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A new capacitance-to-digital converter (CDC) that gives a digital output proportional to the measurand kx , independent of its nominal capacitance, is reported in this paper. Various CDCs are available in the market, but their output is a function of the nominal value C_{0} of the sensor. Thus, a manual correction is required in the output, whenever a new capacitive sensor is interfaced to such CDCs. Moreover, the C_{0} of the sensors is usually a large value compared with the change in capacitance due to kx . Thus, in a typical CDC, a large percentage of the output counts/bits is used to measure and represent the C_{0} leading to an underutilization of the hardware as far as the measurement of kx is concerned. The proposed CDC uses a new automatic calibration (AC), employing a switched-capacitor (SC) circuit-based voltage source in a feedback topology, and provides an output independent of the C0 of the sensor employed. The proposed CDC is based on an SC dual-slope technique and possesses the advantages of the dual-slope conversion method. The CDC circuit is designed such that the entire full scale can be used for representing the change in the kx . In addition to this advantage, the AC helps to remove the dependence on the accuracy of the reference capacitor employed in the CDC. A detailed analysis of the effect of various sources of errors in the CDC has been conducted and presented in this paper. A prototype of the proposed CDC has been developed and tested. The results obtained show that the output of the CDC is not a function of the C0~(C0 varied from 60 pF to 1.46 nF) of the sensors interfaced. [ABSTRACT FROM AUTHOR]

Electrical capacitance tomography (ECT) attempts to image the permittivity distribution of an object by measuring the electrical capacitance between sets of electrodes placed around its periphery. Image reconstruction in ECT is a nonlinear ill-posed inverse problem, and regularization methods are needed to stabilize this inverse problem. The reconstruction of complex shapes (sharp edges) and absolute permittivity values is a more difficult task in ECT, and the commonly used regularization methods in Tikhonov minimization are unable to solve these problems. In the standard Tikhonov regularization method, the regularization matrix has a Laplacian-type structure, which encourages smoothing reconstruction. A Helmholtz-type regularization scheme has been implemented to solve the inverse problem with complicated-shape objects and the absolute permittivity values. The Helmholtz-type regularization has a wavelike property and encourages variations of permittivity. The results from experimental data demonstrate the advantage of the Helmholtz-type regularization for recovering sharp edges over the popular Laplacian-type regularization in the framework of Tikhonov minimization. Furthermore, this paper presents examples of the reconstructed absolute value permittivity map in ECT using experimental phantom data. [ABSTRACT FROM AUTHOR]

The ordinary orifice transducer widely used in process industries for flow rate measurement produces a differential pressure which is generally measured by a DP cell and thus may suffer from various problems like leakage of process fluid, corrosion of diaphragm materials, etc. In this paper, the design of a noncontact capacitance-type orifice transducer for the measurement of flow rate of a conducting liquid through a pipeline has been described. In the proposed transducer, the use of a diaphragm-type DP cell is not needed, and thus, the problems associated with DP cell are avoided. The theoretical analysis of the flow transducer is presented in this paper. The performance of the flow transducer along with that of the signal conditioner for flow of tap water through a pipeline has been tested experimentally. The experimental results are presented in this paper. A good linearity and repeatability of the sensor capacitance, transducer output, and signal conditioner output with flow rate have been observed. [ABSTRACT FROM PUBLISHER]

A microelectromechanical systems (MEMS) temperature sensor based on a cascade three-stage “bent-beam” structure is described in this paper. A suspended structure mechanically deforms in response to the change in ambient temperature, and then, a displacement is obtained; the structure is composed of three cascaded systems in order to enhance sensor sensitivity. The final conversion is made to an electrical signal that is obtained by using an interdigitated capacitor having one electrode fixed to the substrate and one electrode embedded into the moving tip of the MEMS sensor. The device has been conceived to operate passively in harsh environments where high temperatures could harm active electronic devices. The readout of the unknown temperature is therefore remotely performed by coupling the variable MEMS capacitor to a fixed inductor to compose a resonant LC circuit, which is magnetically coupled to a reader circuit placed outside the environment where the measurement takes place. The temperature to be measured is therefore first converted into a displacement that, in turn, induces a change in a capacitor value; a variation in the resonant frequency of an LC circuit is finally observed through the remote readout circuit. This paper focuses on the analytical and numerical modeling of both the temperature-to-displacement and displacement-to-capacitance conversions, on the design and fabrication of an experimental prototype, on the experimental validation where results are extensively presented and commented, and, finally, on the design of the integrated resonant device for contactless measurements. [ABSTRACT FROM PUBLISHER]

