Conductivity measuring device

Abstract

The utility model relates to the technical field of conductivity measurement, in particular to a conductivity measuring device which comprises a four-electrode type conductivity sensor, a first voltage acquisition unit, a second voltage acquisition unit and a main control unit, the first voltage acquisition unit is electrically connected with two outer driving electrode ends of the four-electrode type conductivity sensor respectively, and the second voltage acquisition unit is electrically connected with two outer driving electrode ends of the four-electrode type conductivity sensor respectively. The second voltage acquisition unit is electrically connected with two inner induction electrode ends of the four-electrode type conductivity sensor, the main control unit is electrically connected with the first voltage acquisition unit and the second voltage acquisition unit, and two outer driving electrode ends of the four-electrode type conductivity sensor are responsible for applying current in a solution. The two inner induction electrode ends of the four-electrode type conductivity sensor are used for measuring the potential drop, and the current does not pass through the inner induction electrode ends for measuring the voltage, so that the polarization phenomenon of the traditional two-electrode type conductivity sensor caused by electrolysis and other reactions on the surfaces of the inner induction electrodes due to the passing current can be avoided.

Description

TECHNICAL FIELD

[0001] The utility model relates to conductivity measurement technical field, especially relate to a conductivity measuring device. BACKGROUND

[0002] At present, the measurement of solution conductivity generally adopts two-electrode measurement method, by inserting two electrodes into the measured solution, adding a constant amplitude voltage signal (usually sinusoidal voltage, frequency 1kHz-3kHz) between the electrodes, then measuring the current flowing through the electrode, calculating the conductivity according to Ohm's law, and then combining the electrode constant to obtain the conductivity, which is a simple and direct measurement method widely used in China; However, the above measurement method has the following shortcomings:

[0003] 1. Electrode polarization problem:

[0004] When measuring low resistance (i.e. high conductivity) solution, if the frequency of the alternating current measurement signal is too low, due to the presence of a certain direct current component in the measurement power supply, polarization effect will occur, electrode polarization will cause a layer of charge layer to form on the electrode surface, hindering the normal passage of current, making the measurement result inaccurate; In order to reduce or eliminate the error caused by polarization effect on conductivity measurement, a higher measurement frequency is required for low resistance solution measurement, so that the oxidation and reduction reactions on the electrode surface occur rapidly, but this increases the complexity of measurement and the requirements for measurement equipment.

[0005] 2. Capacitance influence problem:

[0006] When measuring high resistance (i.e. low conductivity) solution, the influence of the cell capacitance is greater; Because the presence of capacitance will affect the measurement of alternating current signal, resulting in that the frequency of the measured alternating current signal cannot be too high, otherwise the capacitive reactance will bring a large error to the measurement, which limits the application range and measurement accuracy of two-electrode conductivity measurement method in low conductivity solution measurement.

[0007] 3. Electrode surface contamination problem:

[0008] The electrode is easily contaminated by impurities, precipitates and other impurities in the measured solution during long-term use; The contamination on the surface of the electrode will change the effective area and surface state of the electrode, thereby changing the electrode constant and causing the measurement result to deviate; And this contamination will gradually accumulate over time, requiring regular cleaning and calibration of the electrode, increasing the maintenance cost and workload of the measurement.

[0009] 4. Cable resistance influence:

[0010] When the cable in the measuring circuit is long, the resistance of the cable itself will affect the measurement result; the cable resistance will be in series with the solution resistance between the electrodes, increasing the total resistance measured, thus causing errors in the calculated conductivity value; in some occasions requiring long distance measurement or higher measurement accuracy, the influence of the cable resistance cannot be ignored. Utility model content

[0011] The technical problem to be solved by the utility model is: a conductivity measuring device can avoid the generation of polarization phenomenon, thereby improving the accuracy of conductivity measurement.

[0012] In order to solve the above technical problem, the utility model adopts the technical scheme that:

[0013] A conductivity measuring device, comprising a four-electrode conductivity sensor, a first voltage acquisition unit, a second voltage acquisition unit and a master control unit, the first voltage acquisition unit is respectively connected with two outer driving electrode terminals of the four-electrode conductivity sensor, the second voltage acquisition unit is respectively connected with two inner sensing electrode terminals of the four-electrode conductivity sensor, and the master control unit is connected with the first voltage acquisition unit and the second voltage acquisition unit.

