CN219266409U - Four-electrode conductivity value detection circuit - Google Patents
Four-electrode conductivity value detection circuit Download PDFInfo
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- CN219266409U CN219266409U CN202320150035.8U CN202320150035U CN219266409U CN 219266409 U CN219266409 U CN 219266409U CN 202320150035 U CN202320150035 U CN 202320150035U CN 219266409 U CN219266409 U CN 219266409U
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Abstract
The utility model provides a four-electrode conductivity value detection circuit, which relates to the technical field of conductivity value measurement and comprises an MCU (micro control unit), a signal excitation module, a four-electrode conductivity cell module and a signal acquisition and conversion module, wherein the MCU is connected with the signal excitation module and outputs a control signal to the signal excitation module, and the signal excitation module converts the control signal into a constant current signal; the signal excitation module is connected with the four-electrode conductivity cell module and outputs a current signal to the four-electrode conductivity cell module; the four-electrode conductivity cell module is connected with the signal acquisition and conversion module, outputs a voltage signal to the signal acquisition and conversion module for acquisition, and the signal acquisition and conversion module converts and amplifies the voltage signal; the signal acquisition conversion module is connected with the MCU, the MCU receives the converted and amplified voltage signal, performs operation, outputs a conductance value, realizes the four-electrode measurement technology, and avoids the influence on measurement accuracy caused by polarization effect in a two-electrode scheme.
Description
Technical Field
The utility model relates to the technical field of conductivity measurement, in particular to a four-electrode conductivity detection circuit.
Background
Conductivity is the inverse of resistivity, and for a solution, the level of conductivity directly reflects the ability of the solution to conduct electricity. The amount of the total dissolved solids in the solution can be deduced according to the conductivity, so that the quality of industrial water and domestic water can be detected by measuring the conductivity of the water body, and the method has very important significance for accurate measurement of the conductivity. In particular to the application in the technical fields of chemical industry, medicine, food, ocean development and the like.
The conductivity sensor is used as an important means for measuring the conductivity of the aqueous solution, and generally adopts an electrode type; the electrode type conductivity sensor can be divided into two electrodes, three electrodes, four electrodes, six electrodes, seven electrodes, eight electrodes and the like according to the number of the electrodes, and currently, a two-electrode technology is mainly adopted in China. The electrode can generate polarization effect in some solutions, the electrode polarization effect has great influence on the measurement precision and stability, even if the alternating current signal test is adopted, the two-electrode technology is adopted for sampling and exciting signals are the same electrode, the polarization effect and the pollution of the electrode can influence the measurement precision, and the multi-electrode technology can effectively avoid the related problems caused by the polarization effect in the two-electrode scheme. Therefore, the scheme provides a four-electrode measurement technology.
Disclosure of Invention
In order to overcome the defects in the prior art, the utility model provides a four-electrode conductivity value detection circuit.
The technical scheme adopted for solving the technical problems is as follows: in a four electrode conductance value detection circuit, the improvement comprising: the device comprises an MCU, a signal excitation module, a four-electrode conductivity cell module and a signal acquisition and conversion module, wherein the MCU is connected with the signal excitation module and outputs a control signal to the signal excitation module, and the signal excitation module converts the control signal into a constant current signal; the signal excitation module is connected with the four-electrode conductivity cell module and outputs a current signal to the four-electrode conductivity cell module; the four-electrode conductivity cell module is connected with the signal acquisition and conversion module, outputs a voltage signal to the signal acquisition and conversion module for acquisition, and the signal acquisition and conversion module converts and amplifies the voltage signal; the signal acquisition and conversion module is connected with the MCU, and the MCU receives the converted and amplified voltage signal, performs operation and outputs a conductivity value.
In the above circuit, the signal excitation module comprises a dual operational amplifier chip U1, a plurality of sampling resistors connected in parallel and a switch SW1, the dual operational amplifier chip U1 comprises an operational amplifier U1A and an operational amplifier U1B,
the positive input port of the operational amplifier U1B is connected with the MCU, the positive input port of the operational amplifier U1A is connected with the output port of the operational amplifier U1B, the negative input port of the operational amplifier U1A is connected with one end of a parallel sampling resistor, the other end of the parallel sampling resistor is connected with a switch SW1, the common ground of the switch SW1 is grounded, and the switch SW1 is used for switching and selecting different sampling resistors;
the output port of the operational amplifier U1A is connected with the four-electrode conductivity cell module, a first connection point is arranged between the negative input port of the operational amplifier U1A and the parallel sampling resistor, the first connection point is connected with the four-electrode conductivity cell module, and the output port and the first connection point of the operational amplifier U1A output current signals to the four-electrode conductivity cell module.