This paper describes how to calibrate four-terminal-pair (4TP) admittance standards using a new short-bar method with a modified Z-matrix expression containing a coefficient C1. The short-bar method is an effective way of measuring of a signal to the standard with better signal-to-noise ratio (S/N) for higher impedance standards, particularly 1 pF. This allows a 1-pF capacitor to be calibrated using direct measurement at frequencies reported for calibrations. As this method does not require the equivalent circuit for interpolation using measurements at frequencies beyond the reported frequencies, it can be applied to 4TP admittance calibration, where the 4TP sections have the same mechanical structure as lower impedance standards. [ABSTRACT FROM AUTHOR]

This paper describes the design of the front-end measurement circuit for a miniature electrical capacitance tomography system. This is based on a charge-transfer circuit and is implemented as a custom CMOS integrated circuit that is mounted close to the electrodes to reduce parasitic capacitance. The design has been informed by a 3-D finite-element simulation using the Ansoft Maxwell software. Simulation results suggest that, with averaging, a minimum measurable capacitance change of 100 aF (10-16F) is possible. This paper presents an analytical description of the circuit which, uniquely for such an application, is based on MOSFETs operating in weak inversion. The system has an average sensitivity of 40 mV/fF and can deliver an unprecedented 6250 measurement frames/s. The sensor comprises eight electrodes that are formed on a conical orifice, fabricated using ultrasonic drilling and a minimum diameter of 0.5 mm, through a ceramic substrate. The cross-sectional tomographic images of static objects, which are reconstructed offline, are presented. [ABSTRACT FROM AUTHOR]

A new type of calculable capacitor was initially built at the National Institute of Metrology, China, in cooperation with the National Measurement Institute, Australia. The capacitor realized the SI unit of capacitance at 1 pF, with an uncertainty of 20 parts in 10^9 . A simplified operational approach was used that avoids the complex substitution measuring process with small-value capacitors. The details of novel aspects of the installation and adjustment processes are presented, together with the experimental results and an initial uncertainty estimation. [ABSTRACT FROM PUBLISHER]

The conventional capacitance-type liquid level sensor consists of an insulated solid metallic rod electrode immersed in the liquid contained in a metallic storage tank, or two such identical electrodes in a nonmetallic storage tank. Such metallic rods may suffer from the self-inductance effect which varies nonlinearly with the level. In this paper, we present a modified capacitance-type level sensor in which effect of self-inductance of the metallic rod has been eliminated. The theoretical equations describing the operation of the sensor are derived. The sensor is designed and tested experimentally and is found to follow the theoretical equations. The experimental results are also presented. A very good linearity of the sensor is observed. [ABSTRACT FROM PUBLISHER]

This paper presents a front-end circuit with pulsewidth modulation (PWM) output for a capacitive sensor interface. A single-MOSFET-based capacitance-ratio-modulated current (CRMC) circuit is proposed to transform the sensed capacitance into a current proportional to a capacitance ratio. The proposed single-MOSFET-based CRMC circuit not only saves a lot of chip area but also lowers power consumption. Then, a dual-slope integration circuit transforms further the modulated current into PWM output. A prototype chip is designed and fabricated with a 0.35- \mu\m complementary metal–oxide–semiconductor process and has a core area of 0.09 \mm^2. The measurement results of the prototype chip demonstrate an accuracy value of up to 9.3 bit with 54- \mu\W power consumption. The microwatt power consumption and the small chip area of the proposed front-end circuit make it very suitable for a capacitive sensor interface in smart sensor chips. [ABSTRACT FROM PUBLISHER]

Recently, capacitive sensors, which consist of a sense capacitor and a reference capacitor, have been considered for a sensor array for monitoring biomolecular reactions. Although a capacitance-to-frequency converter (CFC) may be a simple and effective solution for reading a capacitive difference between the sensor capacitors, prior versions lack sufficient accuracy. In this paper, we present a more accurate CFC, which produces a single pulse stream in a wide range of frequencies. This circuit saves residual charges and accumulates them when discharging an integrator capacitor. Implemented in 0.35-\mu\m CMOS technology, our circuit improves the accuracy from about 6% to 0.13\%. [ABSTRACT FROM AUTHOR]

