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This paper proposes a measurement technique for telemetric systems working with passive resistive sensors from the kilohm order. It permits calculating sensor output through analytical formulas, from system parameters and the real part of system impedance measured at readout inductor’s terminals. Impedance measurement is performed always at a fixed frequency, when inductors are at a fixed relative position. Formulas were derived through specific analyses, starting from a circuit model of the system. The technique was validated by finding the output of discrete commercial resistors attached to an inductor. A difference lower than 0.98% was obtained between resistors’ values calculated through the proposed technique, and their values measured by means of an impedance analyzer. Finally, we applied the technique to a real application, i.e., temperature monitoring in an enclosed environment. We used a telemetric configuration with a Pt1000 sensor to monitor the temperature inside an oven wirelessly. The results pointed out that the technique permitted to estimate the temperature with an average difference of 2.2 °C with respect to a reference. Then, uncertainty on calculated temperature was equal to ±1.2 °C. In general, work analyses highlight that measuring impedance real part may be preferred than measuring its phase angle. These achievements show the feasibility of estimating the output of a resistive sensor through the proposed technique. [ABSTRACT FROM AUTHOR]

Grid-connected wind turbines (WTs) are required to have low-voltage ride-through (LVRT) capability. On-site LVRT test is a convincing certificating method. To tackle the limited accessibility and harsh conditions of on-site test for offshore WTs, this paper proposes a remote testing method, which places the testing device on shore to produce the specified fault voltages through a subsea cable to the WT. For further eliminating the effects of introduced cable on LVRT test, a stepwise voltage sag generation strategy is applied to suppress the overvoltage and maintain required voltage sags. First, the LVRT testing requirements and voltage sag specification need to be considered in a practical test are introduced. The stepwise generation strategy and its implementation procedure based on the designed testing device are presented. Second, the effects of submarine cable on the WT-side voltage are analyzed under different generation stages of voltage sags. Next, the testing device’s impedance configuration method, based on the derived residual voltage expression, is given to generate the required steady-state voltage sags. Finally, simulation results indicate that with the proposed method, the effects of cable can be eliminated and the required grid faults can be emulated for remote LVRT test. [ABSTRACT FROM AUTHOR]

The availability of real-time information about the biological activity is a valuable matter in wastewater treatment employing activated sludge processes, and this is represented by the oxygen uptake rate (OUR). In these processes, OUR measurements have been used as a fast indicator of changes in waste load or influx of toxic organic compounds and for monitoring of the process efficiency. In this paper, we propose a method for OUR estimation by using Kalman filters and PWM control of the dissolved oxygen (DO) concentration in the activated sludge reactor. The proposed method presents a shorter response time than the standard online procedure and a lower measurement uncertainty compared to a previous feedback control method, which estimates the OUR from values of the applied control signal and the DO concentration measurements. Simulations are presented to illustrate the method and experiments are performed in a bench scale activated sludge reactor to show the applicability of the proposed estimator in a real system. The results confirm the fast response of the proposed method and its consistency with respect to the standard procedure for OUR computation. [ABSTRACT FROM AUTHOR]

The electrical arc occurring in the sliding contact between the supply contact line and the current collector (pantograph) of an electrical locomotive is a fast transient phenomenon able to degrade progressively the line-to-pantograph contact quality and, consequently, the continuity of operation. In order to increase the energy efficiency of the railway system, an inexpensive solution is constituted by the detection of the arc event by the analysis of voltage and current measurements already available on-board train. An essential activity to reach this objective is to set up a reliable electrical model of the railway system in which the arc events originate. To this end, this paper presents a combination of experimental and simulation analysis for the development of an electrical model of a direct current (dc) 3 kV railway system, which is aimed at better understanding the propagation of conducted effects generated by arc events. First, a laboratory experimental activity is carried out to investigate the electrical dynamic characteristics of the arc in a controlled environment. Then, a model of the dc railway system is derived and validated by using the experimental data collected in a measurement campaign on-board train. Finally, a sensitivity analysis of the main model parameters is carried out. [ABSTRACT FROM AUTHOR]

