranges of the pump speed V0 and the pump speed V3 are 20 - 30 mL / min; the ranges of the pump speed V1 and the pump speed V2 are 5 - 15 mL / min.

[0020] Preferably, the magnitude relationship among the pump speed V0, the pump speed V1, the pump speed V2, and the pump speed V3 is not fixed.

[0021] Preferably, the pump speed of the peristaltic pump is realized by the PTO pulse frequency sent by the PLC control system per unit time to the stepper motor driver of the peristaltic pump.

[0022] Preferably, the signal acquisition is that the detector of the liquid level photoelectric detection switch converts the optical signal emitted by the light source of the liquid level photoelectric detection switch into an electric current signal through the photoelectric effect, and then converts it into a voltage signal through a signal amplification circuit. A m is the latest voltage signal collected under the current time base unit △t0.

[0023] Preferably, the time base unit △t0 for the signal acquisition is 0.1 s - 0.5 s, and the time base unit △t1 is 0.05 s - 0.2 s.

[0024] Preferably, the set threshold signal range n is 0.005 V - 0.02 V.

[0025] Preferably, the method for obtaining the average value uA is to remove one minimum value and one maximum value from the N signals, and then perform an average calculation.

[0026] Preferably, the calculation method for the quantification judgment threshold is to first perform error elimination and curve fitting on the values of the N signals collected, and then use the derivative method to find the zero point as the quantification judgment threshold.

[0027] Advantages of the present invention.

[0028] Compared with the existing water quality analysis equipment using the optical detection method to quantify liquids, the beneficial effects of the present invention are as follows:

[0029] 1. Automatically obtain quantitative judgment threshold;

[0030] By collecting signals in different time base units and performing relevant threshold calculations in the control system, the threshold of the optimal quantitative position can be accurately obtained and automatically set, avoiding rough judgments based on manually set thresholds.

[0031] 2. Applicable to different light source systems and quantitative analysis of weakly absorbing liquids with different properties, with high accuracy;

[0032] Because the optical detection signal of the complete liquid level change is collected, even if the wavelength of the photoelectric liquid level switch is different or the properties of the liquid being measured vary, the liquid volume can be accurately quantified based on the automatically found threshold and control method. This photoelectric liquid level detection system is suitable for various light sources and can accurately quantify liquids with different properties.

[0033] 3. Eliminate misjudgments caused by interference such as bubbles and dead volume;

[0034] The present invention adopts a back-and-forth pumping method plus judgment to achieve liquid quantification, wherein the pump speed changes during the pumping process and there is a period of stillness. These measures can effectively eliminate the interference caused by bubbles and dead volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 Flowchart of the present invention.

[0037] Figure 2 It is a structural diagram of the optical quantitative device of the present invention.

[0038] Figure 3 To quantify the different stages of weakly absorbing liquids.

[0039] Figure 4 The signal change curve of the liquid level photoelectric detection switch for quantitative weak absorption liquid.

[0040] Figure 5 It is a linear relationship diagram of the total nitrogen online equipment of water quality of the present invention.

[0041] Figure 6 It is the signal change curve of the liquid level photoelectric detection switch that quantitatively absorbs the liquid. DETAILED DESCRIPTION

[0042] 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. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0043] Embodiment 1

[0044] As Figure 1 shown, a high-precision optical quantification method for weakly absorbing liquids is as follows:

[0045] Step 1: Turn on the photoelectric liquid level switch, and the peristaltic pump extracts the weakly absorbing liquid to be quantified at a certain pump speed V0; the set pump speed V0 is 20 - 30 mL / min.

[0046] The motor of the peristaltic pump is a stepper motor. The PLC control system sends out PTO equidistant pulse signals to drive the stepper motor through a stepper motor driver to realize the extraction of the liquid. The pump speed of the peristaltic pump is mainly realized by the PTO pulse frequency sent by the PLC control system per unit time to the stepper motor driver of the pump. The greater the frequency, the faster the rotation speed.

[0047] Figure 2 Shown is a common liquid level photoelectric detection quantification device. The A port is used to both extract and discharge the liquid. The B port is connected to power devices such as the peristaltic pump. The ordinary quantification method relies on power devices such as the peristaltic pump to extract the weakly absorbing liquid and enter it into the metering tube from the bottom of the metering tube. When the concave liquid level of the weakly absorbing liquid reaches the optical path position of the upper liquid level photoelectric detection switch or the lower liquid level photoelectric detection switch, the volume quantification of the weakly absorbing liquid is completed. Then, the peristaltic pump rotates in reverse to discharge the weakly absorbing liquid from the metering tube into a specified container.

