CN113281549B - Modified digital multimeter and method for measuring pH and ion concentration of solution - Google Patents
Modified digital multimeter and method for measuring pH and ion concentration of solution Download PDFInfo
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- CN113281549B CN113281549B CN202110591975.6A CN202110591975A CN113281549B CN 113281549 B CN113281549 B CN 113281549B CN 202110591975 A CN202110591975 A CN 202110591975A CN 113281549 B CN113281549 B CN 113281549B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/12—Circuits for multi-testers, i.e. multimeters, e.g. for measuring voltage, current, or impedance at will
- G01R15/125—Circuits for multi-testers, i.e. multimeters, e.g. for measuring voltage, current, or impedance at will for digital multimeters
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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
- G01N27/302—Electrodes, e.g. test electrodes; Half-cells pH sensitive, e.g. quinhydron, antimony or hydrogen electrodes
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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
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/36—Glass electrodes
Abstract
The invention relates to a modified digital multimeter and a method for measuring the pH and ion concentration of a solution, wherein the modified digital multimeter is used for expanding the functions of the digital multimeter, the expanded functions comprise a pH measuring function and an ion concentration measuring function, the modified digital multimeter comprises a selection switch, and the selection switch is connected in series in a voltage dividing resistor combination branch circuit in the digital multimeter; when the selection switch is disconnected, the digital multimeter is arranged at a mV measuring gear, a voltage measuring end of the digital multimeter is directly connected with a measuring digital meter head, and the voltage measuring end is used for connecting a pH measuring electrode or an ion concentration measuring electrode; and when the selection switch is closed, the normal function of the digital multimeter is restored. Compared with the prior art, the method has the advantages of low cost, good determination effect and the like.
Description
Technical Field
The invention relates to the technical field of measuring instruments, in particular to a modified digital multimeter and a method for measuring pH and ion concentration of a solution.
Background
Potentiometry is an electrochemical analysis method, which uses the correspondence between the electrode potential in a chemical cell and the concentration of a certain component in a solution to realize quantitative determination. The direct potential method is a method for directly calculating the activity or concentration of ions to be measured by measuring the electromotive force of a chemical battery based on an nernst equation, and is mainly applied to a pH electrode and various ion selective electrodes. The method is simple and convenient to use, rapid in measurement and free from destroying the equilibrium relation in the solution.
The pH value measurement is applied to various fields of environmental protection, oceans, medicine, machinery, food, agriculture, chemical industry and the like, wherein a pH meter is an indispensable measuring tool, and the principle of the pH meter is a potential relative measurement method. When the pH value of the solution is measured by a potentiometric method, the electrode system consists of a pH glass electrode and a saturated calomel electrode, if the pH electrode is a positive electrode, when the activity of hydrogen ions in the solution changes, the electromotive force of the positive electrode and the pH value of the solution have the following relationship:
wherein E is the electromotive force of the battery composed of a pH glass electrode and a calomel electrode, E 0 R is the gas constant, T is the absolute temperature, and F is the faraday constant for standard electromotive force.
Let K-2.30259 RT/F (positive for negative pH electrode), the difference between the two different solution pH (Δ pH-pH) 2 -pH 1 ) Measured potential difference (Δ E ═ E) from the same 2 -E 1 ) The relationship between them is:
ΔpH＝ΔE/K (2)
from (2), it can be seen that the pH of the solution to be measured can be calculated by converting the chemical signal into an electrical signal using the glass electrode and measuring the potential difference between the solution to be measured and the solution with the known pH. Other ion-selective electrodes may also be used to perform ion content determination.
The digital multimeter is composed of a digital measuring meter head as a core and a peripheral circuit. The meter head carries out analog-to-digital (A/D) conversion on the input signal, and the input signal is decoded and driven by the circuit and finally displayed on a display screen.
However, when the multimeter is used for measuring voltage, the peripheral circuit of the multimeter can reduce the original approximately 10000M omega input resistance of the meter head to about 10M omega, which is smaller than the internal resistance of the common glass electrode about 100M omega, and the multimeter cannot be used for pH measurement. The existing pH meter can only measure the precise potential and pH, and has single function and higher price.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a modified digital multimeter and a method for measuring the pH and the ion concentration of a solution.