In this paper, a resolution enhancement method for direct interfacing of inductive sensors, without employing analog-to-digital converter and/or external driver circuit, is presented. In order to achieve better resolution with minimum relative error and current consumption factors, different schemes are implemented which vary in terms of: 1) step-input voltage provision methodology, i.e., through microcontroller ($\mu \text{C}$) pin or through external supply; 2) number of switches used; and 3) method of voltage detection, i.e., either using capture module or employing built-in comparator only. The maximum achievable resolution limits are explored by reducing the lower reference voltage ($\text{V}_{\mathrm {Ref L}}$) in case of detection through built-in analog comparator and/or reducing the series resistance. The one-point calibration technique is used to determine the accuracy. The experiments are performed at 16-MHz clock frequency in the inductance range of: 1) 10–100 $\mu \text{H}$ and 2) 100–1000 $\mu \text{H}$. The results show that in the limits of a maximum current sourcing/sinking capacity of a typical $\mu \text{C}$ , i.e., 40 mA, the proposed methodology enhances the resolution to $4~\mu \text{H}$ with a relative error of 1.2 in the percentage of full-scale span (%FSS). The maximum nonlinearity error in %FSS for inductance range 10–100 $\mu \text{H}$ and 100–1000 $\mu \text{H}$ is 1.1% and <0.4%, respectively. [ABSTRACT FROM AUTHOR]

Based on a capacitively coupled contactless conductivity detection ( \C^4\D) technique, a new method for the online flow pattern identification of gas–liquid two-phase flow is proposed. This paper includes two parts: First, a new \C^4\D sensor (the single-shield \C^4\D sensor), which is suitable for the parameter measurement of gas–liquid two-phase flow, is developed, and second, with the developed single-shield \C^4\D sensor, the flow pattern identification of gas–liquid two-phase flow is studied by combining the wavelet analysis technique and the support vector machine technique. The experimental results show that the developed single-shield \C^4\D sensor is successful. It has the advantages of low cost, simpler construction, better stability, and better measurement performance. The experimental results also indicate that the proposed flow pattern identification method is effective, and the identification accuracy results are satisfactory. In five different pipes (the inner diameters are 1.8, 2.8, 4, 6.1, and 7.8 mm, respectively), the identification accuracy results for typical flow patterns (stratified, wavy, bubbly, slug, and annular flow) are all above 91%. This paper verifies that \C^4\D is a promising technique for flow pattern identification of gas–liquid two-phase flow, and it may have a broad perspective in related industrial field. [ABSTRACT FROM AUTHOR]

This paper presents an effective approach to the fault diagnosis of pulsewidth modulated (PWM) DC–DC power converters. It is based on a multilayer multivalued neuron neural network with a complex QR decomposition. This network is used to identify the parameter values running out of tolerance range in two topologies of PWM DC–DC converters, namely, the buck and boost circuits. The proposed technique is based on measurements of steady-state voltages and currents waveforms. [ABSTRACT FROM AUTHOR]

Power usage reduction and efficiency enhancement of measurement devices are a major challenge in self-powered wireless sensor nodes and also sensors implanted in the human body. Such instruments should be usually operated using the limited environmental energy resources. Electrochemical sensors and potentiostats are extensively used in this context for the measurement of chemical components. In these cases, a lot of research has focused on internal processing blocks power reduction of the potentiostat circuit. In this paper, a discrete current mode (DCM) switching potentiostat is presented, which can significantly reduce the static power usage at the output stage of the potentiostat compared with linear output stage counterparts. Using time-domain analyses, the unexpected oscillatory behavior of a continuous current mode (CCM) output stage switching potentiostat is investigated. Consecutively, it is shown that in current fabrication processes, this configuration will consume more power than the DCM topology. The correctness of the designs and analyses are shown using both simulation and experimental results. The simulated 0.18- $\mu \text{m}$ CMOS DCM output stage potentiostat has an efficiency of 95% at an output load of $12~\mu \text{A}$ , while the long-channel MOSFET-based prototype implementation shows an efficiency of 64%. [ABSTRACT FROM AUTHOR]