Loopback tests for a differential mixed-signal device under test (DUT) have rarely been attempted since any imbalance introduced by design-for-test (DfT) circuitry on differential signaling delivers an imperfect sinusoidal wave to the DUT input or output, thereby degrading the DUT performance. In addition, this methodology inherently suffers from fault masking. These problems trigger low test accuracy and serious yield loss. This paper presents a novel methodology for the efficient prediction of individual DUT dynamic performance parameters with a radio-frequency (RF) transformer in loopback mode to overcome the imbalance of DfT circuitry and the fault masking. Cascaded RF transformers with different multiplicative weights are selected in three combinations by a multiplexer to create three separate loopback responses. These responses are used to characterize the DUT dynamic performance. Hardware measurement results show that this approach can be effectively used to predict the specifications of a DUT. [ABSTRACT FROM AUTHOR]

This paper proposes a new multifunctional tactile sensor for detection of material hardness. The proposed sensor is the semielliptic structure imitating the human finger and consists of several piezoelectric ceramic transducers arranged on the surface part and a parallel plate condenser on the upper side. Capacitance values are simultaneously measured by the front electrodes of piezoelectric ceramic transducers and the parallel plate condenser. They depend on material hardness, and their values exhibit different characteristics versus the hardness. Therefore, higher detection ability is provided from two types of capacitance values. In the experiment, three kinds of materials—aluminum, acrylic resin, and silicone rubbers with four grades of hardness—were prepared. The detection of hardness was demonstrated by two types of capacitance measurements: the front electrodes and the parallel plate condenser. The results indicated that the proposed tactile sensor was useful for detection of material hardness although there are some problems that must be clearly addressed. [ABSTRACT FROM PUBLISHER]

The small inductance of an inductive transducer generally linearly changes with a process variable, but their measurement by the usual inductive bridge circuit like the Maxwell bridge, the Maxwell–Wien Bridge, the Hay bridge, etc., suffers from errors due to the effect of the stray capacitance between bridge nodal points and the ground and the stray inductance on the inductive coil, respectively. The conventional Wagner–Earth technique is not suitable for continuous measurement. In this paper, a modified operational-amplifier-based Maxwell–Wien bridge measurement technique has been proposed in which the effect of stray capacitance and inductance is minimized. In the first phase of the experiment, the bridge performance has been studied with a known variable inductor, and in the second phase, the same experimentation was done by replacing the variable inductor with an inductive coil having an adjustable core position for the measurement of displacement. The linear characteristics over a wide range of displacement with good repeatability, linearity, and variable sensitivity have been described. [ABSTRACT FROM PUBLISHER]

A novel technique for monitoring the condition of metallized polypropylene film (MPPF) capacitors installed in the dc link of railway power trains is proposed in this paper. The technique is based on the capacitance estimation of the two different capacitors used in the dc link (dc filtering and 2F filter capacitors), and it is done without adding any extra sensor or filter to the respective traction drive scheme. Therefore, the proposed method is implemented using software but not additional hardware for the different trains. Two other important passive component parameters of the traction drive are also monitored, all of them by means of curve fitting based on the least-mean-square (LMS) algorithm. The proposed technique is implemented and validated at simulation and experimental levels, using MATLAB/Simulink and a 1.2-MW traction drive test bench. Very accurate results are obtained, and the predictive maintenance of MPPF capacitors for different topologies of railway power trains can be set through the proposed technique. [ABSTRACT FROM AUTHOR]

This paper describes how to calibrate a four- terminal-pair (4TP) LCR meter at the right (90°) angle. The LCR meter uses the right angle signal to process a synchronous detector as a vector signal receiver. The right-angle calibration method uses, at a minimum, one variable-phase signal generator (SG) and a phase shift circuit. The SG does not require a precision right angle, but it does need good phase stability. The described phase shifter provides the required differential phase of nearly the right angle. As a result, the right-angle phase deviation of the LCR meter is better than 65 μrad (0.223′) with 37-μrad (0.127′) uncertainty at 10 MHz. This method is also applicable to the phase calibration of a vector network analyzer. [ABSTRACT FROM AUTHOR]

This paper presents a new realization of standards for ac-dc difference at voltages ranging from 1 to 4 V and frequencies of up to 1 MHz. This work has mainly been focused on improving the determination of the components of ac-dc difference that most significantly contributed to the uncertainty of the previous realization. These components are the ac-dc difference due to skin effect, transmission line effect, and the interaction between parasitic inductances and capacitances, which is described here as the LIC effect. As a result, combined 1 - σ uncertainties as low as 4.3 μV/V at 1 MHz have been achieved. [ABSTRACT FROM AUTHOR]

