CN218974467U - Conductivity measurement sampling circuit - Google Patents
Conductivity measurement sampling circuit Download PDFInfo
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- CN218974467U CN218974467U CN202223485693.7U CN202223485693U CN218974467U CN 218974467 U CN218974467 U CN 218974467U CN 202223485693 U CN202223485693 U CN 202223485693U CN 218974467 U CN218974467 U CN 218974467U
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Abstract
The utility model provides a conductivity measurement sampling circuit which comprises a main control MCU unit, a unipolar signal excitation unit, a signal acquisition unit, an AC/DC conversion unit, four-electrode conductivity electrodes, a communication unit and a working power supply unit. The working power supply unit supplies power for the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit, the main control MCU unit and the communication unit. The unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit and the communication unit are all connected with the main control MCU unit. The four-electrode conductivity electrodes are respectively connected with the unipolar signal excitation unit and the signal acquisition unit. The AC/DC conversion unit is connected with the signal acquisition unit. The circuit design of the utility model is simplified, the current sampling resistor is not required to be switched under different concentrations, the control method is optimized, the wide-range conductivity sampling range and high-precision acquisition are achieved, and the design purpose of sensor miniaturization can be met.
Description
Technical Field
The utility model relates to the technical field of conductivity testing, in particular to a conductivity measurement sampling circuit.
Background
Conductivity is a basic electrochemical parameter that measures the conductivity of a liquid and is often used to characterize the concentration of conductive ions in a solution. The conductivity not only represents the strength of the conductivity of the liquid, but also is an important index for measuring the chemical quantities of solution components, pH value, electrolyte concentration, water quality and the like, and has a quite important role in the conductivity parameters of natural water bodies. The current four-electrode conductivity measurement is used, so that the electrode polarization effect of the conductivity of two electrodes is effectively eliminated, and the wide-range water quality environment monitoring requirement cannot be met; the existing four-electrode conductivity monitoring instrument adopts dual-power supply and bipolar pulse, increases the complexity of the design of a power supply circuit, has higher requirements on the power supply, has higher overall power consumption, needs to increase the attenuation conversion of a circuit sampling signal to meet the sampling input range of 0-3.3V of an ADC, has high complexity of the whole sampling circuit, has high requirements on an operational amplifier, also needs to switch current sampling resistors under different concentrations, and cannot meet the design of miniaturized conductivity sampling.
Disclosure of Invention
In order to solve the problems, the utility model is realized by the following technical scheme:
a conductivity measurement sampling circuit, comprising: the device comprises a main control MCU unit, a unipolar signal excitation unit, a signal acquisition unit, an AC/DC conversion unit, four-electrode conductivity electrodes, a communication unit and a working power supply unit;
the working power supply unit supplies power to the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit, the main control MCU unit and the communication unit;
the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit and the communication unit are all connected with the main control MCU unit;
the four electrode conductivity electrodes are respectively connected with the unipolar signal excitation unit and the signal acquisition unit;
the AC/DC conversion unit is connected with the signal acquisition unit;
the main control MCU unit is used for generating direct-current voltages with different magnitudes and PWM excitation signals with different frequencies according to different concentrations and transmitting the direct-current voltages and the PWM excitation signals to the unipolar signal excitation unit; the unipolar signal excitation unit is used for generating excitation signals according to the direct-current voltage and the PWM excitation signals and transmitting the excitation signals to the four-electrode conductivity electrode; the four-electrode conductivity electrode is used for completing unipolar signal excitation according to the received excitation signal, generating voltage and transmitting the voltage to the signal acquisition unit; the signal acquisition unit is used for measuring a water body equivalent alternating voltage signal according to the voltage and transmitting the alternating voltage signal to the AC/DC conversion unit; the AC/DC conversion unit is used for converting an alternating current voltage signal into a direct current voltage signal and transmitting the direct current voltage signal to the ADC sampling of the main control MCU unit.
Further, the four-electrode conductivity electrode comprises two groups of current electrodes and voltage electrodes; one group of current electrodes and voltage electrodes are connected with the unipolar signal excitation unit, and the other group of current electrodes and voltage electrodes are connected with the signal acquisition unit.