The purpose of the invention can be realized by the following technical scheme:
a kind of transformation digital multimeter, is used for expanding the function of the digital multimeter, the expanded function includes pH measurement function, ion concentration measurement function, the said transformation digital multimeter includes the selector switch, the said selector switch connects in the divider resistance combination branch in the digital multimeter in series;
when the selection switch is disconnected, the digital multimeter is arranged at a mV measuring gear, the voltage measuring end of the digital multimeter is directly connected with a measuring digital meter head, and the voltage measuring end is used for connecting a pH measuring electrode or an ion concentration measuring electrode;
and when the selection switch is closed, the normal function of the digital multimeter is restored.
Preferably, when the pH measuring electrode or the ion concentration measuring electrode is a composite electrode, the composite electrode is connected to a voltage measuring end of a digital multimeter through an adapter.
The method for measuring the pH value of the solution adopts the modified digital multimeter to measure the pH value of the solution.
Preferably, the specific method for performing the solution pH measurement is:
disconnecting the selector switch, placing the digital multimeter at a mV measuring gear, and connecting the pH measuring electrode to a voltage measuring end of the digital multimeter;
measuring the voltage of the solution with known pH by using a modified digital multimeter, and correcting the linear relation between the pH and the measured voltage to obtain a pH-voltage function;
and measuring the voltage of the solution to be measured by using the modified digital multimeter, and obtaining the pH value of the solution to be measured by using a pH-voltage function.
The method for measuring the solution ion concentration adopts the modified digital multimeter to measure the solution ion concentration.
Preferably, the specific method for measuring the ion concentration of the solution is as follows:
disconnecting the selector switch, placing the digital multimeter at a mV measuring gear, and connecting the ion concentration measuring electrode to a voltage measuring end of the digital multimeter;
measuring the voltage of the solution with the known ion concentration by using a modified digital multimeter, and correcting the linear relation between the ion concentration and the measured voltage to obtain an ion concentration-voltage function;
and measuring the voltage of the solution to be measured by using the modified digital multimeter, and obtaining the ion concentration of the solution to be measured by using the ion concentration-voltage function.
Compared with the prior art, the invention has the following advantages:
the invention realizes the performance improvement of the existing digital multimeter, can measure the pH value and the ion concentration of the solution, has the characteristics of simple and convenient instrument, low cost, high precision and the like compared with the existing pH meter or potentiometer, has small structural change, does not reduce the original function of the digital multimeter, and is easy to produce and make into a new-type commodity, thereby having direct application prospect.
Drawings
FIG. 1 is a schematic circuit diagram of a prior art digital multimeter;
FIG. 2 is a schematic circuit diagram of a modified digital multimeter of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. Note that the following description of the embodiments is merely a substantial example, and the present invention is not intended to be limited to the application or the use thereof, and is not limited to the following embodiments.
Example 1
Fig. 1 is a schematic circuit diagram of a conventional digital multimeter, where if a solution potential difference measured by the conventional digital multimeter is directly measured, the solution potential difference is an electromotive force of a circuit when a measurement range is connected to 200mV, according to a formula:
E＝U inner part +U Outer cover ＝Ir+IR
The relationship between E and R (i.e. the internal resistance of the glass electrode) and the relationship between R (the total resistance of the divider resistor combined branch in the digital multimeter) can be known from the above formula. Because the internal resistance of the glass electrode is extremely high (usually 10-150M Ω), if we connect it into the direct current voltage measurement circuit, the internal resistance (R) of the glass electrode is much greater than the total resistance of the divider resistance combination branch in the digital multimeter (R ═ 1k Ω +9k Ω +90k Ω +900k Ω +9M Ω ═ 10M Ω) (R > > R), so that the internal resistance in the circuit cannot be ignored but has a great influence on the measurement result. Therefore, the external resistance (R) of the circuit can be increased to be far greater than the internal resistance (R) of the glass electrode, and the purpose of measuring the micro potential difference of the solution can be achieved.
