K. K. Tejaswini

Bio: K. K. Tejaswini is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Capacitive sensing & Capacitor. The author has an hindex of 3, co-authored 4 publications receiving 18 citations.

A Capacitive-Coupled Noncontact Probe for the Measurement of Conductivity of Liquids

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.

Conductivity Measurement Using Non-Contact Potential Electrodes and a Guard Ring

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.

An auto-balancing signal conditioning scheme for non-contact measurement of conductivity 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.

Inductive-Capacitive Coupled Probe for Non-Contact Measurement of Liquid Conductivity

Abstract: This paper presents a non-contact inductive and capacitive coupled method of measurement of conductivity of liquids. The current through a pre-set column of liquid is established through induction. The voltage drop across the preset column of liquid is measured through capacitive coupled electrodes. The absence of contacting electrodes ensures that the method is free from effects due to contamination / corrosion of electrodes. The method proposed ensures that the measurement of the voltage drop across the column is independent of the values of the coupling capacitances of the capacitive coupled electrode. Hence, any deviation in the fabrication of the probe has negligible influence on the measured conductivity. Results obtained from a prototype unit built and tested show that the maximum relative error in the conductivity measurement is $ and the measured conductivity values are independent of the values of the coupling capacitors.

An Impedimetric Cu-Polymer Sensor-Based Conductivity Meter for Precision Agriculture and Aquaculture Applications

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.

A Capacitive-Coupled Noncontact Probe for the Measurement of Conductivity of Liquids

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.

A self-adaptive and wide-range conductivity measurement method based on planar interdigital electrode array

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.

Analysis of a Direct Microcontroller Interface for Capacitively Coupled Resistive Sensors

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.

Low-noise electric field sensor

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.