In the above circuit, the plurality of parallel sampling resistors include a sampling resistor RS1, a sampling resistor RS2 and a sampling resistor RS3 which are connected in parallel, one ends of the sampling resistor RS1, the sampling resistor RS2 and the sampling resistor RS3 are all connected with the negative input port of the operational amplifier U1A, the other ends are all connected with the switch SW1, and the sampling resistor RS1, the sampling resistor RS2 or the sampling resistor RS3 can be selectively turned on by the switching of the switch SW 1.
In the circuit, the four-electrode conductive cell module comprises an electrode P1, an electrode P2, an electrode P3 and an electrode P4 which are sequentially connected in series,
electrode P1 is connected with the output port of the operational amplifier U1A, electrode P4 is connected with the first connection point, and receives a current signal;
the electrode P2 and the electrode P3 are connected with the signal acquisition and conversion module, and output voltage signals to the signal acquisition and conversion module for acquisition.
In the circuit, the signal acquisition and conversion module comprises an instrument amplifier U2, wherein a positive input port of the instrument amplifier U2 is connected with the electrode P2, and a negative input port of the instrument amplifier U2 is connected with the electrode P3 to acquire voltage signals;
the output port of the instrument amplifier U2 is connected with the MCU, and the voltage signal after conversion and amplification is output to the MCU.
In the circuit, the MCU is connected with the display screen LCD, and outputs the conductance value to the display screen LCD for display.
The beneficial effects of the utility model are as follows: the four-electrode measuring technology is realized, and the influence of polarization effect on measuring precision in a two-electrode scheme is avoided; the voltage at two ends of the measured object can be directly collected without collecting the measured current value at the same time, the circuit is relatively simple, the number of components is reduced, the reliability is improved, and the cost is reduced; the Kelvin measurement principle is adopted, so that the precision is high.
Drawings
Fig. 1 is a block diagram of a four-electrode detection scheme in the prior art.
Fig. 2 is a schematic block diagram of a four-electrode conductance detection circuit according to the present utility model.
Fig. 3 is a schematic circuit diagram of a four-electrode conductivity detection circuit according to the present utility model.
Fig. 4 is a schematic diagram of a four-electrode principle in a four-electrode conductivity detection circuit according to the present utility model.
Detailed Description
The utility model will be further described with reference to the drawings and examples.
The conception, specific structure, and technical effects produced by the present utility model will be clearly and completely described below with reference to the embodiments and the drawings to fully understand the objects, features, and effects of the present utility model. It is apparent that the described embodiments are only some embodiments of the present utility model, but not all embodiments, and that other embodiments obtained by those skilled in the art without inventive effort are within the scope of the present utility model based on the embodiments of the present utility model. In addition, all the coupling/connection relationships referred to in the patent are not direct connection of the single-finger members, but rather, it means that a better coupling structure can be formed by adding or subtracting coupling aids depending on the specific implementation. The technical features in the utility model can be interactively combined on the premise of no contradiction and conflict.
Referring to fig. 1, in the conventional four-electrode detection, generally, a sampling voltage is used as an excitation signal, the voltage is loaded to a measured object to generate a current, and the current flowing through the measured object is collected to determine the conductance value of the measured object, so that the detection needs a multi-channel ADC circuit, the circuit structure is relatively complex, and the cost is relatively high.