Because the internal resistance of the meter head of the digital multimeter is extremely high (up to 10000M omega) and is far greater than the internal resistance of the glass electrode, the output resistance of an integrated circuit (namely the meter head) can be changed into the external resistance of a peripheral circuit, and the neglect of the resistance of the glass electrode is realized.
Therefore, as shown in fig. 2, the present embodiment provides a modified digital multimeter, which is used for expanding functions of the digital multimeter, where the expanded functions include a pH measurement function and an ion concentration measurement function, the modified digital multimeter includes a selection switch, the selection switch is connected in series in a voltage dividing resistor combination branch of the digital multimeter, and K in fig. 2 is a rotary switch.
When the selection switch is disconnected, the digital multimeter is arranged at a mV measuring gear, the voltage measuring end of the digital multimeter is directly connected with a measuring digital meter head, and the voltage measuring end is used for connecting a pH measuring electrode or an ion concentration measuring electrode;
and when the selection switch is closed, the normal function of the digital multimeter is restored.
When the pH measuring electrode or the ion concentration measuring electrode is a composite electrode, the composite electrode is connected to a voltage measuring end of the digital multimeter through an adapter, and the composite electrode comprises a combination of an ion selective electrode and a reference electrode, a composite glass electrode or a combination of a glass electrode and a reference electrode.
The implementation method of adding the precision potentiometer or the pH measurement function on the digital multimeter increases the function of the multimeter for measuring the pH or the ion concentration by improving the input resistance of the existing multimeter during voltage measurement, and the functions of the multimeter are connected with the ion selective electrode or the glass electrode through the adapter to measure the voltage and calculate the pH. The method has the advantages of simple preparation process, low cost and good determination effect, is completely compatible with the functions of the conventional multimeter, does not influence the conventional functions of the multimeter, and is an effective, easily-realized and easily-produced new function expansion device for the multimeter.
Example 2
The embodiment provides a method for measuring the pH of a solution, which is implemented by using the modified digital multimeter in embodiment 1, and the method specifically comprises the following steps:
disconnecting the selector switch, placing the digital multimeter at a mV measuring gear, and connecting the pH measuring electrode to a voltage measuring end of the digital multimeter;
measuring the voltage of the solution with known pH by using a modified digital multimeter, and correcting the linear relation between the pH and the measured voltage to obtain a pH-voltage function;
and measuring the voltage of the solution to be measured by using the modified digital multimeter, and obtaining the pH value of the solution to be measured by using a pH-voltage function.
Specifically, the method comprises the following steps: and an adapter is inserted between the COM and the V plug wire port of the multimeter, and a plug of the composite electrode is inserted at the other end of the adapter. In this embodiment, the glass electrode is a positive electrode, and if the insertion manner of the adapter is changed to change the glass electrode to a negative electrode, the following measurement results are different from each other in positive and negative values, and the experimental result is not affected.
And placing the digital multimeter at a level of 200mV, sequentially washing the composite glass electrode with distilled water and a standard solution to be measured, immersing the composite glass electrode into the standard solution, balancing and stabilizing the composite glass electrode for 2 minutes, and measuring a voltage value, wherein the temperature of the solution is about 20 ℃. The voltage reading for the standard pH buffer at pH4.00 was 160.8mV and the voltage reading for the standard pH buffer at pH6.86 was-3.0 mV. The slope of the potential change per unit pH was calculated to be-57.27 (mV/pH), close to the theoretical value of 58.2 at 20 degrees Celsius (mV/pH), and was used for pH measurements. The linear relationship between pH and mV was calculated as: mV-57.3 pH + 390.5.
After the composite pH electrode was washed with the sprite, the electrode was immersed in a beaker containing the sprite, and the measurement voltage was 198.9mV, and the pH was 3.33 according to the above linear relationship, which was consistent with the measurement result using a pH meter.