With the wide application of the high-speed electrical machine with the active magnetic bearings (AMBs), improving the dynamic response and the resolution of the displacement sensor for AMBs becomes an actual challenge for industrial development. This paper proposes a self-differential eddy current displacement sensor (ECDS) for radial AMBs system. The phase advance network method was utilized to improve the dynamic characteristic for the sensor based on the equivalent transfer function model. The reason of the sensor-to-sensor crosstalk was analyzed in detail to provide a theoretical basis for improving the resolution of the sensor. First, the operating principle of the ECDS was analyzed in detail. Second, the miniaturization design was presented: the two symmetrical probe coils were used as the working inductors in the Hartley oscillation circuit to form a self-differential structure to simplify the measuring circuit observably, and suppress the common mode interference. Third, the dynamic characteristic of the sensor and the sensor-to-sensor crosstalk was described and compensated. Finally, a series of experiments was carried out to test the sensor performance. The experimental results showed that the ECDS with the features of the minimum circuit, the wide bandwidth, and the high resolution can greatly improve the controllability of the AMBs system. [ABSTRACT FROM AUTHOR]

A new, simple, and high accuracy dual slope inductance-to-digital converter (DSIDC) suitable for differential reluctance sensors is presented in this paper. Differential reluctance sensors have two inductors that vary in a push–pull manner with respect to measurand. In many such sensors, the relationship between inductance and measurand is nonlinear. It is known that a small linear range can be obtained by taking the difference between the values of the sensor inductances. The proposed DSIDC accepts the sensor inductances having nonlinear characteristics and provides a linear digital output directly proportional to the measurand [without employing a dedicated analog-to-digital converter (ADC)]. The output of the DSIDC is linear for the full range of the sensor. As the output is in digital form, it can be easily stored and processed in a digital system. The DSIDC is based on dual-slope ADC principle and possesses many advantages. The effect of various parameters on the performance of the DSIDC was analyzed, quantified, and presented in this paper. A prototype DSIDC has been built and tested with a differential variable reluctance based displacement transducer. Output from the DSIDC was linear for the full range of input. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a transceiver architecture for wireless on-wafer test systems. To obtain a compact transceiver, the dc–ac converter, an essential component in typical wireless power transfer (WPT) systems, is removed. Instead of the converter, the output power of the oscillator is used as the transmitted power in the transmitter. To reduce the number of required inductors in the transceiver and, hence, the chip size, the inductor of the cross-coupled oscillator is used as the transmitter coil. Consequently, the proposed transceiver becomes sufficiently simple and compact to be applied to wireless on-wafer test systems. To verify the feasibility of the proposed topology, we designed the proposed transceiver using the 180-nm RFCMOS technology. From the measurement results of various designed transmitters and receivers, we obtain a maximum efficiency of 37% when the transmitter power is approximately 11.5 dBm. From the measured results, we successfully prove the feasibility of the proposed transceiver for wireless on-wafer test systems. [ABSTRACT FROM AUTHOR]

Strain monitoring allows obtaining critical information regarding the conditions of several systems. It would help, for example, to avoid possible structural damages. However, not all the existing devices are suitable to accomplish this task for a great number of applications, because of the characteristics of measurement environment, which prevent the use of batteries or wired connections. The use of telemetric devices may overcome these limitations, since they rely on the magnetic coupling between two inductors for wireless sensor supply and data transmission. The work treated in this paper presents a technique that permits us to calculate the output of a resistive strain gauge from a measurement of system impedance phase performed at a specific frequency, when distance between the inductors is fixed. We validated the method using a real device working with a low-cost sensor fabricated through inkjet-printing technology on a flexible substrate. We applied successive deformations, until 1% of sensor length at rest position. Calculated strain presents a percentage deviation from measured values going from 0.7% to 7%, whereas the highest uncertainty is 0.02% of sensor length at rest. Experimental results put in evidence, on one hand, the potential of inkjet printing to fabricate valid sensing elements and, on the other hand, that the proposed approach is successful in strain estimation. [ABSTRACT FROM AUTHOR]

