Method and apparatus for liquid impedance measurement using a four-electrode device

Abstract

A method (100) for liquid impedance measurement using a four-electrode device comprising an electrode structure (210) is provided. The method (100) comprises applying (10) a sinusoidal voltage signal on first (202) and second (204) outer electrodes of the electrode structure and performing current and voltage measurements on the electrode structure. The method (100) further comprises applying (20) the sinusoidal voltage signal on a reference impedance (220) and performing current and voltage measurements on the reference impedance. The method (100) further comprises calculating an outer impedance between the first (202) and second (204) outer electrodes based on a subset of the measurements. The method (100) further comprises calculating (40) an inner impedance between the first (206) and second (208) inner electrodes based on a subset of the measurements, wherein the inner impedance represents a liquid impedance. A four-electrode device (200) for performing the method (100) is also provided.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for measuring liquid impedance using a four-electrode device. Background Technology

[0002] For example, the impedance of liquids such as water can provide information about their contamination, salinity, etc., because dissolved salts or other types of ions typically affect the electrical properties of water. Measuring the conductivity of water usually involves measuring the impedance between a pair of electrodes exposed in the water, where impedance is proportional to the reciprocal of conductivity. Prior art impedance measurement techniques using two or four electrodes are known. However, these techniques, suitable for field use, have low accuracy, and accurate impedance measurements of liquids using such techniques typically require laboratory conditions. Therefore, an improved method is needed for performing two-electrode or four-electrode liquid impedance measurements under field conditions. Summary of the Invention

[0003] The purpose of this invention is to provide an improved method for measuring liquid impedance under field conditions.

[0004] According to a first aspect, a method is provided for measuring liquid impedance using a four-electrode device including an electrode structure. The method includes applying a sinusoidal voltage signal to a first outer electrode and a second outer electrode of the electrode structure and performing a first set of measurements, the first set of measurements including: measuring a value proportional to the current flowing through the first and second outer electrodes; measuring a value proportional to the voltage drop across the first and second outer electrodes; and measuring a value proportional to the voltage drop across a first inner electrode and a second inner electrode of the electrode structure. The method further includes applying the sinusoidal voltage signal to a reference impedance and performing a second set of measurements, the second set of measurements including: measuring a value proportional to the current flowing through the reference impedance; and measuring a value proportional to the voltage drop across the reference impedance. The method further includes calculating the external impedance between the first and second outer electrodes based on: the reference impedance; the value proportional to the current flowing through the first and second outer electrodes; the value proportional to the voltage drop across the first and second outer electrodes; the value proportional to the current flowing through the reference impedance; and the value proportional to the voltage drop across the reference impedance. The method further includes calculating the internal impedance between the first inner electrode and the second inner electrode based on: the calculated external impedance; the value proportional to the voltage drop across the first and second outer electrodes; and the value proportional to the voltage drop across the first and second inner electrodes.

[0005] The electrode structure can be immersed in a liquid to perform impedance measurements. Therefore, a sinusoidal voltage signal can be applied to the liquid between the first and second external electrodes; the current through the first and second external electrodes can be the current through the liquid between them; the voltage drop between the first and second external electrodes can be the voltage drop through the liquid between them; the external impedance can be the impedance of the liquid between them; and the internal impedance can be the impedance of the liquid between the first and second internal electrodes. This method facilitates accurate liquid impedance measurement if the liquid to be measured is associated with a relatively low impedance, i.e., even if the measured impedance of the liquid is comparable to the internal impedance of the four-electrode device. Such internal impedance may undesirably exist when applying and / or amplifying the sinusoidal voltage signal, leading to measurement distortion, because, for example, a significant voltage drop may exist across the internal impedance when measuring the impedance of a low-impedance liquid. By taking into account this internal impedance through the above-described measurement steps of the four-electrode structure and the reference impedance, this method improves the accuracy of liquid impedance measurements using the four-electrode device. Therefore, this method may be suitable for situations where the liquid to be measured is water (determined to be drinking water). This water may contain ions, salts, etc., which may significantly increase the conductivity of the water, thereby reducing the measured impedance. Therefore, this method can facilitate accurate water quality determination based on water impedance. Compared to traditional accurate liquid impedance methods that typically require a more clinical setting for accurate liquid impedance measurements, the four-electrode device is further suitable for use in field conditions, requiring minimal maintenance and power.

