A method and system for reducing temperature drift and improving detection accuracy of water pollution factors

Abstract

The present invention discloses a method and system for reducing temperature drift and improving the detection accuracy of water pollution factors. The method includes the following steps: putting a sample into a colorimetric cell to generate a digestion reaction; adjusting the wavelength of the incident light source according to the pollution factor in the sample to be detected; using the same photodetector to simultaneously detect the light intensity of the light source emission end and the light intensity of the transmitted light of the colorimetric cell, and converting them into a reference end voltage signal and a detection end voltage signal; using the reference end voltage signal to correct the detection end voltage signal to obtain a corrected voltage signal; analyzing the corrected voltage signal to obtain the pollution factor value in the sample. The present invention uses the light intensity of the light source emission end to correct the light intensity of the transmitted light. Since the same photodetector is used, the influence of the noise signal can be eliminated, the detection accuracy is improved, the temperature drift is reduced, and the data error, accuracy and repeatability are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution factor detection such as pollution sources and surface water, and specifically to a method and system for reducing temperature drift and improving water pollution factor detection accuracy, in particular to a water pollution factor detection system. Background Art

[0002] At present, the assessment factors (detection indicators) for pollution sources and surface water in my country mainly include chemical oxygen demand (CODcr), ammonia nitrogen (NH3-N), total phosphorus (TP), total nitrogen (TN), and permanganate index (CODmn). The national standard methods are mainly based on chemical methods of laboratory analysis, which are complicated and time-consuming to operate, and cannot be monitored in real time, and cannot meet the development requirements of modern environmental monitoring.

[0003] To this end, Chinese invention patent CN 102680462 B discloses a method and monitoring device for online monitoring of the content of multiple heavy metals in water, using a measuring light source that can provide multiple wavelengths or continuous wavelengths; controlling the sampling, reaction and color development of the system, using a specific wavelength of light in the measuring light source to measure the absorbance of the colorimetric solution by an optical detection device, the optical detection device is an optical sensor or a spectrometer; after the control system measures the content of heavy metal pollutants corresponding to the light of a specific wavelength in the water sample to be tested, the determination of the heavy metal content corresponding to the light of this wavelength is completed; the color development measurement is cyclically performed until the determination of the content of all heavy metal pollutants is completed. This scheme uses a spectrometer with a spectroscopic function to determine the content of heavy metal substances in various different waters by detecting the transmitted light of the colorimetric pool. Although the monitoring efficiency is improved, since the received signal of the photodetector in the spectrometer is generally very weak, and the signal output by the photodetector is often deeply buried in the noise, the detection result is greatly affected by noise and temperature drift, the detection accuracy is low, and the repeatability is poor.

[0004] In view of this, it is necessary to improve the existing water pollution factor detection methods and systems to reduce temperature drift and improve the detection accuracy of water pollution factors. Summary of the invention

[0005] In view of the above-mentioned defects, the technical problem to be solved by the present invention is to provide a method and system for reducing temperature drift and improving the detection accuracy of water pollution factors, so as to solve the problems of low detection accuracy and poor repeatability in the prior art.

[0006] To this end, the present invention provides a method for reducing temperature drift and improving the detection accuracy of water pollution factors, comprising the following steps:

[0007] The sample is put into the colorimetric cell to produce a digestion reaction with the reagent in the colorimetric cell;

[0008] Adjust the wavelength of the light source according to the contamination factor in the sample to be tested;

[0009] The same photodetector is used to simultaneously detect the light intensity at the light source emission end and the light intensity of the transmitted light after emitting the colorimetric cell, and the light intensity at the light source emission end is converted into a reference end voltage signal ADref, and the light intensity of the transmitted light is converted into a detection end voltage signal ADmea;

[0010] The detection terminal voltage signal ADmea is corrected using the following formula ADxz=ADmea / ADref to obtain a corrected voltage signal ADxz;

[0011] The correction voltage signal ADxz is analyzed using the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample.

[0012] In the above method, preferably, different pollution factors in the water body are detected by changing the wavelength of the light source and replacing the reagent.

[0013] In the above method, preferably, the pollution factors include any one or more of the following:

[0014] Chemical oxygen demand, ammonia nitrogen, total phosphorus, total nitrogen and permanganate index.