Further, the unipolar signal excitation unit comprises a unipolar pulse group, a first unipolar excitation group and a second unipolar excitation group;
the single-polarity pulse group comprises two paths of single-pole double-throw analog switches connected with the main control MCU unit, one path of normally-open contact and the other path of normally-closed contact of the two paths of single-pole double-throw analog switches are connected with reference voltage, one path of normally-closed contact and the other path of normally-open contact are connected with direct-current voltage, and two paths of control pins are connected with the PWM excitation signal;
the direct-current voltage and the PWM excitation signal generate two paths of unipolar pulse excitation signals under the rising of the reference voltage, and the two paths of unipolar pulse excitation signals are respectively transmitted to a first unipolar excitation group and a second unipolar excitation group.
Further, the first unipolar excitation group comprises a feedback operational amplifier, the non-inverting input end of which is connected with one output end of the two paths of single-pole double-throw analog switches, the inverting input end of the feedback operational amplifier is connected with a group of current electrodes, and the output end of the feedback operational amplifier is connected with a group of voltage electrodes;
the second unipolar excitation group comprises an acquisition operational amplifier, the non-inverting input end of which is connected with the other output end of the two paths of single-pole double-throw analog switches, the inverting input end of the acquisition operational amplifier is connected with the current electrode of the other group, and the output end of the acquisition operational amplifier is connected with the voltage electrode of the other group;
the two paths of unipolar pulse excitation signals are respectively input into the non-inverting input ends of the feedback operational amplifier and the collecting operational amplifier, and the inverting input ends of the feedback operational amplifier and the collecting operational amplifier change along with the change of the non-inverting input ends of the feedback operational amplifier and the collecting operational amplifier to generate excitation signals and transmit the excitation signals to the current electrode.
Further, the signal acquisition unit comprises two paths of single-pole single-throw analog switches connected with the output ends of the acquisition operational amplifier and a first following operational amplifier, wherein the in-phase input end of the first following operational amplifier is connected with the output ends of the two paths of single-pole single-throw analog switches; the reverse input end of the acquisition operational amplifier is connected with the normally open port of the two paths of single-pole single-throw analog switches through an acquisition resistor, one end of the acquisition resistor, which is far away from the two paths of single-pole single-throw analog switches, is connected with the AC/DC conversion unit, one path of signal output of the two paths of single-pole single-throw analog switches is connected with the output end of the acquisition operational amplifier, the other path of signal output is connected with the non-inverting input end of the first following operational amplifier, and the output end of the first following operational amplifier is connected with the AC/DC conversion unit;
the voltage electrodes of the four-electrode conductivity electrodes generate voltage under the excitation of the unipolar pulse excitation signal, the voltage is acquired by a sampling resistor to obtain an equivalent alternating voltage signal of the water body to be detected, and the alternating voltage signal is transmitted to the AC/DC conversion unit.
Further, the AC/DC conversion unit comprises two paths of single-pole four-throw analog switches, a second following amplifier, and a third following amplifier, wherein the output end of the second following amplifier is connected with one path of two contacts and two paths of three contacts of the single-pole four-throw analog switches, and the non-inverting input end of the third following amplifier is connected with two paths of four contacts of the single-pole four-throw analog switches; the signal control pin of the two-way single-pole four-throw analog switch is connected with the level output pin of the main control MCU unit, the in-phase input end of the second following amplifier is connected with the output end of the acquisition resistor, the output end of the first following operational amplifier is connected with one-way three-contact and two-way two-contact of the single-pole four-throw analog switch, and the output end of the third following amplifier is connected with the ADC port of the main control MCU unit; one path of four contacts of the single-pole four-throw analog switch is connected with two paths of one contacts, one path of four contacts is connected with one path of one contact through a capacitor, two paths of one contacts are connected with two paths of four contacts through a capacitor, and one path of pins are connected with two paths of pins through a capacitor;
and the phase difference of PWM control signals output by the level output pin of the main control MCU unit to the signal control pin of the two-path single-pole four-throw analog switch is 90 degrees.
Further, the reverse input end of the feedback operational amplifier is connected with the current electrode through a fifth resistor and a fifth capacitor, the output end of the feedback operational amplifier is connected with the voltage electrode through an eleventh capacitor and a fourteenth resistor, a tenth capacitor is connected between the common end of the fifth resistor and the fifth capacitor and the output end of the feedback operational amplifier, a fifteenth resistor is connected between the common end of the eleventh capacitor and the fourteenth resistor and the reverse input end of the feedback operational amplifier, and the output end of the collecting operational amplifier is connected with the other group of voltage electrodes through a third capacitor and a third resistor.