[0014] Further, the first voltage acquisition unit comprises an instrument amplifier U2, the positive input terminal and the negative input terminal of the instrument amplifier U2 are respectively connected with two outer driving electrode terminals of the four-electrode conductivity sensor in one-to-one correspondence, and the output terminal of the instrument amplifier U2 is connected with the master control unit.

[0015] Further, the first voltage acquisition unit further comprises a resistance R6, one end of the resistance R6 is connected with the positive power supply terminal of the instrument amplifier U2, and the other end of the resistance R6 is connected with the negative power supply terminal of the instrument amplifier U2.

[0016] Further, the first voltage acquisition unit further comprises a resistance R2, a resistance R8, a capacitor C6 and a capacitor C13, one end of the resistance R2 is connected with the outer driving electrode terminal of the four-electrode conductivity sensor, the other end of the resistance R2 is respectively connected with one end of the capacitor C6 and the negative input terminal of the instrument amplifier U2, the other end of the capacitor C6 is grounded, one end of the resistance R8 is connected with the outer driving electrode terminal of the four-electrode conductivity sensor, the other end of the resistance R8 is respectively connected with one end of the capacitor C13 and the positive input terminal of the instrument amplifier U2, and the other end of the capacitor C13 is grounded.

[0017] Further, the first voltage acquisition unit further includes a capacitor C8, one end of the capacitor C8 is electrically connected with the other end of the resistor R2, one end of the capacitor C6 and the inverting input terminal of the instrument amplifier U2 respectively, and the other end of the capacitor C8 is electrically connected with the other end of the resistor R8, one end of the capacitor C13 and the non-inverting input terminal of the instrument amplifier U2 respectively.

[0018] Further, the second voltage acquisition unit includes an instrument amplifier U1, the non-inverting input terminal and the inverting input terminal of the instrument amplifier U1 are connected with two inner sensing electrode terminals of the four-electrode conductivity sensor in one-to-one correspondence respectively, and the output terminal of the instrument amplifier U1 is electrically connected with the master control unit.

[0019] Further, the second voltage acquisition unit further includes a resistor R4, one end of the resistor R4 is electrically connected with the positive power supply terminal of the instrument amplifier U1, and the other end of the resistor R4 is electrically connected with the negative power supply terminal of the instrument amplifier U1.

[0020] Further, the second voltage acquisition unit further includes a resistor R1, a resistor R7, a capacitor C5 and a capacitor C11, one end of the resistor R1 is electrically connected with one inner sensing electrode terminal of the four-electrode conductivity sensor, the other end of the resistor R1 is electrically connected with one end of the capacitor C5 and the inverting input terminal of the instrument amplifier U1 respectively, the other end of the capacitor C5 is grounded, one end of the resistor R7 is electrically connected with another inner sensing electrode terminal of the four-electrode conductivity sensor, the other end of the resistor R7 is electrically connected with one end of the capacitor C11 and the non-inverting input terminal of the instrument amplifier U1 respectively, and the other end of the capacitor C11 is grounded.

[0021] Further, the second voltage acquisition unit further includes a capacitor C7, one end of the capacitor C7 is electrically connected with the other end of the resistor R1, one end of the capacitor C5 and the inverting input terminal of the instrument amplifier U1 respectively, and the other end of the capacitor C7 is electrically connected with the other end of the resistor R7, one end of the capacitor C11 and the non-inverting input terminal of the instrument amplifier U1 respectively.

[0022] Further, the master control unit includes a chip U6, the model number of the chip U6 is STM32L433CBT6, the fourteenth pin of the chip U6 is electrically connected with the first voltage acquisition unit, and the fifteenth pin of the chip U6 is electrically connected with the second voltage acquisition unit.