Referring to fig. 2, the utility model provides a four-electrode conductivity value detection circuit, which comprises an MCU, a signal excitation module 10, a four-electrode conductivity cell module 20 and a signal acquisition and conversion module 30, wherein the MCU is connected with the signal excitation module 10 and outputs a control signal to the signal excitation module 10, and the signal excitation module 10 converts the control signal into a constant current signal; the signal excitation module 10 is connected with the four-electrode conductivity cell module 20 and outputs a constant current signal to the four-electrode conductivity cell module 20; the four-electrode conductivity cell module 20 is connected with the signal acquisition and conversion module 30, and outputs a voltage signal to the signal acquisition and conversion module 30 for acquisition, and the signal acquisition and conversion module 30 converts and amplifies the voltage signal; the signal acquisition and conversion module 30 is connected with the MCU, and the MCU receives the converted and amplified voltage signal, performs operation and outputs a conductance value. The four-electrode measuring technology is realized, and the influence of polarization effect on measuring precision in a two-electrode scheme is avoided. Further, the MCU is connected with the display screen LCD, and outputs the conductance value to the display screen LCD for display.
Referring to fig. 2, the signal excitation module 10 Is a voltage-controlled constant current source circuit, and generates a constant alternating current Is according to a control signal of the MCU, and outputs the constant alternating current Is to the four-electrode conductivity cell module 20, and the signal acquisition and conversion module 30 Is responsible for acquiring differential voltage signals from two ends of a measured object of the four-electrode conductivity cell module 20, converting the differential voltage signals into single-ended voltage signals, and amplifying the voltage signals; the MCU acquires the voltage signals processed by the signal acquisition and conversion module 30 through the ADC interface, performs digital filtering, calculates phase difference, calculates conductance value, and outputs calculated results through an LCD display screen, a communication interface and the like. When the circuit works, constant alternating current Is generated according to a control signal of the MCU, the constant alternating current Is flows through a measured object R to generate voltage V, the voltage V Is amplified and filtered by the signal acquisition and conversion module 30 and then Is sent to an ADC interface of the MCU, the MCU calculates R=V/Is according to the acquired value V and the known quantity Is, and the conductance value Y=1/R Is calculated according to the R. Thus, the conductance value of the object to be measured is obtained. The circuit takes the alternating current constant current source as an excitation signal, can directly collect the voltages at two ends of a measured object, does not need to collect and measure current values at the same time, is relatively simple, reduces the number of components, improves the reliability and reduces the cost. Since the input impedance of the acquisition and conversion module 30 is very high, it can reach 1012 ohms, the leakage current is negligible, and the measurement accuracy is not affected.
Referring to fig. 3, the signal excitation module 10 includes a dual op-amp chip U1, a plurality of parallel sampling resistors and a switch SW1, the dual op-amp chip U1 includes an operational amplifier U1A and an operational amplifier U1B, the plurality of parallel sampling resistors includes a sampling resistor RS1, a sampling resistor RS2 and a sampling resistor RS3,
the positive input port of the operational amplifier U1B is connected with the DAC interface of the MCU, receives a control signal, the negative input port of the operational amplifier U1B is connected with the output port to form a voltage follower circuit, the output port is also connected with the positive input port of the operational amplifier U1A, one ends of the sampling resistor RS1, the sampling resistor RS2 and the sampling resistor RS3 are all connected with the negative input port of the operational amplifier U1A, the other ends are all connected with the switch SW1, the common end of the switch SW1 is grounded, and the sampling resistor RS1, the sampling resistor RS2 or the sampling resistor RS3 can be selectively conducted through the switching of the switch SW 1. The output port of the operational amplifier U1A is connected with the four-electrode conductivity cell module 20, and a first connection point 40 is arranged between the negative input port of the operational amplifier U1A and the parallel sampling resistor, the first connection point 40 is connected with the four-electrode conductivity cell module 20, and the output port of the operational amplifier U1A and the first connection point 40 output current signals to the four-electrode conductivity cell module 20.
Referring to fig. 3, the four-electrode conductivity cell module 20 includes an electrode P1, an electrode P2, an electrode P3, and an electrode P4 sequentially connected in series, where the resistor RL1, the resistor RL2, and the resistor RLX in fig. 3 are used to represent the resistance of the measured object (typically, the measured liquid) between the four electrodes, so as to describe the working principle of the four-electrode conductivity cell module 20, the electrode P1 is connected with the output port of the operational amplifier U1A, and the electrode P4 is connected with the first connection point 40, and receives the current signal; the electrode P2 and the electrode P3 are connected with the signal acquisition and conversion module 30, and output voltage signals to the signal acquisition and conversion module 30 for acquisition.
