An auto-balancing signal conditioning scheme for non-contact measurement of conductivity of water
14 May 2018-pp 1-5
TL;DR: An auto-balancing signal conditioning scheme to measure resistance and hence conductivity of water in an insulating tube through capacitively coupled electrodes that overcomes the problems of electrode polarization and contamination associated with conventional contact based approach of conductivity measurement of water.
Abstract: This paper presents a signal conditioning approach to measure resistance and hence conductivity of water in an insulating tube through capacitively coupled electrodes. In the scheme presented, the electrodes are electrically insulated from water and measurement is taken through couple of capacitances formed between the electrode and water column. The capacitive coupling overcomes the problems of electrode polarization and contamination associated with conventional contact based approach of conductivity measurement of water. The large reactance of the coupling capacitors, compared to the resistance of the water column under measurement, is a challenge. Moreover, the variations in the coupling capacitor over time presents another challenge. The auto-balancing signal conditioning scheme presented here overcome these challenges by providing an output that is directly proportional to the resistance under measurement and is independent of the value of the coupling capacitors. Test results on a prototype of the proposed circuit show that the maximum error in the resistance measurement is less than 0.9 % and the output is independent of the coupling capacitors.
Citations
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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.
11 citations
Cites background from "An auto-balancing signal conditioni..."
...noncontact conductivity probe, presented earlier [21], is now...
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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: 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.
5 citations
Cites background or methods from "An auto-balancing signal conditioni..."
...Table II compares the proposed method with existing ones [10], [13], [14], [18]–[20]....
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...The proposed conductivity probe can be used as both flow-through type and immersion type whereas [13] and [14] can be used only for flow-through...
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...In [13] a conductivity measurement probe with capacitive coupled electrodes operated by an auto-balancing signal conditioning circuit is portrayed....
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TL;DR: In this paper, a capacitance-to-digital converter (CDC) is proposed for series RC sensors that requires/prefers sinusoidal excitation, which is useful for grounded as well as floating capacitive sensors.
Abstract: A new Capacitance-to-Digital Converter (CDC) applicable for series RC sensors that requires/prefers sinusoidal excitation is proposed in this paper. The CDC presented works based on a dual-slope technique and it gives a digital output as a function of unknown capacitance of a series RC sensor, i.e., a capacitive sensor with a capacitor and a resistor in series in its electrical equivalent circuit. Output of the CDC is not sensitive to the series resistor. The CDC is useful for grounded as well as floating capacitive sensors, which needs to be excited with a sine wave for best performance. Applications of such capacitive sensors include ice detection, sterility testing of packed food products, etc. A sinusoidal Howland current source can be used to excite a grounded capacitive sensor while a simple current source with a special stabilization scheme that suppresses the effect due to static errors of opamp has been developed for floating capacitive sensor and presented in this paper. A prototype of the proposed CDC for a floating capacitive sensor has been built and tested in the laboratory. Measurement results for the sensor capacitance showed a worst case error of 0.13% for a range of 100 pF, proving the efficacy of the proposed scheme. Keywords-Capacitance-to-digital converter; capacitive sensor; floating capacitive sensor; current source for capacitive sensors.
4 citations
References
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TL;DR: In this article, the authors proposed a novel circuit configuration, capable of handling fast transients and small capacitance changes by the evaluation of the signals of a capacitive sensor network, which is based on a conventional bridge measurement method being complemented with a control loop and high-order filters in order to cancel the effect of the environmental interference, the in-circuit noise, the propagation delay of the measuring signal and the parasitic elements.
Abstract: This study describes a novel circuit configuration, capable of handling fast transients and small capacitance changes by the evaluation of the signals of a capacitive sensor network. The circuit is based on a conventional bridge measurement method being complemented with a control loop and high-order filters in order to cancel the effect of the environmental interference, the in-circuit noise, the propagation delay of the measuring signal and the parasitic elements. Through the first circuit tests, applying to the proposed measurement configuration, it was possible to detect capacitance changes in the order of 100 ppm of the nominal capacitance value with a sampling frequency of 2 kHz. The state of the art measurement configurations compare the rectified measurement signal of the capacitive sensor with that of a reference capacitance. The difference signal, already having a considerable noise content because of the diode-rectification is then further amplified. The measurement configuration proposed in the study is however amplifying the difference of the unrectified signals. Owing to the rectification being applied only after the gain stage, the noise of the rectifier unit is considerably smaller compared with other solutions. This method is having further potentials especially by means of measurement speed and accuracy.
14 citations
"An auto-balancing signal conditioni..." refers background or methods in this paper
...The prototype circuit developed provides an output proportional to the resistance alone while the scheme in [17] is designed to trace changes in the capacitance rather than resistance....
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...Individual high pass filters are used at the outputs of OA1, and OA2 to avoid any low frequency signal/noise that may be present [17]....
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19 Oct 2012
TL;DR: A new four-electrode smart sensor is proposed for water conductivity measurements of aquaculture monitoring with the main advantages of these sensors include a high precision, a good stability and an intrinsic capability to minimize errors caused by polarization.
Abstract: Conductivity is regard as a key technical parameter in modern intensive fish farming management. The water conductivity sensors are sophisticated devices used in the aquaculture monitoring field to understand the effects of climate changes on fish ponds. In this paper a new four-electrode smart sensor is proposed for water conductivity measurements of aquaculture monitoring.The main advantages of these sensors include a high precision, a good stability and an intrinsic capability to minimize errors caused by polarization. A temperature sensor is also included in the system to measure the water temperature and, thus, compensate the water-conductivity temperature dependence. The prototype developed is appropriate for conductivity measurement in the range of 0-50mS/cm, 0-40 ℃. A cure relationship was found between the out-put value of each standard solution measured by the sensor and the electric conductivity concentration.
7 citations
"An auto-balancing signal conditioni..." refers background in this paper
...Two electrode conductivity meters have low accuracy due to unconfined current path, polarization and contact or lead resistance [5]....
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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
"An auto-balancing signal conditioni..." refers background in this paper
...In order to solve this problem, a modified topology is reported in [15], [16]....
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5 citations
"An auto-balancing signal conditioni..." refers background in this paper
...Electrode conductivity meters can only be used to measure the conductivity of liquids with unsuspended solids and noncorrosive liquids [9]....
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10 May 2011
TL;DR: In this article, a method of fusing measurement data of a set of conductivity ring sensors to determine the average water holdup of oil-water two-phase flow within a horizontal pipeline was introduced.
Abstract: This paper introduces a method of fusing measurement data of a set of conductivity ring sensors to determine the average water holdup of oil-water two-phase flow within a horizontal pipeline. A six-ring conductivity sensor was built with 1kHz sampling rate, which delivers the generalized dimensionless conductivity and predicts the average water holdup based on Maxwell equation. An adaptive weighting algorithm is then brought forward to fuse the dimensionless conductivity and Maxwell equation to optimize the overall prediction upon average water holdup. The results suggest that the data fusion method reduces average relative error with 5.9%.
5 citations
"An auto-balancing signal conditioni..." refers background in this paper
...Thus, it will be very useful if the conductance can be measured through capacitively coupled electrodes, avoiding the direct contact of electrodes with the water [12], [13]....
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