[0023] The utility model discloses the beneficial effect lies in:

[0024] The scheme is characterized in that the four-electrode conductivity sensor, the first voltage acquisition unit, the second voltage acquisition unit and the main control unit are arranged, the first voltage acquisition unit is electrically connected with two outer driving electrode terminals of the four-electrode conductivity sensor respectively, the second voltage acquisition unit is electrically connected with two inner sensing electrode terminals of the four-electrode conductivity sensor respectively, the two outer driving electrode terminals of the four-electrode conductivity sensor are responsible for applying current in the solution, and the two inner sensing electrode terminals of the four-electrode conductivity sensor are used for measuring potential drop, so that the input impedance of the first voltage acquisition unit is designed to be relatively large, so that the two inner sensing electrode terminals are basically not passed through by current, and therefore the polarization phenomenon caused by electrolysis reaction on the surface of the inner sensing electrode of the traditional two-electrode conductivity sensor due to the passing current can be avoided, and the precision of conductivity measurement can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The connection block diagram of the conductivity measurement device of the utility model;

[0026] Figure 2 The circuit principle diagram of the first voltage acquisition unit of the conductivity measurement device of the utility model;

[0027] Figure 3 The circuit principle diagram of the second voltage acquisition unit of the conductivity measurement device of the utility model;

[0028] Figure 4 The circuit principle diagram of the analog selection unit, the alternating voltage generation unit and the voltage follower unit of the conductivity measurement device of the utility model;

[0029] Figure 5 The circuit principle diagram of the main control unit of the conductivity measurement device of the utility model;

[0030] REFERENCE SIGNS:

[0031] 1, four-electrode conductivity sensor; 2, first voltage acquisition unit; 3, second voltage acquisition unit; 4, main control unit. DETAILED DESCRIPTION

[0032] In order to make the technical content, the purposes and the effects of the utility model clear, the following will be described in detail in combination with the embodiments and the drawings.

[0033] Please refer to Figure 1 The technical scheme of the utility model is characterized in that:

[0034] The utility model provides an electric conductivity measuring device, including four electrode conductivity sensor, first voltage acquisition unit, second voltage acquisition unit and host computer unit, first voltage acquisition unit is connected with two outer drive electrode end of four electrode conductivity sensor respectively, second voltage acquisition unit is connected with two inner sensing electrode end of four electrode conductivity sensor respectively, host computer unit is connected with first voltage acquisition unit and second voltage acquisition unit respectively.

[0035] From the above description, the utility model has the beneficial effect that:

[0036] The utility model discloses a four electrode conductivity sensor, first voltage acquisition unit, second voltage acquisition unit and host computer unit are set up, and first voltage acquisition unit is connected with two outer drive electrode end of four electrode conductivity sensor respectively, and second voltage acquisition unit is connected with two inner sensing electrode end of four electrode conductivity sensor respectively, and two outer drive electrode end of four electrode conductivity sensor is responsible for the current application in solution, and two inner sensing electrode end of four electrode conductivity sensor is used for measuring potential drop, so only needs to design the input impedance of first voltage acquisition unit to be relatively big, so two inner sensing electrode end is basically no current through, can avoid the polarization phenomenon of traditional two electrode conductivity sensor to cause electrolytic reaction on the surface of inner sensing electrode by current, thereby can improve the precision of conductivity measurement.

[0037] Further, the first voltage acquisition unit includes an instrument amplifier U2, the positive input terminal and the inverting input terminal of the instrument amplifier U2 are connected with the two outer drive electrode ends of the four electrode conductivity sensor one by one, and the output terminal of the instrument amplifier U2 is electrically connected with the host computer unit.

[0038] Further, the first voltage acquisition unit further includes a resistor R6, one end of the resistor R6 is electrically connected with the positive power supply end of the instrument amplifier U2, and the other end of the resistor R6 is electrically connected with the negative power supply end of the instrument amplifier U2.

[0039] From the above description, the resistor R6 is used as a gain control resistor, and the gain can be controlled by configuring the parameters of the resistor R6.