[0048] Figure 4 is the signal change curve for the whole process detection from the beginning when the weakly absorbing liquid to be quantified enters the metering tube to a certain distance (generally about 1 cm higher) where the concave liquid level of the liquid completely exceeds the optical path of the liquid level photoelectric detection switch. From stage a to stage e, when the liquid is discharged from the inside of the metering tube again, the change of the detected signal curve is completely reversible, that is, from stage e to stage i. For each different weakly absorbing liquid, the height position of the concave liquid level in the metering tube corresponding to the minimum signal value detected by the liquid level photoelectric detection switch (i.e., the lowest point of the parabola in the figure) is the same. And the complete quantification process of the quantification method of this patent is from Figure 4 stage a to stage g, and the liquid level changes of the weakly absorbing liquid in the corresponding different stages are as Figure 3 shown.

[0049] The range of pump speed V0 is the best pump speed obtained by testing on the R&D equipment, which belongs to the fast range because this stage is the quantitative starting stage, that is, Figure 4 Neutralization Figure 3 The a stage described in is not a critical stage of the entire quantitative process, so a rapid extraction method can be used to shorten the time of this stage.

[0050] The quantitative detection method of weakly absorbing liquids in the present invention is based on optical signal detection and the Lambert-Beer law. The detection device used is a liquid level photoelectric detection switch. The light source of the liquid level photoelectric switch can emit light, and the changes in the transmitted light signal during the entire quantitative process can be collected through its own detector, thereby providing the PLC control system with threshold value calculation analysis and threshold value setting. Many liquid reagents or analytical water samples currently used in water quality analysis equipment are weakly absorbing liquids relative to the light source of the liquid level photoelectric switch used for their quantitative determination. Different weakly absorbing liquids also have different absorption capacities for the light emitted by the same set of liquid level photoelectric detection switches. For example, Figure 4 In the curves shown above, different weakly absorbing liquids have the same height within the metering tube at the same moment, but their signal intensities, as shown on the ordinate, vary. This method can more accurately identify the optimal quantitative threshold for each weakly absorbing liquid under the same set of optical level detection switches, resulting in more accurate quantitative measurement of different weakly absorbing liquids.

[0051] Step 2: The control system collects the detection signal in time base unit △t0 and calculates the latest voltage signal A m With the last signal A m-1 The difference △A is calculated and whether the difference △A satisfies |△A|≥0.01V. If not, continue to extract at the pump speed V0, collect signals, calculate the difference △A, and recycle until the requirements are met, then proceed to step 3.

[0052] Signal acquisition is achieved through Figure 2 The liquid level photoelectric detection switch shown on the right side is realized by the detector (specifically a photodiode) and the subsequent signal amplification circuit. The final signal collected is a converted voltage signal. The light source of the liquid level light source detection switch emits light, which is partially absorbed by the liquid to be measured in the metering tube. The unabsorbed light passes through the metering tube and irradiates the liquid level optical detection switch detector on the right (i.e., the photoelectric diode). The light signal is converted into a current signal through the photoelectric effect, and then converted into a voltage signal through the subsequent signal amplification circuit for subsequent PLC control system analysis and calculation. m That is, the latest voltage signal collected in the current time base unit.

[0053] The specific implementation method of recycling can be found in Figure 1Each diamond shown in [the figure] is a judgment node. When the conditions inside the diamond are met, the PLC control system will control the metering device to enter the next step. When the requirements inside the diamond are not met, it will return to the previous step to continue pumping the liquid, collect detection signals, calculate the difference between the two most recent signals to determine whether the conditions inside the diamond are met. If not, the process will continue.

[0054] The time base unit △t0 for signal acquisition is 0.1s - 0.5s. This time base unit is a reasonable range set based on the peristaltic pump speed and the liquid absorption signal change curve. At this time, the extraction of the liquid to be metered is in Figure 3 stage a in [the figure]. At this time, the change in the acquired signal is not obvious. Therefore, a wider time base unit can be used to shorten the time in the early stage of metering, thereby reducing the entire metering process time.

