Differential Current Measurement Research Articles

Buck Converter Current Measurement Using Differential Amplifier

The accuracy of the measured current is a preeminent parameter for Current Control based Power Converter applications to ensure genuine operation of the designed converter. The current measurement accuracy can be affected by several parameters which includes the type of technology used, components used for the selected technology, aging, usage, operating and environmental conditions. The effect of gain resistors and their manufacturing tolerances on differential amplifier-based buck converter current measurement is investigated in this work. The analysis mainly focused on the output voltage variation and its accuracy with respect to the change in gain resistance tolerances. The gain resistors with 5%, 1%, 0.5% and 0.1% manufacturing tolerances taken for the worst-case analysis and the calculated performance results are compared and verified with the simulation results. The Operational amplifiers (Op-Amp) for high frequency power converter applications must operate in a high frequency noise environment and the intended current measuring system must manage common mode noise disturbances paired with the signal to be measured. Based on the Common Mode Rejection Ratio (CMRR) the common mode voltages and noise signals will effectively get filtered out. Lesser CMRR results in lower common mode signal rejection, resulting in poor precision and noise rejection. In differential amplifiers, the CMRR predominantly depends on gain resistors. So, the variations in Common Mode Rejection Ratio due to gain resistor tolerances also analyzed and compared with the output voltage variations. Besides the effects of resistor tolerances, this paper also examines the effect of Op-Amp offset voltage on output accuracy specifically for low magnitude input currents. The obtained results from this analysis clearly shows that the gain resistors with 0.1% tolerance gives maximum accuracy with improved CMRR and accuracy at low magnitude input currents will get well improved by using Op-Amps with Low Offset voltage specifications.

Unsupervised Machine Learning for Missing Clamp Detection from an In-Service Train Using Differential Eddy Current Sensor

The rail fastening system plays a crucial role in railway tracks as it ensures operational safety by fixing the rail on to the sleeper. Early detection of rail fastener system defects is crucial to ensure track safety and to enable maintenance optimization. Fastener inspections are normally conducted either manually by trained maintenance personnel or by using automated 2-D visual inspection methods. Such methods have drawbacks when visibility is limited, and they are also found to be expensive in terms of system maintenance cost and track possession time. In a previous study, the authors proposed a train-based differential eddy current sensor system based on the principle of electromagnetic induction for fastener inspection that could overcome the challenges mentioned above. The detection in the previous study was carried out with the aid of a supervised machine learning algorithm. This study reports the finding of a case study, along a heavy haul line in the north of Sweden, using the same eddy current sensor system mounted on an in-service freight train. In this study, unsupervised machine learning models for detecting and analyzing missing clamps in a fastener system were developed. The differential eddy current measurement system was set to use a driving field frequency of 27 kHz. An anomaly detection model combining isolation forest (IF) and connectivity-based outlier factor (COF) was implemented to detect anomalies from fastener inspection measurements. To group the anomalies into meaningful clusters and to detect missing clamps within the fastening system, an unsupervised clustering based on the DBSCAN algorithm was also implemented. The models were verified by measuring a section of the track for which the track conditions were known. The proposed anomaly detection model had a detection accuracy of 96.79% and also exhibited a high score of sensitivity and specificity. The DBSCAN model was successful in clustering missing clamps, both one and two missing clamps, from a fastening system separately.

Towards a Kinetic Modeling of the Changes in the Electrical Properties of Cable Insulation during Radio-Thermal Ageing in Nuclear Power Plants. Application to Silane-Crosslinked Polyethylene.

The radio-thermal ageing of silane-crosslinked polyethylene (Si-XLPE) was studied in air under different dose rates (6.0, 8.5, 77.8, and 400 Gy·h−1) at different temperatures (21, 47, and 86 °C). The changes in the physico-chemical and electrical properties of Si-XLPE throughout its exposure were determined using Fourier transform infrared spectroscopy coupled with chemical gas derivatization, hydrostatic weighing, differential scanning calorimetry, dielectric spectroscopy and current measurements under an applied electric field. From a careful analysis of the oxidation products, it was confirmed that ketones are the main oxidation products in Si-XLPE. The analytical kinetic model for radio-thermal oxidation was thus completed with relatively simple structure–property relationships in order to additionally predict the increase in density induced by oxidation, and the adverse changes in two electrical properties of Si-XLPE: the dielectric constant and volume resistivity R. After having shown the reliability of these new kinetic developments, the lifetime of Si-XLPE was determined using a dielectric end-of-life criterion deduced from a literature compilation on the changes in R with for common polymers. The corresponding lifetime was found to be at least two times longer than the lifetime previously determined with the conventional end-of-life criterion, i.e., the mechanical type, thus confirming the previous literature studies that had shown that fracture properties degrade faster than electrical properties.