[0006] The first and second external electrodes are responsible for current injection, while the remaining electrodes (i.e., the first and second internal electrodes) are configured to measure the voltage between them. In practice, due to the small current flowing through the internal electrodes, a limited amount of electrochemical reactions, such as electroplating and corrosion, occur on these electrodes. These electrochemical reactions can affect the effective measurement area of ​​the electrodes. Therefore, the proposed method can help reduce these electrochemical reactions, thereby improving the accuracy of voltage measurement between the internal electrodes and thus improving impedance. Furthermore, the four-electrode structure can reduce the influence of electrode-electrolyte phenomena.

[0007] Throughout this disclosure, calculations of, for example, external impedance and internal impedance are disclosed using equations. Naturally, the corresponding calculations can be performed using appropriate equations. However, as will be readily apparent to those skilled in the art, such calculations can be performed in several different mathematically equivalent ways (e.g., at different orders or similar). The description of corresponding calculations as "representable" via appropriate equations should be understood to encompass such mathematically equivalent operations.

[0008] According to an embodiment, the processor or circuit is configured to: calculate the external impedance, as can be expressed as:

[0009]

[0010] And the internal impedance is calculated, as can be expressed as:

[0011]

[0012] Among them, Z T Z is the external impedance. i Z is the internal impedance. r For the reference impedance, ~I r The value, ~V, is proportional to the current passing through the reference impedance. o The value, ~V, is proportional to the voltage drop across the first and second external electrodes. r For the value that is proportional to the voltage drop across the reference impedance, ~I s The value is proportional to the current passing through the first external electrode and the second external electrode, and ~V i The value is proportional to the voltage drop on the first inner electrode and the second inner electrode of the electrode structure.

[0013] Therefore, it facilitates the direct calculation of internal impedance, which can reduce the power consumption of the four-electrode device and thus improve the quality of the four-electrode device under field conditions.

[0014] The tilde ~ preceding some of the quantities above and below indicates "proportionate to". Therefore, ~X should be understood as a value proportional to X, that is, X multiplied by a proportionality constant.

[0015] According to an embodiment, each application of the sinusoidal voltage signal includes the application of the sinusoidal voltage signal by a digital-to-analog converter (DAC).

[0016] A DAC can provide a sinusoidal voltage signal with well-defined amplitude, frequency, and phase, thereby improving the accuracy of the measured / calculated liquid impedance. The sinusoidal voltage signal can be amplified by a power buffer (discussed further below), which may contain internal impedance that is taken into account when determining the liquid impedance.

[0017] According to an embodiment, each measurement includes conversion by an analog-to-digital converter (ADC). The ADC can facilitate further analysis of the measurement data.

[0018] According to an embodiment, each measurement includes recording a time series.

[0019] Preferably, each time series includes data from one or more periods to form a (truncated) sine function for further analysis, which may improve the accuracy of the method.

[0020] According to an embodiment, each measurement further includes applying a Discrete Fourier Transform (DFT) to the recorded time series.

[0021] DFT can facilitate computationally efficient methods for further analysis of recorded (sinusoidal) time series.

[0022] According to an embodiment, applying the Discrete Fourier Transform includes converting each recorded time series into a corresponding spectrum, and the measurement further includes: determining the dominant frequency bin of the spectrum; and determining a measurement value based on the dominant frequency bin. This is a particularly efficient method for removing noise or other artifacts from the recorded time series.

[0023] According to a second aspect, a four-electrode device for measuring liquid impedance is provided. The four-electrode device includes an electrode structure comprising a first outer electrode, a second outer electrode, a first inner electrode, and a second inner electrode. The four-electrode device further includes a reference impedance and a signal generator configured to generate a sinusoidal voltage signal, wherein the four-electrode device is configured to measure: a value proportional to the current flowing through the first and second outer electrodes; a value proportional to the voltage drop across the first and second outer electrodes; a value proportional to the voltage drop across the first and second inner electrodes of the electrode structure; a value proportional to the current flowing through the reference impedance; and a value proportional to the voltage drop across the reference impedance. The four-electrode device further includes a processor or circuit configured to calculate the external impedance between the first external electrode and the second external electrode based on: the reference impedance; the value proportional to the current flowing through the first and second external electrodes; the value proportional to the voltage drop across the first and second external electrodes; the value proportional to the current flowing through the reference impedance; and the value proportional to the voltage drop across the reference impedance. The four-electrode device further includes the internal impedance between the first internal electrode and the second internal electrode based on: the calculated external impedance; the value proportional to the voltage drop across the first and second external electrodes; and the value proportional to the voltage drop across the first and second internal electrodes.