Example 3
The embodiment provides a method for measuring solution ion concentration, which is implemented by using the modified digital multimeter in embodiment 1, and the specific method is as follows:
disconnecting the selector switch, placing the digital multimeter at a mV measuring gear, and connecting the ion concentration measuring electrode to a voltage measuring end of the digital multimeter;
measuring the voltage of the solution with the known ion concentration by using a modified digital multimeter, and correcting the linear relation between the ion concentration and the measured voltage to obtain an ion concentration-voltage function;
and measuring the voltage of the solution to be measured by using the modified digital multimeter, and obtaining the ion concentration of the solution to be measured by using the ion concentration-voltage function.
An adapter is inserted between COM and V plug wire ports of the digital multimeter, and two wires led out from a plug at the other end of the adapter are respectively connected with connecting wires of a fluorine ion selective electrode and a saturated calomel electrode. In this embodiment, the glass electrode is a positive electrode, and if the insertion manner of the adapter is changed, the glass electrode is changed into a negative electrode, the following measurement results are different from each other in positive and negative values, and the experimental result is not affected.
And placing a digital multimeter at a level of 200mV, sequentially washing the composite glass electrode with distilled water and a standard solution to be detected, immersing the composite glass electrode into the standard solution, and measuring a voltage value after balancing and stabilizing for 2 minutes, wherein the voltage reading of the standard fluorine ion solution with the concentration of A is Va (mV), and the voltage reading of the standard fluorine ion solution with the concentration of B is vb (mV). Calculating to obtain a linear relation between the fluorine ion concentration C and mV: mV-E + klgC, where k-Va-Vb)/(lgA-lgB) and E-Va-klgA.
Washing the fluorine ion selective electrode and the saturated calomel electrode, immersing the electrode into a to-be-measured solution beaker containing a total ion intensity adjusting buffer to measure the voltage Vx (mV), and obtaining the concentration C (10) of fluorine ions by calculation according to the linear relation (Vx-E)/k 。
The above embodiments are merely examples and do not limit the scope of the present invention. These embodiments may be implemented in other various manners, and various omissions, substitutions, and changes may be made without departing from the technical spirit of the present invention.
Claims (4)
1. A modified digital multimeter is characterized by being used for expanding functions of the digital multimeter, wherein the expanded functions comprise a pH measurement function and an ion concentration measurement function, the modified digital multimeter comprises a selection switch, and the selection switch is connected in series with a divider resistor combination branch in the digital multimeter;
when the selection switch is disconnected, the digital multimeter is arranged at a mV measuring gear, the voltage measuring end of the digital multimeter is directly connected with a measuring digital meter head, and the voltage measuring end is used for connecting a pH measuring electrode or an ion concentration measuring electrode;
and when the selection switch is closed, the normal function of the digital multimeter is restored.
2. The modified digital multimeter of claim 1, wherein when the pH or ion concentration measuring electrode is a composite electrode, the composite electrode is connected to a voltage measuring terminal of the digital multimeter via an adapter.
3. A method of measuring the pH of a solution, characterized in that the pH of the solution is measured using the modified digital multimeter of claim 1 or 2;
the specific method for measuring the pH of the solution comprises the following steps:
disconnecting the selector switch, placing the digital multimeter at a mV measuring gear, and connecting the pH measuring electrode to a voltage measuring end of the digital multimeter;
measuring the voltage of the solution with known pH by using a modified digital multimeter, and correcting the linear relation between the pH and the measured voltage to obtain a pH-voltage function;
and measuring the voltage of the solution to be measured by using the modified digital multimeter, and obtaining the pH value of the solution to be measured by using a pH-voltage function.
4. A method of measuring the solution ion concentration, characterized in that the solution ion concentration is measured using the modified digital multimeter of claim 1 or 2;
the specific method for measuring the ion concentration of the solution comprises the following steps:
disconnecting the selector switch, placing the digital multimeter at a mV measuring gear, and connecting the ion concentration measuring electrode to a voltage measuring end of the digital multimeter;
measuring the voltage of the solution with the known ion concentration by using a modified digital multimeter, and correcting the linear relation between the ion concentration and the measured voltage to obtain an ion concentration-voltage function;
and measuring the voltage of the solution to be measured by using the modified digital multimeter, and obtaining the ion concentration of the solution to be measured by using the ion concentration-voltage function.
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