CN203643391U - Self-adaption ion meter - Google Patents
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- CN203643391U CN203643391U CN201320664350.9U CN201320664350U CN203643391U CN 203643391 U CN203643391 U CN 203643391U CN 201320664350 U CN201320664350 U CN 201320664350U CN 203643391 U CN203643391 U CN 203643391U
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- 229910021641 deionized water Inorganic materials 0.000 description 6
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Abstract
The utility model discloses a self-adaption ion meter. The self-adaption ion meter comprises a data processor and an ion measurement probe and further comprises an A/D (Analogue/Digital) conversion circuit and a temperature detection circuit which are electrically connected with the input port of the data processor, wherein the A/D conversion circuit uses a 24-bit Sigma-Delta type AD converter; the input port of the A/D conversion circuit uses a BNC (Bayonet Nut Connector) port; the BNC port is connected with the BNC port of the ion measurement port in a matched manner; the temperature measurement circuit comprises a digital temperature sensor detection circuit for measuring an environment temperature and a thermistor resistance detection circuit for measuring a solution temperature. The self-adaption ion meter disclosed by the utility model has the advantages of simplicity and easiness in use, strong adaptive capacity and high measurement precision.
Description
Technical Field
The utility model relates to an ionization gauge, more specifically the theory that says so relates to self-adaptation ionization gauge, belongs to electrochemistry technical field.
Background
At present, the micro analysis of ions is widely applied in teaching and experiment of analytical chemistry, chemical engineering, energy and environmental protection, and an ion meter consisting of an Ion Selective Electrode (ISE) is used for measuring the concentration of the ions, which is a commonly used method. The ion meter is used for measuring the ion concentration in the solution, is based on the electrochemical reaction of the ion selective electrode, however, the electromotive force of the ion selective electrode has a certain correlation coefficient relation with the temperature, and the ion selective electrode can cause the phenomenon of deterioration along with the prolonging of the using time due to the manufacturing or using reasons, thereby influencing the testing precision, and how to develop the easy-to-use and accurate ion meter is a difficult problem which troubles engineering technicians for a long time.
SUMMERY OF THE UTILITY MODEL
The utility model aims to solve the technical problem that, overcome prior art's shortcoming, provide a simple easy-to-use, adaptability is strong, the high self-adaptation ionometer of measurement accuracy.
In order to solve the technical problem, the utility model provides an adaptive ion meter, including data processor and ion measuring probe, still include with the AD converting circuit and the temperature detection circuit that data processor's input port electricity is connected.
The A/D conversion circuit adopts a 24-bit sigma-delta type AD converter, the input port of the AD converter adopts a BNC interface, and the BNC interface is matched and connected with the BNC interface of the ion measurement probe. The measurement accuracy of the 24-bit sigma-delta type AD converter reaches one millionth, the requirements of the measured electromotive force and the weak electromotive force are met, and the measurement accuracy is improved. The BNC interface is directly connected with the BNC interface of the ion measuring probe in a matching way, and is simple and easy to use.
The temperature detection circuit comprises a digital temperature sensor detection circuit for measuring the ambient temperature and a thermistor detection circuit for measuring the solution temperature, so that the adaptability of the ion meter is improved, and the measurement precision of the ion meter is further improved.
The utility model discloses technical scheme's further limit is for, 24 position sigma-delta type AD converters are chip HX530, chip HX530 adopts the internal crystal oscillator that the oscillation frequency is 11.0592MHZ to set for the gain and be 4 times or 8 times, chip HX530 both guaranteed the precision and the cost is reduced, the internal crystal oscillator of taking certainly, direct complete conversion action, and the most probable outside device that reduces makes the ion meter small, portable.
Furthermore, the input end of the A/D conversion circuit is connected with an impedance matching circuit, an operational amplifier chip adopted by the impedance matching circuit is TLV271C or TLV271BCD, the operational amplifier chip adopts a dual-power processing circuit, and when the operational amplifier chip is TLV271C, the input impedance of the operational amplifier chip is as high as 1012Ohm, which meets the requirement of impedance, and the VIOMAX of the impedance is 10 mv; when the operational amplifier chip is TLV271BCD, the VIOMAX is 2mv, the noise is lower, and the precision is higher.