[0040] Further, the first voltage acquisition unit further comprises a resistor R2, a resistor R8, a capacitor C6 and a capacitor C13, one end of the resistor R2 is electrically connected with the outer driving electrode end of the four-electrode conductivity sensor, the other end of the resistor R2 is electrically connected with one end of the capacitor C6 and the inverting input end of the instrument amplifier U2 respectively, the other end of the capacitor C6 is grounded, one end of the resistor R8 is electrically connected with the outer driving electrode end of the four-electrode conductivity sensor, the other end of the resistor R8 is electrically connected with one end of the capacitor C13 and the non-inverting input end of the instrument amplifier U2 respectively, the other end of the capacitor C13 is grounded.

[0041] As can be known from the above description, the resistor R2, the resistor R8, the capacitor C6 and the capacitor C13 constitute an RC low-pass filter, which filters out common-mode interference signals.

[0042] Further, the first voltage acquisition unit further comprises a capacitor C8, one end of the capacitor C8 is electrically connected with the other end of the resistor R2, one end of the capacitor C6 and the inverting input end of the instrument amplifier U2 respectively, the other end of the capacitor C8 is electrically connected with the other end of the resistor R8, one end of the capacitor C13 and the non-inverting input end of the instrument amplifier U2 respectively.

[0043] As can be known from the above description, the capacitor C8 can effectively filter out differential-mode interference signals.

[0044] Further, the second voltage acquisition unit comprises an instrument amplifier U1, the non-inverting input end and the inverting input end of the instrument amplifier U1 are connected with the two inner sensing electrode ends of the four-electrode conductivity sensor one by one respectively, and the output end of the instrument amplifier U1 is electrically connected with the master control unit.

[0045] Further, the second voltage acquisition unit further comprises a resistor R4, one end of the resistor R4 is electrically connected with the positive power supply end of the instrument amplifier U1, and the other end of the resistor R4 is electrically connected with the negative power supply end of the instrument amplifier U1.

[0046] As can be known from the above description, the resistor R4 serves as a gain control resistor, and the gain can be controlled by configuring the parameters of the resistor R4.

[0047] Further, the second voltage acquisition unit further comprises a resistor R1, a resistor R7, a capacitor C5 and a capacitor C11, one end of the resistor R1 is electrically connected with one inner sensing electrode end of the four-electrode conductivity sensor, the other end of the resistor R1 is electrically connected with one end of the capacitor C5 and the inverting input end of the instrument amplifier U1 respectively, the other end of the capacitor C5 is grounded, one end of the resistor R7 is electrically connected with the other inner sensing electrode end of the four-electrode conductivity sensor, the other end of the resistor R7 is electrically connected with one end of the capacitor C11 and the non-inverting input end of the instrument amplifier U1 respectively, and the other end of the capacitor C11 is grounded.

[0048] As can be seen from the above description, the resistor R1, the resistor R7, the capacitor C5 and the capacitor C11 form an RC low-pass filter, which filters out common-mode interference signals.

[0049] Further, the second voltage acquisition unit further comprises a capacitor C7, one end of the capacitor C7 is electrically connected with the other end of the resistor R1, one end of the capacitor C5 and the inverting input end of the instrument amplifier U1 respectively, and the other end of the capacitor C7 is electrically connected with the other end of the resistor R7, one end of the capacitor C11 and the non-inverting input end of the instrument amplifier U1 respectively.

[0050] As can be seen from the above description, the capacitor C7 can effectively filter out differential-mode interference signals.

[0051] Further, the main control unit comprises a chip U6, the model of the chip U6 is STM32L433CBT6, the fourteenth pin of the chip U6 is electrically connected with the first voltage acquisition unit, and the fifteenth pin of the chip U6 is electrically connected with the second voltage acquisition unit.

[0052] Please refer to Figures 1 to 5 , the embodiment one of the utility model is:

[0053] Please refer to Figure 1 , a conductivity measuring device, characterized in that, including four electrode conductivity sensor 1, first voltage acquisition unit 2, second voltage acquisition unit 3 and main control unit 4, first voltage acquisition unit 2 is electrically connected with two outer driving electrode ends of four electrode conductivity sensor 1 respectively, second voltage acquisition unit 3 is electrically connected with two inner sensing electrode ends of four electrode conductivity sensor 1 respectively, main control unit 4 is electrically connected with first voltage acquisition unit 2 and second voltage acquisition unit 3 respectively.

