CN110146575B - Temperature and concentration detection and automatic control device based on three-electrode chemical system - Google Patents
Temperature and concentration detection and automatic control device based on three-electrode chemical system Download PDFInfo
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Abstract
The invention discloses a temperature and concentration detection and automatic control device based on a three-electrode chemical system, which comprises: the power and three electrode system detection device, constant potential drive module, digital-to-analog converter, signal conditioning module, analog-to-digital converter, treater, temperature sensor, power drive arrangement, temperature regulation apparatus, concentration adjusting device and the display control device who is connected with the power respectively, wherein: the constant power supply driving module is respectively and electrically connected with the three-electrode system detection device and the digital-to-analog converter; the signal conditioning module is respectively and electrically connected with the three-electrode system detection device and the analog-to-digital converter; the analog-to-digital converter is electrically connected with the processor and the temperature sensor respectively; the processor is respectively electrically connected with the display control device and the power driving device; the power driving device is electrically connected with the temperature adjusting device and the concentration adjusting device respectively. The method realizes accurate, rapid and real-time measurement of the concentration of the chloride ions in the solution, and can realize closed-loop control of the temperature of the solution and the concentration of the chloride ions in the solution.
Description
Technical Field
The invention relates to the technical field of detection of concentration, in particular to a temperature and concentration detection and automatic control device based on a three-electrode chemical system.
Background
Chloride ion is a common ion component in water, the concentration of chloride ion is an important index in water quality measurement, the concentration of chloride ion is also one of important parameters in the fields of chemical research, biomedicine, building materials and the like, and the method for measuring the concentration of chloride ion in a laboratory mainly comprises the following steps: the method comprises a test paper method, an ion titration method, an ion chromatography method, a spectrophotometry method, an atomic absorption method and an electrochemical method, wherein the test paper method cannot carry out quantitative analysis, the ion titration method is complicated to operate, large in error and pollution, a detection instrument of the ion chromatography method is large and expensive, the spectrophotometry method is large in pollution and high in measurement cost, the atomic absorption method is high in requirements for solution chromaticity and turbidity degree and high in measurement cost, an electrochemical measurement device in a laboratory is a traditional electrochemical workstation, and the electrochemical workstation is not suitable for non-traditional electrodes, particularly for research of electrode arrays.
At present, the electrochemical measurement of the chloride ion concentration is mainly completed by utilizing a three-electrode electrochemical measurement system formed by electrodes such as an ion selective electrode, the domestic research on the three-electrode test system is still in the laboratory simulation stage, and most of the research is focused on the manufacturing aspect of the electrodes. The temperature of the solution to be measured is an important factor influencing the final measurement, the chloride ion concentration measuring instrument in the prior art can only realize the measurement at constant temperature, and the measurement result can generate errors due to the change of the temperature of the solution.
Therefore, the invention discloses a temperature and concentration detection and automatic control device based on a three-electrode chemical system, which realizes accurate, rapid and real-time measurement of the concentration of chloride ions in a solution and can realize closed-loop control of the temperature of the solution and the concentration of the chloride ions in the solution.
Disclosure of Invention
Aiming at the defects in the prior art, the invention discloses a temperature and concentration detection and automatic control device based on a three-electrode chemical system, which realizes accurate, rapid and real-time measurement of the concentration of chloride ions in a solution and can realize closed-loop control of the temperature of the solution and the concentration of the chloride ions in the solution.
In order to solve the technical problems, the invention adopts the following technical scheme:
temperature, concentration detection and automatic control device based on three electrode chemistry systems includes: the power and three electrode system detection device, constant potential drive module, digital-to-analog converter, signal conditioning module, analog-to-digital converter, treater, temperature sensor, power drive arrangement, temperature regulation apparatus, concentration adjusting device and the display control device who is connected with the power respectively, wherein:
the constant potential driving module is respectively and electrically connected with the three-electrode system detection device and the digital-to-analog converter;
the signal conditioning module is respectively and electrically connected with the three-electrode system detection device and the analog-to-digital converter;
the analog-to-digital converter is electrically connected with the processor and the temperature sensor respectively;
the processor is respectively electrically connected with the display control device and the power driving device;
the power driving device is electrically connected with the temperature adjusting device and the concentration adjusting device respectively.