Referring to fig. 3, the signal acquisition and conversion module 30 includes an instrumentation amplifier U2, where a positive input port of the instrumentation amplifier U2 is connected to the electrode P2, and a negative input port is connected to the electrode P3, and acquires a voltage signal; the output port of the instrument amplifier U2 is connected with the MCU, and the voltage signal after conversion and amplification is output to the MCU.
As shown in fig. 2 and 3, the signal excitation module 10 converts a 1KHz sinusoidal signal output by an MCU, which is a model GD32L233RC, into a current signal. The model of the dual operational amplifier chip U1 is TL082, and the operational amplifier U1A and the operational amplifier U1B are two independent amplifier units of the dual operational amplifier chip U1. The specific principle is as follows: the operational amplifier U1B is a voltage follower and is used for impedance transformation and driving a later-stage constant current source circuit, and the operational amplifier U1A is a voltage-controlled constant current source circuit. In this embodiment, the number of selectable sampling resistors is 3, which are sampling resistor RS1, sampling resistor RS2 and sampling resistor RS3 respectively. In the following, a sampling resistor RS1 is taken as an example according to the principle of operational amplifier deficiency and short-circuit deficiency.
When the MCU output voltage is Vin at a certain moment, then:
operational amplifier U1A voltage at the same direction: v+=vin
Operational amplifier U1A reverse side current: i- =0
According to the principle of virtual short: v+ = V-
The inverting terminal voltage of the operational amplifier U1A: v- = I c ×r1
Operational amplifier U1A outputs a current: is=ic
So that: is=vin/RS 1, i.e. the voltage of Vin determines the output current Is of the operational amplifier U1A.
Therefore, the sampling resistor RS1, the sampling resistor RS2 and the sampling resistor RS3 can be used to adjust the shift of the output current Is, and when the voltage Is (RL 1+ RLX + RL 2) generated by the output current Is flowing through the measured object (RL 1+ RLX + RL 2) exceeds the maximum output voltage swing of the operational amplifier U1A, the constant current source cannot be maintained in the constant current state. At this time, the constant current value (i.e., the output current Is) may be adjusted by adjusting the switch SW1 to select the sampling resistor RS1, the sampling resistor RS2 or the sampling resistor RS3 to select different values of the sampling resistor so as to ensure the measurement accuracy. The change-over switch SW1 may be an electronic switch or a mechanical switch.
As shown in fig. 3 and 4, the four-electrode conductivity cell module 20 is composed of an electrode P1, an electrode P2, an electrode P3 and an electrode P4, wherein the electrode P1 and the electrode P4 are excitation signal electrodes, the electrode P2 and the electrode P3 are sampling electrodes, when the electrodes are inserted into a measured object (generally, a measured liquid), and when a current is applied between the electrode P1 and the electrode P4, according to ohm law u=i×r, the electrode P2 and the electrode P3 generate a voltage for the signal acquisition and conversion module 30 to acquire. When the electrodes are polarized or polluted, the values equivalent to the resistance RL1 and the resistance RL2 change, the impedance of the sampling electrode P2 and the sampling electrode P3 (namely the input impedance of the instrument amplifier U2) is extremely high, the measurement of the resistance RLX of the measured object is not influenced, and the influence of electrode pollution on the measurement of the conductivity value is avoided.
Referring to fig. 3, the type of the instrumentation amplifier U2 in the signal acquisition and conversion module 30 is INA128, rg is gain control thereof, and the principle is a precision differential amplifier, and the amplification factor thereof is: vadc= (V1-V2) 50kΩ/Rg.
The four-electrode measuring technology is adopted in the scheme, the voltage sampling electrode and the exciting electrode are mutually separated and work independently (Kelvin measuring principle), the current on the sampling electrode is almost zero, and the influence of electrode polarization phenomenon on measuring precision can be effectively avoided.
The four-electrode conductivity value detection circuit realizes the measurement technology by four electrodes, and avoids the influence of polarization effect on measurement accuracy in a two-electrode scheme; the voltage at two ends of the measured object can be directly collected without collecting the measured current value at the same time, the circuit is relatively simple, the number of components is reduced, the reliability is improved, and the cost is reduced; the Kelvin measurement principle is adopted, so that the precision is high.