Furthermore, a power supply input port of the A/D conversion circuit is connected with a reference power supply, the reference power supply adopts a reference voltage chip MCP1541, the provided reference voltage is 4.096V, and the accuracy of the measured electromotive force reaches 4.096 x 10-3mv。
Furthermore, the digital temperature sensor detection circuit adopts a digital temperature sensor DS18B20, and the temperature detected by the temperature sensor DS18B20 is in the range of-55 ℃ to +125 ℃.
Furthermore, the thermistor detection circuit comprises an NTC thermistor, a voltage distribution circuit and an operational amplification circuit, the NTC thermistor is connected with an input port of the voltage distribution circuit, an output port of the voltage distribution circuit is connected with an input port of the operational amplification circuit, an output port of the operational amplification circuit is connected with an input port of the data processor, and the NTC thermistor is inserted into the solution to directly measure the temperature of the solution, so that the measurement of the actual temperature is ensured, and the measurement precision is improved.
Furthermore, the temperature-sensitive circuit detection circuit also comprises a voltage-stabilized power supply circuit, the voltage-stabilized power supply circuit comprises a voltage-stabilized power supply chip TL431, a voltage output port of the voltage-stabilized power supply circuit is respectively connected with the NTC thermistor and the acquisition circuit, and the voltage-stabilized power supply circuit provides 2.5V of reference voltage for a singlechip of the acquisition circuit and provides voltage for the NTC thermistor.
The utility model has the advantages that: the utility model provides a self-adaptation ionization gauge and its method of measuring ion concentration uses 24 bit sigma-delta type AD converters, accords with the electromotive force of quilt and weak demand, has improved the measuring precision to adopt BNC interface and ion measuring probe's BNC interface direct matching connection, simple easy-to-use; moreover, the chip HX530 not only ensures the precision, but also reduces the cost, the internal crystal oscillator of the chip directly finishes the conversion action, and external devices are reduced to the maximum extent, so that the ion meter has small volume and is convenient to carry; the utility model discloses according to ionic probe's degradation degree, dynamic testing, according to ambient temperature or solution temperature's difference, reliably calculate the ionic strength of test sample, make the measuring accuracy higher, more accurate.
Drawings
Fig. 1 is a schematic structural diagram of an adaptive ion meter according to the present invention;
FIG. 2 is a circuit diagram of the A/D conversion circuit and the operational amplifier circuit of the ion meter of the present invention;
FIG. 3 is a circuit diagram of a digital temperature sensor detection circuit of the ion meter of the present invention;
FIG. 4 is a circuit diagram of a thermistor detection circuit of the ion meter of the present invention;
fig. 5 is a circuit diagram of a voltage-stabilized power supply circuit of the thermistor detection circuit of the ion meter of the present invention.
Detailed Description
The Nernst (Nernst) equation is an equation that has important applications in the electrochemical direction in physicochemical chemistry. It can calculate the electromotive force of the reversible battery theoretically, which is specifically expressed as: for either cell reaction: aA + bB = cC + dD,
wherein,is a standard electrode potential; r is the gas constant 8.31441J (K × mol); t is the temperature; n is the electron transfer number in the electrode reaction; f is the Faraday constant 96.487Kj/(V mol).
For the ion selective electrode method (ISE), the nernst equation can be expressed as:
wherein, E0: the standard electrode potential, which depends on the potential of a reference electrode of the used electrode, the liquid junction potential and the like, E0 can be regarded as a constant term for the same electrode (including a composite electrode or an electrode pair consisting of a separate ion electrode and the reference electrode); r is the gas constant, typically 8.31441 joules/(kelvin moles); t is temperature (in Kelvin); n is the electron transfer number in the electrode reaction; faradaic constant 96487 coulomb/mole, which can be 96.487 kilojoules/(volts x mole); cx is the ion concentration in the solution; yx: is the activity coefficient. During the measurement process, the change of Yx is small and can be regarded as a constant;
from the RT/nF dimension it can be seen that:
namely: in volts.
