A Capacitive-Coupled Noncontact Probe for the Measurement of Conductivity of Liquids
14 Jan 2019-IEEE Transactions on Instrumentation and Measurement (IEEE)-Vol. 68, Iss: 5, pp 1602-1610
TL;DR: An auto-balancing signal conditioning scheme presented here overcomes the problem posed by the large capacitive reactances and provides directly a measurable output proportional only to the conductance of the liquid.
Abstract: A noncontact (capacitive-coupled) probe for the measurement of the conductivity of liquids is presented. Insulation introduced between the measurement electrodes and the liquid intrudes a couple of coupling capacitances. Though the capacitive coupling overcomes the problems of electrode polarization and contamination associated with contacting electrodes, the large reactances of the coupling capacitors pose a problem in the measurement of comparatively very small resistance of the liquid. An auto-balancing signal conditioning scheme presented here overcomes the problem posed by the large capacitive reactances and provides directly a measurable output proportional only to the conductance of the liquid. Error analysis of the probe presented herein helps the optimal design of the probe. A worst case error of ± 0.9% was obtained from a prototype noncontact conductivity probe, developed and tested.
Citations
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TL;DR: In this paper, a two-electrode type conductivity sensor, using copper as electrodes, coated with a polyimide layer called DQN-60, is presented.
Abstract: This paper presents a two-electrode type conductivity sensor, using copper as electrodes, coated with a polyimide layer called DQN-60. This sensor is specially designed to be robust yet inexpensive for applications like precision farming and fishery. A new conductivity sensing principle is proposed which is based on impedimetric measurement (both magnitude and phase) at a frequency of 200 kHz. This sensing principle is developed by analyzing the electrical equivalent model of the proposed sensor and is aimed at eliminating the effect of the interface impedance and the cell capacitance thus making the measurement linear and accurate. A prototype meter is developed with 3.75% maximum full-scale error in the range of 0.5 $\mu \text{S}$ /cm to 20 mS/cm. The temperature compensation, calibration, and detailed experimental results are also discussed.
11 citations
TL;DR: A high-precision and wide-range measurement method based on a novel planar interdigital electrode sensor array and a self-adaptive algorithm that can maintain precise measurement from $0.5~\mu \text{s}$ /cm to 500ms/cm.
Abstract: Conductivity is a crucial parameter in water quality detection, which can roughly represent overall concentration of various inorganic ions. However, traditional conductivity sensors can only afford high performance measurement in a relatively low range while the concentration may vary much more in realworld water environment. This paper proposes a high-precision and wide-range measurement method based on a novel planar interdigital electrode sensor array and a self-adaptive algorithm. The array is composed of 3 pairs of planar electrodes with various cell constants aiming at different subdivided conductivity sections. The follow-up circuit and the self-adaptive algorithm keep the optimal electrode pair dominates the output of the array. Numerical simulations were utilized to optimize sensor parameters before fabrication. PCB manufacturing technique was used which guaranteed a relatively low manufacturing cost and stable performance. Experiments were conducted to verify the sensing performance and results showed that the array can maintain precise measurement from 0.5μs/cm to 500ms/cm.
11 citations
Cites background from "A Capacitive-Coupled Noncontact Pro..."
...designed a capacitive-coupled probe for noncontact measurement of the conductivity of liquids [4]....
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TL;DR: A novel approach to directly interface a capacitively coupled resistive sensor to a microcontroller is presented in this article, and it is shown that it is independent of the accuracy of the charging capacitor, supply voltage, and preset threshold voltage.
Abstract: A novel approach to directly interface a capacitively coupled resistive sensor to a microcontroller is presented in this article. The existing measurement schemes for such sensors are complex. In addition, the coupling capacitance often also holds important data. The proposed simple measurement system, for such series RC sensors, is capable of measuring both the resistance and the coupling capacitance. A detailed analysis on the effect of the nonidealities on the resistance measurement showed that it is independent of the accuracy of the charging capacitor, supply voltage, and preset threshold voltage. The performance of the proposed scheme has been evaluated by building suitable prototypes. Initially, a setup was designed such that the measurement was not limited by the nonidealities of the microcontroller. The test results from this showed a maximum error of 0.28% and 0.96% for the resistance and capacitance measurement, respectively. The subsequent study with the microcontroller interface exhibited a maximum error of 0.91% (resistance) and 2.94% (capacitance). Noise and resolution studies have also been conducted and the results are presented. The accuracy of the prototype is promising, with a measurement time of 5 ms per parameter. This is a practical, low-power, low-cost measurement system as it provides digital data on the resistance and capacitance, in series, using only a microcontroller, and a couple of passive components.