Preferably, the three-electrode system detection device comprises a working electrode, a reference electrode and an auxiliary electrode, wherein the working electrode, the reference electrode and the auxiliary electrode are all ion selective electrodes.
Preferably, the method comprises the following steps when measuring the ion concentration:
measuring the actual chloride ion concentration in the chloride ion solution to be measured by adopting a chronoamperometry;
and (4) carrying out temperature compensation on the actual chloride ion concentration by adopting a temperature compensation method to obtain the compensated chloride ion concentration.
Preferably, in the step of performing temperature compensation on the actual chloride ion concentration by using the temperature compensation method to obtain the compensated chloride ion concentration:
based on the formula
Carrying out temperature compensation on the actual chloride ion concentration;
in the formula:
Rsmis the equivalent resistance, R, of the interface formed by the ion selective membrane and the solution to be measuredmIs the equivalent resistance of the ion selective membrane interface, n is the electron transfer number, F is the Faraday constant, EHFor the detection voltage applied to the working electrode, R is the ideal gas constant, K is the constant, T is the absolute temperature of the solution, I is the response current of the electrode at steady state, pClTThe chloride ion concentration is the chloride ion concentration when temperature compensation is performed.
Preferably, the temperature adjusting device comprises an electric heating rod and a semiconductor refrigerating piece which are respectively electrically connected with the power driving device.
Preferably, the concentration adjusting device comprises a chloride ion solution input water pump and a purified water input water pump which are respectively electrically connected with the power driving device, and the concentration of the chloride ion solution input by the chloride ion solution input water pump is greater than that of the chloride ion solution to be detected.
The invention discloses a temperature and concentration detection and automatic control device based on a three-electrode chemical system, which comprises: the power and three electrode system detection device, constant potential drive module, digital-to-analog converter, signal conditioning module, analog-to-digital converter, treater, temperature sensor, power drive arrangement, temperature regulation apparatus, concentration adjusting device and the display control device who is connected with the power respectively, wherein: the constant potential driving module is respectively and electrically connected with the three-electrode system detection device and the digital-to-analog converter; the signal conditioning module is respectively and electrically connected with the three-electrode system detection device and the analog-to-digital converter; the analog-to-digital converter is electrically connected with the processor and the temperature sensor respectively; the processor is respectively electrically connected with the display control device and the power driving device; the power driving device is electrically connected with the temperature adjusting device and the concentration adjusting device respectively. The method realizes accurate, rapid and real-time measurement of the concentration of the chloride ions in the solution, and can realize closed-loop control of the temperature of the solution and the concentration of the chloride ions in the solution.
Drawings
For purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made in detail to the present invention as illustrated in the accompanying drawings, in which:
FIG. 1 is a schematic structural diagram of a temperature and concentration detection and automatic control device based on a three-electrode chemical system disclosed in the present invention;
FIG. 2 is an equivalent circuit diagram of an ion-selective electrode in a solution under test;
FIG. 3 is a graph of voltage signals and their corresponding currents calculated according to the Nernst equation;
FIG. 4 is a block diagram of a PID controller;
FIG. 5 is an overall process block diagram;
FIG. 6 is a graph of actual measured temperatures for set temperatures higher than room temperature;
FIG. 7 is a graph of actual measured temperatures for set temperatures lower than room temperature;
FIG. 8 is a graph of measured concentration for a lower set concentration;
FIG. 9 is a measured concentration for a higher set concentration;
FIGS. 10-14 are power circuit diagrams of an embodiment of the present invention;
FIG. 15 is a circuit diagram of a microprocessor according to an embodiment of the present invention;
FIG. 16 is a circuit diagram of a three-electrode system interface according to an embodiment of the present invention;
FIG. 17 is a schematic diagram of a potentiostat circuit in accordance with one embodiment of the invention;
FIG. 18 is a circuit diagram of a signal conditioning circuit according to an embodiment of the present invention;
FIG. 19 is a circuit diagram of an analog-to-digital conversion circuit according to an embodiment of the present invention;
FIG. 20 is a digital to analog conversion circuit diagram according to an embodiment of the present invention;
FIG. 21 is a circuit diagram of a temperature sensor according to an embodiment of the present invention;
FIG. 22 is a key circuit diagram according to an embodiment of the present invention;
FIG. 23 is a circuit diagram of a display panel according to an embodiment of the present invention;
FIG. 24 is a circuit diagram of a debug download circuit according to an embodiment of the present invention;
FIG. 25 is a circuit diagram of an indicator light according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the invention discloses a temperature and concentration detection and automatic control device based on a three-electrode chemical system, comprising: the power and three electrode system detection device, constant potential drive module, digital-to-analog converter, signal conditioning module, analog-to-digital converter, treater, temperature sensor, power drive arrangement, temperature regulation apparatus, concentration adjusting device and the display control device who is connected with the power respectively, wherein:
the constant potential driving module is respectively and electrically connected with the three-electrode system detection device and the digital-to-analog converter;
the signal conditioning module is respectively and electrically connected with the three-electrode system detection device and the analog-to-digital converter;
the analog-to-digital converter is electrically connected with the processor and the temperature sensor respectively;
the processor is respectively electrically connected with the display control device and the power driving device;
the power driving device is electrically connected with the temperature adjusting device and the concentration adjusting device respectively.