Hereinafter, RT/nF is taken as the theoretical slope and is referred to as STheory of the inventionI.e. by
Since R and F are constants and n depends on the number of electron transfers in the electrode reaction, it is constant for the same type of electrode and they are variable for different types of electrodes.
Therefore, the first and second electrodes are formed on the substrate,
(where K is a constant and the number is equal to R/F);
the nernst equation may be expressed as E = E0-STheory of the invention*ln(CX*YX)。
If the ion-selective electrode (ISE) fully satisfies the nernst equation, the case of solutions of unknown concentration C1 is seen below. For C1 there is E1=E0-STheory of the invention*ln(C1*YX) (in this case E1 is a known quantity from the test and C1 is an unknown quantity) and E0 is the electromotive force from fully deionized water, which is a constant quantity).
This makes it possible to obtain: ln (C)1*Yx)=(E1-E0)/(-STheory of the invention) And (3) obtaining:
since Yx is constant, the density value can be obtained from the above equation.
But if the slope no longer satisfies S due to manufacturing discreteness of the Ion Selective Electrode (ISE) and aging in the applicationTheory of the inventionHow to find its actual slope and thus the actual concentration value. We derive this relationship below.
Since the electromotive force of E0 for fully deionized water can be considered constant, even though it is due to manufacturing discreteness or aging in the applicationDeionized water was obtained, although there may be differences. Assuming the aged electrode has an E0 of E00, the ion selective electrode is calibrated with a solution of known concentration C2 (in this case C2 is a known number). Thus, E2=E00-SPractice of*ln(C2*YX) Namely: sPractice of=（E00-E2)/ln(C2*YX) At this time, SPractice ofIs measured at the same temperature, and is S if the temperature is T1Practice of（T1)。
If the temperature is changed, the same temperature is kept when the E0 is measured and the electrode electromotive force E2 of the ion concentration C2 is measured, and the S of any temperature Tx can be calculatedPractice ofHas a value of SPractice of(Tx), from which the actual value of S can be obtained.
With SPractice ofValue of (a) replaces STheory of the inventionThe concentration of the solution can be obtainedTherefore, if the electromotive force values of the solutions of two concentrations and the electromotive force value E00 of deionized water can be measured, S can be obtainedPractice of(TX) and YXThen, for a solution with unknown concentration, the value of electromotive force is measured to be Ex, and the concentration C is obtainedX。
Based on the nernst equation principle, as long as the value of electromotive force Ex and temperature value Tx are surveyed, the concentration of solution can be obtained, consequently, the utility model relates to an ionometer and its method of measuring ion concentration, specific embodiment is as follows.
Example 1
The schematic structural diagram of the adaptive ion meter provided in this embodiment is shown in fig. 1, and includes a data processor, an ion measurement probe, an a/D conversion circuit electrically connected to an input port of the data processor, and a temperature detection circuit, and the structure of the adaptive ion meter is described in detail below.
(1) A/D conversion circuit
Since the value of the electromotive force varies from 0mv to 1000mv, the a/D conversion circuit employs a 24-bit sigma-delta type AD converter whose measurement accuracy is one millionth at 20 bits in order to improve the accuracy. Since the ion electrode is a slow reaction device, the electromotive force output by the ion electrode cannot be suddenly changed, and the general response time of the ion electrode is 30 seconds to 2 minutes, in this embodiment, the slow 24-bit sigma-delta type AD converter HX530 is selected, and the output rate is set to 10HZ, which can ensure that the obtained data can meet the measurement requirement, thereby ensuring the accuracy and reducing the cost.