In this paper, an attempt has been made to design a low-cost noncontact capacitance-type level sensor for a conducting liquid. The sensor is in the form of a uniform circular cylinder made of insulating material like glass, ceramic, plastic, etc. The sensor is connected with the metallic- or nonmetallic-type liquid storage tank, in which the conducting liquid column is taken as one electrode, and a noninductively wound short-circuited outside coil is taken as the other electrode of a variable capacitor. The change in capacitance due to the change of liquid level is measured by a modified linear operational-amplifier-based De' Sauty bridge network with adjustable bridge sensitivity. The bridge output after amplification and rectification may be used to drive a direct current indicator calibrated in level. The studies have been made with high-density polyethylene and glass tube sensors separately in both metallic and nonmetallic storage tanks with tap water as the conducting liquid, and the experimental results of the static characteristics of the level sensors with percentage error from linearity are presented in the paper. These results are found to have good linearity and repeatability within acceptable limits. [ABSTRACT FROM AUTHOR]

Accurate measurement of the static electrical conductivity provides a great insight into the characteristics and quality status of various materials. To overcome some limitations of the traditional measurement methods, there has been a growing interest toward the investigation of enhanced techniques for measuring electrical conductivity. In this regard, time-domain reflectometry (TDR) has attracted considerable attention, also due to the possibility of simultaneously monitoring different physical parameters. Although initially introduced for monitoring soil properties, the application of the TDR-based technique might be an interesting and cost-effective means in many other fields. However, the accuracy of traditional TDR-based electrical conductivity measurements is strongly influenced by the preliminary calibration technique. On such basis, in this paper, two innovative approaches for a more straightforward and accurate evaluation of the electrical conductivity are presented. The first method relies on the combination of the TDR measurement with transmission-line modeling (TLM); the second method simply relies on a couple of independent capacitance measurements (ICMs) performed through an LCR meter. As a further goal, the metrological performance of this last method is compared with that of the traditional method, thus validating its applicability. Experimental results and related uncertainty analysis on various samples demonstrate that the proposed alternative method is definitely suitable for a simpler and accurate estimation of the static electrical conductivity, also when dealing with moistened soils. [ABSTRACT FROM AUTHOR]

A dual-slope capacitance-to-digital converter (CDC) that operates on the elements of a differential capacitive sensor and provides a digital output that is linearly proportional to the physical quantity being sensed by the sensor is presented and analyzed in this paper. The converter topology is so chosen that a linear digital output is obtained for not only a sensor possessing linear input-output characteristics but also a sensor possessing inverse characteristics. The digital output in the proposed converter is dependent only on, apart from the sensitivity of the sensor, a dc reference voltage. Hence, high accuracy and linearity are easily obtained by employing a precision dc reference. Since the proposed CDC is based on the popular dual-slope analog-to-digital converter structure, it possesses all the advantages (resolution, accuracy, and immunity to noise and component parameter variations) and limitations (requirement of auto-zero and low conversion speed) applicable to the dual-slope technique. A prototype built and tested for a typical differential capacitive sensor with a nominal capacitance value of 250 pF gave a worst-case error of less than 0.05%. [ABSTRACT FROM AUTHOR]

A new method for capacitance increase is proposed, thus allowing for capacitance standards with a sixfold higher value than those currently found in the market. The method can be used for capacitance increase in any standard and provides a solution for calibration problems of high-capacitance four-terminal meters. The increase in capacitance is based on the introduction of inductive coupling between the current and potential circuits in devices with four electrodes. The output capacitance is created by the summation of the capacitive and inductive parameters that were formed in various channels. The operating frequency range resides at the left of the resonant frequency and is separated from the resonance by a range of frequencies called "protective band." The limitations on the width of this band and the quality factor are considered in this paper and are discussed in depth. It is shown that standards should be calibrated on each operating frequency when using the proposed method. The uncertainties of the method are also analyzed, and the factors that affect the uncertainty increase are clearly indicated. Simulation and experimental results are presented to verify the proposed method and demonstrate its feasibility. [ABSTRACT FROM AUTHOR]