10 citations
Cites background from "A Capacitive-Coupled Noncontact Pro..."
...3034969 without exposing the measurement electrodes to the water [1], thereby avoiding the possibility of errors in the measurement...
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...For instance, in [1] and [11], the circuits are relatively complex with the requirement of a precise sinusoidal excitation and a phase-sensitive detector....
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...For low values of Rx (say, lower than 1 k ) with a coupling capacitance of 2 nF [1], the discharge time will...
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...The schemes employed so far in the existing capacitively coupled resistive sensing applications [1], [10], [11] have their limitations....
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...The same is valid when an insulated electrode is kept inside the pipe [1]....
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Patent•
13 Aug 2004
Abstract: A system for measuring the free space electric field comprises an ultra high impedance of the antenna disposed in an electric field to generate a signal from the electric field. Amplifier having an input port is provided to amplify the signal. Amplifier generates an input bias current, the current is combined with the signal to produce an input potential at the input port. Connected to an electrical circuit ground connection to an input port, comprising at least one circuit element for controlling the input potential to stabilize the signal at the input port.
5 citations
TL;DR: The signal conditioning circuit is developed such that the measurement of the voltage-drop across the column of the liquid and hence the determination of the conductivity of the liquids unaffected by the coupling capacitances of the potential electrodes do not affect the performance.
Abstract: The basic principle of a noncontact method of measurement of conductivity of liquids, presented earlier, is analysed to evolve design rules to have minimal error in the measurement. In this method, the current is sent through the liquid whose conductivity is to be measured by induction and the voltage across the liquid column is measured using capacitive coupled electrodes and the conductivity computed therefrom. Hence, problems that arise due to contamination or corrosion of contacting electrodes are eliminated. The signal conditioning circuit is developed such that the measurement of the voltage-drop across the column of the liquid and hence the determination of the conductivity of the liquids unaffected by the coupling capacitances of the potential electrodes. Thus, small deviations that can creep in during manufacturing of the probe (manufacturing tolerances) do not affect the performance. An error analysis of the proposed system was carried out and the practicality of the scheme verified by developing and testing a prototype. The test results showed a worst-case error of 0.82% in conductivity measurements. The facts that the proposed method is unaffected by the coupling capacitors and the presence of materials kept outside of the probe were also verified.
4 citations
Cites background from "A Capacitive-Coupled Noncontact Pro..."
...The capacitive coupled noncontact-type conductivity measurement methods [19]–[21] have insulated ring shaped electrodes to make the current path confined....
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References
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Book•
01 Jan 1980
TL;DR: In this paper, the authors present a comprehensive overview of electrode processes and their application in the field of chemical simulation, including potential sweep and potential sweep methods, coupled homogeneous chemical reactions, double-layer structure and adsorption.
Abstract: Major Symbols. Standard Abbreviations. Introduction and Overview of Electrode Processes. Potentials and Thermodynamics of Cells. Kinetics of Electrode Reactions. Mass Transfer by Migration and Diffusion. Basic Potential Step Methods. Potential Sweep Methods. Polarography and Pulse Voltammetry. Controlled--Current Techniques. Method Involving Forced Convention--Hydrodynamic Methods. Techniques Based on Concepts of Impedance. Bulk Electrolysis Methods. Electrode Reactions with Coupled Homogeneous Chemical Reactions. Double--Layer Structure and Adsorption. Electroactive Layers and Modified Electrodes. Electrochemical Instrumentation. Scanning Probe Techniques. Spectroelectrochemistry and Other Coupled Characterization Methods. Photoelectrochemistry and Electrogenerated Chemiluminescence. Appendix A: Mathematical Methods. Appendix B: Digital Simulations of Electrochemical Problems. Appendix C: Reference Tables. Index.
20,533 citations
TL;DR: In this paper, the authors present a survey of electrochemical methods and their applications, focusing on the following categories: electrochemical water treatment methods, electrochemical method fundamentals and applications, and student solutions manual.
Abstract: Electroanalytical methods colorado state university. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications. electrochemical methods student solutions manual. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications. electrochemical methods student solutions manual. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications. customer reviews electrochemical methods. electrochemical water treatment methods sciencedirect. electrochemical methods fundamentals and applications. electrochemical methods student solutions manual. electrochemical methods fundamentals and applications. electrochemical methods 2nd edition textbook solutions. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications. electrochemical methods fundamentals and applications
5,804 citations
"A Capacitive-Coupled Noncontact Pro..." refers background or methods in this paper
...Two electrode conductivity meters have low accuracy due to unconfined current path, polarization, and contact or lead resistance [1]–[3]....