Compared with the prior art, the temperature sensor can be used for measuring the temperature of the solution to be measured, and the temperature compensation is carried out on the measured actual chloride ion concentration according to the obtained temperature information to obtain the compensated chloride ion concentration, so that the measurement error caused by the temperature change of the solution is avoided. In addition, the invention creatively combines the solution concentration detection, the solution temperature control and the solution concentration control together and can be used as an experimental device for schools and various research institutions.
In conclusion, the method and the device realize accurate, rapid and real-time measurement of the concentration of the chloride ions in the solution, and can realize closed-loop control of the temperature of the solution and the concentration of the chloride ions in the solution.
In the prior art, the chloride ion detection method comprises the following steps: the method comprises a titration method, a spectrophotometry method, an ion chromatography method, an atomic absorption method, an ion selective electrode method and the like, wherein the ion selective electrode method is selected for concentration measurement, and the method has the characteristics of low development cost, simplicity in implementation, strong expansibility, high measurement speed, high accuracy and the like.
In the method, electrodes such as an ion selection electrode and the like form a three-electrode electrochemical measurement system, a timing current method is adopted to detect the concentration of the solution, a constant potential circuit can be formed by a high-precision digital-to-analog converter and an operational amplifier during specific implementation, current-voltage conversion is carried out on a weak current response signal of the electrode, high-gain amplification and filtering are simultaneously realized, the conditioned voltage is measured by the high-precision analog-to-digital converter, a temperature sensor can realize real-time detection on the temperature of the solution, and meanwhile, the temperature compensation is carried out on the detection result of the concentration of the chloride ions through an algorithm, so that the accuracy of the detection result of the concentration of the chloride ions is improved.
In order to accurately measure the potential change on the chloride ion working electrode and improve the detection sensitivity, the invention adopts a chloride ion concentration detection method of a three-electrode system timing current method, measures the solution concentrations at different temperatures by adopting temperature compensation according to the relation between the ion concentration and the temperature of the Nernst equation, measures the response current of the sodium chloride solutions at different concentrations by the timing current method, and calibrates the sodium chloride solutions with standard concentration.
In specific implementation, the three-electrode system detection device comprises a working electrode, a reference electrode and an auxiliary electrode, wherein the working electrode, the reference electrode and the auxiliary electrode are all ion selective electrodes.
The three-electrode system is an electrochemical sensor which is used for electrochemical measurement more frequently, and corresponding three electrodes are a working electrode, a reference electrode and an auxiliary electrode.
Working Electrode (WE): the electrode which reacts with the substance electrochemically is called as the working electrode, and the commonly used working electrodes include glassy carbon disc electrode, gold disc electrode, platinum disc electrode and other metal disc-shaped working electrodes, as well as sheet metal working electrode, powdery electrode, modified electrode and the like.
Reference Electrode (RE): is the electrode that is compared for reference when measuring the electrode potential. A standard hydrogen electrode is an ideal electrode and is not easy to implement in practice. Therefore, when actually measuring the electrode potential, the electrode with accurately known and stable electrode potential is used as the reference electrode.