[0015] The present invention also provides a system for reducing temperature drift and improving the detection accuracy of water pollution factors, comprising a colorimetric cell for causing a sample to produce a digestion reaction, an LED light source for providing incident light to the colorimetric cell, and a transmission end photoelectric detector for detecting the transmitted light transmitted through the colorimetric cell, wherein the transmission end photoelectric detector converts the light intensity of the transmitted light into a detection end voltage signal ADmea, and further comprising:

[0016] An emission end photodetector, which is the same as the transmission end photodetector, is disposed at the emission end of the LED light source and is used to detect the light intensity of the emitted light of the LED light source and convert it into a reference end voltage signal ADref;

[0017] A correction unit, used for correcting the detection terminal voltage signal ADmea by using the formula ADxz=ADmea / ADref to obtain a corrected voltage signal ADxz;

[0018] The analysis unit is used to analyze the corrected voltage signal ADxz by utilizing the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample.

[0019] In the above system, preferably, the LED light source is driven by a constant current source type photoelectric emission circuit, and the constant current source type photoelectric emission circuit includes:

[0020] A constant current driver, wherein a CS pin is connected to a GND pin via an external resistor, and the wavelength of the LED light source is changed by adjusting the external resistor.

[0021] In the above system, preferably, the emission-end photodetector and the transmission-end photodetector both include a preamplifier circuit, a main amplifier circuit and a filter circuit, and the emission light of the LED light source is sequentially converted into a reference-end voltage signal ADref through the preamplifier circuit, the main amplifier circuit and the filter circuit of the emission-end photodetector, and the transmission light is sequentially converted into a detection-end voltage signal ADmea through the preamplifier circuit, the main amplifier circuit and the filter circuit of the transmission-end photodetector.

[0022] It can be seen from the above technical solutions that the method and system for reducing temperature drift and improving the detection accuracy of water pollution factors provided by the present invention solve the problems of low detection accuracy and poor repeatability in the prior art.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The same photoelectric detector as the detection end is used to collect the light intensity at the light source emission end and correct the light intensity of the transmitted light. This can eliminate the influence of noise signals, improve detection accuracy, reduce temperature drift, and greatly improve data error, accuracy and repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces and describes the drawings required for use in the embodiments of the present invention or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 A flow chart of a method for reducing temperature drift and improving the detection accuracy of water pollution factors provided by the present invention;

[0027] Figure 2 A schematic diagram of a system for reducing temperature drift and improving water pollution factor detection accuracy provided by the present invention;

[0028] Figure 3 Schematic diagram of a circuit of a constant current source type photoelectric emission circuit in the present invention;

[0029] Figure 4 is a schematic diagram of a transmission-end photodetector in the present invention;

[0030] Figure 5 is a circuit diagram of the main amplifier circuit in the present invention;

[0031] Figure 6 is a circuit diagram of the filter circuit in the present invention;

[0032] Figure 7 It is the test result data of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the accompanying drawings of the embodiments of the present invention to clearly and completely describe the technical solutions of the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] The implementation principle of the present invention is:

[0035] The same photodetector is used to simultaneously detect the light intensity at the light source emission end and the light intensity of the transmitted light after emitting the colorimetric cell, and the light intensity at the light source emission end is converted into a reference end voltage signal ADref, and the light intensity of the transmitted light is converted into a detection end voltage signal ADmea;

[0036] The detection terminal voltage signal ADmea is corrected using the formula ADxz=ADmea / ADref to obtain a corrected voltage signal ADxz;

[0037] The correction voltage signal ADxz is analyzed using the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample.

[0038] The solution provided by the present invention utilizes the light intensity of the light source emission end to correct the light intensity of the transmitted light. Since the same photodetector is used, the influence of the noise signal in the photodetector can be eliminated, the detection accuracy is improved, the temperature drift is reduced, and the data error, accuracy and repeatability are greatly improved.

[0039] In order to more clearly explain and illustrate the technical solution and implementation of the present invention, several preferred specific embodiments for implementing the technical solution of the present invention are introduced below.

[0040] It should be noted that the directional words such as "inside, outside", "front, back" and "left, right" in this article are expressed based on the product usage status. Obviously, the use of the corresponding directional words does not constitute a limitation on the protection scope of this scheme.

[0041] Specific embodiment one.

[0042] See also Figure 1 , Figure 1This is a flow chart of a method for reducing temperature drift and improving the detection accuracy of water pollution factors provided in a specific embodiment of the present invention.

