A Capacitance-to-Digital Converter with Sinusoidal Excitation Suitable for Series RC Sensors
15 Feb 2020-International Journal on Smart Sensing and Intelligent Systems (Exeley Inc.)-Vol. 7, Iss: 5, pp 1-5
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.
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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
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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.
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14 May 2018
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.
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Cites background from "A Capacitance-to-Digital Converter ..."
...In order to solve this problem, a modified topology is reported in [15], [16]....
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References
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40,330 citations
"A Capacitance-to-Digital Converter ..." refers background in this paper
...There are measurement circuits [1], [7] that determine the capacitance value of the sensor in the RC series model....
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01 Jan 2015
12,972 citations
"A Capacitance-to-Digital Converter ..." refers background or methods in this paper
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TL;DR: A simple and efficient seat occupancy detector that combines inductive and capacitive proximity sensing principles and successfully senses human proximity and distinguishes it from other conductive objects is presented.
Abstract: This paper presents a simple and efficient seat occupancy detector. A seat occupancy detector is an integral part of the airbag safety system and, in its simplest form, provides the (occupied or vacant) status of the seat to the airbag control unit. Although the occupancy sensing methods based on a capacitive principle are efficient, they typically require electrodes to be placed in the surface layer of the sitting and backrest areas of the seat. The proposed sensor uses a simple electrode structure, and it is placed below the seat foam in the sitting area of the seat. These features promise a less-expensive sensor as it can be easily manufactured and installed in a seat. The new sensor combines inductive and capacitive proximity sensing principles. The sensor detects the presence of an occupant exploiting the shielding effect of the electric field while its inductive proximity feature senses the presence of conductive objects (e.g., laptop) that may be placed in the seat and helps to achieve reliable occupancy sensing. The measurement system uses a signal conditioning unit based on a carrier frequency principle. A prototype sensing system has been built, and its application as a seat occupancy sensing system in a vehicle has been verified. The developed system successfully senses human proximity and distinguishes it from other conductive objects.
100 citations
"A Capacitance-to-Digital Converter ..." refers background in this paper
...Moreover, in many applications, a sinusoidal excitation is preferred in the measurement of capacitance of the sensors [4], [8], [9]....
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TL;DR: In this article, a capacitive humidity sensor with a porous silicon (PS) dielectric and electronics is presented, where the adsorption of water vapor by the PS layer leading to change of its effective Dielectric constant is modeled with an effective medium approximation (EMA).
Abstract: A novel hygrometer is presented, comprising a capacitive humidity sensor with a porous silicon (PS) dielectric and electronics. The adsorption of water vapor by the PS layer leading to change of its effective dielectric constant is modeled with an effective medium approximation (EMA). A simple, but precise, phase-sensitive electronic circuit has been developed. This detects any change of phase of a sinusoidal signal transmitted through the PS dielectric and correlates to ambient humidity. It is outlined how the nonlinear response of the sensor is compensated through piecewise linearization. The sensor is tested in combination with the phase detection circuitry. Excellent linearity over the entire range of relative humidity is achieved. Experimental results show a resolution better than 0.1% and an accuracy of 2% (near the transition region) and better than 0.1% (otherwise). The response time is less than 10 s with good stability.
47 citations
"A Capacitance-to-Digital Converter ..." refers background or methods in this paper
...Moreover, in many applications, a sinusoidal excitation is preferred in the measurement of capacitance of the sensors [4], [8], [9]....
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...This model is a representation for capacitive sensors used in applications such as humidity sensing [4], flow measurement, etc....
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01 Jan 1996
TL;DR: In this article, the authors proposed a low noise and gain-flattened Er3+-doped fiber amplifier (EDFA) with a cascade configuration for wavelength division multiplexing (WDM) signals.
Abstract: We propose a novel low noise and gain-flattened Er3+-doped fiber amplifier (EDFA) with a cascade configuration for wavelength division multiplexing (WDM) signals. In this configuration, a 1480-nm pumped fluoride-based EDFA is joined to a 980-nm pumped silica-based EDFA through an optical isolator. By adjusting the silica-based Er3+-doped fiber length in the silica-based EDFA, we realized an excellent flat gain EDFA with a gain excursion of less than 0.9 dB and noise figure of 5.7 zt 0.2 dB, and a low noise EDFA with a noise figure of 5 f 0.2 dB and a gain excursion of less than 1.4 dB, for 8 channel WDM signal in the 1532-1560-nm wavelength region.
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Additional excerpts
...A similar strategy is reported in [13] to provide bias current to an opamp....
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