Further, an eleventh resistor is further connected in series between the non-inverting input end of the third follower amplifier and the two paths of single-pole four-throw analog switches, the non-inverting input ends of the eleventh resistor and the third follower amplifier are further connected with a sixth capacitor, and the other end of the sixth capacitor is grounded.
Compared with the prior art, the technical scheme of the utility model has the following beneficial effects:
(1) The main control MCU unit generates direct current voltages with different magnitudes and PWM excitation signals with different frequencies according to different concentrations, and transmits the direct current voltages and the PWM excitation signals to the unipolar signal excitation unit and the signal acquisition unit; the unipolar signal excitation unit and the signal acquisition unit generate excitation signals according to the direct-current voltage and the PWM excitation signals, and transmit the excitation signals to the four-electrode conductivity electrodes; the four-electrode conductivity electrode completes unipolar signal excitation according to the received excitation signal, generates voltage and transmits the voltage to the signal acquisition unit; the signal acquisition unit is used for measuring an equivalent alternating voltage signal of the water body according to the voltage and transmitting the alternating voltage signal to the AC/DC conversion unit; the AC/DC conversion unit converts the alternating current voltage signal into a direct current voltage signal and transmits the direct current voltage signal to the ADC of the main control MCU unit for sampling, and the direct current voltage signal and the conductivity are in a linear relationship of the first power, so that the conductivity of the measured water body is obtained, and the circuit has the advantages of simple structure, high measurement precision and stable measurement and can meet the long-term online monitoring.
(2) The measuring single-path of the utility model does not need to switch circuit sampling resistors under different concentrations, optimizes the control method, achieves wide-range conductivity sampling range and high-precision acquisition, and can meet the design purpose of sensor miniaturization.
(3) The AC/DC conversion of the utility model utilizes the multichannel analog switch and the capacitor circuit to complete the AC/DC signal conversion, and can complete the sampling without an additional conversion module, so that the circuit structure is simple and the power consumption is low.
Drawings
FIG. 1 is a schematic block diagram of a conductivity measurement sampling circuit provided by an embodiment of the present utility model;
FIG. 2 is a schematic circuit diagram of a four-electrode conductivity electrode provided in an embodiment of the present utility model;
FIG. 3 is a schematic circuit diagram of a master MCU unit according to an embodiment of the present utility model;
FIG. 4 is a schematic circuit diagram of a unipolar signal excitation unit according to an embodiment of the present utility model;
FIG. 5 is a schematic circuit diagram of a signal acquisition unit according to an embodiment of the present utility model;
fig. 6 is a schematic circuit diagram of an AC/DC conversion unit according to an embodiment of the present utility model;
fig. 7 is a schematic circuit diagram of a communication unit according to an embodiment of the present utility model;
fig. 8 is a schematic circuit diagram of an operating power supply unit according to an embodiment of the present utility model.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present utility model more apparent, the technical solutions of the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model, and it is apparent that the described embodiments are some embodiments of the present utility model, but not all embodiments of the present utility model. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the utility model. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.
Referring to fig. 1, a conductivity measurement sampling circuit includes a main control MCU unit, a unipolar signal excitation unit, a signal acquisition unit, an AC/DC conversion unit, four-electrode conductivity electrodes, a working power supply unit, and a communication unit.
The working power supply unit supplies power for the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit, the main control MCU unit and the communication unit, the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit and the communication unit are all connected with the main control MCU unit, the four-electrode conductivity electrode is respectively connected with the unipolar signal excitation unit and the signal acquisition unit, and the AC/DC conversion unit is connected with the signal acquisition unit.
The main control MCU unit generates direct current voltages with different magnitudes and PWM excitation signals with different frequencies according to different concentrations, and transmits the direct current voltages and the PWM excitation signals to the unipolar signal excitation unit and the signal acquisition unit; the unipolar signal excitation unit and the signal acquisition unit generate excitation signals according to the direct-current voltage and the PWM excitation signals, and transmit the excitation signals to the four-electrode conductivity electrodes; the four-electrode conductivity electrode completes unipolar signal excitation according to the received excitation signal, generates voltage and transmits the voltage to the signal acquisition unit; the signal acquisition unit is used for measuring an equivalent alternating voltage signal of the water body according to the voltage and transmitting the alternating voltage signal to the AC/DC conversion unit; the AC/DC conversion unit converts the alternating current voltage signal into a direct current voltage signal and transmits the direct current voltage signal to the ADC of the main control MCU unit for sampling, and the direct current voltage signal and the conductivity are in a first-order linear relation, so that the conductivity of the measured water body is obtained. The communication unit feeds back the measured conductivity to the host computer.