[0043] like Figure 1 As shown, the method comprises the following steps:

[0044] Step 110, putting the sample into the colorimetric cell to produce a digestion reaction with the reagent in the colorimetric cell.

[0045] Step 120, adjusting the wavelength of the LED light source according to the pollution factor in the sample to be detected.

[0046] Step 130, using the same photodetector to simultaneously detect the light intensity at the light source emission end and the light intensity of the transmitted light after emitting the colorimetric cell, and converting the light intensity at the light source emission end into a reference end voltage signal ADref, and converting the light intensity of the transmitted light into a detection end voltage signal ADmea;

[0047] Step 140, using the formula ADxz=ADmea / ADref to correct the detection terminal voltage signal ADmea to obtain a corrected voltage signal ADxz;

[0048] Step 150 , analyzing the corrected voltage signal ADxz using the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample.

[0049] The system will have a built-in linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light. This linear relationship is obtained through multiple pre-calibrations, just like the existing technology. Of course, the standard curve in the existing technology can also be used. In this case, the test process needs to be exactly the same as the standard curve, for example: using the same reagents, test temperature and other test conditions.

[0050] The scheme of the present invention obtains the corrected transmittance value of the optical detection absorbance of the colorimetric cell to restore the original theoretical concentration of the specific substance and eliminate the influence caused by temperature and circuit noise.

[0051] The above steps describe a method for detecting a specific pollution factor in a sample, such as any one of chemical oxygen demand (CODcr), ammonia nitrogen (NH3-N), total phosphorus (TP), total nitrogen (TN), and permanganate index (CODmn). Whichever one needs to be detected, it is necessary to change the wavelength of the emitted light of the LED light source, as well as the corresponding reagents and test conditions according to the pollution factor, and compare the results with the preset corresponding curves.

[0052] Therefore, through multiple tests and analyses, the values ​​of various pollution factors in the samples are obtained.

[0053] Specific embodiment two.

[0054] See also Figure 2 , Figure 2 A schematic diagram of a system for reducing temperature drift and improving water pollution factor detection accuracy provided in a second specific embodiment of the present invention, that is, a water pollution factor detection system, which can reduce temperature drift and improve water pollution factor detection accuracy.

[0055] like Figure 2 As shown, the system includes an LED light source 10 , an emission end photodetector 20 , a digestion reaction colorimetric cell 30 , a transmission end photodetector 40 , a calibration unit 50 and an analysis unit 60 .

[0056] The LED light source 10 is used to generate a parallel monochromatic light beam, and vertically passes through the digestion reaction colorimetric cell 30. The LED light source 10 can be a monochromatic LED light source, or the emitted light emitted by the LED light source 10 can be filtered into monochromatic light.

[0057] The emission-end photodetector 20 and the transmission-end photodetector 30 have the same structure (parameters).

[0058] The emission end photodetector 20 is arranged at the emission end of the LED light source, and is used to detect the light intensity of the emitted light of the LED light source 10, and convert it into a reference end voltage signal ADref, and output it to the correction unit 50. The light emitted by the LED light source can be divided into two parts by a spectroscope, one part is emitted into the digestion reaction colorimetric cell 30, and the other part is emitted to the emission end photodetector 20 for light intensity detection.

[0059] The digestion reaction colorimetric cell 30 is used to input the contamination factor and generate a digestion reaction with the detection reagent therein. The digestion reaction colorimetric cell 30 adopts the existing technology and can adjust the temperature to correspond to different detection factors.

[0060] The transmission end photodetector 40 is used to detect the transmission light emitted from the digestion reaction colorimetric cell 30 , and convert the light intensity of the transmission light into a detection end voltage signal ADmea, and output it to the correction unit 50 .

[0061] The correction unit 50 corrects the detection terminal voltage signal ADmea using the following formula ADxz=ADmea / ADref to obtain a corrected voltage signal ADxz.

[0062] The analysis unit 60 is used to analyze the correction voltage signal ADxz by using the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample.

[0063] In the specific embodiment 2, the LED light source 10 is driven by a constant current source type photoelectric emission circuit. The circuit uses QX7136 (U3) to build a low static current, low voltage difference LED constant current driver. QX7136 has built-in soft start, overheat protection, and low voltage protection.

