CN112432975A - Method for measuring liquid conductivity - Google Patents

Method for measuring liquid conductivity Download PDF

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CN112432975A
CN112432975A CN202110101276.9A CN202110101276A CN112432975A CN 112432975 A CN112432975 A CN 112432975A CN 202110101276 A CN202110101276 A CN 202110101276A CN 112432975 A CN112432975 A CN 112432975A
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singlechip
conductivity
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CN112432975B (en
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卫平强
吴红平
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Nanjing Yijing New Material Technology Co ltd
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    • G01—MEASURING; TESTING
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    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid

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Abstract

The invention discloses a method for measuring the conductivity of liquid, which comprises the following steps: s1: placing two metal electrodes in the liquid, respectively connecting a first pin and a second pin of the singlechip, then equating the electrical parameter characteristics of the liquid to be parallel capacitance and resistance, simultaneously connecting a resistance in parallel, and then connecting a resistance in series between the first pin and the metal electrodes to form a measuring circuit; s2: a first pin of the single chip microcomputer repeatedly transmits a group of level signals, and a second pin of the single chip microcomputer repeatedly transmits a group of pulse signals, so that the charging and discharging time of the two metal electrodes is consistent, and the polarization effect is avoided; s3: and sampling for multiple times by using the sampling pin of the singlechip in the process of transmitting the level signal by the first pin, and calculating to obtain the conductivity according to the sampling value. The invention not only can effectively avoid the problem of liquid polarization, but also has the characteristics of simple circuit, high measurement precision and the like.

Description

Method for measuring liquid conductivity
Technical Field
The invention relates to the technical field of measurement of liquid conductivity, in particular to a method for measuring liquid conductivity.
Background
With the rapid development of industrial and agricultural production, and with the production and living of human beings, the measurement of the conductivity of a solution has been a very important topic. For example, in the field of new energy vehicles, the measurement of the conductivity of a solution in a lithium battery on an electric vehicle is a key technology, and influences the energy utilization rate, the endurance mileage, the peak power and the like of the electric vehicle. In the field of water treatment, a lot of useful information can be obtained by measuring the conductivity of water, and water quality detection plays a crucial role in water pollution control and whole water environment protection. If the fluorine content is too high, the teeth may be stained, which may cause a dental disease, namely, plaque, and serious patients may completely collapse their teeth. Even the domestic sewage discharged in daily life can spread various diseases. Therefore, the method can also find that the detection of the quality of the drinking water has very important significance in the aspect of drinking water safety of people.
Current measurements of liquid conductivity are generally divided into three categories: ultrasonic measurement, electromagnetic measurement, and electrode measurement. The former two methods have the disadvantages of limited use range, high cost, narrow measurement range and the like. Therefore, the electrode type conductivity measurement method is the most commonly used measurement method at present, and many high-end instruments applied in the current market are expensive, low-end instruments are low in precision and insufficient in resolution. As shown in the following figure, the circuit of the voltage division method which is widely applied in the market at present is shown in the following figure, two metal electrodes are placed in a solution, a resistor is connected in series on a line, and a singlechip samples the voltage division value of the solution resistor, so that the resistance of the solution is calculated and converted into the conductivity. Conductivity is the inverse of resistance. The partial pressure method ignores the capacitive effect in solution: the principle is as follows: two IO pins of the single chip microcomputer respectively drive and output high and low levels, equivalent resistance in the solution can generate partial pressure, and the partial pressure value is sent to analog quantity of the single chip microcomputer for AD conversion. Namely: as can be seen from the above equation, the voltage value and the conductivity are measured as inversely proportional functions, and if the final measured physical quantity and the conductivity are in a direct or inverse proportional relationship, the measured value may not be sufficiently resolved at the high value or the low value. Namely: the rate of change of the measured value becomes smaller and smaller with the change of the physical quantity, thus resulting in insufficient accuracy of measurement.
Disclosure of Invention
It is an object of the present invention to provide a method for measuring the conductivity of a liquid. The invention not only can effectively avoid the problem of liquid polarization, but also has the characteristics of simple circuit, high measurement precision and the like.