Auxiliary electrode (CE): the auxiliary electrode, also called counter electrode, is used to pass a current to effect the polarization of the study electrode. The auxiliary electrode acts as an anode when studying the cathodic process, and the auxiliary electrode acts as a cathode when studying the anodic process. The area of the auxiliary electrode is generally larger than that of the research electrode, so that the current density on the auxiliary electrode is reduced, and the auxiliary electrode is basically not polarized in the measuring process, therefore, a platinum wire or a platinum sheet electrode is commonly used as the auxiliary electrode, and metal materials which keep inertia in the research medium, such as Ag, Ni, W, Pb and the like, can also be used.
In the specific implementation of the invention, a PC L-1 type chloride ion selective electrode of Shanghai Reye corporation is used as a working electrode, a DJS-1 type platinum conductance electrode of Shanghai Reye corporation is used as an auxiliary electrode, and a 217 type double-salt bridge saturated calomel electrode is used as a reference electrode.
In specific implementation, the method comprises the following steps of:
measuring the actual chloride ion concentration in the chloride ion solution to be measured by adopting a chronoamperometry;
and (4) carrying out temperature compensation on the actual chloride ion concentration by adopting a temperature compensation method to obtain the compensated chloride ion concentration.
The ion selective electrode is an electrochemical sensor for measuring the ion activity or concentration in a solution by using a membrane potential, and the ion selective electrode method is a method for measuring the specific ion concentration by using the current response or potential response of the ion selective electrode in the measured solution.
The ion selective electrode mainly comprises three parts:
(1) the interface formed by the ion selective membrane and the solution to be measured has equivalent capacitance CmsEquivalent resistance of Rms；
(2) Ion selective membrane interface with equivalent capacitance of CmEquivalent resistance of Rm；
(3) The interface formed by the ion selective membrane and the substrate material has equivalent capacitance of CsmEquivalent resistance of Rsm。
The equivalent circuit of the three parts is shown in figure 2. Due to the equivalent resistance R of the solution to be measuredsMuch less than Rms、RmAnd RsmThus R is detectedsAnd can be ignored.
From FIG. 2, EHCan be divided into 3 parts as shown in formula (22):
EH＝Esm+Em+Ems(22)
in the formula, EHFor the detection voltage applied to the working electrode, EsmAnd EmsRespectively, matrix-membrane potential and membrane-solution interface potential, EmIs the membrane potential.
According to the Nernst equation, EmsThe ion concentration in the solution to be measured is related to the following formula (23):
wherein α is the activity of the ion to be measured in the solution, K is constant, R is ideal gas constant, T is absolute temperature of the solution, n is electron transfer number, F is Faraday constant at T1Within time, Cms、CmAnd CsmCharging the capacitor, when the capacitor is full, the current tends to be stable, and at this time Esm、EmsAlso tends to stabilize the value:
Esm＝IMRsm(24)
Em＝IMRm(25)
wherein IMIs the response current at the time of stabilization. Obtained by substituting formulae (23) to (25) for formula (22):
the response current I can be obtained from the formula (26)MThe expression is as follows:
in the formula (I), the compound is shown in the specification,
in formula (27), the negative logarithm of the chloride ion concentration is often represented by pCl ═ lg α thus:
chronoamperometry is a simple and widely used electrochemical detection technique. The working principle is as follows: measuring the voltage between the working electrode and the auxiliary electrode by applying a voltage to keep the voltage between the working electrode and the reference electrode constantAnd (4) calculating the chloride ion concentration of the detected solution according to the Nernst equation. The applied pulsed voltage signal and its corresponding current are shown in fig. 3. EHTo detect the voltage, EHApplied between WE and RE, when a very high response current suddenly occurs between WE and CE, with t1The chloride ions in the solution to be detected enter the electrode within the time, the response current can be rapidly reduced, when the concentration of the chloride ions on the two sides of the electrode membrane reaches the balance, the response current tends to be stable, and t is generally taken1Response current I after time end stabilizationMAnd calculating the ion concentration of the solution. ELFor a set voltage, the set time is t2And setting the voltage to enable the chlorine ions in the electrode to be diffused into the solution again, so that the electrode is restored to the original state.
In specific implementation, the temperature compensation method is used for carrying out temperature compensation on the actual chloride ion concentration to obtain the compensated chloride ion concentration:
performing temperature compensation on the actual chloride ion concentration based on formula (31);
according to the basic principle of the ion selective electrode method, the temperature of the detected solution is a non-negligible variable in the Nernst equation, experiments show that the temperature has an extremely important influence on the result of chloride ion detection, and the accuracy of the final detection result can be ensured only by performing temperature compensation on the result measured by the ion selective electrode method.