[0064] Specific circuits such as Figure 3 As shown, the VDD pin of the constant current driver chip QX7136 is connected to the anode of the LED light source, and the LED pin is connected to the cathode of the LED light source; the CS pin is connected to the external resistor R14, and the output current of the LED light source is adjusted by adjusting the external resistor R14, thereby changing the wavelength of the LED light source, and the DRV pin is set to be suspended. The VDD pin and the GND pin are connected through a capacitor C4 for protection.

[0065] In the specific embodiment 2, the output current is adjusted within the range of 10 mA to 400 mA by adjusting the low temperature drift external resistor R14. Since the required current IF=10-20 mA, the external resistor R14 is selected to be 2.7Ω-5.3Ω.

[0066] The external resistor R14 is a multi-position resistor, and each position corresponds to an output wavelength.

[0067] The corresponding relationship between the pollution factor and the wavelength of the LED light source is as follows:

[0068]

[0069]

[0070] The signals received by photodetectors are generally very weak, and the signals output by photodetectors are often buried deep in noise. Therefore, to process such weak signals, preprocessing is generally required first to filter out most of the noise and amplify the weak signal to the voltage amplitude required by the subsequent processor.

[0071] The structure of the emission-end photodetector 20 is the same as that of the transmission-end photodetector 30 . The specific circuit thereof will be described below by taking the transmission-end photodetector 30 as an example.

[0072] like Figure 4 As shown, the transmission end photodetector 40 includes a preamplifier circuit 41 , a main amplifier circuit 42 and a filter circuit 43 .

[0073] The preamplifier circuit 41 adopts a photodiode preamplifier circuit, which is used to convert the detected light intensity signal into a voltage signal. It belongs to the prior art and will not be described in detail here.

[0074] The circuit of the main amplifier circuit 42 can be as follows: Figure 5An example shown is used to amplify the voltage signal output by the preamplifier circuit 41.

[0075] The circuit of the filter circuit 43 can be adopted as follows Figure 6 In one example shown, a first-order low-pass filter circuit is used to remove noise outside the useful signal frequency band, including environmental noise and noise introduced by the preamplifier.

[0076] The first-order low-pass filter circuit contains active devices such as integrated operational amplifiers. The operational amplifier has high input impedance, low output impedance, high open-loop gain and good stability, and it has a simple structure and excellent performance.

[0077] A specific implementation of the present invention is as follows. The results of multiple tests are shown in the figure. The test results of transmittance are very stable, and the data error, accuracy and repeatability are greatly improved. The influence of noise interference can be eliminated, the detection accuracy is improved, and the temperature drift is reduced.

[0078] The principle of eliminating the influence of noise signals in the present invention is explained as follows:

[0079] ADxz=ADmea / ADref;

[0080] Among them, ADref is the voltage at the light detection reference end, ADmea is the voltage at the light detection measurement end, and ADxz is the corrected light transmittance value obtained through correction calculation.

[0081] Since the optical detection reference end and the optical detection measurement end use the same optical detection circuit and are in the same temperature and humidity environment, the light source detection noise signals caused by temperature, circuit noise and other reasons should have a geometric relationship, that is:

[0082] △ADref=ADref×Nref;

[0083] △ADmea=ADmea×Nmea;

[0084] Nref=Nmea, Nref is the reference end signal change rate, such as 5% or 10%; Nmea is the measurement end signal change rate.

[0085] 1. Error analysis of existing technology algorithms:

[0086] ADmea1=(ADmea0+ΔADmea0)=(ADmea0+ADmea0×Nmea)=ADmea0×(1+Nmea);

[0087] Therefore, ADmea1 / ADmea0=(1+Nmea).

[0088] It can be seen from the calculation results that the noise signal △ADmea has a great influence on the actual value error, accuracy and repeatability of the measurement results. And because this noise signal is bound to exist and is difficult to avoid, in actual detection, even if every possible means are used for noise shielding, circuit improvement, and constant temperature control, it is only possible to reduce the influence of Nmea, but it cannot be eradicated.

[0089] 2. Error analysis using the correction algorithm of the present invention:

[0090] ADxz=ADmea / ADref=(ADmea+△ADmea) / (ADref+△ADref)

[0091] =(ADmea+ADmea×Nmea) / (ADref+ADref×Nref)

[0092] =ADmea×(Nmea+1) / ADref×(Nref+1);

[0093] Because Nmea=Nref, ADxz=ADmea / ADref.