[0024] This aspect generally presents the same or corresponding advantages as the first aspect. The aforementioned features related to the first aspect also apply to this second aspect when applicable.

[0025] According to an embodiment, the processor or circuit is configured to calculate the external impedance, as can be expressed as:

[0026]

[0027] And the internal impedance is calculated, as can be expressed as:

[0028]

[0029] Among them, Z T Z is the external impedance. i Z is the internal impedance. r For the reference impedance, ~I r The value, ~V, is proportional to the current passing through the reference impedance. o The value, ~V, is proportional to the voltage drop across the first and second external electrodes. r For the value that is proportional to the voltage drop across the reference impedance, ~I s The value is proportional to the current passing through the first external electrode and the second external electrode, and ~V i The value is proportional to the voltage drop on the first and second inner electrodes of the electrode structure.

[0030] According to an embodiment, the four-electrode device further includes a first switch and a second switch configured to switch the path that the sinusoidal voltage signal can traverse between the electrode structure and the reference impedance when the sinusoidal voltage signal is generated. Therefore, the first and second switches can be arranged such that the reference impedance is electrically decoupled from the electrode structure when the sinusoidal voltage signal traverses the electrode structure, and vice versa. This is a particularly energy-efficient method for measuring the electrical characteristics of different components using a single voltage source.

[0031] According to an embodiment, the signal generator includes a digital-to-analog converter (DAC).

[0032] According to an embodiment, the four-electrode device further includes: a first analog-to-digital converter (ADC) configured to measure a value proportional to the voltage drop across the first and second external electrodes and a value proportional to the voltage drop across the reference impedance; a second ADC configured to measure the value proportional to the voltage drop across the first and second internal electrodes; and a third ADC configured to measure the value proportional to the current through the first and second external electrodes and a value proportional to the current through the reference impedance.

[0033] According to an embodiment, the four-electrode device further includes a third switch and a fourth switch arranged to selectively connect to the first ADC. The third and fourth switches can be of a so-called on-off type. Therefore, when these switches are set to "off" mode, the first ADC is electrically decoupled from the rest of the circuitry of the four-electrode device. When the switches are set to "on" mode, data regarding the voltage drop across the external electrode or the reference impedance can be acquired and recorded.

[0034] According to an embodiment, the processor or circuit is further configured to record a time series associated with each of the following: the value proportional to the voltage drop across the first external electrode and the second external electrode; the value proportional to the voltage drop across the reference impedance; the value proportional to the voltage drop across the first internal electrode and the second internal electrode; the value proportional to the current through the first external electrode and the second external electrode; and the value proportional to the current through the reference impedance.

[0035] According to an embodiment, the processor or circuit is further configured to apply a Discrete Fourier Transform (DFT) to each recorded time series. Attached Figure Description

[0036] The above and additional objects, features, and advantages of the present invention will be better understood from the following illustrative and non-limiting detailed description, with reference to the accompanying drawings. In the drawings, similar reference numerals will be used for similar elements unless otherwise stated.

[0037] Figure 1 A flowchart is shown for a method of performing liquid impedance measurement using a four-electrode device including an electrode structure.

[0038] Figure 2A A four-electrode apparatus for measuring liquid impedance is schematically shown.

[0039] Figure 2B The electrode structure of the four-electrode device is schematically shown. Detailed Implementation

[0040] Figure 1 A flowchart is shown for a method 100 for performing liquid impedance measurement using a four-electrode device including electrode structure 210. The four-electrode device is shown. Figure 2A and Figure 2B The following can be advantageously combined Figure 1 See the description for details.

[0041] As part of the method, a four-electrode device or at least an electrode structure can be immersed in a liquid whose impedance is to be measured.

[0042] Method 100 includes applying a sinusoidal voltage signal to the first external electrode 202 and the second external electrode 204 of the electrode structure 210 and performing a first set of measurements 12, 14, and 16. The sinusoidal voltage signal allows for measurements of electrical components as described below. The first set of measurements 12, 14, and 16 includes: measurement 12, a value proportional to the current passing through the first external electrode 202 and the second external electrode 204; measurement 14, a value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204; and measurement 16, a value proportional to the voltage drop across the first internal electrode 206 and the second internal electrode 208 of the electrode structure 210.