High-temperature measurement systems do not allow the use of traditional measurement techniques. In the presence of high temperatures, the proper functioning of electronics is compromised. Furthermore, if the measurement environment is also hermetic, the traditional cabled measurement technique cannot be adopted. In this paper, a system composed by a passive sensor placed in the harsh environment and a dedicated readout electronics placed outside in a safe zone is designed and proposed for measuring the temperature up to 330 ^\circ\C. The sensing element is based on a hybrid sensor constituted solely by passive components (an inductor connected to a planar micromachined variable capacitor). The hybrid sensor can be placed inside high-temperature and hermetic measuring environment, while the temperature data can be measured telemetrically by an external reading unit, located in the safe environment. In this paper, the system is presented using novel electronic circuits of the readout unit, which permit to avoid the need of an expensive commercial impedance analyzer. The wireless measurement electronics was designed and characterized; the results obtained and reported in this paper are quite in good agreement with those measured by a reference commercial impedance analyzer. The complete measurement system is presented as a viable solution to the measurement of high temperatures in harsh or enclosed industrial environments. [ABSTRACT FROM PUBLISHER]

This paper presents a handheld robust battery-operated contact-based ovality meter suitable for the measurement of ovality in pipeline in a plant site or in any industrial establishment. The ovality meter is mainly composed of a specially designed inductor with ferrite core. This inductor constitutes the part of an $LC$ -type logic gate oscillator (LGO). A change in the sensor position during the measurement of pipe diameter causes a small change in inductance, which in turn changes the pulse frequency of the LGO when it is powered by 5 V dc. Thus, frequency, the output of the instrument that is displayed on the liquid crystal display of the embedded processor, is a function of displacement. By measuring the diameter of pipe specimen at different locations, the ovality is computed. In the present design, the range of position measurement is about 25 mm. The sensitivity in position measurement up to 10 mm is $\sim 850$ Hz/mm, which further reduces in higher range (>10 to 25 mm). Such a sensitivity in the position measurement seems to be quite suitable for ovality measurement. [ABSTRACT FROM PUBLISHER]

The modulated scatterer technique (MST) has shown promise for applications in microwave imaging, electric field mapping, and materials characterization. Traditionally, MST scatterers are dipoles centrally loaded with an element capable of modulation (e.g., a p-i-n diode). By modulating the load element, signals scattered from the MST scatterer are also modulated. However, due to the small size of such scatterers, it can be difficult to reliably detect the modulated signal. Increasing the modulation depth (MD; a parameter related to how well the scatterer modulates the scattered signal) may improve the detectability of the scattered signal. In an effort to improve the MD, the concept of electrically invisible antennas is applied to the design of MST scatterers. This paper presents simulations and measurements of MST scatterers that have been designed to be electrically invisible during the reverse bias state of the modulated element (a p-i-n diode in this case), while producing detectable scattering during the forward bias state (i.e., operate in an electrically visible state). The results using the new design show significant improvement to the MD of the scattered signal as compared with a traditional MST scatterer (i.e., dipole centrally loaded with a p-i-n diode). [ABSTRACT FROM PUBLISHER]

The gallium nitride transistors suffer from current collapse effect in operation regions, which leads the dynamic ON-resistance to increase when high voltage is applied to the transistor. Dynamic ON-resistance under practical application conditions is also an important factor for the reliability and conduction efficiency of transistors. To measure the dynamic ON-resistance and evaluate the current collapse effect, a softswitching circuit based on synchronous buck topology is proposed in this paper. To apply high-voltage and high-current stresses to the device without additional spikes and oscillation, resonance technique has been employed. As a result, the proposed circuit could produce sufficient power stresses to the devices with general equipment. To achieve accurate measurement of ON-resistance under switching operations and eliminate the saturation of oscilloscope probes, an active voltage clamp circuit is developed. Operation principles and design analysis of the circuit are described in this paper. The dynamic ON-resistance measurement method is illustrated in detail. Furthermore, a prototype circuit has been built. A simulation and experiments were carried out to verify the performance of the system. A comparison of the active clamp circuit with common voltage probes is presented through the measurement results. The experimental results confirm that dynamic ON-resistance can be accurately measured using the proposed circuit and the current collapse effect can be evaluated under practical operation conditions with high precision. [ABSTRACT FROM PUBLISHER]