Referring to fig. 2, the four-electrode conductivity electrode includes two sets of current electrodes CONDB, current electrodes CONDC, voltage electrodes CONDA and voltage electrodes CONDD, respectively.
Referring to fig. 3, in this embodiment, the main control MCU U7 uses MKV30F64VFM10, and the main control MCU U7 generates dc voltages of different magnitudes and PWM excitation signals of different frequencies according to different concentrations, specifically, the self-contained DAC of the main control MCU generates dc voltage of 200mV and PWM excitation signal of 2Khz at low concentration, the self-contained DAC of the main control MCU generates dc voltage of 100mV and PWM excitation signal of 3Khz at medium concentration, and the self-contained DAC of the main control MCU generates dc voltage of 50mV and PWM excitation signal of 4Khz at high concentration. The PWM excitation signal is output through 10, and the dc voltage is output through 9 pins. In PWM excitation signals which generate direct current voltages with different magnitudes and different frequencies according to different concentrations, the concentration defining method comprises the following steps: and (3) setting a PWM excitation signal with low concentration by default initially, judging whether the voltage signal obtained under attack is in a calibrated signal range, if so, not switching the concentration, if not, switching to medium concentration, and comparing the obtained voltage signal with the calibrated signal range again, and so on.
Referring to fig. 4, the unipolar signal excitation unit includes a unipolar pulse group, a first unipolar excitation group and a second unipolar excitation group. The unipolar pulse group comprises two paths of single-pole double-throw analog switches U2 connected with the main control MCU unit U7, one path of normally-open contact of the two paths of single-pole double-throw analog switches U2 and the other path of normally-closed contact are connected with reference voltage, one path of normally-closed contact and the other path of normally-open contact are connected with the 9 pin of the MCU unit U7 to input direct-current voltage, and the two paths of control pins are connected with the 10 pin of the MCU unit U7 to be connected with PWM excitation signals. The direct-current voltage and the PWM excitation signal generate two paths of unipolar pulse excitation signals under the lifting of the reference voltage, and the two paths of unipolar pulse excitation signals are respectively transmitted to the first unipolar excitation group and the second unipolar excitation group. In this embodiment, the two paths of single-pole double-throw analog switches U2 adopt TS3a5223RSWR, and after the direct-current voltage and the PWM excitation signal output by the main control MCU U7 are raised by the reference voltage, the single-polarity pulse excitation signal PWM2 is output from the 3 pins and the single-polarity pulse excitation signal PWM1 is output from the 9 pins of the two paths of single-pole double-throw analog switches U2.
With continued reference to fig. 4, the first unipolar excitation group includes a feedback operational amplifier U2.1 having a non-inverting input connected to one of the outputs of the two-way single-pole double-throw analog switch U2, the inverting input of the feedback operational amplifier U2.1 is connected to the current electrode CONDC, and the output of the feedback operational amplifier U2.1 is connected to the voltage electrode CONDD. The unipolar pulse excitation signal PWM2 is input to the non-inverting input of the feedback operational amplifier U2.1, and the inverting input of the feedback operational amplifier U2.1 changes along with the change of the non-inverting input to generate an excitation signal and is transmitted to the current electrode CONDC.
The non-inverting input end of the second unipolar excitation group is connected with the collection operational amplifier U1.1 connected with the other output end of the two paths of single-pole double-throw analog switches U2, the inverting input end of the collection operational amplifier U1.1 is connected with the current electrode CONDB through the first resistor R1 and the first capacitor C1, and the output end of the collection operational amplifier U1.1 is connected with the voltage electrode CONDA. The unipolar pulse excitation signal PWM1 is input to the non-inverting input of the collection operational amplifier U1.1, and the inverting input of the collection operational amplifier U1.1 changes along with the change of the non-inverting input to generate an excitation signal and transmits the excitation signal to the current electrode CONDA. And completing excitation of the four-electrode conductivity electrode.