The liquid level in a tank should be measured for most applications. In this paper, a new capacitive method is presented to detect the liquid level. Existing methods are generally approximations based on the large difference between the dielectric constants of the liquids and the air. The method proposed here eliminates the effect of air and gives the accurate reading of the liquid level in the tank. The main advantage of the method is that it can directly be applied to any kind of nonconductive liquid without calibration. The method is based on the measurements of capacitances of three parallel plate capacitive structures, which are designated as level, reference, and air sensors. It is mathematically proven that the method completely eliminates different factors, which affect the readings, such as air and temperature. The capacitance measurements are performed using a capacitance-to-digital converter integrated circuit, which can measure very small capacitances up to ±4 fF error. The result of a computer simulation, which demonstrates the performance and limitations of the proposed structure, is also provided. [ABSTRACT FROM AUTHOR]

This paper presents a simple yet efficient seat occupancy detection scheme based on a capacitive sensing principle. Parameters such as the presence, position, and type of the occupant of the seat are essential for successful air-bag control in vehicles. Without this information, during a collision, the air bag may be inflated to an empty seat (ES), wasting it and, hence, leading to allied repair and reinstallation. Also, if deployed, it can cause fatal injuries to infants in rear-facing infant seats. The proposed capacitive sensor system detects the presence of an occupant and provides information about the occupant's position. A prototype occupancy detection system has been developed, and the feasibility of the new method has been validated through practical tests. The developed system takes 200 μs to complete a measurement and, hence, promises real-time operation of the air-bag system. The presented method employs a carrier-frequency method and lock-in-amplifier technique to measure the capacitances. Thus, the influence of external electromagnetic fields on the final result is kept low. [ABSTRACT FROM AUTHOR]

A digital converter that directly translates variations in the capacitances of a differential-type capacitive sensor to a proportional digital value is described in this paper. A conventional dual-slope, analog-to-digital converter is suitably modified to obtain direct capacitance-to-digital conversion (CDC). Analysis of the proposed technique indicates that the effects of nonidealities and variations in circuit parameters on the performance of the CDC is either in the form of a gain error and/or an offset, both of which can be easily compensated. Simulation studies and experimental results obtained from a prototype built and tested prove the efficacy of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, a monolithic complimentary metal-oxide-semiconductor (CMOS) autocompensated sensor transducer for capacitive measuring systems is newly presented. The proposed converter is compact and robust to integrate in capacitive measuring systems. The proposed autocompensated sensor transducer is attractive due to the fact that a digitized signal is produced without realizing the analog-to-digital converter. Hence, the hardware cost could be reduced. Furthermore, the output signal of the proposed transducer is a pulse stream; it could be easily sent over a wide range of transmission media, such as package switch networks (PSNs), radios, and optical, infrared (IR), and ultrasonic media. Another innovation is that the proposed automatic compensation circuits enhance and compensate the linear relation between the variable capacitance of the detected sensor and the output digital frequency over a wide dynamic frequency range. Measurement results have successfully verified the functions and the performance of the proposed autocompensated sensor transducer and confirmed that it is possible to apply it to the air pressure sensor. The area of this chip is 940 × 1080 µm², and the power consumption is 6.4 mW. The proposed transducer is not only suitable for capacitive measuring systems but also practical for application in the front-end systems of the wireless sensor network. [ABSTRACT FROM AUTHOR]

High-resolution digital voltmeters (DVMs) can be widely used when precise measurements are needed, but input circuitry can contribute to the results of measurement. Therefore, to make uncertainty of measurement as small as possible for a particular measurement, it is necessary to characterize its input parameters. In this paper, the methods for the determination of input resistance, input capacitance, and input offset current of widely used precise DVMs HP 3458A with 8 1/2-digit resolution are presented. The method with voltage source and high-ohmic divider resistor has been developed for the determination of both input offset current IS and input resistance RV. The second method with the source of the linear voltage ramp and the picoampermeter is primarily used for the determination of input capacitance CV. It was shown that the input offset current of voltmeters is in the range of picoamperes with relative instability of approximately ±0.1, the input resistance is in the range of teraohms with the same relative instability of ±0.1, and the input capacitance was measured to be in the range of a few hundred picofarads with uncertainty of a few picofarads. [ABSTRACT FROM AUTHOR]

A linear variable differential capacitive transducer for the measurement of planar angles (from 00 to 360°) is presented in this paper. The sensor part of the transducer is made of parallel plates of standard and easy-to-fabricate shapes, and the signal-conditioning electronics are realized, employing a couple of simple relaxation oscillators. The output of the transducer is only dictated by a pair of dc reference voltages, and hence, high accuracy and linearity over the entire range (from 0° to 360°) are easily obtained by the use of precision dc reference voltages. Detailed analysis indicates that the sensitivity of the transducer is minimal for variations in different parameters. Experimental results obtained on a prototype transducer that has been built and tested establish the efficacy of the proposed transducer. The worst-case error of the prototype transducer is found to be less than 0.1%. [ABSTRACT FROM AUTHOR]

