CN105806915A - Device and method for detecting concentration of potassium and sodium ions in nutrient solution - Google Patents
Device and method for detecting concentration of potassium and sodium ions in nutrient solution Download PDFInfo
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- 229910001414 potassium ion Inorganic materials 0.000 title claims abstract description 143
- 229910001415 sodium ion Inorganic materials 0.000 title claims abstract description 123
- 235000015097 nutrients Nutrition 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims abstract description 39
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 title claims abstract description 35
- 239000011591 potassium Substances 0.000 title claims abstract description 35
- 150000002500 ions Chemical class 0.000 claims abstract description 98
- NPYPAHLBTDXSSS-UHFFFAOYSA-N Potassium ion Chemical compound [K+] NPYPAHLBTDXSSS-UHFFFAOYSA-N 0.000 claims abstract description 75
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 claims abstract description 70
- 230000004044 response Effects 0.000 claims abstract description 67
- 230000001052 transient effect Effects 0.000 claims abstract description 44
- 238000001514 detection method Methods 0.000 claims abstract description 33
- 238000012937 correction Methods 0.000 claims abstract description 27
- 230000035945 sensitivity Effects 0.000 claims abstract description 24
- 239000000243 solution Substances 0.000 claims description 77
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 18
- 230000011218 segmentation Effects 0.000 claims description 18
- 230000000694 effects Effects 0.000 claims description 17
- 238000012545 processing Methods 0.000 claims description 13
- 230000003993 interaction Effects 0.000 claims description 12
- 239000011159 matrix material Substances 0.000 claims description 12
- 239000011780 sodium chloride Substances 0.000 claims description 9
- 238000006243 chemical reaction Methods 0.000 claims description 8
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Inorganic materials [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 claims description 7
- 239000011259 mixed solution Substances 0.000 claims description 6
- 238000004458 analytical method Methods 0.000 claims description 3
- 239000004973 liquid crystal related substance Substances 0.000 claims description 3
- 239000013589 supplement Substances 0.000 claims description 3
- 230000008901 benefit Effects 0.000 abstract description 4
- 238000010586 diagram Methods 0.000 description 9
- 238000012360 testing method Methods 0.000 description 9
- 239000012528 membrane Substances 0.000 description 8
- 238000005259 measurement Methods 0.000 description 7
- 239000011734 sodium Substances 0.000 description 7
- 229910052700 potassium Inorganic materials 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 4
- 230000002452 interceptive effect Effects 0.000 description 4
- 238000002156 mixing Methods 0.000 description 3
- 238000012549 training Methods 0.000 description 3
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 2
- 206010063385 Intellectualisation Diseases 0.000 description 2
- 230000003321 amplification Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910001424 calcium ion Inorganic materials 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000006870 function Effects 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 230000000704 physical effect Effects 0.000 description 2
- 230000008636 plant growth process Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000002689 soil Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 238000012706 support-vector machine Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 229910021607 Silver chloride Inorganic materials 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
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- 238000012217 deletion Methods 0.000 description 1
- 230000037430 deletion Effects 0.000 description 1
- 238000001739 density measurement Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000018514 detection of nutrient Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 235000013399 edible fruits Nutrition 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000035558 fertility Effects 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 230000012010 growth Effects 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 229940056932 lead sulfide Drugs 0.000 description 1
- 229910052981 lead sulfide Inorganic materials 0.000 description 1
- RVPVRDXYQKGNMQ-UHFFFAOYSA-N lead(2+) Chemical compound [Pb+2] RVPVRDXYQKGNMQ-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 235000021049 nutrient content Nutrition 0.000 description 1
- 239000006174 pH buffer Substances 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- OJMIONKXNSYLSR-UHFFFAOYSA-N phosphorous acid Chemical compound OP(O)O OJMIONKXNSYLSR-UHFFFAOYSA-N 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 235000010333 potassium nitrate Nutrition 0.000 description 1
- 239000004323 potassium nitrate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000035807 sensation Effects 0.000 description 1
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 235000013311 vegetables Nutrition 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/333—Ion-selective electrodes or membranes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/27—Association of two or more measuring systems or cells, each measuring a different parameter, where the measurement results may be either used independently, the systems or cells being physically associated, or combined to produce a value for a further parameter
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Abstract
The invention provides a device and a method for detecting the concentration of potassium and sodium ions in a nutrient solution. The device comprises a potassium ion selective electrode, a sodium ion selective electrode, a reference electrode, a single-chip microcomputer, a temperature sensor and a touch display screen, wherein the concentration of potassium and sodium ions in the nutrient solution is converted into potential signals by the potassium ion selective electrode, the sodium ion selective electrode and the reference electrode; the single-chip microcomputer acquires transient response signals and steady response signals of the ion selective electrodes in real time; cross sensitivity correction is performed with a CART (classification and regression tree) algorithm; the temperature sensor converts detected temperature of the nutrient solution into a digital signal and inputs the digital signal to the single-chip microcomputer for temperature compensation, the concentration of potassium and sodium ions in the nutrient solution is acquired, and a result is displayed. The detection device has the advantages of low cost, stable performance, high precision, simplicity and convenience in operation, capability of performing automatic cross sensitivity correction and temperature compensation and the like. The detection error of the potassium and sodium ion selective electrodes can be effectively reduced with the correction method.