The input port of the 24-bit sigma-delta type AD converter adopts a BNC interface, and the BNC interface is matched and connected with the BNC interface of the ion measurement probe. The 24-bit sigma-delta type AD converter is a chip HX530, adopts an internal crystal oscillator with the oscillation frequency of 11.0592MHZ, and sets the gain to be 4 times or 8 times. Since HX530 gives a full-scale differential input range (FSR) [ V (inp) -V (inn) ] of ± 0.5(VREF/GAIN) V, the FSR range is ± 500mv, which is the electromotive force range of a general ion-selective electrode, because the reference is 4.096V with 4 times GAIN. And because the AD converter is internally provided with an 11.059MHZ internal crystal oscillator, the AD converter has fewer external devices and can directly complete the conversion action, and meanwhile, the AD converter is provided with a programmable gain function and can adaptively adjust the amplification factor of the input electromotive force, thereby achieving the purpose of amplifying the measured value.
Since the output of the ion measuring probe is a tiny electromotive force, the output impedance is very high, and is mostly 108The input impedance is selected to be 10 because of the small signal variation and the easy interference to the signal12The ohmic operational amplifier forms an impedance matching circuit. The impedance matching circuit is connected with the input end of the A/D conversion circuit, the adopted operational amplifier chip is TLV271C, and the input impedance of the operational amplifier chip is as high as 1012Ohm, VIOMAX is 10mv, meet the requirement of impedance. And the operational amplifier chip adopts a dual-power processing circuit, can amplify positive and negative signals, and can be directly matched when electromotive force is positive or negative.
Meanwhile, a power supply input port of the A/D conversion circuit is connected with a reference power supply, the reference power supply adopts a reference voltage chip MCP1541, the provided reference voltage is 4.096V, and the measurement precision of the A/D conversion circuit is 4.096 x 10-3mv, namely 0.004mv, further ensures the measurement precision of the ionization gauge.
The circuit diagram of the a/D conversion circuit and the operational amplifier circuit thereof is shown in fig. 2, and includes a terminal J1, an operational amplifier U2, an a/D converter U1 and a reference voltage chip VR1, wherein the terminal J1 adopts a BNC interface, and can be directly connected with the BNC interface of the ion electrode. The output port of the binding post J1 is connected with a pin 3 of an operational amplifier U2 after anti-interference processing, the operational amplifier adopts a chip TLV271C, a pin 1 and a pin 5 of the operational amplifier adopt double power supply processing, positive and negative signals can be amplified, and electromotive force can be directly matched when the electromotive force is positive or negative. The A/D converter adopts a chip HX530, an input port of the chip HX530 is connected with an output port l of an operational amplifier U2, a power supply interface of the chip HX is connected with a voltage output port of a reference voltage chip VR1, the reference voltage chip VR1 adopts MCP1541 which is 4.096V, the maximum initial precision error is 1 percent, the MCP is used as an input reference of the HX530, an electromotive force signal of an ion electrode is subjected to impedance conversion through TLV271C and then directly sent to a first channel of the HX530, and a second channel is empty and not used. After the data is converted by the HX530, the data can be read out in a serial data mode through a data interface, so that the electromotive force of the ion electrode can be directly displayed on the singlechip. 5V is used for supplying power to the analog part of HX530, and 3V is used for supplying power to the digital part of HX530, so that the HX530 can be ensured to use the reference of 4.096V, and the digital part can be ensured to directly exchange signals with a single chip microcomputer of a 3V system without level conversion.
(2) Temperature detection circuit
The temperature detection circuit comprises a digital temperature sensor detection circuit for measuring the ambient temperature and a thermistor detection circuit for measuring the solution temperature.
The digital temperature sensor detection circuit employs a digital temperature sensor DS18B 20. Its circuit diagram is shown in fig. 3, pin 1 is grounded, pin 3 is connected to the power supply, and pin 2 is used as output end and connected to the data processing. The environment temperature is directly measured by a digital temperature sensor detection circuit, the detection temperature range is-55 ℃ to +125 ℃, the environment temperature on the plate can be directly read, and the environment temperature can be directly equivalent to the temperature of the solution for use.