In the formula:
because g and h are related to temperature, the temperature of the electrode is compensated at different temperatures, and the precision and the stability of the chloride ion electrode are improved. From the formula (29), pCl without temperature compensation is known0The calculation formula of (2):
in the formula: t is0At a Kelvin temperature of 25 ℃ (298K),
pCl with temperature compensation obtained by the formula (29)TThe calculation formula of (2):
in the formula:
according to the above analysis, each measurement chronoamperometry was set to 10 cycles, the first 5 cycles being used for electrode and detection system balancing; last 5 cycles of extraction of t1Response current I at end-of-time stabilityMAnd averaging to obtain the response current value for calculating the concentration of the ions to be measured.
In the invention, the PT100 temperature sensitive resistor is adopted to measure the temperature, and the resistance of the PT100 temperature sensitive resistor has a good linear relation with the temperature, so that the data processing is easy.
In specific implementation, the temperature adjusting device comprises an electric heating rod and a semiconductor refrigerating sheet which are respectively electrically connected with the power driving device.
During specific implementation, the concentration adjusting device comprises a chloride ion solution input water pump and a purified water input water pump which are respectively electrically connected with the power driving device, and the concentration of the chloride ion solution input by the chloride ion solution input water pump is greater than that of the chloride ion solution to be detected.
In engineering practice, the most widely used regulator control law is proportional, integral and derivative control, abbreviated as PID control, also known as PID regulation. The PID controller has been known for nearly 70 years, and is one of the main technologies of industrial control due to its simple structure, good stability, reliable operation and convenient adjustment. When the structure and parameters of the controlled object cannot be completely mastered or an accurate mathematical model is not obtained, and other technologies of the control theory are difficult to adopt, the structure and parameters of the system controller must be determined by experience and field debugging, and the application of the PID control technology is most convenient. PID first appears in analog control systems, and a conventional analog PID controller accomplishes its function through hardware (electronic, pneumatic, and hydraulic components). With the advent of computers, it was transplanted into computer control systems to replace the original hardware-implemented functions with software, thereby forming a digital PID controller, the algorithm of which is called digital PID algorithm. The digital PID controller has very strong flexibility, and parameters can be adjusted on line according to experiments and experiences, so that better control performance can be obtained. The control block diagram is shown in fig. 4.
Wherein:
p: proportionality, is the input deviation multiplied by a constant.
I: integral, i.e. the Integral operation is performed on the input deviation.
D: derivative, which performs a differential operation on the input deviation.
The PID calculation formula is as follows:
in the formula: u (T) is the output value of the current PID controller, err (T) is the error between the actual value and the set value at the time T, derr (T) is the differential of err (T) at the time T, k is the proportionality coefficient, TITo integrate the time constant, TDIs the differential time constant. To implement PID on a computer or other processor, the above formula must be discretized to facilitate the computer or other processor's calculations.
To implement PID on a computer or other processor, the above formula must be discretized to facilitate the computer or other processor's calculations.
The formula of the discretized PID calculation is as follows:
in the formula: u (k) is the output of the sampling PID controller at the k time, err (k) is the error between the actual value and the set value at the k time, and err (k-1) is the sampling at the k-1 timeError between actual value and set value, KpIs the scaling factor and T is the sampling period.
According to the invention, the solution is heated by using the electric heating rod, refrigeration is realized by using the semiconductor refrigerating sheet, the difference is made between the temperature measured by the temperature sensor and the set temperature and is sent to the temperature PID controller, and the output of the heating controller or the output of the refrigerating controller is set according to the output of the temperature PID controller, so that the purpose of regulating and controlling the temperature is realized.
According to the invention, the chlorine ion concentration of the solution is controlled by pumping a concentrated solution containing chlorine ions or purified water containing no chlorine ions into the container by using a water pump, the difference is sent into a chlorine ion concentration PID controller according to the difference between the measured result of the chlorine ion concentration and the set chlorine ion concentration, and the concentrated solution containing chlorine ions or purified water containing no chlorine ions is judged and the water pump is controlled according to the output of the chlorine ion concentration PID controller.
In the invention, the processor can adopt a microprocessor STM32F103C8T6 based on an ARM-cortex M3 kernel, an IARembeddedWorkBenchIDE is used for developing a program of the STM32F103C8T6, and the program is downloaded and debugged on the IDE, wherein the whole program block diagram is shown in FIG. 5.