[0054] Please refer to Figure 2 , the first voltage acquisition unit 2 includes instrument amplifier U2, the non-inverting input end and the inverting input end of the instrument amplifier U2 are connected with two outer driving electrode ends of four electrode conductivity sensor 1 one by one respectively, and the output end of the instrument amplifier U2 is electrically connected with the main control unit 4.

[0055] Please refer to Figure 2 , the first voltage acquisition unit 2 further includes resistor R6, one end of the resistor R6 is electrically connected with the positive power supply end of the instrument amplifier U2, and the other end of the resistor R6 is electrically connected with the negative power supply end of the instrument amplifier U2.

[0056] Please refer to Figure 2The first voltage acquisition unit 2 further comprises a resistor R2, a resistor R8, a capacitor C6 and a capacitor C13, one end of the resistor R2 is electrically connected with the outer driving electrode end of the four-electrode conductivity sensor 1, the other end of the resistor R2 is electrically connected with one end of the capacitor C6 and the inverting input end of the instrument amplifier U2 respectively, the other end of the capacitor C6 is grounded, one end of the resistor R8 is electrically connected with the outer driving electrode end of the four-electrode conductivity sensor 1, the other end of the resistor R8 is electrically connected with one end of the capacitor C13 and the non-inverting input end of the instrument amplifier U2 respectively, the other end of the capacitor C13 is grounded.

[0057] Please refer to Figure 2 The first voltage acquisition unit 2 further comprises a capacitor C8, one end of the capacitor C8 is electrically connected with the other end of the resistor R2, one end of the capacitor C6 and the inverting input end of the instrument amplifier U2 respectively, the other end of the capacitor C8 is electrically connected with the other end of the resistor R8, one end of the capacitor C13 and the non-inverting input end of the instrument amplifier U2 respectively.

[0058] The first voltage acquisition unit 2 further comprises a capacitor C2, a capacitor C4, a resistor R5, a capacitor C10, a capacitor C14 and a capacitor C16, and the specific relationship between each component is described in the following table: Figure 2 The capacitor C2, the capacitor C4, the resistor R5, the capacitor C10, the capacitor C14 and the capacitor C16 all play a filtering role.

[0059] Please refer to Figure 3 The second voltage acquisition unit 3 comprises an instrument amplifier U1, the non-inverting input end and the inverting input end of the instrument amplifier U1 are connected with the two inner sensing electrode ends of the four-electrode conductivity sensor 1 one by one respectively, and the output end of the instrument amplifier U1 is electrically connected with the main control unit 4.

[0060] Please refer to Figure 3 The second voltage acquisition unit 3 further comprises a resistor R4, one end of the resistor R4 is electrically connected with the positive power supply end of the instrument amplifier U1, and the other end of the resistor R4 is electrically connected with the negative power supply end of the instrument amplifier U1.

[0061] Please refer to Figure 3The second voltage acquisition unit 3 further comprises a resistor R1, a resistor R7, a capacitor C5 and a capacitor C11, one end of the resistor R1 is electrically connected with one inner sensing electrode end of the four-electrode conductivity sensor 1, the other end of the resistor R1 is electrically connected with one end of the capacitor C5 and the inverting input end of the instrument amplifier U1 respectively, the other end of the capacitor C5 is grounded, one end of the resistor R7 is electrically connected with the other inner sensing electrode end of the four-electrode conductivity sensor 1, the other end of the resistor R7 is electrically connected with one end of the capacitor C11 and the non-inverting input end of the instrument amplifier U1 respectively, the other end of the capacitor C11 is grounded.

[0062] Please refer to Figure 3 The second voltage acquisition unit 3 further comprises a capacitor C7, one end of the capacitor C7 is electrically connected with the other end of the resistor R1, one end of the capacitor C5 and the inverting input end of the instrument amplifier U1 respectively, the other end of the capacitor C7 is electrically connected with the other end of the resistor R7, one end of the capacitor C11 and the non-inverting input end of the instrument amplifier U1 respectively.