[0043] Method 100 further includes applying the sinusoidal voltage signal 20 to the reference impedance 220 and performing a second set of measurements 22, 24. Performing the second set of measurements 22, 24 includes measuring 22 a value proportional to the current through the reference impedance; and measuring 24 a value proportional to the voltage drop across the reference impedance.

[0044] The reference impedance 220 can be any suitable component with a known impedance, which may depend on the voltage applied to that component. For example, the reference impedance 220 can be a common resistor with a known resistance. Alternatively, the reference impedance 220 can be a capacitor, an inductor, or a combination thereof.

[0045] Method 100 further includes calculating the external impedance between the first external electrode and the second external electrode based on: the reference impedance 220; the value proportional to the current through the first external electrode 202 and the second external electrode 204; the value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204; the value proportional to the current through the reference impedance 220; and the value proportional to the voltage drop across the reference impedance 220.

[0046] Method 100 further includes calculating the internal impedance between the first internal electrode 206 and the second internal electrode 208 based on: the calculated external impedance; the value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204; and the value proportional to the voltage drop across the first internal electrode 206 and the second internal electrode 208. Therefore, the method may include five different measurements 12, 14, 16, 22, 24, which may be time-series measurements, for determining the impedance between the first internal electrode 206 and the second internal electrode 208, i.e., determining the impedance of liquid present between the first electrode 206 and the second electrode 208.

[0047] The measured impedance between the first internal electrode 206 and the second internal electrode 208 indicates the number of charge carriers (ions) dissolved in the water. However, if the applied voltage is relatively high, the water itself will also generate ions. Therefore, the impedance of an aqueous solution is generally not linear, and when a certain potential threshold is exceeded, the water may dissociate and generate additional charge carriers. Therefore, it is desirable to control the applied voltage (between the external electrodes 202 and 204) to prevent runaway reactions.

[0048] The calculation of external impedance 30 can be expressed as:

[0049]

[0050] Furthermore, the calculation of the internal impedance 40 can be expressed as:

[0051]

[0052] Among them, Z T Z is the external impedance. i Z is the internal impedance. r The reference impedance is 220Ω, ~I r The value, ~V, is proportional to the current passing through the reference impedance 220. o For a value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204, ~V r For the value that is proportional to the voltage drop across the reference impedance 220, ~I s The value is proportional to the current passing through the first external electrode 202 and the second external electrode 204, and ~V i The value is proportional to the voltage drop of the first inner electrode 206 and the second inner electrode 208 of the electrode structure 210.

[0053] As mentioned above, the tilde ~ preceding some of the quantities above and below indicates "proportionate to". Therefore, ~X should be understood as a value proportional to X, that is, X multiplied by a proportionality constant. Furthermore, different quantities can be associated with different such proportionality constants.

[0054] The corresponding proportionality constant can be adjusted according to the needs of the corresponding calculation, as is generally known to technicians.

[0055] Specifically, as an example, ~V i and ~V o Different differential amplifiers can be used for measurement. Therefore, these two quantities may be associated with different gains. Thus, in applications used to obtain Z... iPrior to the above formula, as is known or, for example, measured during the calibration procedure, the gain of the corresponding differential amplifier can be balanced between these two quantities, i.e., such that the two quantities in the ratio have the same proportionality constant. The same applies to other quantities discussed herein, such that a particular ratio (i.e., the ratio included in the formula for calculating Z) is balanced between these two quantities. i and / or Z T The related quantities in a ratio have similar proportionality constants. Different proportionality constants in a particular ratio can be balanced before or after calculating the value of that ratio, as is easily understood by a technician.

[0056] Applying a 10 or 20 sinusoidal voltage signal may include applying the sinusoidal voltage signal by a digital-to-analog converter (DAC) 230. The sinusoidal voltage signal may be amplified by a power buffer 235. The power buffer is associated with an internal impedance 236. This internal impedance 236 is undesirably caused by electrical components present in the power buffer 235, and this internal impedance... Figure 2A The power buffer 235 is schematically shown externally as box 236. The internal impedance 236 can cause significant distortion in impedance measurements on electrode structure 210 or reference impedance 220, and may lead to inaccurate impedance measurements. This is particularly true for impedance measurements of relatively conductive liquids, such as water associated with high salinity or contaminated with other types of ions. This is because a significant voltage drop also occurs across the internal impedance 236, resulting in erroneous voltage drops across other electrical components involved. Method 100 can reduce or substantially eliminate this inaccurate impedance measurement, for example, by performing the aforementioned measurements on reference impedance 220.