Description
Technical Field
The invention belongs to the field of intelligent instruments, protected agriculture and soilless culture nutrient solution detection, and particularly relates to a device and a method for detecting the concentration of potassium ions and sodium ions in a nutrient solution.
Background
Soilless culture is an important aspect in protected agriculture. Soilless culture production of crops such as flowers, vegetables, fruits and the like has high requirements on high-efficiency intensification degree. Wherein, the management of water and nutrient ions is crucial, and poor management can result in low benefit and increased water and fertilizer cost and energy consumption. Therefore, as precision agriculture advances towards automation, modernization and intellectualization, the technology and equipment for detecting the ion concentration of the nutrient solution urgently need to realize real-time, automation, intellectualization and miniaturization.
At present, due to the wide application of soilless culture, the detection of the ion concentration of the nutrient solution is also widely concerned by people, for example, patent CN1793887A discloses an on-line full-automatic sodium ion concentration analyzer, which measures through a measuring tank and a secondary intelligent instrument. Patent CN102654476A discloses a lead ion selective electrode with self-repairing function and its preparation, which is composed of selective membrane, polyvinyl chloride (PVC) tube, Ag/AgCl internal reference electrode, internal filling liquid, electrode end cap, and outgoing line. The hollow nano lead sulfide with special morphology is applied to the analysis technology of the ion selective electrode (TSF) for the first time, and the ion selective electrode has the advantages of self-repairing function, long service life, quick detection response, high sensitivity and capability of quickly and accurately detecting lead ions in a solution. Patent CN1380973A discloses an ion concentration measuring device, which continuously measures the ion concentration by a differential conductivity meter. Patent CN103091502A discloses a mobile device based on multichannel ion selective electrode method measures soil fertility, can freely remove in the field, can make whole fixed point borrow, stirring, detection, calculation, record process controllable and serialization, pollution-free, be applicable to the multiple spot continuous sampling test in a large scale field, can study the multiple nutrient content distribution condition of soil simultaneously. Patent CN102558724A discloses an inductive membrane for potassium ion selective electrode, its production method and application, which is characterized by that the solute and one or several solvents are uniformly mixed, after the solvent is volatilized, the membrane is formed, and the membrane is used for measuring block-like sensation of electrolyte potassium ionThe ion selective electrode should be membrane. Patent CN102645477A discloses an iterative operation method for determining concentration by using ion selective electrode, which uses an iterative operation method of Davies formula to directly calculate the concentration of ions, and overcomes the disadvantage that high concentration of ionic strength regulator and pH buffer agent need to be added into the liquid to be determined in the traditional method. A multi-component detection device available from CleanGrow of Ireland for selectively detecting Ca2+,Cl-，K+、Na+,NO3 -，NH4 +6 indexes. The Chinese science automation system also successfully develops an on-line detection system for the components of the nutrient solution. The detectors have the defects that an ion concentration detection system is large in size and inconvenient to carry, cross sensitive effect, namely interference ions, has large influence on detection precision, measurement environment temperature has large influence on measurement precision, manual temperature compensation operation is complex, the test cost is high and the like.
Ion-selective electrodes are a class of electrochemical sensors whose potential is linear with the logarithm of the activity of a given ion in solution. Therefore, it can directly convert the concentration of the detected ions into an electrical signal, i.e. a potential. However, the sensitive membrane of the ion selective electrode is not only sensitive to a single ion, but also has a large influence on the detection accuracy of the ion selective electrode due to the existence of interfering ions, and ions with similar physical properties usually generate a cross-sensitive phenomenon between the ion selective electrodes, and how to suppress or compensate the influence is a hot point of research in the field of the ion selective electrode in the present year. Patent CN102135516A discloses a method and device for detecting the concentration of phosphite or sulfate ions on line, which detects the ion concentration by establishing a least squares support vector machine training model. Patent CN102175737A discloses an ion selective electrode cross sensitivity correction method and device for on-line detection of nutrient solution components, which performs least squares support vector machine regression training according to a predetermined proportional relation of potassium ions and calcium ions in the plant growth process, and establishes a cross sensitivity correction model to obtain the potassium ion concentration at any time in the plant growth process to be detected. However, the solution uses the growth and absorption rule of the plant as a predetermined proportional relation, and the correction model needs to be calculated and determined again every time the crop is replaced, so that the universality is poor and the practical requirement is difficult to achieve.
Disclosure of Invention
The invention provides a device and a method for detecting the concentration of potassium and sodium ions in a nutrient solution, aiming at the problems that the existence of interfering ions in the prior art has great influence on the detection precision of ion selection electrodes, and ions with similar physical properties usually generate cross sensitivity between the mutual ion selection electrodes.