[0055] Step 3: The peristaltic pump continues to pump the liquid at pump speed V1, and further determines whether the difference △A satisfies |△A| ≤ nV. Under normal circumstances at this time, the difference △A is a negative value with little fluctuation. When the above requirements are not met, continue to pump and collect signals at pump speed V1. When satisfied, proceed to the next step. Here, n represents the difference between the two signals collected by the liquid level photoelectric detection switch during the set liquid level metering process reaching the set threshold signal range, such as Figure 4 the absolute value of the difference between the signal values corresponding to the upper and lower red lines in stage c as described in [the figure].

[0056] The set pump speed V1 is 5 - 15 mL / min. This pump speed range is a better pump speed for metering liquids obtained from tests on the equipment we developed. Because this stage can be regarded as Figure 4 stage b in [the figure]. The change in the acquired signal curve is relatively fast, and the next stage is stage c. The signal values acquired in this stage will be used to analyze and calculate the threshold, which belongs to a critical stage. This pump speed belongs to the slow speed range. Such a setting can reduce the large liquid inertia and metering error caused by too high a pump speed, and avoid missing the acquisition of some key signals. A smaller pump speed will not have an obvious effect on further improving the metering accuracy, but will instead increase the metering time.

[0057] In the set threshold voltage nV, n is 0.005V - 0.02V. n uses a non-zero value: Such a setting will make Figure 4The time period between the two red lines in the c stage is the c stage, with a certain buffer interval, so that more signals can be collected in this stage for subsequent threshold analysis and calculation, avoiding the accidental error caused by the fluctuation of the quantitative device due to external factors, which may lead to errors in the final threshold calculation. For example, if this value is selected as 0, the signals collected in the c stage may only be a few close signal values. Once a bubble enters the optical path position of the liquid level photoelectric detection switch, it will cause huge fluctuations, which is not conducive to the calculation of the final threshold, and the representativeness of the obtained threshold is also weak.

[0058] Step 4: The peristaltic pump continues to pump the liquid at a pump speed V2, and collects N signals within this period of time with a time base unit △t1 and sends them to the storage unit for subsequent processing. At the same time, the difference △A judgment continues.

[0059] Set the time base unit △t1 to 0.05s - 0.2s. This step is in Figure 4 the c stage described above. The signal values collected in this stage are used for subsequent threshold calculation and analysis. The more and denser the signal values are collected (i.e., the smaller the time base unit), the more conducive it is to calculate the optimal threshold and make it more representative. N is the number of signals collected in this stage.

[0060] The range of the pump speed V2 is the same as that of the pump speed V1, belonging to the slow speed, 5 - 15 mL / min. Because this stage is a critical stage, the slower the pump speed, the more detailed and representative the collected signals are.

[0061] Step 5: When the difference △A ≥ nV, the peristaltic pump pumps the liquid at a pump speed V3. At this time, the difference △A gradually increases to a fixed positive value, then lasts for a period of time, and then gradually decreases. Then, it is judged again whether |△A| ≤ 0.01V. If not satisfied, repeat this step. If satisfied, proceed to the next step.

[0062] As Figure 4 described above, when entering the d stage from the c stage, the signals collected by the liquid level photoelectric detection switch increase from small to large, and this difference is a positive value. Repeating this step is mainly to judge whether the quantitative process enters the e stage from the d stage. If not satisfied, it means that it is still in the d stage, and the liquid needs to be pumped again for judgment until the requirements for entering the e stage are finally met. After entering the e stage, the pumping of the liquid to be quantified can be stopped, and the subsequent threshold analysis, calculation and setting can be started. Without this process, that is, starting the subsequent steps in the d stage, it may be due to the insufficient height of the liquid in the metering tube and the instantaneous large pressure inertia when the peristaltic pump reverses and starts again, resulting in the concave liquid level of the liquid to be quantified being directly squeezed out and being lower than the position of the quantitative threshold, so that the judgment in the subsequent step 7 cannot be satisfied and will repeat continuously or be forced to stop by the control system after a certain time.

[0063] Set the pump speed V3 to 20 - 30 mL / min. This stage isFigure 4 In the d stage, which is a non-critical stage, the speed range of the pump speed V3 belongs to the fast speed range, and this range can shorten the entire metering time. The difference ΔA gradually increases to a fixed positive value, which can be seen from Figure 4 the change in the slope of the curve in the d stage in

[0064] The magnitude relationship among the pump speeds V0, V1, V2, and V3 is not fixed and is not restricted. The time base units Δt0 and Δt1 for the above-mentioned signal acquisition are not restricted and can be 100 ms, or 10 ms, or 1 s, etc.; this needs to be determined according to the size of the optical path of the device using the liquid level photoelectric detection switch to quantify the liquid, and also needs to be determined according to the hardware conditions of the PLC control system.