[0057] Each measurement of 12, 14, 16, 22, or 24 may include conversion by analog-to-digital converters (ADCs) 240, 250, and 260. The first ADC 240 can be configured to measure ~V. o and ~V r The second ADC 250 can be configured to measure ~V i The third ADC260 can be configured to measure ~I s and~I r .

[0058] The first ADC 240, the second ADC 250, and the third ADC 260 can correspond to the first ADC channel, the second ADC channel, and the third ADC channel, respectively.

[0059] A first differential amplifier 245 can be electrically connected to a first ADC 240. The first differential amplifier 245 can record voltage signals detected on the first external electrode 202 and the second external electrode 204 or on the reference impedance 220, amplify these signals, and forward them to the first ADC 240. The first differential amplifier 245 can be associated with a first gain. Therefore, the magnitude of the first gain can set a specific proportionality constant for a particular measurement value. Thus, if a similar gain is used during both measurements 14 and 24, then ~V o and ~V r It can be associated with a similar proportionality constant.

[0060] The second differential amplifier 255 can be electrically connected to the second ADC 250. The second differential amplifier 255 can record the voltage signals input from the first internal electrode 206 and the second internal electrode 208, amplify these signals, and forward them to the second ADC 250. The second differential amplifier 255 can be associated with a second gain. The second gain does not necessarily have to be equal to the first gain. Therefore, during measurement, the first differential amplifier 245 and the second differential amplifier 255 can be associated with different gains. In applications used to obtain Z... i Before applying the above formula, the first and second gains can be balanced, i.e., the two quantities in the ratio can have the same proportionality constant. The same applies to the other quantities discussed in this paper, such that a specific ratio (i.e., the ratio included in the formula for calculating Z) is achieved. i and / or Z T The related quantities in a ratio have similar proportionality constants. Different proportionality constants in a particular ratio can be balanced before or after calculating the value of that ratio, as is easily understood by a technician.

[0061] The transimpedance amplifier TIA 265 can be electrically connected to a third ADC 260 to convert current originating from electrode structure 210 or reference impedance 220. Therefore, the TIA 265 can enable the measurement of ~I via the third ADC 260. s and~I r .

[0062] Each measurement (12, 14, 16, 22, 24) may include recording a time series. Because a sinusoidal voltage signal is applied, the time series of the corresponding measurements (12, 14, 16, 22, 24) exhibits sinusoidal characteristics. Therefore, preferably, the measured value ~V o ~V r ~V i 、~I s and~I rSampling can be performed at a frequency at least twice the frequency of the applied sinusoidal voltage signal to record a time series of measurements. Multiple periods of each time series can be recorded. This is to enable further frequency analysis and possible noise reduction / denoising (discussed further below).

[0063] Each measurement 12, 14, 16, 22, 24 can further include applying a Discrete Fourier Transform (DFT) to the recorded time series. Applying the DFT can include converting each recorded time series into a corresponding spectrum. Therefore, the measurement can further include determining the dominant frequency band of the spectrum and determining the measurement value based on the dominant frequency band. Thus, a single frequency or at least a relatively narrow frequency band corresponding to the dominant frequency band can be determined through DFT analysis. In practice, the Fourier coefficients associated with the measurement value based on the dominant frequency band may be relatively large compared to any other Fourier coefficients for the remaining frequency bands. Other Fourier coefficients can be set to zero or at least reduced in size before transforming the (modified) spectrum back to the time domain. This is because the sinusoidal characteristics of the recorded time series can be expected to be associated with the frequency corresponding to the determined dominant frequency. Therefore, noise or other measurement artifacts can be suppressed before further analysis of the corresponding time series.

[0064] DFT analysis can output multiple values, such as ten; the magnitude and phase of each time series, such that the quantity A related to a specific time can be expressed as A = |A|e^(-1 / 2). j(ωt-θ) Where |A| is the absolute value of the amplitude of A, θ is the phase shift of A, and ω is the angular frequency of A. After performing a DFT analysis, the individual (angular) frequency considered allows for the direct calculation of the overall phase shift θ in the above equation. Typically, the phase shifts between different recorded time series may differ from each other.