[0063] The second voltage acquisition unit 3 further comprises a capacitor C1, a capacitor C3, a resistor R3, a capacitor C9, a capacitor C12 and a capacitor C15, and the specific relationship between each component thereof please refer to Figure 3 The capacitor C1, the capacitor C3, the resistor R3, the capacitor C9, the capacitor C12 and the capacitor C15 all play a filtering role;

[0064] Please refer to Figure 5 The main control unit 4 comprises a chip U6, the model of the chip U6 is STM32L433CBT6, the fourteenth pin of the chip U6 is electrically connected with the first voltage acquisition unit 2, and the fifteenth pin of the chip U6 is electrically connected with the second voltage acquisition unit 3.

[0065] The main control unit 4 further comprises a capacitor C29, a resistor R15, a resistor R16, a capacitor C40, a capacitor C34, a crystal oscillator Y1, a capacitor C23, a resistor R14, a capacitor C28 and a capacitor C35, and the specific relationship between each component thereof please refer to Figure 5 The capacitor C29, the resistor R15, the resistor R16, the capacitor C40, the capacitor C34 and the crystal oscillator Y1 adapt the crystal oscillator circuit and are used for providing a clock signal; the capacitor C23 is used for power filtering; the resistor R14 is used for pulling down to select a main control working mode; the capacitor C28 and the capacitor C35 are used for power filtering; and the resistor R16 and the resistor C40 constitute a reset circuit.

[0066] The conductivity measuring device further comprises an analog selection unit, an alternating voltage generating unit, a voltage follower unit, a connector J1 and a resistor R13 as a sampling resistor, the alternating voltage generating unit acts on the outer driving electrode terminals (DJ1 terminal and DJ4 terminal) through the resistor R13, the current of the loop of the DJ1 terminal and the DJ4 terminal is dynamically adjusted in real time through the voltage feedback of the resistor R13, and the constant current effect is achieved; the analog selection unit comprises an analog switch U3, a capacitor C17 and a capacitor C22, the alternating voltage generating unit comprises an amplifier U4B, a resistor R10, a resistor R9, a resistor R12 and a capacitor C19, and the voltage follower unit comprises an amplifier U4A, a capacitor C18, a capacitor C20, a resistor R11 and a capacitor C21, and the specific relationship between the components will be described with reference to Figure 4 .

[0067] In conclusion, the conductivity measuring device provided by the utility model, through setting four-electrode conductivity sensor, first voltage acquisition unit, second voltage acquisition unit and main control unit, the first voltage acquisition unit is respectively connected with two outer driving electrode terminals of the four-electrode conductivity sensor, the second voltage acquisition unit is respectively connected with two inner sensing electrode terminals of the four-electrode conductivity sensor, two outer driving electrode terminals of the four-electrode conductivity sensor are responsible for applying current in the solution, and two inner sensing electrode terminals of the four-electrode conductivity sensor are used for measuring potential drop, so that only the input impedance of the first voltage acquisition unit is designed to be relatively large, so that two inner sensing electrode terminals are basically without current passing through, so that the polarization phenomenon caused by electrolysis reaction on the surface of the inner sensing electrode of the traditional two-electrode conductivity sensor due to passing current can be avoided, and the precision of conductivity measurement can be improved.

[0068] The above only describes the embodiments of the utility model, and does not limit the patent range of the utility model, and any equivalent transformation or direct or indirect application in the related technical field based on the content of the utility model specification and drawings is also included in the patent protection range of the utility model.

Claims

1. An electrical conductivity measuring device, characterized in that, The application relates to a four-electrode conductivity sensor, a first voltage acquisition unit, a second voltage acquisition unit and a main control unit, the two outer driving electrode terminals of the four-electrode conductivity sensor are respectively electrically connected with the first voltage acquisition unit, the two inner sensing electrode terminals of the four-electrode conductivity sensor are respectively electrically connected with the second voltage acquisition unit, and the main control unit is electrically connected with the first voltage acquisition unit and the second voltage acquisition unit.