[0094] It can be seen from the calculation results that after the correction calculation results, the influence of the noise signals △ADref and △ADmea are fundamentally eliminated, and the numerical error, accuracy and repeatability of the data are greatly improved.

[0095] Based on the description of the above specific embodiments, the method and system for reducing temperature drift and improving the detection accuracy of water pollution factors provided by the present invention have the following advantages compared with the prior art:

[0096] First, the same photoelectric detector as the detection end is used to collect the light intensity at the light source emission end and correct the light intensity of the transmitted light. This can eliminate the influence of noise signals, improve detection accuracy, reduce temperature drift, and greatly improve data error, accuracy and repeatability.

[0097] Secondly, by changing the wavelength of the LED light source and replacing the detection reagents, the values ​​of various pollution factors in the sample can be obtained, further improving efficiency.

[0098] Third, the photodetector consists of a preamplifier circuit, a main amplifier circuit and a filter circuit. The filter circuit uses a first-order low-pass filter circuit to remove noise outside the useful signal frequency band, including environmental noise and noise introduced by the preamplifier.

[0099] Finally, it should be noted that the terms "comprises", "includes" or any other variants thereof as used herein are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0100] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone should be aware that any structural changes made under the inspiration of the present invention, and any technical solutions that are the same or similar to the present invention, fall within the protection scope of the present invention.

Claims

1. A method for reducing temperature drift and improving the detection accuracy of water pollution factors, characterized in that: The following steps are involved: The sample is put into the colorimetric cell to produce a digestion reaction with the reagent in the colorimetric cell; Adjust the wavelength of the light source according to the contamination factor in the sample to be tested; The same photodetector is used to simultaneously detect the light intensity at the light source emission end and the light intensity of the transmitted light after emitting the colorimetric cell, and the light intensity at the light source emission end is converted into a reference end voltage signal ADref, and the light intensity of the transmitted light is converted into a detection end voltage signal ADmea; The detection terminal voltage signal ADmea is corrected using the following formula ADxz=ADmea / ADref to obtain a corrected voltage signal ADxz; Analyzing the corrected voltage signal ADxz using the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample; Among them, ADref is the voltage of the light detection reference end, ADmea is the voltage of the light detection measurement end, and ADxz is the corrected light transmittance value obtained through correction calculation.

2. The method according to claim 1, characterized in that By changing the wavelength of the light source and replacing the reagent, different pollution factors in the water body can be detected.

3. The method according to claim 2, characterized in that The pollution factors include any one or more of the following: Chemical oxygen demand, ammonia nitrogen, total phosphorus, total nitrogen and permanganate index.

4. A system for reducing temperature drift and improving the detection accuracy of water pollution factors, comprising a colorimetric cell for causing a sample to produce a digestion reaction, an LED light source for providing incident light to the colorimetric cell, and a transmission end photoelectric detector for detecting the transmitted light transmitted through the colorimetric cell, wherein the transmission end photoelectric detector converts the light intensity of the transmitted light into a detection end voltage signal ADmea, characterized in that: Also includes: An emission end photodetector, which is the same as the transmission end photodetector, is disposed at the emission end of the LED light source and is used to detect the light intensity of the emitted light of the LED light source and convert it into a reference end voltage signal ADref; The correction unit is used to correct the detection terminal voltage signal ADmea using the formula ADxz=ADmea / ADref to obtain a corrected voltage signal ADxz; wherein ADref is the voltage of the light detection reference terminal, ADmea is the voltage of the light detection quantity terminal, and ADxz is the corrected light transmittance value obtained through correction calculation; An analysis unit, used to analyze the corrected voltage signal ADxz by using the linear relationship between the pollution factor value and the light intensity voltage signal of the transmitted light to obtain the pollution factor value in the sample; The LED light source is driven by a constant current source type photoelectric emission circuit, and the constant current source type photoelectric emission circuit includes: A constant current driver, wherein the CS pin is connected to the GND pin via an external resistor, and the wavelength of the LED light source is changed by adjusting the external resistor; The emission end photodetector and the transmission end photodetector both include a preamplifier circuit, a main amplifier circuit and a filter circuit. The emission light of the LED light source is converted into a reference end voltage signal ADref through the preamplifier circuit, the main amplifier circuit and the filter circuit of the emission end photodetector in sequence, and the transmission light is converted into a detection end voltage signal ADmea through the preamplifier circuit, the main amplifier circuit and the filter circuit of the transmission end photodetector in sequence.

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