The technical scheme of the invention is as follows: a method for measuring the conductivity of a liquid, comprising the steps of:
s1: two metal electrodes are placed in the liquid and respectively connected with first pin and second pin of single-chip microcomputer, and then the electric parameter characteristics of the liquid are equivalent to parallel capacitors
Figure DEST_PATH_IMAGE002
And a resistor
Figure DEST_PATH_IMAGE004
Simultaneously connecting a resistor in parallel
Figure DEST_PATH_IMAGE006
And a resistor is connected in series between the first pin and the metal electrode
Figure DEST_PATH_IMAGE008
Forming a measuring circuit;
s2: a first pin of the single chip microcomputer repeatedly transmits a group of level signals, and a second pin of the single chip microcomputer repeatedly transmits a group of pulse signals, so that the charging and discharging time of the two metal electrodes is consistent, and the polarization effect is avoided;
s3: and sampling for multiple times by using the sampling pin of the singlechip in the process of transmitting the level signal by the first pin, and calculating to obtain the conductivity according to the sampling value.
In the above method for measuring the conductivity of the liquid, in step S2, the level signal transmitted by the first pin sends out a set of waveforms every 2S, where the waveforms are high level for 1ms, low level for 2ms, high level lasts for 1ms again, and finally low level all the time; the pulse signal transmitted by the second pin sends a group of pulses every 2s, and the waveform of the pulses is high level 2 ms; wherein, the high level in the pulse signal and the low level of 2ms in the level signal are transmitted at the same time, and the waveforms of the two signals are symmetrical.
In the foregoing method for measuring the conductivity of the liquid, in step S3, the sampling pin of the single chip microcomputer samples 4 times every 2S, and the sampling time points are respectively 0.1ms, 1.1ms, 3.1ms and 4.1ms when the level signal changes from low level to high level for the first time.
In the method for measuring the conductivity of the liquid, the charge and discharge formula of the capacitor during the charge and discharge of the two metal electrodes is as follows:
the charging formula is as follows:
Figure DEST_PATH_IMAGE010
；
discharge formula:
Figure DEST_PATH_IMAGE012
；
in the formula:
Figure DEST_PATH_IMAGE014
，
Figure DEST_PATH_IMAGE016
a resistance equivalent to an electrical parameter characteristic of the liquid;
Figure DEST_PATH_IMAGE018
is a resistor
Figure 9737DEST_PATH_IMAGE008
The resistance value of (1);
Figure 100002_DEST_PATH_IMAGE020
is a resistor
Figure 274496DEST_PATH_IMAGE006
The resistance value of (1);
Figure 100002_DEST_PATH_IMAGE022
is time;
Figure DEST_PATH_IMAGE024
a capacitance equivalent to an electrical parameter characteristic of the liquid;
Figure 100002_DEST_PATH_IMAGE026
supplying power level to the pins of the singlechip;
and calculating according to the four sampling values:
Figure 100002_DEST_PATH_IMAGE028
；
in the formula:
Figure DEST_PATH_IMAGE030
is a 4-time mode value converted from the sampling value of the singlechip,
Figure DEST_PATH_IMAGE032
the sampling value of the singlechip at a first sampling time point is obtained;
Figure DEST_PATH_IMAGE034
is an analog quantity reference level of the singlechip,
Figure DEST_PATH_IMAGE036
the sampling value of the singlechip at the second sampling time point is obtained;
Figure DEST_PATH_IMAGE038
the sampling value of the singlechip at the third sampling time point is obtained;
Figure DEST_PATH_IMAGE040
the sampling value of the singlechip at the fourth sampling time point is obtained;
establishing the following relation according to the 4-time mode value converted from the sampling value of the single chip microcomputer:
Figure DEST_PATH_IMAGE042
in the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE044
is proportional to;
Figure DEST_PATH_IMAGE045
，
Figure 611978DEST_PATH_IMAGE016
a resistance equivalent to an electrical parameter characteristic of the liquid;
Figure 555663DEST_PATH_IMAGE018
is a resistor
Figure 990187DEST_PATH_IMAGE008
The resistance value of (1);
Figure DEST_PATH_IMAGE046
is a resistor