The present invention achieves the above-described object by the following technical means.
The device for detecting the concentration of potassium and sodium ions in nutrient solution is characterized by comprising a potassium ion selection electrode, a sodium ion selection electrode, a reference electrode, a multi-channel signal selector, a signal processing circuit, a single chip microcomputer, a temperature sensor and a human-computer interaction device, wherein the potassium ion selection electrode and the sodium ion selection electrode are both connected with the multi-channel signal selector, and the multi-channel signal selector and the reference electrode are both connected with the single chip microcomputer through the signal processing circuit; the temperature sensor and the human-computer interaction device are connected with the single chip microcomputer;
the multi-channel signal selector is used for selecting one of the potassium ion selective electrode and the sodium ion selective electrode to work simultaneously with the reference electrode according to an instruction of the human-computer interaction device;
the potassium ion selective electrode and the reference electrode work cooperatively to measure the concentration of potassium ions in the nutrient solution;
the sodium ion selective electrode and the reference electrode work cooperatively to measure the concentration of sodium ions in the nutrient solution;
the signal processing circuit calculates potential signals of potassium ion concentration and sodium ion concentration according to values measured by the potassium ion selective electrode, the sodium ion selective electrode and the reference electrode, converts the potential signals of the potassium ion concentration and the sodium ion concentration into analog signals which can be identified by the singlechip and transmits the analog signals to the singlechip;
the temperature sensor is used for collecting and detecting the temperature of the nutrient solution and transmitting a temperature signal to the singlechip;
the single chip microcomputer carries out analog-to-digital conversion on potassium ion concentration, sodium ion concentration potential signals and the temperature of the nutrient solution, an improved CART tree regression algorithm is adopted for fitting and calculating, the ratio of potassium ion concentration to sodium ion concentration is solved through a decoupling matrix, the potassium ion concentration to sodium ion concentration is substituted into a correction model of a cross sensitive effect to calculate the potassium ion concentration and the sodium ion concentration, temperature compensation is carried out on the obtained potassium ion concentration and sodium ion concentration according to the temperature of the nutrient solution, and finally the result is output to a human-computer interaction device for displaying.
Furthermore, the human-computer interaction device is a touch display screen.
The detection method of the detection device for the concentration of potassium and sodium ions in the nutrient solution is characterized by comprising the following steps:
(1) data acquisition:
the man-machine interaction device controls a multi-channel signal selector to select one path of signal in the potassium ion selective electrode or the sodium ion selective electrode to subtract the reference electrode signal, so that a potential signal of potassium and sodium ion concentration or sodium ion concentration in the nutrient solution is obtained, and the potential signals of the potassium ion concentration and the sodium ion concentration are converted into analog signals which can be identified by the single chip microcomputer and transmitted to the single chip microcomputer; the temperature sensor detects the temperature of the nutrient solution in real time, converts a temperature signal into a digital signal and transmits the digital signal into the singlechip;
(2) and (3) calculating the accurate potassium and sodium ion concentrations by adopting a cross-sensitive automatic correction compensation method:
firstly, analog-to-digital conversion is carried out on analog signals of potassium ion concentration and sodium ion concentration in a single chip microcomputer to obtain transient response data and steady-state response data;
the resulting transient response data is then treated as pure KNO3The transient response curves of the solution and the pure NaCl solution are togetherThe method comprises the steps of establishing a tree structure by using a CART tree regression algorithm, splitting each unit of an input space in a recursion mode, traversing the whole transient response curve, and performing segmentation and linear fitting (x) by using characteristic points as segmentation basesi,f(xi) And (x)i+1,f(xi+1) Linear equation between leaf nodes, error analysis of the leaf nodes based on linear fit, total error value of the entire transient response curve
Wherein f (x) is the transient response curve, point (x)i,f(xi) ) is a selected feature point;
when the total error value of the selected whole curve is minimum, the k characteristic points are the optimal segmentation characteristic points x1,x2,x3,…,xk(ii) a Segmenting the curve by using the optimal segmentation characteristic points to obtain a regression line of each leaf;
then, with pure KNO3Taking a k-1 section fitting straight line of transient response of the solution and the pure NaCl solution as a matrix base, taking the concentration ratio of potassium ions and sodium ions as an influence coefficient, taking a k-1 section fitting straight line of transient response of the mixed solution as a synthetic value, and decoupling through a decoupling matrix to obtain the concentration ratio of potassium ions and sodium ions; the decoupling matrix is:
wherein, ckDenotes the activity of the ion k, bkDenotes the selection coefficient, V, of ion k by the ion-selective electrodekRepresenting the output potential of the ion-selective electrode,represents the potential of the reference electrode, the zero potential of the ion andthe sum of the bridge potentials;
finally, obtaining a cross sensitivity correction model of the potassium and sodium ion selective electrode from the steady state response data and the influence coefficient
And satisfies the following conditions:
wherein R represents a gas constant of 8.31 (J/mol. multidot.K), T represents an absolute temperature, and Z representsiDenotes the charge of the ion i, F denotes the Faraday constant 96487(C/mol), biDenotes the interference coefficient of ion i with respect to k ion-selective electrode, ciWhich represents the concentration of the ion i,which represents the zero potential of the ion i,which represents the potential of the reference electrode,representing the bridge potential;
substituting the concentration ratio of the potassium ions to the sodium ions into a cross sensitivity correction model of a potassium ion selective electrode and a sodium ion selective electrode to obtain the concentrations of the potassium ions and the sodium ions;
(3) temperature compensation:
and carrying out temperature compensation on the obtained concentration value, and finally outputting the result to a touch liquid crystal screen for displaying.