[0065] Alternatively, frequency analysis can be performed using algorithms other than DFT (e.g., the Goertzel algorithm).

[0066] Figure 2A A four-electrode device 200 for liquid impedance measurement is shown. The four-electrode device 200 includes an electrode structure 210 comprising a first external electrode 202, a second external electrode 204, a first internal electrode 206, and a second internal electrode 208. The four-electrode device 200 further includes a reference impedance 210 and a signal generator 230 configured to generate a sinusoidal voltage signal.

[0067] Figure 2BThe electrode structure 210 of the four-electrode device 200 is schematically shown. Electrodes 202, 204, 206, and 208 may be metallic and are substantially parallel to each other. One pair of electrodes (i.e., the first outer electrode 202 and the second outer electrode 204) is responsible for current injection, while the remaining pair (i.e., the first inner electrode 206 and the second inner electrode 208) are voltage measurement electrodes.

[0068] The four-electrode device 200 or at least the electrode structure 210 can be configured to be immersed in a liquid from which its impedance is to be measured. The four-electrode device 200 is configured to measure: a value proportional to the current passing through the first external electrode 202 and the second external electrode 204; a value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204; a value proportional to the voltage drop across the first internal electrode 206 and the second internal electrode 208 of the electrode structure 210; a value proportional to the current passing through the reference impedance 210; and a value proportional to the voltage drop across the reference impedance 210.

[0069] The four-electrode device 200 further includes a processor or circuit configured to calculate the external impedance between the first external electrode 202 and the second external electrode 204 based on: a reference impedance 210; the value proportional to the current flowing through the first external electrode 202 and the second external electrode 204; the value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204; the value proportional to the current flowing through the reference impedance 210; and the value proportional to the voltage drop across the reference impedance 210. The processor or circuit is further configured to calculate the internal impedance between the first internal electrode 206 and the second internal electrode 208 based on: the calculated external impedance; the value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204; and the value proportional to the voltage drop across the first internal electrode 206 and the second internal electrode 208.

[0070] Specifically, refer to Figure 2A The four-electrode device 200 may include a processor 290. The processor 290 may be configured to control the circuitry of the four-electrode device 200. Specifically, the processor 290 may be configured to control, for example, a first switch 280, a second switch 282, a third switch 284, a fourth switch 286, a first differential amplifier 245, a second differential amplifier 255, a transimpedance amplifier TIA 265, a signal generator 230, a first analog-to-digital converter (ADC) 240, a second ADC 250, and / or a third ADC 260. The processor 290 may control the corresponding components to perform the disclosed methods.

[0071] Processor 290 (also referred to as processing unit 290) may be implemented as a general-purpose processing unit and / or a general-purpose processor. Alternatively, however, processor 290 may be implemented as firmware, for example, arranged in an embedded system, or as a specially designed processing unit, such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).

[0072] Furthermore, a computer program product may be provided, comprising computer-readable instructions that, when executed on processor 290, cause the processor to control quad-electrode device 200 to perform the disclosed method.

[0073] Some of the features of the four-electrode device 200 disclosed above and below have been discussed in conjunction with method 100 and are referred to herein.

[0074] The four-electrode device 200 can be implemented in equipment suitable for field conditions. Therefore, appropriate seals and other weather-resistant protection devices can be present in such equipment. The electrode structure 210 can be at least partially immersed in the liquid environment 250 where impedance measurement is to be performed. Therefore, when the four-electrode device 200 performs impedance measurement, the four-electrode structure 210 is at least partially immersed in the liquid environment 250. Thus, the four electrodes 202, 204, 206, and 208 form three intermediate regions R1, R2, and R3, where each region is associated with a specific impedance. Specifically, the region R1 between the first inner electrode 206 and the second inner electrode 208 is associated with the considered liquid impedance Z. i Related.

[0075] Furthermore, the four-electrode device 200 can be configured to monitor ongoing measurements wirelessly or via wired means, thereby providing monitoring of water quality in, for example, remote areas.