An improved error analysis of an existing capacitance scaling system for supporting measurements of higher valued (10 nF to 100 μF) ceramic-dielectric four-terminal-pair (4TP) capacitance standards over the 100-Hz to 100-kHz frequency range is described. The capacitance scaling system uses a commercial impedance (inductance-capacitance-resistance) meter and a single-decade inductive voltage divider as an impedance comparator. Four-terminal-pair capacitors in decade (10: 1) steps from 10 nF to 100 F are measured. The system's 10:1 scaling error is determined using 100-pF and 1-nF air-dielectric 4TP capacitance standards with known capacitance and loss characteristics over frequency. This paper discusses the significant reductions in measurement uncertainty that were attained through the use of improved calibration standards and measurement method refinements. Details of the uncertainty analysis for a 10-nF capacitor (in the 100-Hz to 10-kHz frequency range) and verification data are presented. [ABSTRACT FROM AUTHOR]

The aim of this study is to achieve a noninvasive imaging system of the temperature patterns in the human head using temperature dependence of permittivity. The reconstruction of temperature patterns in the brain model is presented using the capacitance measurement method. In this paper, the method is improved to compensate for scarcity of data. The reconstruction of temperature rise in the cylindrical head model is demonstrated using the improved method. The spatial resolution has been improved. It has been also suggested that the detection of the temperature rise in the brain was possible by using the temperature change pattern in the skull region if the temperature at a point in the brain changes. [ABSTRACT FROM AUTHOR]

An arc-electrode capacitive sensor has been developed for quantitative characterization of permittivity of cylindrical dielectric rods. The material property of the cylindrical test piece can be inversely determined from the sensor output capacitance based on a theoretical model. For the modeling process, the electrostatic Green's function due to a point source exterior to a dielectric rod is derived. The sensor output capacitance is numerically calculated using the method of moments (MoM), in which the integral equation is set up based on the electrostatic Green's function. Numerical calculations on sensor configuration optimization are performed. Calculations also demonstrate the quantitative relationship between the sensor output capacitance and the test-piece dielectric and structural properties. Capacitance measurements on different dielectric rods with different sensor configurations have been performed to verify the validity of the numerical model. Very good agreement (to within 3%) between theoretical calculations and measurement results is observed. [ABSTRACT FROM PUBLISHER]

The design of a reconfigurable capacitive sensor array interface comprised of a subsystem able to read an array of capacitive-type sensors and an embedded processor is described. Each sensor is connected to a ring oscillator, which translates capacitive changes into a variable-frequency pulse train. An in-depth analysis of the oscillator behavior including all parasitic elements has been performed, and the use of a Schmitt trigger at the inverter chain is proposed to assure oscillation for capacitance values ranging from 1 to 1500 pF. The oscillation frequency is estimated by using a 16-b counter and the appropriate user-defined counting interval ranging from a few microseconds to several seconds in order to achieve maximum accuracy within the entire capacitance range. The 2-B word thus produced can be sent to a host computer through a serial or parallel interface for further processing. To demonstrate the concept, a 16-channel interface has been described in a hardware description language and implemented on a complex programmable logic device. Measurement of two different capacitive pressure sensors developed in-house reveals frequency sensitivity values of - 252.1 and -9.54 Hz/fF, which are in good agreement with the expected values derived by the analytic relations. [ABSTRACT FROM AUTHOR]

A new feature-based technique is introduced to solve the nonlinear forward problem (FP) of the electrical capacitance tomography with the target application of monitoring the metal fill profile in the lost foam casting process. The new technique is based on combining a linear solution to the FP and a correction factor (CF). The CF is estimated using an artificial neural network (ANN) trained using key features extracted from the metal distribution. The CF adjusts the linear solution of the FP to account for the nonlinear effects caused by the shielding effects of the metal. This approach shows promising results and avoids the curse of dimensionality through the use of features and not the actual metal distribution to train the ANN. The ANN is trained using nine features extracted from the metal distributions as input. The expected sensors readings are generated using ANSYS software. The performance of the ANN for the training and testing data was satisfactory, with an average root-mean-square error equal to 2.2%. [ABSTRACT FROM AUTHOR]