Further, the temperature compensation method in the step (3) is:
temperature compensation is carried out on the concentrations of potassium and sodium ions by a temperature compensation formula obtained by an nernst equation
Wherein c isSupplement deviceRepresents the compensated ion concentration, cOriginal sourceRepresenting the measured concentration of the primary ion, TSign boardIndicating the temperature, T, at which the ion-selective electrode is calibratedMeasuringIndicating the measured temperature of the sensor.
Further, in the step (2), when the response curve is divided, the first point and the last point of the curve are added to three points in the curve, and the total five points are used as characteristic points to segment the transient response curve, so that the total error of four segments of fitted straight lines which are connected end to end by the five points is minimum.
Compared with the common nutrient solution ion concentration detection device and method, the nutrient solution potassium and sodium ion concentration detection device and the cross-sensitive automatic correction compensation method have the beneficial effects that:
(1) the detection device is simple and convenient to operate, good in real-time performance, high in detection precision, strong in cross sensitivity effect resistance, strong in temperature interference resistance and convenient to carry;
(2) by taking transient response and steady-state response as training samples and establishing a nutrient solution ion selective electrode potassium and sodium ion cross sensitivity automatic correction model and a temperature compensation method by adopting a CART tree regression algorithm, the cross sensitivity effect of potassium and sodium ions and the interference of temperature on selective electrodes can be effectively inhibited, and the influence of the potassium and sodium ion cross sensitivity phenomenon on the measurement precision of the ion selective electrodes is effectively improved.
Drawings
FIG. 1 is a block diagram of a device for detecting the concentration of potassium and sodium ions in a nutrient solution according to the present invention;
FIG. 2 is a schematic diagram of a multiplexer and signal processing circuit according to the present invention;
FIG. 3 is a touch display head interface diagram according to the present invention;
FIG. 4 is a concentration measurement interface diagram according to the present invention;
FIG. 5 is a data query interface according to the present invention;
FIG. 6 is a final state response diagram of a potassium ion selective electrode for a nutrient solution ion selective electrode potassium and sodium ion cross-sensitivity auto-calibration method according to the present invention;
FIG. 7 is a diagram of the final state response of the potassium ion selective electrode to sodium ions for the method for automatically correcting the potassium and sodium ion cross sensitivity of the nutrient solution ion selective electrode according to the present invention;
FIG. 8 is a graph of the effect of cross-sensitivity of potassium ion selective electrodes used in the present invention;
FIG. 9 is a graph showing the transient response of a potassium ion selective electrode used in the present invention to potassium ions;
FIG. 10 is a graph showing the transient response of a potassium ion selective electrode to sodium ions used in the present invention;
FIG. 11 is a CART cut-off graph of the transient response curve of potassium ions to a potassium ion selective electrode used in the present invention;
FIG. 12 is a CART cut-out of the transient response curve of potassium ion selective electrodes to sodium ions used in the present invention;
FIG. 13 is a graph of the transient response of a potassium ion selective electrode used in the present invention in a mixed nutrient solution;
FIG. 14 is a CART cut-out of the transient response curve of a potassium ion selective electrode used in the present invention in a mixed nutrient solution.
Detailed Description
The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.