The circuit diagram of the thermistor detection circuit is shown in fig. 4, the thermistor detection circuit comprises an NTC thermistor, a voltage distribution circuit and an operational amplifier circuit, the NTC thermistor is connected with an input port of the voltage distribution circuit, namely, the NTC thermistor R2 is connected with an input port 3 of the sampling singlechip LMV358 after being divided by a divider resistor R3. The output port of the voltage distribution circuit is connected with the input port of the operational amplification circuit, and the output port of the operational amplification circuit is connected with the input port of the data processor. NTC thermal resistance carries out the partial pressure with R3 then sends into the positive terminal of fortune amplifier, then sends into the AD0 sampling end of singlechip and gathers, and the temperature that can directly read out current temperature is corresponding to the table through the temperature resistance that inside producer provided.
The circuit diagram of the regulated power supply circuit is shown in fig. 5, and the regulated power supply circuit comprises a regulated power supply chip TL431, and a voltage output port of the regulated power supply circuit is respectively connected with the NTC thermistor and the acquisition circuit. TL431 is used as a voltage-stabilized output and has two functions, 1 is to provide a reference voltage of 2.5V for the singlechip, and 2 is to provide a power supply voltage for NTC thermal resistor R2.
The method for measuring the ion concentration by the adaptive ion meter comprises the following steps:
(1) the ion measuring probe is placed in deionized water, and the electromotive force of the measured deionized water is the standard electrode electromotive force E00The data are converted by an A/D conversion circuit and then transmitted to a data processor; placing an ion measuring probe at an ion concentration of C2In the solution of (2), measuring the electromotive force E2The data are converted by an A/D conversion circuit and then transmitted to a data processor; the ambient temperature is measured by a temperature sensor of the ion meter and is directly equivalent to the actual temperature of the solutionAnd Tx, transmitting the actual temperature to the data processor.
(2) Calibrating coefficients of the Nernst equation at different temperatures, SPractice of(Tx)＝(E00-E2)/ln(C2*YI) Wherein E is00Is a standard electrode electromotive force, E2Is an ion concentration of C2Electromotive force of the solution of (1); yx: is the activity coefficient; tx is the ion concentration of C2The actual temperature of the solution of (a); measuring S at different temperaturesPractice of(Tx), and then a temperature-coefficient relation table is prepared and stored in the ionization gauge.
(3) Placing an ion measuring probe in a solution to be measured, measuring actual electromotive force Ex, converting the actual electromotive force Ex through an A/D conversion circuit, and transmitting the actual electromotive force Ex to a data processor; the ambient temperature is measured by a temperature sensor of the ionization gauge, directly equivalent to the actual temperature Tx of the solution, and transmitted to the data processor.
(4) The data processor processes the data according to the Nernst equation to obtain the ion concentration in the solution
Wherein Cx is the ion concentration in the solution; yx is activity coefficient; e00Is a standard electrode electromotive force; ex is the actual electromotive force; tx is the actual temperature.
And (3) experimental verification:
the test was carried out using a composite chloride ion electrode of Shanghai L corporation as an experiment.
The data measured at a constant temperature of 25 ℃ are shown in Table 1:
table 1:
Electromotive forces of 0.1mol/l and 0.0001mol/l were selected to calculate SPractice of(TX) and YXObtaining an equation set:
Spractice of（TX)=(290-93)/ln(0.1*Yx)，
SPractice of（TX)=(290-263)/ln(0.0001*Yx)，
Solving this equation yields:
Spractice of（TX)=24.61，
Yx=e10.307454444=29955.08703。
The molar concentration of the solution at an electromotive force of 208mv was then calculated:
the test and calculation error is 6.5%, which is much lower than +/-10% of the error of the composite chloride ion electrode, and meets the required value.