Iarsysems are providers of embedded system development tools and services. The company was established in 1983 and provided products including: the system comprises an Integrated Development Environment (IDE) with a C/C + + compiler and a debugger, a real-time operating system, middleware, a development kit, a hardware simulator and a state machine modeling tool, wherein the IARembeddWorkBranch is an integrated development environment IAREW developed for a microprocessor by IARSystems, and chip kernel platforms such as ARM, AVR, 8051, MSP430 and the like are supported.
The IAREmbeddedWorkbenchworARM (IAREWARM) is an integrated development environment suitable for ARM processors, and is mainly characterized by comprising highly optimized IARARCC/C + + Compiler, a powerful editor, an IARARCMAssembler, a project manager, IARXRAR and X L IB library building programs, an IARD L IBC/C + + runtime library and the like
The invention can use IARembeddedWorkBranchForARM8.32.2, and the design of module driving programs such as ADC, DAC, display screen and the like and the design of data processing algorithm are completed in the integrated development environment.
Before using the device of the invention, debugging is needed, including:
debugging a three-electrode system detection device:
according to the principle of measuring the concentration of the chloride ions by a chronoamperometry, when a step signal with a certain magnitude is applied between the working electrode and the reference electrode, a very high response current is generated between the working electrode and the auxiliary electrode, the response current rapidly decreases along with the entrance of the chloride ions in the solution to be measured into the electrode, and when the ion concentrations on the two sides of the electrode membrane reach balance, the response current tends to be stable, so that the concentration of the chloride ions in the solution can be obtained through the stabilized current.
When 0.5V step voltage is applied to the auxiliary electrode, the current of the working electrode changes suddenly and then is stabilized within 500 milliseconds, the ADC is started to measure the stabilized voltage, and the average value is taken after multiple measurements to obtain a value related to the concentration of chloride ions in the solution to be measured.
Debugging a temperature adjusting device:
the relation between the resistance of the PT100 temperature sensor and the temperature is a linear relation, a constant current of 1mA is applied to the PT100 through a programmable current source of an ADC chip, the voltage generated on the PT100 is sent to the ADC for measurement, so that the temperature of the temperature sensor and the output value of the ADC are also in a linear relation, a thermometer with the precision of 1% and the PT100 are used for simultaneously measuring to obtain a plurality of groups of values of the ADC and the values of the thermometer, Matlab is used for linear fitting, a fitting formula is obtained and written into a microprocessor, and the output of the ADC can be converted into the temperature. The temperature after PT100 fitting was compared with the temperature measured by the thermometer, and the results are shown in table 1.
TABLE 1 temperature measurement Module test data
A PID closed-loop negative feedback control algorithm is adopted to maintain the required solution temperature, a driving module is controlled according to the output of the PID algorithm to realize refrigeration or heating, and as the temperature control belongs to a hysteresis control system, a hysteresis control parameter setting model (a Ziegler-Nichols parameter setting method) commonly used in industrial control can be adopted as shown in Table 2.
TABLE 2 Ziegler-Nichols tuning model
Wherein:
kc: and only adopting a Kp value when the steady-state error of the control system reaches the minimum as far as possible under the control condition of a proportional link.
Pc: and the oscillation period of the system is controlled under the control condition of only adopting a proportion link.
Ti: the integration time of the system is controlled.
Td: the differential time of the system is controlled.
T: the PID controls the sampling computation period.
Kp, Ki, Kd: the parameter being tuned.
After multiple times of setting, the set temperature is 45.00 ℃ to 27 ℃ at room temperature, and the actual effect of temperature control PID is shown in FIG. 6.
The set temperature was 20.00 ℃ < room temperature 27 ℃ and the actual effect of temperature control PID is shown in fig. 7.
Therefore, the temperature control error is within +/-0.07 ℃ of the set temperature, and the expectation is met.
Debugging a concentration adjusting device:
repeatedly calibrating the value acquired by the three-electrode system by using standard chloride ions with different concentrations to obtain the corresponding relation between the acquired value and the concentration of the standard solution, fitting to obtain a formula, writing the formula into a microprocessor, substituting the real-time temperature into the formula for temperature compensation, and finally obtaining the concentration of the chloride ions in the solution acquired by the three-electrode system. And measuring other three standard solutions with different concentrations by using a three-electrode system to verify the accuracy of the detection result, wherein the obtained results are shown in table 3.
