Conductivity Measurement Using Non-Contact Potential Electrodes and a Guard Ring
15 Jun 2019-IEEE Sensors Journal (Institute of Electrical and Electronics Engineers (IEEE))-Vol. 19, Iss: 12, pp 4688-4695
TL;DR: In this article, the contact-type potential terminals of a traditional four-lead conductivity probe are replaced with non-contacting terminals thus preventing electrode corrosion and contamination affecting the conductivity measurement.
Abstract: This paper presents an improved method for the measurement of the conductivity of a liquid. In the proffered technique, the contact-type potential terminals of a traditional four lead conductivity probe are replaced with non-contacting terminals thus preventing electrode corrosion and contamination affecting the conductivity measurement. An additional guard electrode introduced in the present design ensures that the current through the external/surrounding medium becomes negligible thus reducing the error due to current flow, external to the probe. A self-balancing signal conditioning circuit, specially designed to suit the probe, alleviates the new problems of the modified probe. Simulation results and the results obtained from a prototype built and tested establish the efficacy of the proposed technique. The worst case error was found to be ± 0.78% with the prototype probe.
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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 or methods from "Conductivity Measurement Using Non-..."
...Compared to the method presented in [22], where three electrodes are in contact with the liquid, the present method uses contact-free electrodes and hence does not suffer from problems due to contaminated electrodes and hence can be used for measurement of conductivity of corrosive liquids....
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...The conductivity meter with noncontact-type potential electrodes and a guard ring [22], proposed earlier, can be used for both flow-through and immersion methods of measurement, but the electrodes to send the current through the liquid are still in contact with the liquid which can cause problems due to corrosion...
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TL;DR: In this article, a multi-electrodes conductance probe, namely 2.2RE, is proposed to accurately measure the gas void fraction (GVF) within annulus flow.
Abstract: Gas-liquid two-phase flow in annulus channels is encountered in several industrial applications, and the Gas Void Fraction (GVF) measurement of such flow is crucial for either monitoring or controlling processes. However, the challenging constraints surrounding annular channels, such as the relatively small distance between the inner and outer pipelines and the non-intrusive accessibility to the inner pipeline, made the GVF measurement difficult to be handled using existing GVF measurement techniques. This paper suggests a new multi-electrodes conductance probe to accurately measure the GVF within annulus flow. The design was finalized after several iterative tunings, followed by an optimization step where a new objective function was suggested to maximize the measurement sensitivity by searching for the optimal relative placement of the electrodes. This was facilitated using COMSOL Multiphysics software, where extensive numerical simulations were done on two types of conductance probes. This has led us to conclude that the new suggested conductance probe, namely 2.2RE probe, which consists of 2 × 2 ring electrodes, can yield a high measurement sensitivity within the target sensing domain, in terms of electric field homogeneity and concentration, using a reasonable amount of hardware compared to other previous works. Indeed, two-dimensional (2D) and three-dimensional (3D) visualization of the current streamlines showed the ability of the 2.2RE probe to handle more efficiently different two-phase flow configurations in the annulus. Furthermore, the geometry of the 2.2RE probe was optimized after a comprehensive analysis of the probe dimensions’ effect on its performance. Series of experiments were conducted on a 2.2RE prototype which was designed according to the optimal dimensions to assess the probe response for bubbly and annular flow patterns. The maximum GVF value which was experimentally considered for bubbly and annular patterns were 0.31 and 0.95 , respectively. The 2.2RE probe showed a slight dependency on the flow pattern where it exhibited a linear and quasi-linear relationships of the probe output voltage function of the GVF for bubbly and annular flow patterns, respectively. The comparison of experimental and numerical data revealed that the numerical model matches well the experimental data with a maximal relative error of 7.32 % . A calibration procedure of the 2.2RE probe was initiated and assessed numerically, and an accurate estimation of the GVF could be achieved.
3 citations
24 Aug 2020
TL;DR: In this article, a noncontact capacitively coupled probe for the measurement of the liquid fill level and conductivity in a partially filled but horizontally kept pipe is presented, which is designed to provide voltage directly proportional to the resistance of the water column.
Abstract: A noncontact capacitively coupled probe for the measurement of the liquid fill level and conductivity in a partially filled but horizontally kept pipe is presented. Capacitively coupled electrodes are used for conductivity measurements, but the error is high when the tube is partially filled with liquid. In this letter, we propose to use the values of the coupling capacitors formed between the liquid column and conductive electrodes to calculate the fill level and estimate the conductivity of water in the pipe. The resistance of the liquid column is determined using a recently reported autobalancing signal conditioning circuit. The circuit is designed to provide voltage directly proportional to the resistance of the water column. Voltages at the relevant nodes of the circuit are tapped to compute the equivalent coupling capacitance values. The resistance of the liquid column along with fill level determined through coupling capacitance values helps in measuring the conductivity of water flowing through the pipe. A worst-case error of ±0.9% was obtained in measuring the conductivity, and a worst-case error less than 0.52% was observed in the water fill level measurement from a prototype noncontact water conductivity measurement probe for a partially filled pipe that has been developed and tested.
1 citations
Cites background from "Conductivity Measurement Using Non-..."
...Similarly, a conductivity measurement probe with a guard ring was proposed in [10] in which the potential also electrodes are noncontact type....
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TL;DR: In this article , a configurable detection chip for liquid conductivity using a dual-frequency sinusoidal signal technique is presented, which improves the detection accuracy by effectively avoiding the measurement error caused by polarization effect and capacitance effect.