As shown in figure 1, the device for detecting the concentration of potassium ions and sodium ions in nutrient solution comprises a potassium ion selective electrode, a sodium ion selective electrode, a reference electrode, a multi-channel signal selector, a signal processing circuit, a single chip microcomputer, a temperature sensor and a touch display screen. The potassium ion selective electrode and the sodium ion selective electrode are both connected with a multi-channel signal selector, and the multi-channel signal selector and the reference electrode are both connected with the single chip microcomputer through a signal processing circuit. And the temperature sensor and the touch display screen are connected with the single chip microcomputer. The multi-channel signal selector is used for selecting one of the potassium ion selection electrode and the sodium ion selection electrode to work simultaneously with the reference electrode according to an instruction of the touch display screen. The potassium ion selective electrode and the reference electrode cooperatively work to measure the concentration of potassium ions in the nutrient solution, and the sodium ion selective electrode and the reference electrode cooperatively work to measure the concentration of sodium ions in the nutrient solution. The signal processing circuit calculates potential signals of potassium ion concentration and sodium ion concentration according to values measured by the potassium ion selective electrode, the sodium ion selective electrode and the reference electrode, converts the potential signals of the potassium ion concentration and the sodium ion concentration into analog signals which can be identified by the singlechip and transmits the analog signals to the singlechip. The temperature sensor is used for collecting and detecting the temperature of the nutrient solution and transmitting a temperature signal to the single chip microcomputer. The single chip microcomputer carries out analog-to-digital conversion on potassium ion concentration, sodium ion concentration potential signals and the temperature of the nutrient solution, an improved CART tree regression algorithm is adopted for fitting and calculating, the ratio of potassium ion concentration to sodium ion concentration is solved through a decoupling matrix, the potassium ion concentration to the sodium ion concentration is substituted into a correction model of a cross sensitive effect to calculate the potassium ion concentration and the sodium ion concentration, temperature compensation is carried out on the obtained potassium ion concentration and sodium ion concentration according to the temperature of the nutrient solution, and finally the result is output to a touch display screen to be displayed.
The working process is as follows: after the power is switched on, the measurement is started by controlling a touch display screen, firstly, a path of signal in a potassium ion selective electrode or a sodium ion selective electrode is selected by a multi-path selector, is subtracted from a reference electrode signal, the concentration of potassium or sodium ions in nutrient solution is converted into a potential signal, the potential signal is converted into an analog signal which can be identified by a single chip microcomputer through a signal processing circuit, the analog signal is transmitted into the single chip microcomputer to be subjected to analog-to-digital conversion and real-time acquisition, the acquisition starts from the electrode entering the solution, the transient response of the ion selective electrode is acquired in real time at the rate of once per second until the. The method comprises the steps of segmenting a transient response curve by taking five time points in total, namely 5 seconds, 160 seconds and the middle three time points, fitting and calculating by adopting an improved CART tree regression algorithm, determining the selection of the characteristic points under the condition of minimum total error value, comparing the characteristic points with four segments of fitting lines of pure potassium ions and pure sodium ions, solving the weight ratio of the potassium ions and the sodium ions, namely the ratio of the concentrations of the potassium ions and the sodium ions, by using a decoupling matrix, and substituting the weight ratio into a correction model of a cross sensitivity effect to obtain more accurate concentration values of the potassium ions and the sodium ions. Meanwhile, the temperature sensor converts the temperature of the detected nutrient solution into a digital signal, transmits the digital signal into the single chip microcomputer, performs temperature compensation on the obtained concentration value, and finally outputs the result to the touch liquid crystal screen for displaying.
As shown in figure 2, the signal processing circuit of the nutrient solution potassium and sodium ion concentration detection device consists of a multiplexer, a differential amplification circuit, an effective value measurement module and a voltage follower. Firstly, a multiplexer selects a signal and a reference electrode signal to be sent to a differential amplifier. Because a large common-mode signal exists between the outputs of the ion selection electrode and the reference electrode, a differential amplification circuit is adopted for signal processing, and then the processed signal is input into an AD conversion module for conversion. Due to the high internal resistance of the electrodes, typically up to 106Omega, therefore, the AD712 is adopted as an operational amplifier, and the input impedance is as high as 3 × 1012And omega, the design requirement is met. In the differential amplifier circuit, when R1 ═ R2, R4 ═ R5, and R6 ═ R7. The magnification is (1+2R1/R3) (R6/R4). Respectively selecting R1 ═ R2 ═ R3578 ═ R2-The theoretical magnification factor is 29.48 times, 4.7K Ω, 1K Ω when R5 is equal to R4, and 2.2K Ω when R6 is equal to R7. And then, the amplified signal is sent to an effective value measuring module circuit to obtain a stable level signal, and finally, the level signal is output through a voltage follower.
As shown in fig. 3, a first line of the touch display head interface diagram of the present invention is the name of the detection device of the present invention, and the following three lines are 3 keys, which are respectively density measurement, data query, and data deletion; FIG. 4 is a concentration measurement interface, with potassium and sodium ion concentrations on the left and nutrient solution temperature and detection timing on the lower side; fig. 5 is a data query interface, which records the concentration curves of detected potassium and sodium ions in the form of coordinates and with time as an axis.
From the above, it can be seen that: the corresponding detection device for the concentrations of the potassium ions and the sodium ions in the nutrient solution only takes the single chip microcomputer as a core, and is added with a part of peripheral circuits and sensors, so that the detection requirements of the potassium ions and the sodium ions in the nutrient solution for agricultural soilless culture can be met, and the detection device has the advantages of simplicity and convenience in operation, good real-time performance, high detection precision, strong cross sensitivity resistance, strong temperature interference resistance and convenience in carrying.