In this embodiment, the inverting input terminal of the feedback operational amplifier U2.1 is connected to the current electrode CONDC through the fifth resistor R5 and the fifth capacitor C5, the output terminal of the feedback operational amplifier U2.1 is connected to the voltage electrode CONDD through the eleventh capacitor C11 and the fourteenth resistor R14, the tenth capacitor C10 is connected between the common terminal of the fifth resistor R5 and the fifth capacitor C5 and the output terminal of the feedback operational amplifier U2.1, the fifteenth resistor R15 is connected between the common terminal of the eleventh capacitor C11 and the fourteenth resistor R14 and the inverting input terminal of the feedback operational amplifier U2.1, and the output terminal of the collecting operational amplifier U1.1 is connected to the other group of voltage electrodes CONDA through the third capacitor C3 and the third resistor R3.
Referring to fig. 5, the signal acquisition unit includes two paths of single-pole single-throw analog switches U6 connected to the output terminals of the acquisition operational amplifier U1.1, and a first following operational amplifier U1.2 having an in-phase input terminal connected to the output terminals of the two paths of single-pole single-throw analog switches U6; the common end of the first resistor R1 and the first capacitor C1 is connected with the normally open port of the two paths of single-pole single-throw analog switches U6 through the acquisition resistor R4, one end of the acquisition resistor R4, which is far away from the two paths of single-pole single-throw analog switches U6, is connected with the AC/DC conversion unit, one path of SIGNAL output COM1 of the two paths of single-pole single-throw analog switches U6 is connected with the output end of the acquisition operational amplifier U1.1, the other path of SIGNAL output COM2 is connected with the non-inverting input end of the first following operational amplifier U1.2, and the output end of the first following operational amplifier U1.2 is connected with the SIGNAL2 to the AC/DC conversion unit.
In this embodiment, the two-way single-pole single-throw analog switch U6 adopts TS3a4741DGKR, and the 3 pins and 7 pins of the two-way single-pole single-throw analog switch U6 are both connected with the 30 pins of the main control MCU unit U7.
The voltage electrode CONDD and the voltage electrode CONDA generate certain voltage under the excitation of the unipolar pulse excitation SIGNALs PWM1 and PWM2, the voltage is collected by the sampling resistor R4, and the equivalent alternating voltage SIGNAL2 of the water body to be measured is measured through the conversion of the two paths of single-pole single-throw analog switches U6 and the first following operational amplifier U1.2, and the alternating voltage SIGNAL2 is transmitted to the AC/DC conversion unit.
Referring to fig. 6, the ac/DC conversion unit includes two paths of single-pole four-throw analog switches U4, a second follower amplifier U1.3 with an output end connected to two paths of single-pole four-throw analog switches U4, and a third follower amplifier U1.4 with an in-phase input end connected to two paths of single-pole four-throw analog switches U4, each of which has two I/O ports. The non-inverting input end of the second following amplifier U1.3 is connected with the acquisition resistor R4, the output end of the first following operational amplifier U1.2 is connected with two paths of remaining I/O ports of the single-pole four-throw analog switch U4, and the output end of the third following amplifier U1.4 is connected with the ADC port of the main control MCU unit U7.
In this embodiment, the single-pole four-throw analog switch U4 adopts TS3a5017PW, and pins 4 and 11 of the single-pole four-throw analog switch U4 are connected to the output terminal of the first following operational amplifier U1.2, i.e. connected to the ac voltage SIGNAL2.Signal1 is input to the homodromous input end of a second following operational amplifier U1.3, plays the role of potential balance, the output end of the second following operational amplifier U1.3 is connected with the 5 feet and the 12 feet of a single-pole four-throw analog switch U4, the 3 feet and the 10 feet of the single-pole four-throw analog switch U4 are connected, the 3 feet are connected with the 6 feet through a capacitor C8, the 10 feet are connected with the homonymous input end of a third following amplifier U1.4 through a capacitor C9, and the 7 feet and the 9 feet of the single-pole four-throw analog switch U4 are connected through a capacitor C7.
The pins 2 and 14 of the single-pole four-throw analog switch U4 are connected with the pins 32 and 31 of the level output pin of the main control MCU unit, so that the main control MCU unit U7 generates two paths of adjustable PWM control signal inputs to control the single-pole four-throw analog switch U4, an equivalent alternating voltage signal is input to an AC/DC conversion circuit formed by the single-pole four-throw analog switch and the charge-discharge capacitor, and the equivalent alternating voltage signal is converted into a direct voltage signal and then transmitted to an ADC sampling port of the main control MCU unit, and the conductivity of the solution to be measured is obtained. The switching of each channel of the single-pole four-throw analog switch U4 is controlled by inputting IN1 and IN2 signals with a certain time sequence, the input alternating voltage signal finishes voltage polarity change through a capacitor C7, the voltage conversion is finished by utilizing the charge and discharge of a capacitor C8 and a capacitor C9, and the converted direct voltage signal is output to an ADC sampling end after being subjected to passive RC filtering and a third follower amplifier U1.4.