Abstract: This paper presents a configurable detection chip for liquid conductivity using a dual-frequency sinusoidal signal technique. The proposed method improves the detection accuracy by effectively avoiding the measurement error caused by polarization effect and capacitance effect. The detection chip mainly includes a small signal amplifier circuit and a data acquisition and processing circuit. First, the small signal amplifier circuit mainly consists of an operational amplifier circuit and a four-choice data selection circuit, which is regulated to implement a configurable function. Through the negative feedback principle, the signal amplification can reach 84.1 dB. Secondly, the data acquisition and processing circuit comprises a SAR ADC and a digital processing unit, with the former being used for signal acquisition and the latter for signal processing. Finally, the detection chip is implemented using TSMC 65 nm CMOS technology. The signal scaling and processing operates at a low area cost of 0.02 μm2. The worst-case error for conductivity measurements is ±1.1%, and the worst-case error for the chip configuration is less than 0.6%. The results show that the dual-frequency sinusoidal signal technique and chip configuration can greatly reduce the measurement error.
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86 citations
"Conductivity Measurement Using Non-..." refers background in this paper
...water samples of different conductivity values in the range of 22 mS/cm to 70 mS/cm (approximately the sea water conductivity range [17]) are prepared and the conductivity probe was completely immersed in the sample with minimum depth of 20 cm ( more than length of probe as given in Table I) and tested....
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TL;DR: The main advantages of the proposed conductivity sensor include a wide measurement range, an intrinsic capability to minimize errors caused by fouling and polarization effects, and an automatic compensation of conductivity measurements caused by temperature variations.
Abstract: In this paper, a new four-electrode sensor for water conductivity measurements is presented. In addition to the sensor itself, all signal conditioning is implemented together with signal processing of the sensor outputs to determine the water conductivity. The sensor is designed for conductivity measurements in the range from 50 mS/m up to 5 S/m through the correct placement of the four electrodes inside the tube where the water flows. The implemented prototype is capable of supplying the sensor with the necessary current at the measurement frequency, acquiring the sine signals across the voltage electrodes of the sensor and across a sampling impedance to determine the current. A temperature sensor is also included in the system to measure the water temperature and, thus, compensate the water-conductivity temperature dependence. The main advantages of the proposed conductivity sensor include a wide measurement range, an intrinsic capability to minimize errors caused by fouling and polarization effects, and an automatic compensation of conductivity measurements caused by temperature variations.
83 citations
"Conductivity Measurement Using Non-..." refers methods in this paper
...Table II compares the proposed method with existing ones [10], [13], [14], [18]–[20]....
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TL;DR: In this paper, the coaxial cylinders technique was used to measure the electrical conductivity of liquids. But this technique is not suitable for high-accuracy measurements of liquid conductivities.
Abstract: A high-accuracy, calibration-free technique to measure the electrical conductivity of liquids has been developed — the coaxial cylinders technique. Because the liquid under investigation comes in contact only with metal and not with anything dielectric, this technique enables the measurement of the electrical properties of liquids inaccessible by classical high-accuracy techniques. Two coaxial cylindrical electrodes are immersed in the liquid to an arbitrary initial depth, and ac impedance is measured over a wide range of frequency. This process is repeated at many immersions. The electrical conductivity is calculated from the change in measured conductance with immersion. This technique was validated in 1.0, 0.1, and 0.01 D KCl(aq) solutions at room temperature. Measured electrical conductivities were within ±0.5% of the standard reference values.
65 citations
"Conductivity Measurement Using Non-..." refers background in this paper
...conductivity meters suffer from errors introduced due to un-confined current path [3]....
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TL;DR: In this paper, the principles of electrolytic conductance measurements are reviewed, and applications to molten salts and solid electrolytes as well as to aqueous electrolytes are discussed.
Abstract: In this paper the author reviews the principles of electrolytic conductance measurements, citing applications to molten salts and to solid electrolytes as well as to aqueous electrolytes.
63 citations
"Conductivity Measurement Using Non-..." refers background in this paper
...Traditional contact type conductivity meters use a four electrode conductivity probe wherein the two outer electrodes serve as current electrodes and the couple of inner electrodes pick up the potential drop across a pre-fixed liquid column [5], [6]....
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TL;DR: In this article, a miniature high precision conductivity and temperature (CT) sensor system has been developed for ocean salinity monitoring using micro fabrication technology, which has a 1 month battery life at 10 s sampling interval.
Abstract: A miniature high precision conductivity and temperature (CT) sensor system has been developed for ocean salinity monitoring. The CT sensor is manufactured using micro fabrication technology. A novel seven-electrode conductivity cell has been developed which has no field leakage. This is combined with a platinum resistor temperature bridge to produce an integrated CT sensor. A generic impedance measurement circuit has been developed, with three-parameter sine fitting algorithm. It has a 1 month battery life at 10 s sampling interval. Calibration results show that the initial CT accuracies are ±0.03 mS/cm and ±0.01°C, respectively. Testing of the CT sensor has been performed in the north Atlantic and revealed drift in sensor readings after five weeks of operation.
54 citations
"Conductivity Measurement Using Non-..." refers background in this paper
...Traditional contact type conductivity meters use a four electrode conductivity probe wherein the two outer electrodes serve as current electrodes and the couple of inner electrodes pick up the potential drop across a pre-fixed liquid column [5], [6]....
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