TABLE 3 chloride ion measurement Module test data
The method adopts a PID closed-loop negative feedback control algorithm to maintain the required concentration of the chlorine ions in the solution, controls a driving module according to the output of the PID algorithm to realize the high-concentration solution and the low-concentration solution, and can adopt a hysteresis control parameter setting model (a Ziegler-Nichols parameter setting method) commonly used in industrial control as well as the temperature control which belongs to a hysteresis control system.
After multiple times of setting, the set value is 0.5 mol/L, and the actual effect of concentration control PID is shown in FIG. 8.
The set value is 1.86 mol/L, and the actual effect of concentration control PID is shown in FIG. 9.
It can be seen that the solution concentration control error is within the range of. + -. 0.05 mol/L of the set concentration, which satisfies the expectation.
The following is a circuit diagram of an embodiment of the present invention:
1 power supply circuit
The whole circuit system inputs voltage by a battery or a voltage stabilizing source, and devices such as an operational amplifier and the like adopt positive and negative power supplies for power supply, so a power supply module is needed for generating positive and negative voltage.
(1) Voltage of +/-5V
+5V was generated by TI company's L DO chip T L1963 from input power supply regulated voltage as shown in fig. 10.
the-5V is regulated from +5V by the charge pump TPS60403 of the TI company as shown in fig. 11.
(2) The voltage of +/-2.5V and the voltage of +/-2.5V required by ADC are taken as an analog power supply
The +2.5V is obtained from the +5V regulated voltage by the L DO regulated voltage chip RT9013, as shown in fig. 12.
the-2.5V is obtained from-5V voltage stabilization by a negative pressure voltage stabilization chip TPS72301, as shown in FIG. 13.
(3) The microprocessor needs 3.3V power supply, and 3.3V is obtained from +5V voltage stabilization by an L DO voltage stabilization chip SPX3819, as shown in FIG. 14.
2 microprocessor circuit
The device adopts a 32-bit microprocessor STM32F103C8T6 based on an ARM-cortex M3 inner core, has the Flash capacity of 64KB, the SRAM capacity of 20KB and the highest working frequency of 72MHz, can realize hardware multiplication and hardware division in a single period, and has the peripherals of a timer, an ADC, an SPI, I2C, DMA, GPIO, PWM and the like, the working voltage is 2V-3.6V, and the working temperature is-40 ℃ to 85 ℃. The resources and performance are sufficient, the work is stable, and the system is suitable for being used as a microprocessor of the system, as shown in figure 15.
3 three-electrode system interface
The system adopts a three-electrode chloride ion detection method based on a chronoamperometry, and needs three electrodes, namely a working electrode WE, a reference electrode RE and an auxiliary electrode CE. The electrode interface circuit is shown in fig. 16.
4 constant potential rectifier circuit
The potentiostat is the most basic instrument in electrochemical and electric analysis tests. Potentiostat circuits are also the core of many specialized electrochemical test instruments. In the apparatus of this study, a potentiostat was used to control the potential between the working electrode and the reference electrode at a fixed potential. The potentiostat circuit diagram is shown in fig. 17.
5 signal conditioning circuit
Under the drive of the potentiostat, the working electrode generates a response current, which is amplified by current-voltage conversion by an operational amplifier, and then filtered by a second-order active filter circuit to remove noise, as shown in fig. 18.
6 analog-to-digital conversion circuit (ADC)
The ADC is used for measuring the response voltage of the electrode and the temperature, various characteristics are integrated by using 16-bit high-precision analog-to-digital conversion devices ADS1120 and ADS1120 of texas instruments (texas instruments), the ADC is suitable for small-signal measurement, an SPI interface is used, and the circuit is shown in fig. 19.
7 digital-to-analog conversion circuit (DAC)
The DAC output voltage provides the scanning voltage for the potentiostat to achieve different potentiostats, using a high-precision, low-power, low-noise 16-bit digital-to-analog conversion device DAC8562 from texas instruments, which is driven using an SPI interface, the circuit of which is shown in fig. 20.