[0076] The processor or circuit can be configured to calculate the external impedance, as can be expressed by the following equation:

[0077]

[0078] And the internal impedance is calculated, as can be expressed by the following equation:

[0079]

[0080] Among them, Z T Z is the external impedance. i Z is the internal impedance. r The reference impedance is 220Ω, ~I r The value, ~V, is proportional to the current passing through the reference impedance 220. oFor a value proportional to the voltage drop across the first external electrode 202 and the second external electrode 204, ~V r For the value that is proportional to the voltage drop across the reference impedance 220, ~I s The value is proportional to the current passing through the first external electrode 202 and the second external electrode 204, and ~V i The value is proportional to the voltage drop of the first inner electrode 206 and the second inner electrode 208 of the electrode structure 210.

[0081] The corresponding proportionality constant can be adjusted according to the needs of the corresponding calculation, as is generally known to technicians.

[0082] Specifically, as an example, V i and V o Different differential amplifiers can be used for measurement. Therefore, these two quantities may be associated with different gains. Thus, in applications used to obtain Z... i Prior to the above formula, as is known or, for example, measured during the calibration procedure, the gain of the corresponding differential amplifier can be balanced between these two quantities, i.e., such that the two quantities in the ratio have the same proportionality constant.

[0083] The four-electrode device 200 may further include a first switch 280 and a second switch 282, which are configured to switch the path that the sinusoidal voltage signal can traverse between the electrode structure 210 and the reference impedance 220 when the sinusoidal voltage signal is generated. That is, when both the first switch 280 and the second switch 282 are in position A, a measurement across the electrode structure 210 can be performed, and when both the first switch 280 and the second switch 282 are in position B, a measurement across the reference impedance 220 can be performed.

[0084] Signal generator 230 may include a digital-to-analog converter (DAC).

[0085] The four-electrode device 200 may include a first analog-to-digital converter (ADC) 240, a second ADC 250, and a third ADC 260. The first ADC 240 may be configured to measure ~V o and ~V r The second ADC 250 can be configured to measure ~V i The third ADC260 can be configured to measure ~I s and~I r .

[0086] The first ADC 240, the second ADC 250, and the third ADC 260 can correspond to the first ADC channel, the second ADC channel, and the third ADC channel, respectively.

[0087] The four-electrode device 200 may further include a third switch 284 and a fourth switch 286, which are arranged to selectively connect to the first ADC 240. When the third switch 284 and the fourth switch 286 are in position C, the connection of the first ADC 240 is established.

[0088] The processor or circuitry can be further configured to record with ~V o ~V r ~V i 、~I s and~I r Each related time series in the data.

[0089] The processor or circuitry can be further configured to apply the Discrete Fourier Transform (DFT) to each recorded time series.

[0090] In the foregoing, the inventive concept has been described primarily with reference to a limited number of examples. However, as will be readily apparent to those skilled in the art, other examples besides those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A method for performing liquid impedance measurement using a four-electrode device, the four-electrode device including an electrode structure, the method comprising: A sinusoidal voltage signal is applied to the first and second external electrodes of the electrode structure, and a first set of measurements is performed, the first set of measurements including: Measure a value proportional to the current passing through the first external electrode and the second external electrode; Measure a value proportional to the voltage drop across the first and second external electrodes; Measure a value proportional to the voltage drop across the first and second inner electrodes of the electrode structure; The sinusoidal voltage signal is applied across the reference impedance, and a second set of measurements is performed, which includes: Measure a value proportional to the current passing through the reference impedance; Measure a value proportional to the voltage drop across the reference impedance; Calculate the external impedance between the first external electrode and the second external electrode based on the following: The reference impedance, The value is proportional to the current passing through the first external electrode and the second external electrode. The value that is proportional to the voltage drop across the first external electrode and the second external electrode. The value that is proportional to the current passing through the reference impedance, and The value that is proportional to the voltage drop across the reference impedance; and Calculate the internal impedance between the first internal electrode and the second internal electrode based on the following: The calculated external impedance, The value that is proportional to the voltage drop across the first external electrode and the second external electrode, and The value is proportional to the voltage drop across the first internal electrode and the second internal electrode.

2. The method according to claim 1, wherein, The calculation of the external impedance is expressed as follows: And the calculation of the internal impedance is expressed as: in, Z T The external impedance is... Z i The internal impedance is... Z r The reference impedance is... ~I r The value is proportional to the current passing through the reference impedance. ~V o The value is proportional to the voltage drop across the first external electrode and the second external electrode. ~V r The value is proportional to the voltage drop across the reference impedance. ~I s The value is proportional to the current passing through the first external electrode and the second external electrode, and ~V i The value is proportional to the voltage drop on the first inner electrode and the second inner electrode of the electrode structure.