While the preferred embodiment of the present utility model has been described in detail, the present utility model is not limited to the embodiments, and those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present utility model, and these equivalent modifications or substitutions are included in the scope of the present utility model as defined in the appended claims.
Claims (6)
1. A four-electrode conductivity value detection circuit is characterized in that: comprises an MCU, a signal excitation module, a four-electrode conductivity cell module and a signal acquisition and conversion module,
the MCU is connected with the signal excitation module, outputs a control signal to the signal excitation module, and the signal excitation module converts the control signal into a constant current signal;
the signal excitation module is connected with the four-electrode conductivity cell module and outputs a current signal to the four-electrode conductivity cell module;
the four-electrode conductivity cell module is connected with the signal acquisition and conversion module, outputs a voltage signal to the signal acquisition and conversion module for acquisition, and the signal acquisition and conversion module converts and amplifies the voltage signal;
the signal acquisition and conversion module is connected with the MCU, and the MCU receives the converted and amplified voltage signal, performs operation and outputs a conductivity value.
2. A four-electrode conductance value detection circuit according to claim 1, wherein: the signal excitation module comprises a double operational amplifier chip U1, a plurality of sampling resistors connected in parallel and a change-over switch SW1, wherein the double operational amplifier chip U1 comprises an operational amplifier U1A and an operational amplifier U1B,
the positive input port of the operational amplifier U1B is connected with the MCU, the positive input port of the operational amplifier U1A is connected with the output port of the operational amplifier U1B, the negative input port of the operational amplifier U1A is connected with one end of a parallel sampling resistor, the other end of the parallel sampling resistor is connected with a switch SW1, the common ground of the switch SW1 is grounded, and the switch SW1 is used for switching and selecting different sampling resistors;
the output port of the operational amplifier U1A is connected with the four-electrode conductivity cell module, a first connection point is arranged between the negative input port of the operational amplifier U1A and the parallel sampling resistor, the first connection point is connected with the four-electrode conductivity cell module, and the output port and the first connection point of the operational amplifier U1A output current signals to the four-electrode conductivity cell module.
3. A four-electrode conductance value detection circuit according to claim 2, wherein: the sampling resistors connected in parallel comprise a sampling resistor RS1, a sampling resistor RS2 and a sampling resistor RS3 which are connected in parallel, one ends of the sampling resistor RS1, the sampling resistor RS2 and the sampling resistor RS3 are connected with a negative input port of the operational amplifier U1A, the other ends of the sampling resistor RS are connected with a switch SW1, and the sampling resistor RS1, the sampling resistor RS2 or the sampling resistor RS3 can be selectively conducted through the switching of the switch SW 1.
4. A four-electrode conductance value detection circuit according to claim 2, wherein: the four-electrode conductivity cell module comprises an electrode P1, an electrode P2, an electrode P3 and an electrode P4 which are sequentially connected in series,
electrode P1 is connected with the output port of the operational amplifier U1A, electrode P4 is connected with the first connection point, and receives a current signal;
the electrode P2 and the electrode P3 are connected with the signal acquisition and conversion module, and output voltage signals to the signal acquisition and conversion module for acquisition.
5. The four-electrode conductance value detection circuit of claim 4, wherein: the signal acquisition and conversion module comprises an instrument amplifier U2, wherein a positive input port of the instrument amplifier U2 is connected with the electrode P2, a negative input port of the instrument amplifier U2 is connected with the electrode P3, and voltage signals are acquired;
the output port of the instrument amplifier U2 is connected with the MCU, and the voltage signal after conversion and amplification is output to the MCU.
6. A four-electrode conductance value detection circuit according to claim 1, wherein: the MCU is connected with the display screen LCD, and outputs the conductance value to the display screen LCD for display.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202320150035.8U CN219266409U (en) | 2023-01-14 | 2023-01-14 | Four-electrode conductivity value detection circuit |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202320150035.8U CN219266409U (en) | 2023-01-14 | 2023-01-14 | Four-electrode conductivity value detection circuit |
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| CN219266409U true CN219266409U (en) | 2023-06-27 |
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| CN202320150035.8U Active CN219266409U (en) | 2023-01-14 | 2023-01-14 | Four-electrode conductivity value detection circuit |
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