Figure 358720DEST_PATH_IMAGE006
The resistance value of (1);
Figure 79552DEST_PATH_IMAGE024
a capacitance equivalent to an electrical parameter characteristic of the liquid;
Figure 385899DEST_PATH_IMAGE026
supplying power level to the pins of the singlechip;
resistance equivalent according to the resulting electrical parameter characteristic of the liquid
Figure 686430DEST_PATH_IMAGE016
From the relation of conductivity and resistance
Figure DEST_PATH_IMAGE048
Deriving the conductivity of the liquid
Figure DEST_PATH_IMAGE050
。
Compared with the prior art, the liquid level measuring circuit has the advantages that the electrical parameter characteristics of the liquid are equivalent to the parallel capacitance and resistance, the resistance is connected in parallel, the resistance is connected in series between the first pin and the metal electrode, the two resistances are used for dividing and adjusting the charging and discharging time of the circuit, so that the measuring circuit is formed, the first pin of the single chip microcomputer is used for repeatedly transmitting a group of level signals, the second pin of the single chip microcomputer is used for repeatedly transmitting a group of pulse signals, the charging and discharging time of the two metal electrodes is consistent, and the polarization effect is avoided; finally, in the process of level signals transmitted by the first pin, the sampling pin of the singlechip is used for sampling for multiple times, and the conductivity is calculated according to the sampling value, so that the problem of inaccurate measurement precision caused by the fact that the change rate of the measurement value is smaller and smaller along with the change of physical quantity in the background technology by adopting a voltage division method can be solved, and the liquid polarization problem can be effectively avoided. In addition, the invention adopts the algorithm similar to X4 to calculate the conductivity, further improves the measurement accuracy, and has very simple circuit and lower cost.
Drawings
FIG. 1 is a schematic diagram of an algorithmic circuit of the present invention;
FIG. 2 is a timing diagram of the activation of the single-chip microcomputer.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
Example (b): a method for measuring the conductivity of a liquid, comprising the steps of:
s1: as shown in figure 1, two metal electrodes are placed in the liquid and respectively connected with a first pin and a second pin of a singlechip, and then the electrical parameter characteristic of the liquid is equivalent to a parallel capacitor
Figure DEST_PATH_IMAGE051
And a resistor
Figure 614197DEST_PATH_IMAGE004
Simultaneously connecting a resistor in parallel
Figure 505930DEST_PATH_IMAGE006
And a resistor is connected in series between the first pin and the metal electrode
Figure 814421DEST_PATH_IMAGE008
Forming a measuring circuit; the resistance value of the resistor is 1K, the resistance value of the resistor is 1M, and the singlechip is powered by 3.3V;
s2: a first pin of the single chip microcomputer repeatedly transmits a group of level signals, and a second pin of the single chip microcomputer repeatedly transmits a group of pulse signals, so that the charging and discharging time of the two metal electrodes is consistent, and the polarization effect is avoided;
specifically, as shown in fig. 2, a level signal transmitted by the first pin (IO 1) sends a set of waveforms every 2s, where the waveforms are high level 1ms, low level 2ms, high level lasts for 1ms again, and finally, the waveforms are always low level; the pulse signal transmitted by the second pin (IO 2) sends a group of pulses every 2s, and the waveform of the pulses is high level 2 ms; wherein, the high level in the pulse signal and the low level of 2ms in the level signal are transmitted at the same time, and the waveforms of the two signals are symmetrical.
S3: and sampling for multiple times by using a sampling pin of the singlechip in the process of transmitting the level signal by the first pin, wherein the sampled voltage value is equivalent to the sum of partial voltage and charge and discharge of a capacitor, and the conductivity is calculated according to the sampling value.