This paper presents a low cost precise and reliable inductive absolute position measurement system. It is suitable for rough industrial environments, offers a high inherent resolution (0.1%–0.01% of measurement range), can measure target position over a wide measurement range, and can potentially measure multiple target locations simultaneously. The basic position resolution is improved by adding two additional finer pitched receive channels. The sensor works on principles similar to contactless resolvers. It consists of a rectangular antenna printed circuit board and a passive LC resonant circuit. A mathematical model and the equivalent circuit of this kind of sensor are explained in detail. Such sensors suffer from transmitter to receiver coil capacitive crosstalk, which results in a phase sensitive offset. This crosstalk will be analyzed by measurements. Moreover, the mechanical transducer arrangement, the measurement setup, and the measured results will be presented. [ABSTRACT FROM PUBLISHER]

Since electrolytic capacitors are primarily responsible for breakdowns in power electronics converters and have the trait of high failure rate, their reliability is a tremendous concern. Consequently, an appropriate monitoring as well as fault diagnosis system should be laid emphasis on. In this paper, an original and accurate online scheme applied to estimate the output capacitor of the flyback converter is put forward. By analyzing the voltage ripple of the output electrolytic capacitor in detail, an online mathematical model for the equivalent series resistance (ESR) and capacitance (C) is derived. A trigger circuit and an isolated amplification circuit are designed to catch the output voltage ripple values at certain instants of switching cycle, which are sent to digital signal processor for the calculation of ESR and C. The proposed scheme is noninvasive as no extra current sensor is needed. In order to verify the feasibility of the scheme, a prototype of the online monitoring system is built and experiments are conducted. [ABSTRACT FROM AUTHOR]

Characterization and modeling of high-value inductors (hundreds to thousands of henrys) are complex problems, exacerbated when working in the extremely low frequency (ELF) range. This paper details the measurement and characterization of inductors using a vector network analyzer that has a bottom operating frequency of 5 Hz. Using this device, we establish a strategy for measuring the impedance of high-inductance coils—with or without a high-permeability core—and propose a mathematical model that can explain the behavior of these high-inductance coils, which incorporate long lengths of winding wire, as a function of working frequency. These inductors were constructed as part of a research project on ELF electromagnetic fields. The importance of making a complete characterization derives from the need to exploit the largest possible amount of energy captured by the coil, which acts as a sensor. We propose a mixed model of concentrated and distributed parameters that fits the experimental results with an error of about 2% for the frequency range of 5–500 Hz, as part of the characterization process. The effects of the magnetic core on inductance and winding resistance, as a function of frequency, have been characterized in terms of concentration of the magnetic field. [ABSTRACT FROM PUBLISHER]

This paper describes a new method to determine the phase angle errors of ac shunts by measuring the inductance and distributed capacitance. A 1-\Omega shunt of coaxial design has been developed as the time constant standard. A coaxial inductor with identical structure as the time constant standard has been developed. A four-terminal mutual inductor has also been built for the measurement of the inductance of the time constant standard. The method is based on the use of a binary inductive current divider to compare the inductor with the mutual inductor. The standard uncertainty of the inductance measurement of the time constant standard is within 28 pH at frequencies up to 200 kHz. The expanded uncertainty of the phase angle errors is from 0.4 \mu\rad at 1 kHz to 80.0 \mu\rad at 200 kHz at 1 A. [ABSTRACT FROM PUBLISHER]

This paper presents a simple yet effective method to determine the electrical model parameters of the dielectric barrier discharge (DBD) ozone chamber at frequencies above 20 kHz. The method is an alternative to the conventional Lissajous plot estimation method which appears to yield unsatisfactory results in this frequency range. Furthermore, the proposed technique allows for the chamber parameters to be determined at different frequencies—a flexibility which is not easily achievable using the typical Lissajous method. The measurement setup consists of a full-bridge inverter and a high-frequency variable inductor connected to the DBD chamber. The inductor can be adjusted to allow for parameter determination at different frequencies. The chamber parameters obtained from experimental results are validated by applying them in a high-voltage power supply for ozone generator. [ABSTRACT FROM AUTHOR]