3. The method according to claim 1, wherein, Each application of the sinusoidal voltage signal includes the application of the sinusoidal voltage signal by a digital-to-analog converter (DAC).

4. The method according to claim 1, wherein, Each measurement involves conversion by an analog-to-digital converter (ADC).

5. The method according to claim 1, wherein, Each of these measurements includes recording a time series.

6. The method according to claim 5, wherein, Each of the measurements further includes applying the Discrete Fourier Transform (DFT) to the recorded time series.

7. The method according to claim 6, wherein, The application of the Discrete Fourier Transform includes converting each recorded time series into a corresponding spectrum, and the measurement further includes: Determine the dominant frequency band of the spectrum, and The measured value is determined based on the dominant frequency chamber.

8. A four-electrode device for liquid impedance measurement, the four-electrode device comprising: The electrode structure includes: First external electrode; Second external electrode; First internal electrode; and Second internal electrode; Reference impedance; and A signal generator configured to generate a sinusoidal voltage signal. The four-electrode device is configured to measure: A value proportional to the current passing through the first external electrode and the second external electrode; A value proportional to the voltage drop across the first external electrode and the second external electrode; A value proportional to the voltage drop across the first and second inner electrodes of the electrode structure; A value proportional to the current passing through the reference impedance; and The value is proportional to the voltage drop across the reference impedance, and The four-electrode device further includes: A processor or circuit configured to: Calculate the external impedance between the first external electrode and the second external electrode based on the following: The reference impedance, The value is proportional to the current passing through the first external electrode and the second external electrode. The value that is proportional to the voltage drop across the first external electrode and the second external electrode. The value that is proportional to the current passing through the reference impedance, and The value that is proportional to the voltage drop across the reference impedance; and Calculate the internal impedance between the first internal electrode and the second internal electrode based on the following: The calculated external impedance, The value that is proportional to the voltage drop across the first external electrode and the second external electrode, and The value is proportional to the voltage drop across the first internal electrode and the second internal electrode.

9. The four-electrode device according to claim 8, wherein, The processor or circuit is configured to calculate the external impedance, as shown below: And calculate the internal impedance, as shown below: in, Z T The external impedance is... Z i The internal impedance is... Z r The reference impedance is... ~I r The value is proportional to the current passing through the reference impedance. ~V o The value is proportional to the voltage drop across the first external electrode and the second external electrode. ~V r The value is proportional to the voltage drop across the reference impedance. ~I s The value is proportional to the current passing through the first external electrode and the second external electrode, and ~V i The value is proportional to the voltage drop on the first and second inner electrodes of the electrode structure.

10. The four-electrode device according to claim 8, further comprising: A first switch and a second switch are configured to switch the path that the sinusoidal voltage signal can traverse between the electrode structure and the reference impedance when the sinusoidal voltage signal is generated.

11. The four-electrode device according to claim 8, wherein, The signal generator includes a digital-to-analog converter (DAC).

12. The four-electrode device according to claim 8, further comprising: A first analog-to-digital converter (ADC), configured for measurement The value that is proportional to the voltage drop across the first external electrode and the second external electrode, and The value that is proportional to the voltage drop across the reference impedance; The second ADC, which is configured to measure The value that is proportional to the voltage drop across the first internal electrode and the second internal electrode; as well as The third ADC is configured for measurement. The value that is proportional to the current passing through the first external electrode and the second external electrode, and The value is proportional to the current passing through the reference impedance.

13. The four-electrode device according to claim 12, further comprising: A third switch and a fourth switch are arranged to selectively connect to the first ADC.

14. The four-electrode device according to claim 8, wherein, The processor or circuitry is further configured to record time series associated with each of the following: The value that is proportional to the voltage drop across the first external electrode and the second external electrode. The value that is proportional to the voltage drop across the reference impedance. The value that is proportional to the voltage drop across the first internal electrode and the second internal electrode. The value that is proportional to the current passing through the first external electrode and the second external electrode, and The value is proportional to the current passing through the reference impedance.

15. The four-electrode device according to claim 14, wherein, The processor or circuitry is further configured to apply a Discrete Fourier Transform (DFT) to each recorded time series.

16. A computer program product comprising computer-readable instructions that, when executed on a processor, cause the processor to perform the method of claim 1.

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