A new capacitance sensor system was developed with a microcontroller, commercial humidity and temperature sensors, a capacitance-to-digital converter, and a custom-built capacitance sensor. The performance of the system was evaluated by simulation and testing of the prototype. The impact of variations of ambient conditions on the system performance was analyzed, and a model for correcting the humidity and temperature influence was developed. Based on the experimental results obtained in an uncontrolled environment using a standard capacitor of 1 pF, the 24-h stability of the system was estimated to be within 30 parts in 106. The high stability and sensitivity of the system allow its effective use in object-detection applications. Several sensors were constructed and evaluated while sensing various materials under different scenarios. [ABSTRACT FROM AUTHOR]

Presents a study that introduced an interface circuit to measure very small-percentage capacitance variations in capacitive sensors especially suitable for industrial measurements. Principle of operation; Experimental procedure; Results and discussion.

A simple solution is presented for identifying the phase fraction and flow rate of a petroleum carrying pipeline with three-phase stratified smooth and wavy flow. The proposed method mounts a set of semicylindrical electrodes on the internal surface of the Plexiglas pipe to monitor the total capacitance and resistance of the three-phase contents. The phase fractions are determined by relating these electrical properties with the phase angles associated with the interface between water, oil, and gas phases of the mixture. To calculate the flow rate, measured capacitances from two sets of electrodes with known separation distance are cross-correlated to determine time delay. Calculated and measured results demonstrated close agreement. The percentage error exhibited by the proposed inclined capacitive plate technique is calculated and compared with published values. [ABSTRACT FROM AUTHOR]

Discusses the development of a capacitance scaling system. Features of system; Calibration performance of system; Combined standard uncertainty of system.

Similar to phase-locked loops, frequency-locked loops (FLLs) are useful in many applications involving waveform synchronization or synthesis. Simple logic circuit-based relaxation oscillators convert capacitance to frequency, which is a characteristic inverse relationship between output frequency and input capacitance. The oscillator's logic level square-wave output can be fed into an all-digital FLL that will frequency lock to the input signal and produce a digital output word N, where N is inversely proportional to the input frequency. The result is that N is linearly proportional to the unknown capacitance in the oscillator. This novel approach allows a simple FFL implementation for capacitance measurement and is demonstrated in hardware using a capacitive sensor that measures the mass of small quantities of water with an output capacitance range of 75–185 pF. [ABSTRACT FROM PUBLISHER]

An alternative approach for calibrating automated high-voltage current-comparator-based capacitance and dissipation factor bridges is presented. For the calibration, two sinusoidal currents are synthesized with two synchronized signal generators and two resistors and injected into the bridge inputs. The capacitance ratio and dissipation factor simulated by these currents are calculated from an ac voltage ratio estimated from the digitized data, together with the impedance ratio of the resistors. The approach is a refinement of another approach previously published that leads to larger uncertainties but is slightly easier to implement since the digitizers need not be synchronized to the signal generators. It is possible to simulate capacitance ratios ranging from 1: 1 to 10: 1 with relative standard uncertainties of less than 2.0 · 10-5 and dissipation factors ranging from 0 to 0.1 with standard uncertainties of less than 1 · 10-5. [ABSTRACT FROM AUTHOR]

We report on the progress and new results in the setup of the electron counting capacitance standard (ECCS) at Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany. Considerable progress has been made in the operation of the single-electron circuit and in the incorporation of a cryogenic capacitor into the millikelvin refrigerator setup. The single-electron tunneling (SET) circuit comprised a five-junction, single-electron R-pump that showed an electron retention time of more than 600 s, and the circuit was successfully used for the deterministic shuttle transfer of charge packets consisting of few electrons. In addition, the cryogenic capacitor was tested, and its performance was found to be suitable for a high-precision ECCS experiment. [ABSTRACT FROM AUTHOR]

We have measured both the 0.01 Hz (quasi-dc) and 1.0 kHz values of a 20 pF room-temperature air-gap capacitor as a function of the environment. Its dependence on pressure and temperature is found to be small, in contrast to a significant effect of relative humidity. Moreover, this humidity dependence greatly differs for the two measurement frequencies, both in sign and magnitude. This indicates that the surface layers of adsorbed water have a significant effect on the frequency dependence of the capacitance value of air-gap capacitors. [ABSTRACT FROM AUTHOR]

For the investigation of multiphase or multicomponent flows, which are of interest, for instance, in oil extraction and processing or in chemical engineering, there are only few suitable measuring techniques. For this reason, we have developed a high-speed complex permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical permittivity at a high data rate (up to 20 000 samples/s). The performance of the system, as well as its ability to differentiate organic substances, has been analyzed. A time-resolved experiment in an oil-water-gas flow, as well as a two-substance mixing experiment in a stirred tank, is presented. [ABSTRACT FROM AUTHOR]