This paper deals with the concepts of reactive power and reactive current in a nonsinusoidal periodic situation. It is shown that there exists a close relationship between the definitions proposed by Budeanu, Tenti, and Kusters and Moore. A new result is derived associated with the well-known Budeanu reactive power concept. [ABSTRACT FROM PUBLISHER]

For 40 years, it has been known that a four-terminal- pair (4TP) definition achieves the highest accuracy in impedance measurement. While, for ac resistors and capacitors, a 4TP standard definition is commonplace, and 4TP commercial measurement systems are available on the market, for inductors, a two- or three-terminal definition is still the most common. This paper describes the first international intercomparison of inductance performed with 4TP measurement systems and a 4TP travelling standard. At the Istituto Nazionale di Ricerca Metrologica (INRIM), the measurement system is based on a 4TP implementation of the three-voltage method, and traceability is to calibrated ac resistors. At Czech Technical University (CTU), Prague, a 4TP double-balance transformer bridge is employed, and traceability is via calibrated capacitors, ac resistance, and ac resistance ratio. The comparison has been performed in the context of EUROMET Project 607, with a 4TP l00-mH temperature-controlled travelling standard constructed for the purpose. Despite the big differences in the measurement methods and traceability chains, the measurements reported by INRIM and CTU are fully compatible, within their relative expanded uncertainties of 7 x 10-6 and 6.2 x 10-5, respectively. [ABSTRACT FROM AUTHOR]

This article aims at providing a better behavior understanding and performance evaluation of a large-size passive on-chip tapped transformer when used as a transducer in low-frequency integrated microsystems [30–300 kHz]. Thus, a CMOS-based 1:1 transformer, consisting of 70 turns of 1.6-μm-wide top-level metal spaced by 0.6 μm and with a total length of 1.7 mm, has been investigated and tested. The spatial separation between the two transformer windings was set to 70 μm. An electrical equivalent lumped model has been extracted through an exhaustive specific measurement procedure. The model is useful to simulate and evaluate the voltage transformation ratio (TR) between the two transformer windings. The effects of parasitics and imperfect coupling between transformer windings and through the silicon substrate are outlined from the circuit point of view. We report a magnetic coupling coefficient that does not exceed k = 0.15, with a voltage TR of about 0.39 around the resonance frequency of ~5.3 MHz, when the secondary is unloaded. It has been proven that the interwindings capacitance introduced by close conductors of each winding, evaluated to 13 pF, assures the most important role in the power transfer. This article has shown that by optimizing properly the transformer realization and limiting some parasitics elements, the inductive and capacitive links could both play a key role in MEMS transducers through tapped transformers operation around 100-kHz frequencies. [ABSTRACT FROM AUTHOR]

This article aims at providing a better behavior understanding and performance evaluation of a large-size passive on-chip tapped transformer when used as a transducer in low-frequency integrated microsystems [30–300 kHz]. Thus, a CMOS-based 1:1 transformer, consisting of 70 turns of 1.6- $\mu \text{m}$ -wide top-level metal spaced by 0.6 $\mu \text{m}$ and with a total length of 1.7 mm, has been investigated and tested. The spatial separation between the two transformer windings was set to 70 $\mu \text{m}$. An electrical equivalent lumped model has been extracted through an exhaustive specific measurement procedure. The model is useful to simulate and evaluate the voltage transformation ratio (TR) between the two transformer windings. The effects of parasitics and imperfect coupling between transformer windings and through the silicon substrate are outlined from the circuit point of view. We report a magnetic coupling coefficient that does not exceed $k=0.15$ , with a voltage TR of about 0.39 around the resonance frequency of ~5.3 MHz, when the secondary is unloaded. It has been proven that the interwindings capacitance introduced by close conductors of each winding, evaluated to 13 pF, assures the most important role in the power transfer. This article has shown that by optimizing properly the transformer realization and limiting some parasitics elements, the inductive and capacitive links could both play a key role in MEMS transducers through tapped transformers operation around 100-kHz frequencies. [ABSTRACT FROM AUTHOR]