The method for automatically correcting and compensating the cross sensitivity of potassium ions and sodium ions in the corresponding nutrient solution comprises the following specific implementation method:
generally, the membrane potential of an ion-selective electrode follows the nernst equation:
wherein,is the potential of the membrane, and is,is the zero potential of the k ion, akIs the activity of the ion k, zkIs the charge of ion k, F isThe charge is converted to a Faraday constant 96487(C/mol) in moles, R is the gas constant, 8.31 (J/mol. multidot.K), and T is the absolute temperature.
When the interfering ion j is considered,
Rkjis the correlation coefficient of ion k with ion j,
the electrode potential can be obtained
With the reference electrode introduced, the available electrode potential difference is:
whereinFor the bridge potential, it can be expressed by the following formula:
tnthe number of electron transfers.
For convenience of calculation, the solution ion concentration c is usedKSubstitution Activity aKCan be finished to obtainThe multi-ion cross sensitivity correction model is
Considering only the main ion k and the interfering ion j, assuming that the bridge potential is unchanged from the reference electrode potential, and letThe cross sensitivity correction model under two ions can be obtained as
The following is a cross-sensitivity correction method based on the CART algorithm. Collecting the transient response curve f (t) of the ion selection electrode in a single ion solution, traversing the whole transient response curve by adopting a CART tree regression algorithm, and selecting x1,x2,x3,…,xkK feature points of (a), a point (x) can be obtainedi,f(xi) And point (x)i+1,f(xi+1) Equation of a straight line between) is
The total error between these two points is
Then the total error value of the entire curve is
When the total error value of the selected whole curve is minimum, the k characteristic points are the optimal segmentation characteristic points, and the regression line of each leaf and the characteristic fit line h of the transient response are obtained by segmenting the curven(t) of (d). Generally, the more the cross-sensitive ions n are, the more the selected splitting points k are, and the condition k is more than or equal to n +2 is met.
Line h for fitting transient response characteristics of ion selective electrode in mixed solutionMixing of(t), can be seen as the line h fitted by its characteristics at a single ionn(t) and concentration weight ratio pnAre formed by the combined action of
hn(t)＝∑pihi(t)(12)
Therefore, by comparing the cross-sensitivity correction model, a decoupling matrix can be obtained as
Wherein, ckDenotes the activity of the ion k, bkDenotes the selection coefficient, V, of ion k by the ion-selective electrodekRepresenting the output potential of the ion-selective electrode,representing the sum of the reference electrode potential, the ion zero potential and the bridge potential.
The weight ratio p of the cross sensitive ions can be solved according to the formula (12) and the formula (13)nAnd substituting the ion concentration data into a cross sensitivity correction model of the ion selection electrode to obtain the concentration of each ion.
Finally, according to a temperature compensation formula obtained by the nernst equation, the temperature compensation is carried out on the concentration of each ion
Wherein c isSupplement deviceRepresents the compensated ion concentration, cOriginal sourceRepresenting the measured concentration of the primary ion, TSign boardIndicating the temperature, T, at which the ion-selective electrode is calibratedMeasuringIndicating the measured temperature of the sensor.
And the more accurate concentration of each ion can be obtained through calculation.
For illustrating the beneficial effects of the invention, the detection device for the concentration of potassium and sodium ions in the nutrient solution has the characteristics of simple and convenient operation, good real-time performance, high detection precision, strong cross-sensitive effect resistance, strong temperature interference resistance and convenient carrying. And (3) carrying out test tests by taking the mixed nutrient solution of potassium nitrate and sodium chloride as an experimental sample.
The method comprises the following steps that firstly, a sensor calibration test is carried out, the test is completed before formal detection, and calibration is not needed to be carried out again after the calibration is completed. The calibration test is carried out at a temperature of 298.15K and respectively at a KNO of 0.001mol/L to 0.1mol/L3And measuring the final state response potential of the potassium ion selective electrode to potassium ions and sodium ions in the NaCl solution, and displaying the graph 6 and the graph 7, wherein the graph 6 shows the final state response of the potassium ion selective electrode to the potassium ions; fig. 7 is a final state response of a potassium ion selective electrode to sodium ions. The final state response of the potassium electrode to potassium ions can be calculated to be U from the figureo(cK)＝18.83logcK+173.6, the final state response of the potassium electrode to sodium ions is Uo(cNa)＝25.93logcNa+168.1。
Mixing KNO3The solution and the NaCl solution were mixed and the final state response of the potassium electrode in the mixed solution was obtained as shown in the table below.
The upper table is brought into the decoupling matrix
Get it solved
Namely, it is
Cross-sensitivity effects can be seen as shown in figure 8.
Tests were performed on potassium ion selective electrodes and sodium ion selective electrodes. Response characteristics of the potassium ion selective electrode to potassium ions and sodium ions were tested in 0.1mol/L KCl solution and 0.1mol/L NaCl solution, respectively. The transient response curves are shown in fig. 9 and 10, fig. 9 is a transient response curve of a potassium ion selective electrode to potassium ions, and fig. 10 is a transient response curve of a potassium ion selective electrode to sodium ions.