8 temperature sensor circuit
The temperature detection adopts a constant current source scheme for measurement, and the sensor adopts a PT100 platinum thermal resistor, and the resistance value of the platinum thermal resistor can change along with the change of the temperature. A post-PT value of 100 means that it has a resistance of 100 ohms at 0 c and a resistance of about 138.5 ohms at 100 c. The constant 1mA current is output through the programmable current source module of the ADC, the constant 1mA current PT100 generates voltage, the voltage is sent to the AD conversion module of the ADC to complete conversion, temperature data is obtained, and the circuit is shown in FIG. 21.
9 keying circuit
Adopt 6 buttons, be confirm respectively, go up, down, left and right, cancel for debugging or input parameter, 6 buttons insert 6 IO of microprocessor respectively, IO adopts inside pull-up input, presses the button, and IO is pulled down, loosens the button, and IO becomes high, and the circuit is shown in fig. 22.
10 display screen circuit
The circuit is shown in fig. 23, which adopts a 1.3-inch IPS color liquid crystal screen, 240 × 240 resolution, 16-bit RGB565 color format, and 8-bit SPI serial port, and can accept a clock rate of 65MHz at most.
11 debugging download circuit
A 2-wire SWD debugging interface is reserved for debugging and downloading programs, a path of serial port is reserved for debugging or extended use, and a circuit is shown in FIG. 24.
12 indicating lamp circuit
For indicating the working state of the circuit, an RGB three-color L ED lamp is adopted, and the circuit is shown in figure 25.
Finally, it is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that, while the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (2)
1. Temperature, concentration detection and automatic control device based on three electrode chemistry systems, its characterized in that includes: the power and three electrode system detection device, constant potential drive module, digital-to-analog converter, signal conditioning module, analog-to-digital converter, treater, temperature sensor, power drive arrangement, temperature regulation apparatus, concentration adjusting device and the display control device who is connected with the power respectively, wherein:
the constant potential driving module is respectively and electrically connected with the three-electrode system detection device and the digital-to-analog converter;
the signal conditioning module is respectively and electrically connected with the three-electrode system detection device and the analog-to-digital converter;
the analog-to-digital converter is electrically connected with the processor and the temperature sensor respectively;
the processor is respectively electrically connected with the display control device and the power driving device;
the power driving device is electrically connected with the temperature adjusting device and the concentration adjusting device respectively;
the temperature adjusting device comprises an electric heating rod and a semiconductor refrigerating piece which are respectively and electrically connected with the power driving device, and the processor performs PID calculation and controls the electric heating rod or the semiconductor refrigerating piece to increase or decrease the temperature of the solution based on the temperature of the solution measured by the temperature sensor and the preset temperature; the concentration adjusting device comprises a chloride ion solution input water pump and a purified water input water pump which are respectively electrically connected with the power driving device, the concentration of the chloride ion solution input by the chloride ion solution input water pump is greater than that of the chloride ion solution to be detected, and the processor performs PID calculation and controls the chloride ion solution input water pump or the purified water input water pump to increase or decrease the concentration of the chloride ion solution based on the measured concentration of the chloride ion solution and the preset concentration;
the method comprises the following steps when measuring the ion concentration:
measuring the actual chloride ion concentration in the chloride ion solution to be measured by adopting a chronoamperometry;
carrying out temperature compensation on the actual chloride ion concentration by adopting a temperature compensation method to obtain the compensated chloride ion concentration;
the temperature compensation method is adopted to carry out temperature compensation on the actual chloride ion concentration to obtain the compensated chloride ion concentration, wherein:
based on the formula
Carrying out temperature compensation on the actual chloride ion concentration;
in the formula:
Rsmis the equivalent resistance, R, of the interface formed by the ion selective membrane and the solution to be measuredmIs the equivalent resistance of the ion selective membrane interface, n is the electron transfer number, F is the Faraday constant, EHFor the detection voltage applied to the working electrode, R is the ideal gas constant, K is the constant, T is the absolute temperature of the solution, I is the response current of the electrode at steady state, pClTThe chloride ion concentration is the chloride ion concentration when temperature compensation is performed.
2. The apparatus for detecting temperature and concentration and automatically controlling based on a three-electrode chemical system according to claim 1, wherein the three-electrode system detecting means comprises a working electrode, a reference electrode and an auxiliary electrode, and the working electrode, the reference electrode and the auxiliary electrode are all ion selective electrodes.
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