Specifically, as shown in an AD value curve in fig. 2, the sampling pin of the single chip microcomputer samples 4 times every 2s, and the sampling time points are respectively 0.1ms, 1.1ms, 3.1ms and 4.1ms when the level signal changes from low level to high level for the first time;
in the charging and discharging processes of the two metal electrodes, the charging and discharging formula of the capacitor is as follows:
the charging formula is as follows:
Figure 715380DEST_PATH_IMAGE010
corresponding to sampling time points of 0.1ms and 3.1 ms;
discharge formula:
Figure 12501DEST_PATH_IMAGE012
corresponding to sampling time points of 1.1ms and 4.1 ms;
in the formula:
Figure 340714DEST_PATH_IMAGE045
，
Figure 103877DEST_PATH_IMAGE016
a resistance equivalent to an electrical parameter characteristic of the liquid;
Figure 808528DEST_PATH_IMAGE018
is a resistor
Figure 225734DEST_PATH_IMAGE008
The resistance value of (1);
Figure DEST_PATH_IMAGE052
is a resistor
Figure 459269DEST_PATH_IMAGE006
The resistance value of (1);
Figure 211193DEST_PATH_IMAGE022
is time;
Figure 453956DEST_PATH_IMAGE024
a capacitance equivalent to an electrical parameter characteristic of the liquid;
Figure 725668DEST_PATH_IMAGE026
supplying power level to the pins of the singlechip;
and calculating according to the four sampling values:
Figure 395684DEST_PATH_IMAGE028
；
in this embodiment, the AD bit width of the single chip microcomputer is 10 bits, and the calculation formula is:
Figure DEST_PATH_IMAGE054
；
in the formula:
Figure 667528DEST_PATH_IMAGE030
is a 4-time mode value converted from the sampling value of the singlechip,
Figure 323768DEST_PATH_IMAGE032
the sampling value of the singlechip at a first sampling time point is obtained;
Figure 840200DEST_PATH_IMAGE034
is an analog quantity reference level of the singlechip,
Figure DEST_PATH_IMAGE055
the sampling value of the singlechip at the second sampling time point is obtained;
Figure 336909DEST_PATH_IMAGE038
the sampling value of the singlechip at the third sampling time point is obtained;
Figure 79737DEST_PATH_IMAGE040
the sampling value of the singlechip at the fourth sampling time point is obtained;
establishing the following relation according to the 4-time mode value converted from the sampling value of the single chip microcomputer:
Figure 664303DEST_PATH_IMAGE042
in the formula (I), the compound is shown in the specification,
Figure 658410DEST_PATH_IMAGE044
is proportional to;
Figure DEST_PATH_IMAGE056
，
Figure 76753DEST_PATH_IMAGE016
a resistance equivalent to an electrical parameter characteristic of the liquid;
Figure DEST_PATH_IMAGE057
is a resistor
Figure DEST_PATH_IMAGE058
The resistance value of (1);
Figure 87303DEST_PATH_IMAGE046
is a resistor
Figure 350925DEST_PATH_IMAGE006
The resistance value of (1);
Figure 576370DEST_PATH_IMAGE024
a capacitance equivalent to an electrical parameter characteristic of the liquid;
Figure 385189DEST_PATH_IMAGE026
supplying power level to the pins of the singlechip;
calibrated by standard instruments according to the above formula
Figure DEST_PATH_IMAGE059
And
Figure DEST_PATH_IMAGE060
a graph of (a);
finally, according to the curve diagram, the relation between the conductivity and the resistance is calculated
Figure DEST_PATH_IMAGE061
Deriving the conductivity of the liquid
Figure 633767DEST_PATH_IMAGE050
I.e. first obtained
Figure 684769DEST_PATH_IMAGE059
And
Figure 764720DEST_PATH_IMAGE060
according to the standard curve obtained in the subsequent measurement
Figure 259287DEST_PATH_IMAGE059
Correspondingly obtaining the equivalent resistance of the electrical parameter characteristic of the liquid in the standard curve chart
Figure 57478DEST_PATH_IMAGE016
By a resistance
Figure 410706DEST_PATH_IMAGE016
And then the conductivity is obtained.
In summary, the formula
Figure DEST_PATH_IMAGE062
It can be seen that with the liquid
Figure 17268DEST_PATH_IMAGE060
The resolution ratio is further improved by adopting an algorithm similar to X4, so that the overall resolution ratio is at a low resistance value, the high conductivity is greatly improved, and the circuit is very simple. The invention not only can effectively avoid the problem of liquid polarization, but also has the characteristics of simple circuit, high measurement precision and the like.

Claims (4)

1. A method for measuring the conductivity of a liquid, characterized by: the method comprises the following steps:
s1: two metal electrodes are placed in the liquid and respectively connected with first pin and second pin of single-chip microcomputer, and then the electric parameter characteristics of the liquid are equivalent to parallel capacitors
Figure DEST_PATH_IMAGE001
And a resistor
Figure 530097DEST_PATH_IMAGE002
Simultaneously connecting a resistor in parallel
Figure DEST_PATH_IMAGE003
And a resistor is connected in series between the first pin and the metal electrode
Figure 477455DEST_PATH_IMAGE004
Forming a measuring circuit;
s2: a first pin of the single chip microcomputer repeatedly transmits a group of level signals, and a second pin of the single chip microcomputer repeatedly transmits a group of pulse signals, so that the charging and discharging time of the two metal electrodes is consistent, and the polarization effect is avoided;
s3: and sampling for multiple times by using the sampling pin of the singlechip in the process of transmitting the level signal by the first pin, and calculating to obtain the conductivity according to the sampling value.