The starting point (at 5 seconds) and the steady-state end point (at 160 seconds) are set as the first and last feature points. And taking 3 points as feature points according to the fitting features, namely 5 feature points in total. Since there are two different curves, i.e., the transient response curve for K ions and the transient response curve for Na ions, the CART tree algorithm is modified here without requiring that the fitting error value Δ for each curve be minimal, but rather a set of time nodes t is selected1,t2,t3,t4,t5Total value of fitting error f to K ionsK(x) And total value f of fitting error to Na ionNa(x) And the time node when the sum is minimum is the segmentation characteristic point. As shown in FIGS. 11 and 12, FIG. 11 is CART segmentation of the transient response curve of potassium ion selective electrode to potassium ion, and FIG. 12 is the transient response of potassium ion selective electrode to sodium ionCART segmentation of the curve.
The four-segment CART segmentation line segment of the potassium ion transient response curve obtained by the formula (10) is
The four-segment CART segmentation line segment of the sodium ion transient response curve is
The following test was carried out for the mixed solution. KNO of 0.040mol/L is prepared3And 0.025mol/L NaCl mixed solution. And putting a potassium ion selective electrode, a sodium ion selective electrode, a reference electrode and a temperature sensor into the solution to be measured. Transient responses of the potassium ion selective electrode from 5 seconds to 160 seconds after entering the solution were measured, the response potentials are shown in the table below, and the transient response curves are shown in fig. 13.
A CART tree correction method is adopted, four CART segmentation line segments of K, Na ion transient response curves are compared for convenience of calculation, and segmentation characteristic points selected here are five points when the segmentation characteristic points are 5s, 20s, 41s, 80s and 160 s. The cutting result is shown in fig. 14.
Obtain four-segment CART segmentation line segment of
The component ratio p of K ions to Na ionsKAnd pNaIs composed of
fMixing of(t)＝pKfK(t)+pNafNa(t)
And according to the formulas (16) and (17)
To obtain the concentration c of K ions in the solutionKWith Na ion concentration cNaIn a ratio of 0.66: 0.34.
Substituting into cross-sensitive effect formula (15), measuring solution temperature at 28.2 deg.C (301.35K) by temperature sensor, and performing temperature compensation on response potential according to temperature compensation formula
The actual concentration of the comparative solution gave a relative error of 5% for potassium ions.
If a correction method is not adopted, the final state is directly calculated, and the final state response diagram of the potassium ions in the figure 6 can obtain the final state response diagram of the potassium ions, wherein the concentration of the potassium ions is 0.0510mol/L, and the error is 27.5%. Therefore, the detection error of the potassium ion selective electrode can be reduced from 27.5% to 5.25% by adopting the CART algorithm-based cross-sensitivity correction method.
Similarly, the cross sensitivity correction and the temperature compensation are carried out on the sodium ion selective electrode, so that the method can be obtained
The detection error of the potassium ion selective electrode can be reduced from 16.0% to 2.4%.
From the above, it can be seen that: the method for automatically correcting the cross sensitivity of potassium ions and sodium ions and compensating the temperature of the nutrient solution ion selective electrode can effectively correct the influence of the cross sensitivity of potassium ions and sodium ions on the ion selective electrode, so that the detection error of the potassium ion selective electrode is reduced from 27.5% to 5.25%, and the detection error of the potassium ion selective electrode is reduced from 16.0% to 2.4%.
The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.
Claims (5)
1. The device for detecting the concentration of potassium and sodium ions in nutrient solution is characterized by comprising a potassium ion selection electrode, a sodium ion selection electrode, a reference electrode, a multi-channel signal selector, a signal processing circuit, a single chip microcomputer, a temperature sensor and a human-computer interaction device, wherein the potassium ion selection electrode and the sodium ion selection electrode are both connected with the multi-channel signal selector, and the multi-channel signal selector and the reference electrode are both connected with the single chip microcomputer through the signal processing circuit; the temperature sensor and the human-computer interaction device are connected with the single chip microcomputer;
the multi-channel signal selector is used for selecting one of the potassium ion selective electrode and the sodium ion selective electrode to work simultaneously with the reference electrode according to an instruction of the human-computer interaction device;
the potassium ion selective electrode and the reference electrode work cooperatively to measure the concentration of potassium ions in the nutrient solution;
the sodium ion selective electrode and the reference electrode work cooperatively to measure the concentration of sodium ions in the nutrient solution;
the signal processing circuit calculates potential signals of potassium ion concentration and sodium ion concentration according to values measured by the potassium ion selective electrode, the sodium ion selective electrode and the reference electrode, converts the potential signals of the potassium ion concentration and the sodium ion concentration into analog signals which can be identified by the singlechip and transmits the analog signals to the singlechip;
the temperature sensor is used for collecting and detecting the temperature of the nutrient solution and transmitting a temperature signal to the singlechip;
the single chip microcomputer carries out analog-to-digital conversion on potassium ion concentration, sodium ion concentration potential signals and the temperature of the nutrient solution, an improved CART tree regression algorithm is adopted for fitting and calculating, the ratio of potassium ion concentration to sodium ion concentration is solved through a decoupling matrix, the potassium ion concentration to sodium ion concentration is substituted into a correction model of a cross sensitive effect to calculate the potassium ion concentration and the sodium ion concentration, temperature compensation is carried out on the obtained potassium ion concentration and sodium ion concentration according to the temperature of the nutrient solution, and finally the result is output to a human-computer interaction device for displaying.