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...Conductivity can be measured using contact-type electrode conductivity meter [1], [2] or the noncontact-type inductive-type conductivity meter [3], [4]....
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TL;DR: A contactless capacitively coupled conductivity detector for capillary electrophoresis is introduced and the limit of detection of inorganic cations and anions is 200 ppb, as determined for sodium and chloride, respectively.
Abstract: A contactless capacitively coupled conductivity detector for capillary electrophoresis is introduced. The detector consists of two electrodes which are placed cylindrically around the outer polyimide coating of the fused-silica capillary with a detection gap of 2 mm. The electrodes form a cylindrical capacitor, and the electric conductivity of the solution in the gap between the electrodes is measured. A high audio or low ultrasonic frequency for coupling of the ac voltage is used in order to minimize the influence of reactance of the liquid. For an improved version of the detector, two syringe cannulas are used as the electrodes and the capillary is simply assembled into the tubing. This allows an easy placement of the detector on various positions along the capillary. The limit of detection of inorganic cations and anions is 200 ppb, as determined for sodium and chloride, respectively.
480 citations
"A Capacitive-Coupled Noncontact Pro..." refers background or methods in this paper
...Thus, it will be very useful if the conductance can be measured through capacitive-coupled electrodes, avoiding the direct contact of electrodes with the liquid [16]–[20]....
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...A contactless conductivity detection for capillary electrophoresis is presented in [16]....
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...The performance of the schemes given in [16] and [17] can be improved by employing a PSD to process the sig-...
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TL;DR: Theoretical aspects of C(4)D in both the capillary and microchip electrophoresis format have been comprehensively investigated and the method can be considered a mature detection technique.
Abstract: Capacitively coupled contactless conductivity detection (C4D) in the axial electrode configuration was introduced in 1998 as a quantification method for capillary electrophoresis. Its universality allows the detection of small inorganic ions as well as organic and biochemical species. Due to its robustness, minimal maintenance demands and low cost the popularity of this detector has been steadily growing. Applications have recently also been extended to other analytical methods such as ion chromatography, high-performance liquid chromatography and flow-injection analysis. C4D has also found use for detection on electrophoresis based lab-on-chip devices. Theoretical aspects of C4D in both the capillary and microchip electrophoresis format have been comprehensively investigated. Commercial devices are now available and the method can be considered a mature detection technique. In this article, the achievements in C4D for the time period between September 2004 and August 2007 are reviewed.
233 citations
Additional excerpts
...nal from the i-to-v converter [18], [19]....
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TL;DR: The field profiles obtained by scanning a biological tissue show the potential of this methodology for clinical applications, and images obtained from isolated conducting tubes show that it is possible to distinguish two tubes separated 17 mm from each other.
Abstract: A data-acquisition system has been developed to image electrical conductivity of biological tissues via contactless measurements. This system uses magnetic excitation to induce currents inside the body and measures the resulting magnetic fields. The data-acquisition system is constructed using a PC-controlled lock-in amplifier instrument. A magnetically coupled differential coil is used to scan conducting phantoms by a computer controlled scanning system. A 10000-turn differential coil system with circular receiver coils of radii 15 mm is used as a magnetic sensor. The transmitter coil is a 100-turn circular coil of radius 15 mm and is driven by a sinusoidal current of 200 mA (peak). The linearity of the system is 7.2% full scale. The sensitivity of the system to conducting tubes when the sensor-body distance is 0.3 cm is 21.47 mV/(S/m). It is observed that it is possible to detect a conducting tube of average conductivity (0.2 S/m) when the body is 6 cm from the sensor. The system has a signal-to-noise ratio of 34 dB and thermal stability of 33.4 mV//spl deg/C. Conductivity images are reconstructed using the steepest-descent algorithm. Images obtained from isolated conducting tubes show that it is possible to distinguish two tubes separated 17 mm from each other. The images of different phantoms are found to be a good representation of the actual conductivity distribution. The field profiles obtained by scanning a biological tissue show the potential of this methodology for clinical applications.
84 citations
"A Capacitive-Coupled Noncontact Pro..." refers background or methods in this paper
...Conductivity can be measured using contact-type electrode conductivity meter [1], [2] or the noncontact-type inductive-type conductivity meter [3], [4]....
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...Discussion: The noncontact-type conductivity probe discussed above-mentioned does not have polarization problem as the two-electrode conductivty meter [4]....
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