2. Method for measuring the conductivity of a liquid according to claim 1, characterized in that: in step S2, the level signal transmitted by the first pin sends a set of waveforms every 2S, where the waveforms are high level 1ms, low level 2ms, high level lasts for 1ms again, and finally low level all the time; the pulse signal transmitted by the second pin sends a group of pulses every 2s, and the waveform of the pulses is high level 2 ms; wherein, the high level in the pulse signal and the low level of 2ms in the level signal are transmitted at the same time, and the waveforms of the two signals are symmetrical.
3. Method for measuring the conductivity of a liquid according to claim 2, characterized in that: in step S3, the sampling pin of the single chip microcomputer samples 4 times every 2S, and the sampling time points are respectively 0.1ms, 1.1ms, 3.1ms and 4.1ms when the level signal changes from low level to high level for the first time.
4. A method for measuring the conductivity of a liquid according to claim 3, characterized in that: in the charging and discharging processes of the two metal electrodes, the charging and discharging formula of the capacitor is as follows:
the charging formula is as follows:
Figure DEST_PATH_IMAGE005
；
discharge formula:
Figure 169468DEST_PATH_IMAGE006
；
in the formula:
Figure DEST_PATH_IMAGE007
，
Figure 93430DEST_PATH_IMAGE008
a resistance equivalent to an electrical parameter characteristic of the liquid;
Figure 147974DEST_PATH_IMAGE010
is a resistor
Figure DEST_PATH_IMAGE011
The resistance value of (1);
Figure 718764DEST_PATH_IMAGE012
is a resistor
Figure 491548DEST_PATH_IMAGE003
The resistance value of (1);
Figure DEST_PATH_IMAGE013
is time;
Figure 452157DEST_PATH_IMAGE014
a capacitance equivalent to an electrical parameter characteristic of the liquid;
Figure DEST_PATH_IMAGE015
supplying power level to the pins of the singlechip;
and calculating according to the four sampling values:
Figure 298890DEST_PATH_IMAGE016
；
in the formula:
Figure DEST_PATH_IMAGE017
is a 4-time mode value converted from the sampling value of the singlechip,
Figure 821007DEST_PATH_IMAGE018
the sampling value of the singlechip at a first sampling time point is obtained;
Figure 956454DEST_PATH_IMAGE019
is an analog quantity reference level of the singlechip,
Figure DEST_PATH_IMAGE020
the sampling value of the singlechip at the second sampling time point is obtained;
Figure 300847DEST_PATH_IMAGE021
the sampling value of the singlechip at the third sampling time point is obtained;
Figure DEST_PATH_IMAGE022
the sampling value of the singlechip at the fourth sampling time point is obtained;
establishing the following relation according to the 4-time mode value converted from the sampling value of the single chip microcomputer:
Figure 487240DEST_PATH_IMAGE023
in the formula (I), the compound is shown in the specification,
Figure 665412DEST_PATH_IMAGE025
is proportional to;
Figure DEST_PATH_IMAGE026
，
Figure 803001DEST_PATH_IMAGE008
a resistance equivalent to an electrical parameter characteristic of the liquid;
Figure 482244DEST_PATH_IMAGE010
is a resistor
Figure 241253DEST_PATH_IMAGE011
The resistance value of (1);
Figure 714959DEST_PATH_IMAGE027
is a resistor
Figure 307221DEST_PATH_IMAGE003
The resistance value of (1);
Figure 258997DEST_PATH_IMAGE014
a capacitance equivalent to an electrical parameter characteristic of the liquid;
Figure 138091DEST_PATH_IMAGE015
supplying power level to the pins of the singlechip;
resistance equivalent according to the resulting electrical parameter characteristic of the liquid
Figure 782699DEST_PATH_IMAGE008
From the relation of conductivity and resistance
Figure DEST_PATH_IMAGE028
Deriving the conductivity of the liquid
Figure 98143DEST_PATH_IMAGE029
。
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CA980860A (en) * 1973-02-22 1975-12-30 Halogen Controls Apparatus for monitoring and controlling halogen levels in a water treatment system
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