In this embodiment, the phase difference of the two paths of PWM control signals is 90 °, the control frequencies of the two paths of PWM control signals are adjusted according to the conductivities of different concentrations, the accuracy of the conductivity measurement conversion under different concentrations is improved by adopting a piecewise signal processing mode, the conductivity measurement under different concentrations is satisfied by dividing the piecewise signal processing mode into multiple linear modes through calibration, so that the sampled voltage signal and the conductivity value form a first-order linear relationship.
An eleventh resistor R11 is further connected in series between the non-inverting input end of the third following amplifier U1.4 and the two paths of single-pole four-throw analog switches, the non-inverting input ends of the eleventh resistor R11 and the third following amplifier U1.4 are further connected with a sixth capacitor C6, and the other end of the sixth capacitor C6 is grounded. The eleventh resistor R11 and the sixth capacitor C6 form a passive RC low-pass filter circuit for filtering the sampled voltage signal.
Referring to fig. 7, the utility model further provides an implementation circuit of the communication unit.
Referring to fig. 8, the utility model further provides an implementation circuit of the working power supply.
While the foregoing description illustrates and describes the preferred embodiments of the present utility model, it is to be understood that the utility model is not limited to the forms disclosed herein, but is not to be construed as limited to other embodiments, but is capable of use in various other combinations, modifications and environments and is capable of changes or modifications within the scope of the inventive concept, either as described above or as a matter of skill or knowledge in the relevant art. And that modifications and variations which do not depart from the spirit and scope of the utility model are intended to be within the scope of the appended claims.
Claims (8)
1. A conductivity measurement sampling circuit, comprising: the device comprises a main control MCU unit, a unipolar signal excitation unit, a signal acquisition unit, an AC/DC conversion unit, four-electrode conductivity electrodes, a communication unit and a working power supply unit;
the working power supply unit supplies power to the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit, the main control MCU unit and the communication unit;
the unipolar signal excitation unit, the signal acquisition unit, the AC/DC conversion unit and the communication unit are all connected with the main control MCU unit;
the four electrode conductivity electrodes are respectively connected with the unipolar signal excitation unit and the signal acquisition unit;
the AC/DC conversion unit is connected with the signal acquisition unit;
the main control MCU unit is used for generating direct-current voltages with different magnitudes and PWM excitation signals with different frequencies according to different concentrations and transmitting the direct-current voltages and the PWM excitation signals to the unipolar signal excitation unit; the unipolar signal excitation unit is used for generating excitation signals according to the direct-current voltage and the PWM excitation signals and transmitting the excitation signals to the four-electrode conductivity electrode; the four-electrode conductivity electrode is used for completing unipolar signal excitation according to the received excitation signal, generating voltage and transmitting the voltage to the signal acquisition unit; the signal acquisition unit is used for measuring a water body equivalent alternating voltage signal according to the voltage and transmitting the alternating voltage signal to the AC/DC conversion unit; the AC/DC conversion unit is used for converting an alternating current voltage signal into a direct current voltage signal and transmitting the direct current voltage signal to the ADC sampling of the main control MCU unit.
2. A conductivity measurement sampling circuit according to claim 1, wherein said four-electrode conductivity electrode comprises two sets of current and voltage electrodes; one group of current electrodes and voltage electrodes are connected with the unipolar signal excitation unit, and the other group of current electrodes and voltage electrodes are connected with the signal acquisition unit.
3. The conductivity measurement sampling circuit of claim 2, wherein the unipolar signal excitation unit comprises a unipolar pulse set, a first unipolar excitation set, and a second unipolar excitation set;
the single-polarity pulse group comprises two paths of single-pole double-throw analog switches connected with the main control MCU unit, one path of normally-open contact and the other path of normally-closed contact of the two paths of single-pole double-throw analog switches are connected with reference voltage, one path of normally-closed contact and the other path of normally-open contact are connected with direct-current voltage, and two paths of control pins are connected with the PWM excitation signal;
the direct-current voltage and the PWM excitation signal generate two paths of unipolar pulse excitation signals under the rising of the reference voltage, and the two paths of unipolar pulse excitation signals are respectively transmitted to a first unipolar excitation group and a second unipolar excitation group.