[0065] Step 6: The peristaltic pump stops, and the control system obtains the average value uA of the values of the N signals collected in Step 4 according to a certain calculation method, and sets it as the quantitative judgment threshold.

[0066] The method for obtaining the average value uA is to remove one minimum value and one maximum value from the N signals, and then perform an average calculation. In the present invention, the traditional method of removing the minimum value and the maximum value and then calculating the average value is used, and it is not limited to other methods for calculating the average value; in addition, the calculation method for the threshold may not adopt the method described in the present invention that uses the signal difference as the judgment basis, and the collected signal values can be first subjected to error elimination and curve fitting, and then the derivative method can be used to find the zero point as the quantitative judgment threshold. Removing the minimum value and the maximum value and then calculating the average value can eliminate the influence of accidental large fluctuations in the signal caused by external factor fluctuations, making the finally calculated threshold more representative.

[0067] Step 7: Start the peristaltic pump to discharge the liquid in the reverse direction at the pump speed V3, and at the same time collect the real-time signal A based on the time base unit Δt0, and judge whether A - uA ≤ 0.01V. If it is not satisfied, repeat this step; if it is satisfied, proceed to the next step.

[0068] This step is equivalent to Figure 4 returning from the e stage to the c stage in

[0069] In the e stage, the volume of the weakly absorbing liquid to be quantified in the metering tube is greater than the final metered volume. This step is to discharge the part that is more than the final metered volume to complete the quantification.

[0070] The light source of the liquid level photoelectric detection switch emits light. A part of the light can be absorbed by the weakly absorbing liquid to be quantified, and the other part of the unabsorbed light passes through the metering tube and reaches the detector of the photoelectric liquid level detection switch, and is converted into the signal to be collected.

[0071] Step 9: Quantification is completed.

[0072] The speed of the pumping process, i.e., the pump speed, can be set according to the actual quantitative requirements to eliminate interference such as bubbles: the pump speed can be appropriately increased when the signal value fluctuates slightly and when the rate of change of the signal value gradually increases, and the pump speed can be appropriately reduced when approaching the quantitative threshold. The pumping of the liquid is achieved according to the program programmed by the PLC control system according to the pre-determined process steps. The pump speed is determined by the PTO pulse frequency issued by the PLC control system. This combination of fast and slow speeds can reasonably shorten the quantitative time while improving the quantitative accuracy. In addition, the combination of fast and slow speeds can cause the extrusion pressure on the bubbles in the liquid in the metering tube to change rapidly in a short period of time, facilitating the bursting of the bubbles.

[0073] The range of the signal difference nV around the threshold mentioned is not restricted and can be set based on actual conditions. The value of n is set in the PLC control system program. The liquid level photoelectric detection switch is only the hardware component, providing the signal for analysis. The setting of the value of n depends not only on external factors such as the material of the metering tube and the optical path length, but also on the actual situation and the quantitative accuracy requirements. The control system described above can be a PLC system or other system such as a single-chip microcomputer, without limitation here.

[0074] Example 2

[0075] An example of application of a high-precision optical quantitative method for weakly absorbing liquids in Example 1 of the present invention in measuring hexavalent chromium in water quality:

[0076] In this application example, two sets of optical liquid level switches are used with glass measuring tubes to quantitatively analyze related liquids, mainly involving samples, pure water, reagent 1 and reagent 2. The above liquids are all colorless liquids. The wavelength of the light source of the liquid level optical detection switch is 940nm. The specific optical quantitative device is as follows Figure 2 As shown, an upper liquid level light source detection switch and a lower liquid level light source detection switch are respectively provided at the upper part and the lower part of the metering tube.

[0077] The quantitative working principle of the upper liquid level photoelectric detection switch and the lower liquid level photoelectric detection switch is exactly the same. The difference lies in the volume of the liquid that can be quantitatively measured. Generally, the volume of the liquid to be quantitatively measured is Figure 2The volume of liquid extracted from the metering tube between the bottom of the metering tube and the optical path plane of the corresponding liquid level photoelectric detection switch. The volumes of the various liquids involved in the reaction in the analytical equipment are not all the same. Therefore, liquid level photoelectric detection switches with different quantitative volumes are required to achieve corresponding implementation. For example, the upper liquid level light source detection switch can quantitatively measure a volume of 2 mL, while the lower liquid level light source detection switch can quantitatively measure a volume of 0.5 mL.