A new four terminal-pair (4TP) coaxial-bridge system for accurate resistance measurements at frequencies up to 10 MHz has been developed. The deviation of a calculable 4TP 1-kΩ resistance standard, from its dc value, was measured to be -4380 ± 712 μΩ/Ω(2σ) at 10 MHz, which compares well with its calculated value of -4010 ± 850 μΩ/Ω. Quantitative comparisons have also been made between our measurements and calculations with measurements on a state-of-the-art 4TP high-frequency (HF) commercial impedance analyzer, highlighting significant differences for the 1-kΩ measurements at frequencies up to 10 MHz. A quadrature-bridge system, with two 100-pF capacitance and two 1-kΩ resistance standards, operating at 1.6 MHz, has also been developed which verifies the consistency of a number of HF techniques (based on the closure of the metrological impedance triangle) to 0.17%. Finally, we also extend the 4TP calculable geometry of the resistance standards to include capacitance and inductance standards (LCR), thus realizing a universal geometry for precision LCR standards with a calculable frequency-response coefficient. [ABSTRACT FROM AUTHOR]

We propose a new methodology to measure both the dielectric constant and thickness of dielectric coatings on a flat conducting substrate from two capacitance measurements. We discuss the principles of the method and demonstrate its feasibility using 2-D numerical simulations. We present a proof of principles experiment confirming the viability of the method in practice. Finally, we propose and analyze a multisphere electrode geometry. [ABSTRACT FROM AUTHOR]

A new measurement method, called SeCaP, has been used to measure the water content in oil/water dispersions. The measuring principle is based on an oscillator working at approximately 20 MHz. The dielectric property of the medium adjacent to one single free electrode affects the frequency of the oscillator. The dispersion was produced by means of recirculation through a colloid mill. The concentration of water was first increased from zero to approximately 70%. Then, it was reduced from 100% to approximately 45 %. The probe signal correlates very well with the water concentration in the dispersion, especially for the oil continuous case with a correlation coefficient of 0.9998. The instrument represents a new approach of measuring the water content in process streams in, for example, oil production facilities, where it is important to have reliable information on the amount of water that is flowing in the production tubing. [ABSTRACT FROM AUTHOR]

A full-wave numerical analysis was performed for a coaxial line terminated with a complex gap capacitance using a finite-element high-frequency structure simulator. The scattering parameters, input impedance, and spatial distribution of the electromagnetic field have been obtained in the frequency range of 100 MHz to 19 GHz for specimens 8 to 320 pm thick, with a dielectric constant of up to 80. It was found that the residual inductance of the specimen affects the impedance characteristic of the net- work. The inductanceecapacitance resonance is coupled with the cavity resonance. The specimen inductance is linearly dependent on the specimen thickness. At frequencies near the cavity resonance, the specimen section can be treated as a network of a trans- mission line with a capacitance, where the fundamental mode propagates along the diameter of the specimen. Results of the numerical analysis were verified experimentally using water as a model material with a high dielectric constant. Our closed-form formula for input impedance of the network is valid in a wider frequency range than the lumped-element method. The results are useful in improving the accuracy of broadband dielectric measurements in the extended frequency range of thin films with high dielectric constant that are of interest to bio- and nanotechnology. [ABSTRACT FROM AUTHOR]

Presents a study which developed a quantized Hall resistance-based capacitance measurement chain. Description of the measurement chain; Details of measurement equipment; Results.

Illustrates the features of the design of thin dielectric film capacitive displacement transducers (TDFCDT). Design principle; Implementation prototypes; Advantages and disadvantages.

Presents information on a study which described the noninvasive imaging system of temperature-change distribution in the human head by using capacitance measurement. Description of capacitance measurement method; Methodology; Results and discussion; Conclusions.

Presents information on a study which described a low-cost and reliable interface for capacitive sensors based on the use of a relaxation oscillator and microcontroller. Measurement concept; Electrical properties of the capacitive sensing element; Measurement results; Conclusions.

Presents information on a parameter improvement method for the multifilar winding, commonly used in inductive voltage dividers. What the method allows one to determine; Information on the procedures for measuring capacitances between pairs of individual sections and capacitances between an individual section and its shield; Details on the capacitances; What is possible by using this method.