An overview of the development and performance of a special high precision multi-ratio three-stage CT and its application for loss measurements of EHV three-phase shunt reactors with test voltages up to a phase voltage of 1100 kV at Royal SMIT Transformers are presented and discussed. It features current ratios of 500 A/1 A, 400 A/1 A, 300 A/1 A, 200 A/1 A, and 100 A/1 A with ratio errors within $3 \times 10 ^{-6}$ in both magnitude and phase with burdens up to $1.0~\Omega $ and at power frequencies of 50–60 Hz. [ABSTRACT FROM AUTHOR]

Standards with toroidal windings are traditionally used for international comparisons of inductance. The achieved uncertainties of the comparisons are dominated by the rather high temperature coefficient of the traveling standards. Hence, thermoregulated enclosures were developed at Physikalisch- Technische Bundesanstalt (PTB) a few years ago. These have now been refined and their suitability for the transportation of standards has been proven in a bilateral comparison between PTB and VTT Technical Research Centre of Finland Ltd. The agreement was excellent, while the overall uncertainty of the comparison varied from 14 to 62μH/H in the frequency range 100 Hz–2 kHz. [ABSTRACT FROM AUTHOR]

A passive embeddable coupled coil sensor for remote bioprocess pH monitoring is described. The sensor is sterilizable, able to operate in a fluid medium, and small enough to fit inside a small bioreactor or test tube. It consists of a planar spiral inductor connected parallel to a varactor forming an LC resonant circuit. A pH combination electrode made of an iridium/iridium oxide sensing electrode and a silver/silver chloride reference electrode is connected parallel to the varactor. A potential difference change across the electrodes due to pH variation of the medium changes the voltage-dependent capacitance and shifts the resonant frequency of the sensor. An interrogator coil is inductively coupled to the sensor coil and remotely tracks the resonant frequency of the sensor. For in-fluid monitoring, the sensor is encapsulated in a manner that reduces the influence of the permittivity and conductivity of the medium. The sensor, calibrated over 2–12 pH range, exhibits a rapid response with 2.477-MHz/pH sensitivity. The sensor was used for remote pH monitoring of Yarrowia lipolytica and Saccharomyces cerevisiae fermentation in a shake flask over 63 and 25 h, respectively. The experiments demonstrate that the medium pH can be monitored repeatedly with an accuracy of 0.08 pH. [ABSTRACT FROM PUBLISHER]

The precise dc-based measurement of the mutual inductance is one of the key issues in the Joule Balance method used to determine Planck's constant h. Here, a new compensation method with a standard square wave is provided. The dc value of the mutual inductance is obtained by measuring the integral area of the induced voltage. To increase the accuracy of this integral method, we just accurately measure the residual area observed between the induced voltage of the mutual inductor and a synchronously generated standard square wave. Experimental results indicate that this approach is consistent with the previous frequency extrapolation method within 1 ppm. The measurement uncertainty is estimated to be about 0.22 \mu\H/H for the 340-mH mutual inductor at room temperature. A better result of 0.1 ppm could be obtained when the superconducting coil is used. [ABSTRACT FROM PUBLISHER]

The precise measurement of Planck constant h to establish a kind of quantum mass standard is an important but very difficult work. The Joule Balance method, for the same purpose but different from Watt Balance method, has been going on at the National Institute of Metrology for three years. All the measurements were carried out in the atmosphere of an air-conditioned room. The uncertainty is several parts in 10^4 (k=1) and expected to be improved when superconducting coils and other approaches are used further. The principle and progress are described here. [ABSTRACT FROM AUTHOR]

Traditionally, the most precise way to get the mutual inductance value is by a Campbell calculable mutual inductor. Here, an approach of measuring the mutual inductance at low frequency with compensation method is described. A multi-channel direct digital frequency synthesis source is developed to provide stable and precise phase. The mutual inductance is traced to the value of the frequency and resistance directly. The measurement uncertainty is 0.43 ppm at present and could be improved further. [ABSTRACT FROM AUTHOR]

Superconducting inductive and capacitive components seem to be very appealing for many high-precision measurements because of their reduced dissipation. Some tests made at Istituto Nazionale di Ricerca Metrologica have proved the possibility of building inductors with quality factor higher than several thousand in the acoustic frequency band using copper clad Nb-Ti wires. However, the best performances have been obtained with pure Nb wire, in spite of some connection problems. [ABSTRACT FROM AUTHOR]