[0078] like Figure 1 As shown, a high-precision optical quantitative method for weakly absorbing liquids is described. The weakly absorbing liquid quantitative method used in this embodiment mainly involves the following steps:

[0079] (A1) Quantification begins. The light sources of the two liquid level photoelectric detection switches are turned on, and the peristaltic pump extracts the liquid to be measured in the metering tube at a frequency of 70. A frequency of 70 corresponds to a pump speed of 25 mL / min.

[0080] (A2) The control system collects signals with a time base unit of 0.5s, and calculates and judges the difference between the two signal values.

[0081] (A3) When the absolute value of the signal difference is greater than 0.01V, the peristaltic pump continues to pump liquid at a frequency of 50.

[0082] A frequency of 50 corresponds to a pump speed of 15 mL / min.

[0083] (A4) When the absolute value of the signal difference is less than or equal to 0.005V, the liquid is continued to be extracted at a frequency of 30, and the signal is collected with a time base unit of 0.2s. At this time, the control system must not only calculate the signal difference but also save all signal values collected during this period.

[0084] Here, a frequency of 30 corresponds to a pump speed of 5 mL / min.

[0085] (A5) When the absolute value of the signal difference is greater than 0.05V, continue to extract the liquid at a frequency of 50;

[0086] (A6) When the absolute value of the signal difference is less than or equal to 0.01V, the peristaltic pump stops, and the control system calculates the average value of the n collected signal values after proposing a maximum and minimum value, and sets it as the threshold uA of the liquid to be quantified. For example, the threshold value of pure water is 0.3777V.

[0087] (A7) The peristaltic pump reverses and discharges the liquid to be measured in the metering tube at a pump speed of 50, and compares the collected signal value A with the threshold value uA of the liquid to be measured in real time with a time base unit of 0.5 s;

[0088] When it is detected that the difference between the real-time signal value A and the threshold value uA is less than or equal to 0.01V, turn off the light source and stop the peristaltic pump;

[0089] (A9)The quantification of the liquid is completed.

[0090] The quantification of the sample, pure water, reagent 1, and reagent 2 all repeats the above steps. When the volume of a certain liquid to be quantified is 0.5mL, use the above-mentioned lower liquid level photoelectric detection switch to collect signals to achieve quantification. If the quantification volume is 1mL, the upper liquid level photoelectric detection switch can be used. For larger quantification volumes, two liquid level detection switches can be used in combination to achieve it. The sample is the on-site water sample or the prepared standard solution, and reagent 1 and reagent 2 are both prepared according to the reagent preparation method used in the national standard method. Theoretically, the basis for selecting these liquids is that they are weak absorbers relative to the light emitted by the light source of their liquid level photoelectric detection switch.

[0091] The following Table 1 shows the quantification results of different liquid volumes. It can be seen from Table 1 the quantification accuracy of different volumes of the same weak absorption liquid using the quantification method of the present invention. Table 2 shows the results of quantifying different weak absorption liquids using different quantification methods with the same set of quantification devices and control systems. It can be seen from Table 2 that the indication errors of quantifying different liquids using the quantification method of the present invention are all within the range of ±1%. When using the traditional single-threshold method for quantification, the quantification volume accuracies of different weak absorption liquids are also different. Although they are all within the range of ±10%, there are still errors. These are all due to the different absorption abilities of these weak absorption liquids to the light emitted by the light source of the liquid level photoelectric detection switch.

[0092] Table 1 Quantification results of the same liquid with different volumes

[0093]

[0094] Table 2 Quantification results of different weak absorption liquids

[0095]

[0096] Note: Liquid 1 is colorless and transparent, Liquid 2 is pink and transparent, and Liquid 3 is purple-red and transparent.

[0097] Table 3 shows the measurement results of different concentrations of the total nitrogen water quality on-line equipment based on this quantification method. It can be seen from Table 3 that the total nitrogen water quality analysis equipment has a repeatability of less than 2% and an indication error of less than 1% when using this quantification method to quantify different reagents and water samples and measure standard solutions of different concentrations (the general requirement for the repeatability of water quality on-line analysis equipment is ≤3%, and the requirement for the indication error is within ±10%). Thus, it can be known that this quantification method has certain practicability after being applied to the analysis equipment.

[0098] Table 3 Equipment measurement results

[0099]

[0100] Figure 5 For the linear relationship of the test results of different concentrations of this device, Figure 5 mainly, linear fitting was performed on the standard solutions of different concentrations and their absorbances measured by the total nitrogen water quality on-line analysis device using this quantitative method. From the correlation coefficient R 2 it can be seen that the device has good linearity, which also indicates the applicability of the quantitative method of the present invention on this analysis device.