4. A conductivity measurement sampling circuit according to claim 3, wherein said first unipolar excitation group comprises a feedback operational amplifier having its non-inverting input connected to one of the outputs of said two-way single pole double throw analog switch, the inverting input of said feedback operational amplifier being connected to a set of current electrodes, the output of said feedback operational amplifier being connected to a set of voltage electrodes;
the second unipolar excitation group comprises an acquisition operational amplifier, the non-inverting input end of which is connected with the other output end of the two paths of single-pole double-throw analog switches, the inverting input end of the acquisition operational amplifier is connected with the current electrode of the other group, and the output end of the acquisition operational amplifier is connected with the voltage electrode of the other group;
the two paths of unipolar pulse excitation signals are respectively input into the non-inverting input ends of the feedback operational amplifier and the collecting operational amplifier, and the inverting input ends of the feedback operational amplifier and the collecting operational amplifier change along with the change of the non-inverting input ends of the feedback operational amplifier and the collecting operational amplifier to generate excitation signals and transmit the excitation signals to the current electrode.
5. The conductivity measurement sampling circuit according to claim 4, wherein the signal acquisition unit comprises two single-pole single-throw analog switches connected to the output terminals of the acquisition operational amplifier, and a first follower operational amplifier having a non-inverting input terminal connected to the output terminals of the two single-pole single-throw analog switches; the reverse input end of the acquisition operational amplifier is connected with the normally open port of the two paths of single-pole single-throw analog switches through an acquisition resistor, one end of the acquisition resistor, which is far away from the two paths of single-pole single-throw analog switches, is connected with the AC/DC conversion unit, one path of signal output of the two paths of single-pole single-throw analog switches is connected with the output end of the acquisition operational amplifier, the other path of signal output is connected with the non-inverting input end of the first following operational amplifier, and the output end of the first following operational amplifier is connected with the AC/DC conversion unit;
the voltage electrodes of the four-electrode conductivity electrodes generate voltage under the excitation of the unipolar pulse excitation signal, the voltage is acquired by a sampling resistor to obtain an equivalent alternating voltage signal of the water body to be detected, and the alternating voltage signal is transmitted to the AC/DC conversion unit.
6. The conductivity measurement sampling circuit according to claim 5, wherein the AC/DC conversion unit comprises a two-way single-pole four-throw analog switch, a second follower amplifier with an output end connected with one-way two-contact and two-way three-contact of the single-pole four-throw analog switch, and a third follower amplifier with an in-phase input end connected with two-way four-contact of the single-pole four-throw analog switch; the signal control pin of the two-way single-pole four-throw analog switch is connected with the level output pin of the main control MCU unit, the in-phase input end of the second following amplifier is connected with the output end of the acquisition resistor, the output end of the first following operational amplifier is connected with one-way three-contact and two-way two-contact of the single-pole four-throw analog switch, and the output end of the third following amplifier is connected with the ADC port of the main control MCU unit; one path of four contacts of the single-pole four-throw analog switch is connected with two paths of one contacts, one path of four contacts is connected with one path of one contact through a capacitor, two paths of one contacts are connected with two paths of four contacts through a capacitor, and one path of pins are connected with two paths of pins through a capacitor;
and the phase difference of PWM control signals output by the level output pin of the main control MCU unit to the signal control pin of the two-path single-pole four-throw analog switch is 90 degrees.
7. The circuit of claim 5, wherein the inverting input of the feedback operational amplifier is connected to the current electrode through a fifth resistor and a fifth capacitor, the output of the feedback operational amplifier is connected to the voltage electrode through an eleventh capacitor and a fourteenth resistor, a tenth capacitor is connected between the common terminal of the fifth resistor and the fifth capacitor and the output of the feedback operational amplifier, a fifteenth resistor is connected between the common terminal of the eleventh capacitor and the fourteenth resistor and the inverting input of the feedback operational amplifier, and the output of the collecting operational amplifier is connected to the other group of voltage electrodes through a third capacitor and a third resistor.
8. The conductivity measurement sampling circuit of claim 6, wherein an eleventh resistor is further connected in series between the non-inverting input terminal of the third follower amplifier and the two-way single-pole four-throw analog switch, the non-inverting input terminal of the eleventh resistor and the third follower amplifier is further connected with a sixth capacitor, and the other end of the sixth capacitor is grounded.
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