The Nernst equation is an important application equation of physical chemistry, electrochemistry and analytical chemistry, and the application of the Nernst equation and the knowledge of modern electronics are combined to develop an ion measuring instrument with higher precision and easy carrying, thereby having important significance for the teaching of chemical analysis and the application of environmental protection.
Example 2
The structure of the adaptive ion meter provided in this embodiment is substantially the same as that of the adaptive ion meter provided in embodiment 1, and the difference is as follows: the gain of a 24-bit sigma-delta type AD converter in an A/D conversion circuit is set to be 8 times, and the A/D conversion circuit is applied to a scene with relatively small electromotive force. The operational amplifier chip of the impedance matching circuit adopts TLV271BCD, and VIOMAX of the operational amplifier chip is only 2mv, so that the impedance matching circuit is suitable for more accurate measurement.
The method for measuring the ion concentration by the adaptive ion meter of the present embodiment is basically the same as that in embodiment 1, except that:
(I) calibrating the coefficients S of the nernst equation at different temperatures in step (2)Practice ofThe method of (Tx) is: measured temperature of T1S of (1)Practice of(T1) then byIs calculated to obtain SPractice of（Tx)。
(II) the method for measuring the actual temperature Tx in the step (1) and the step (3) comprises the following steps: the actual temperature Tx of the solution is directly measured by inserting a thermistor of an ion meter into the solution to be measured.
The ion meter of the embodiment is more accurate than the ion meter of the embodiment 1 in measurement, and is suitable for occasions with high requirements on precision.
In addition to the above embodiments, the present invention may have other embodiments. All the technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope claimed by the present invention.
Claims (6)
1. The self-adaptive ion meter comprises a data processor and an ion measurement probe, and is characterized by also comprising an A/D conversion circuit and a temperature detection circuit which are electrically connected with an input port of the data processor;
the A/D conversion circuit adopts a 24-bit sigma-delta type AD converter, the input port of the A/D conversion circuit adopts a BNC interface, and the BNC interface is connected with the BNC interface of the ion measurement probe in a matching way;
the temperature detection circuit comprises a digital temperature sensor detection circuit for measuring the ambient temperature and a thermistor detection circuit for measuring the solution temperature.
2. The adaptive ion meter according to claim 1, wherein the 24-bit sigma-delta type AD converter is a chip HX530, the chip HX530 employs an internal crystal oscillator with an oscillation frequency of 11.0592MHZ, and the gain is set to be 4 times or 8 times.
3. The adaptive ion meter according to claim 1, wherein the input end of the A/D conversion circuit is connected with an impedance matching circuit, the impedance matching circuit adopts an operational amplifier chip TLV271C or TLV271BCD, and the operational amplifier chip adopts a dual-power supply processing circuit.
4. The adaptive ion meter according to claim 1, wherein the power input port of the a/D conversion circuit is connected to a reference power supply, the reference power supply adopts a reference voltage chip MCP1541, and the reference voltage is 4.096V.
5. The adaptive ion meter of claim 1, wherein the digital temperature sensor detection circuit employs a digital temperature sensor DS18B 20.
6. The adaptive ion meter according to claim 1, wherein the thermistor detecting circuit includes an NTC thermistor, a voltage distribution circuit, and an operational amplification circuit, the NTC thermistor being connected to an input port of the voltage distribution circuit, an output port of the voltage distribution circuit being connected to an input port of the operational amplification circuit, and an output port of the operational amplification circuit being connected to an input port of the data processor.
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| CN103616416A (en) * | 2013-10-25 | 2014-03-05 | 江苏苏威尔科技有限公司 | Adaptive ion meter and ion concentration measure method by the same |
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| CN103616416A (en) * | 2013-10-25 | 2014-03-05 | 江苏苏威尔科技有限公司 | Adaptive ion meter and ion concentration measure method by the same |
| CN103616416B (en) * | 2013-10-25 | 2016-04-13 | 江苏苏威尔科技有限公司 | The method of self-adaptation ionometer and measurement ion concentration thereof |
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