[0101] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-precision optical quantification method for weakly absorbing liquids, characterized in that, The steps are as follows: Step 1: Turn on the photoelectric liquid level switch, and the peristaltic pump pumps a certain amount of weakly absorbing liquid at a pump speed of V0; Step 2: Collect signals in time base unit △t0, and calculate the latest signal A m and the previous signal A m-1 difference △A, and determine whether the difference △A satisfies |△A|≥0.01 V. If not, continue to extract, collect signals, and calculate the difference △A at pump speed V0, and loop until the requirement is met, then proceed to Step 3; Step 3: The peristaltic pump continues to pump the weakly absorbing liquid at a pump speed of V1, and determine whether the difference △A satisfies |△A|≤nV. If not, continue to pump and collect signals at a pump speed of V1. If satisfied, proceed to Step 4; where n is the set threshold signal range; Step 4: The peristaltic pump continues to pump at a pump speed of V2, and collect N signals within this period of time with a time base unit of △t1, and at the same time continue to judge the difference △A; Step 5: When the difference △A≥nV, the peristaltic pump pumps the liquid at a pump speed of V3, and then judge whether the difference △A satisfies |△A|≤0.01V. If not, repeat this step. If satisfied, proceed to Step 6; Step 6: The peristaltic pump stops, calculate the average value uA of the values of the N signals collected, and set the average value uA as the quantitative judgment threshold; Step 7: Start the peristaltic pump to discharge the weakly absorbing liquid in the reverse direction at a pump speed of V3, collect the real-time signal A based on the time base unit △t0, and judge whether A - uA≤0.01V. If not, repeat this step. If satisfied, proceed to Step 8; Step 8: The peristaltic pump stops and turns off the light source of the liquid level photoelectric detection switch; the quantification ends.

2. The high-precision optical quantitative method for weakly absorbing liquids according to claim 1, characterized in that: The signal change during the whole process of detecting the weakly absorbing liquid to be quantified from the beginning of entering the metering tube to a distance where the concave liquid level completely exceeds the optical path of the liquid level photoelectric detection switch is completely reversible with the signal curve change detected when the weakly absorbing liquid is discharged from the inside of the metering tube again. For each different weakly absorbing liquid, the height position of the concave liquid level in the metering tube corresponding to the minimum signal value detected by the liquid level photoelectric detection switch is the same.

3. The high-precision optical quantification method for weakly absorbing liquid according to claim 1 or 2, characterized in that, The ranges of the pump speed V0 and the pump speed V3 are 20 - 30 mL / min; the ranges of the pump speed V1 and the pump speed V2 are 5 - 15 mL / min.

4. The high-precision optical quantification method for weakly absorbing liquid according to claim 3, characterized in that, The magnitude relationship among the pump speed V0, the pump speed V1, the pump speed V2, and the pump speed V3 is not fixed.

5. The high-precision optical quantification method for weakly absorbent liquids according to claim 3, characterized in that Adjust the pump speed of the peristaltic pump through the PTO pulse frequency issued by the PLC control system per unit time.

6. The high-precision optical quantification method for weakly absorbing liquids according to claim 3, characterized in that, The signal acquisition is that the detector of the liquid level photoelectric detection switch converts the optical signal emitted by the light source of the liquid level photoelectric detection switch into an electric current signal through the photoelectric effect, and then converts it into a voltage signal through a signal amplification circuit. A m is the latest voltage signal acquired under the current time base unit △t0.

7. The high-precision optical quantification method for weakly absorbing liquid according to claim 6, characterized in that, The time base unit △t0 for signal collection is 0.1s - 0.5s, and the time base unit △t1 is 0.05s - 0.2s.

8. The high-precision optical quantitative method for weakly absorbing liquid according to claim 6 or 7, characterized in that The set threshold signal range n is 0.005V - 0.02V.

9. The high-precision optical quantitative method for weakly absorbing liquids according to claim 8, characterized in that: The method for obtaining the average value uA is to remove one minimum value and one maximum value from the N signals, and then perform average calculation.

10. The high-precision optical quantitative method for weakly absorbing liquids according to claim 8, characterized in that: The calculation method of the quantitative judgment threshold is to first perform error elimination and curve fitting on the values of the N signals collected, and then use the derivative method to find the zero point as the quantitative judgment threshold.

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