2. The conductivity measuring device of claim 1, wherein, The first voltage acquisition unit comprises an instrument amplifier U2, the positive-phase input end and the anti-phase input end of the instrument amplifier U2 are respectively connected with the two outer driving electrode terminals of the four-electrode conductivity sensor in one-to-one correspondence, and the output end of the instrument amplifier U2 is electrically connected with the main control unit.

3. The conductivity measuring device of claim 2, wherein, The first voltage acquisition unit further comprises a resistor R6, one end of the resistor R6 is electrically connected with the positive power supply end of the instrument amplifier U2, and the other end of the resistor R6 is electrically connected with the negative power supply end of the instrument amplifier U2.

4. The conductivity measuring device of claim 2, wherein, The first voltage acquisition unit further comprises a resistor R2, a resistor R8, a capacitor C6 and a capacitor C13, one end of the resistor R2 is electrically connected with the outer driving electrode terminal of the four-electrode conductivity sensor, the other end of the resistor R2 is respectively electrically connected with one end of the capacitor C6 and the anti-phase input end of the instrument amplifier U2, the other end of the capacitor C6 is grounded, one end of the resistor R8 is electrically connected with the outer driving electrode terminal of the four-electrode conductivity sensor, the other end of the resistor R8 is respectively electrically connected with one end of the capacitor C13 and the positive-phase input end of the instrument amplifier U2, and the other end of the capacitor C13 is grounded.

5. The conductivity measuring device of claim 4, wherein, The first voltage acquisition unit further comprises a capacitor C8, one end of the capacitor C8 is respectively electrically connected with the other end of the resistor R2, one end of the capacitor C6 and the anti-phase input end of the instrument amplifier U2, and the other end of the capacitor C8 is respectively electrically connected with the other end of the resistor R8, one end of the capacitor C13 and the positive-phase input end of the instrument amplifier U2.

6. The conductivity measuring device of claim 1, wherein, The second voltage acquisition unit comprises an instrument amplifier U1, the positive-phase input end and the anti-phase input end of the instrument amplifier U1 are respectively connected with the two inner sensing electrode terminals of the four-electrode conductivity sensor in one-to-one correspondence, and the output end of the instrument amplifier U1 is electrically connected with the main control unit.

7. The conductivity measuring device of claim 6, wherein, The second voltage acquisition unit further comprises a resistor R4, one end of the resistor R4 is electrically connected with the positive power supply end of the instrument amplifier U1, and the other end of the resistor R4 is electrically connected with the negative power supply end of the instrument amplifier U1.

8. The conductivity measuring device of claim 6, wherein, The second voltage acquisition unit further comprises a resistor R1, a resistor R7, a capacitor C5 and a capacitor C11, one end of the resistor R1 is electrically connected with one inner sensing electrode terminal of the four-electrode conductivity sensor, the other end of the resistor R1 is respectively electrically connected with one end of the capacitor C5 and the anti-phase input end of the instrument amplifier U1, the other end of the capacitor C5 is grounded, one end of the resistor R7 is electrically connected with the other inner sensing electrode terminal of the four-electrode conductivity sensor, the other end of the resistor R7 is respectively electrically connected with one end of the capacitor C11 and the positive-phase input end of the instrument amplifier U1, and the other end of the capacitor C11 is grounded.

9. The conductivity measuring device of claim 8, wherein, The second voltage acquisition unit further comprises a capacitor C7, one end of the capacitor C7 is electrically connected with the other end of the resistor R1, one end of the capacitor C5 and the inverting input end of the instrument amplifier U1 respectively, and the other end of the capacitor C7 is electrically connected with the other end of the resistor R7, one end of the capacitor C11 and the non-inverting input end of the instrument amplifier U1 respectively.

10. The conductivity measuring device of claim 1, wherein, The main control unit comprises a chip U6, the model number of the chip U6 is STM32L433CBT6, the fourteenth pin of the chip U6 is electrically connected with the first voltage acquisition unit, and the fifteenth pin of the chip U6 is electrically connected with the second voltage acquisition unit.

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