2. The potassium and sodium ion concentration detection device of the nutrient solution as claimed in claim 1, wherein the human-computer interaction device is a touch display screen.
3. The method for detecting the concentration of potassium ions and sodium ions in the nutrient solution as claimed in claim 1, which comprises the following steps:
(1) data acquisition:
the man-machine interaction device controls a multi-channel signal selector to select one path of signal in the potassium ion selective electrode or the sodium ion selective electrode to subtract the reference electrode signal, so that a potential signal of potassium and sodium ion concentration or sodium ion concentration in the nutrient solution is obtained, and the potential signals of the potassium ion concentration and the sodium ion concentration are converted into analog signals which can be identified by the single chip microcomputer and transmitted to the single chip microcomputer; the temperature sensor detects the temperature of the nutrient solution in real time, converts a temperature signal into a digital signal and transmits the digital signal into the singlechip;
(2) and (3) calculating the accurate potassium and sodium ion concentrations by adopting a cross-sensitive automatic correction compensation method:
firstly, analog-to-digital conversion is carried out on analog signals of potassium ion concentration and sodium ion concentration in a single chip microcomputer to obtain transient response data and steady-state response data;
the resulting transient response data is then treated as pure KNO3The method comprises the steps of combining transient response curves of a solution and a pure NaCl solution, establishing a tree structure by adopting a CART tree regression algorithm, splitting each unit of an input space in a recursion mode, traversing the whole transient response curve, and carrying out segmentation and linear fitting (x) by taking characteristic points as segmentation bases in a response curve dividing methodi,f(xi) And (x)i+1,f(xi+1) Linear equation between leaf nodes, error analysis of the leaf nodes based on linear fit, total error value of the entire transient response curve
Wherein f (x) is the transient response curve, point (x)i,f(xi) ) is a selected feature point;
when the total error value of the selected whole curve is minimum, the k characteristic points are the optimal segmentation characteristic points x1,x2,x3,…,xk(ii) a Segmenting the curve by using the optimal segmentation characteristic points to obtain a regression line of each leaf;
then, with pure KNO3Taking a k-1 section fitting straight line of transient response of the solution and the pure NaCl solution as a matrix base, taking the concentration ratio of potassium ions and sodium ions as an influence coefficient, taking a k-1 section fitting straight line of transient response of the mixed solution as a synthetic value, and decoupling through a decoupling matrix to obtain the concentration ratio of potassium ions and sodium ions; the decoupling matrix is:
wherein, ckDenotes the activity of the ion k, bkDenotes the selection coefficient, V, of ion k by the ion-selective electrodekRepresenting the output potential of the ion-selective electrode,represents the sum of the reference electrode potential, the ion zero potential and the bridge potential;
finally, obtaining a cross sensitivity correction model of the potassium and sodium ion selective electrode from the steady state response data and the influence coefficient
And satisfies the following conditions:
wherein R represents a gas constant of 8.31 (J/mol. multidot.K), T represents an absolute temperature, and Z representsiDenotes the charge of the ion i, F denotes the Faraday constant 96487(C/mol), biDenotes the interference coefficient of ion i with respect to k ion-selective electrode, ciWhich represents the concentration of the ion i,which represents the zero potential of the ion i,which represents the potential of the reference electrode,representing the bridge potential;
substituting the concentration ratio of the potassium ions to the sodium ions into a cross sensitivity correction model of a potassium ion selective electrode and a sodium ion selective electrode to obtain the concentrations of the potassium ions and the sodium ions;
(3) temperature compensation:
and carrying out temperature compensation on the obtained concentration value, and finally outputting the result to a touch liquid crystal screen for displaying.
4. The method for detecting the concentration of potassium and sodium ions in the nutrient solution according to claim 3, wherein the temperature compensation method in the step (3) is as follows:
temperature compensation is carried out on the concentrations of potassium and sodium ions by a temperature compensation formula obtained by an nernst equation
Wherein c isSupplement deviceRepresents the compensated ion concentration, cOriginal sourceRepresenting the measured concentration of the primary ion, TSign boardIndicating the temperature, T, at which the ion-selective electrode is calibratedMeasuringIndicating the measured temperature of the sensor.
5. The method for detecting the concentration of potassium ions and sodium ions in the nutrient solution as claimed in claim 3, wherein in the step (2), the response curve is divided by selecting three points in the curve plus the first and last points, and taking five points as characteristic points, and the transient response curve is divided, so that the total error of four segments of fitted straight lines formed by connecting the five points end to end is minimized.
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