Supervised Machine Learning Approach for Detecting Missing Clamps in Rail Fastening System from Differential Eddy Current Measurements

The rail fastening system forms an integral part of rail tracks, as it maintains the rail in a fixed position, upholding the track stability and track gauge. Hence, it becomes necessary to monitor their conditions periodically to ensure safe and reliable operation of the railway. Inspection is normally carried out manually by trained operators or by employing 2-D visual inspection methods. However, these methods have drawbacks when visibility is minimal and are found to be expensive and time consuming. In the previous study, the authors proposed a train-based differential eddy current sensor system that uses the principle of electromagnetic induction for inspecting the railway fastening system that can overcome the above-mentioned challenges. The sensor system includes two individual differential eddy current sensors with a driving field frequency of 18 kHz and 27 kHz respectively. This study analyses the performance of a machine learning algorithm for detecting and analysing missing clamps within the fastening system, measured using a train-based differential eddy current sensor. The data required for the study was collected from field measurements carried out along a heavy haul railway line in the north of Sweden, using the train-based differential eddy current sensor system. Six classification algorithms are tested in this study and the best performing model achieved a precision and recall of 96.64% and 95.52% respectively. The results from the study shows that the performance of the machine learning algorithms improved when features from both the driving channels were used simultaneously to represent the fasteners. The best performing algorithm also maintained a good balance between the precision and recall scores during the test stage.

Primary Differential Pulse Method for Partial-Discharge Detection of Oil-Immersed Inverted Current Transformers

This paper proposes the primary differential pulse method (PDPM) for the live partial-discharge (PD) detection of oil-immersed inverted current transformers. The PDPM is based on the differential current measurements that are taken at the high-voltage side of the current transformer under test. The proposed technique overcomes the problem of an internally grounded test tap and identifies the internal PD based on the polarities of current pulses. The PDPM detection system is composed of current sensors, a data-acquisition module, a fiber-optics-based data-transmission module, and an operation mechanism with an insulating rod. The testing results prove that the designed system is effective for the live PD detection and can also effectively differentiate between PD and outside interference for oil-immersed inverted current transformers.

A portable bioelectronic sensing system (BESSY) for environmental deployment incorporating differential microbial sensing in miniaturized reactors.

Current technologies are lacking in the area of deployable, in situ monitoring of complex chemicals in environmental applications. Microorganisms metabolize various chemical compounds and can be engineered to be analyte-specific making them naturally suited for robust chemical sensing. However, current electrochemical microbial biosensors use large and expensive electrochemistry equipment not suitable for on-site, real-time environmental analysis. Here we demonstrate a miniaturized, autonomous bioelectronic sensing system (BESSY) suitable for deployment for instantaneous and continuous sensing applications. We developed a 2x2 cm footprint, low power, two-channel, three-electrode electrochemical potentiostat which wirelessly transmits data for on-site microbial sensing. Furthermore, we designed a new way of fabricating self-contained, submersible, miniaturized reactors (m-reactors) to encapsulate the bacteria, working, and counter electrodes. We have validated the BESSY’s ability to specifically detect a chemical amongst environmental perturbations using differential current measurements. This work paves the way for in situ microbial sensing outside of a controlled laboratory environment.

A Differential Electrochemical Readout ASIC With Heterogeneous Integration of Bio-Nano Sensors for Amperometric Sensing.

A monolithic biosensing platform is presented for miniaturized amperometric electrochemical sensing in CMOS. The system consists of a fully integrated current readout circuit for differential current measurement as well as on-die sensors developed by growing platinum nanostructures (Pt-nanoS) on top of electrodes implemented with the top metal layer. The circuit is based on the switch-capacitor technique and includes pseudodifferential integrators for concurrent sampling of the differential sensor currents. The circuit further includes a differential to single converter and a programmable gain amplifier prior to an ADC. The system is fabricated in [Formula: see text] technology and measures current within [Formula: see text] with minimum input-referred noise of [Formula: see text] and consumes [Formula: see text] from a [Formula: see text] supply. Differential sensing for nanostructured sensors is proposed to build highly sensitive and offset-free sensors for metabolite detection. This is successfully tested for bio-nano-sensors for the measurement of glucose in submilli molar concentrations with the proposed readout IC. The on-die electrodes are nanostructured and cyclic voltammetry run successfully through the readout IC to demonstrate detection of [Formula: see text].

Thin Film Differential Photosensor for Reduction of Temperature Effects in Lab-on-Chip Applications.

This paper presents a thin film structure suitable for low-level radiation measurements in lab-on-chip systems that are subject to thermal treatments of the analyte and/or to large temperature variations. The device is the series connection of two amorphous silicon/amorphous silicon carbide heterojunctions designed to perform differential current measurements. The two diodes experience the same temperature, while only one is exposed to the incident radiation. Under these conditions, temperature and light are the common and differential mode signals, respectively. A proper electrical connection reads the differential current of the two diodes (ideally the photocurrent) as the output signal. The experimental characterization shows the benefits of the differential structure in minimizing the temperature effects with respect to a single diode operation. In particular, when the temperature varies from 23 to 50 °C, the proposed device shows a common mode rejection ratio up to 24 dB and reduces of a factor of three the error in detecting very low-intensity light signals.

Integration of Amorphous Silicon Balanced Photodiodes and Thin Film Heaters for Biosensing Application

This work presents the development and testing of an integrated system for on-chip detection of thermochemiluminescent biomolecules. The activation energy of the reaction is provided by a transparent structure of thin film heaters deposited on one side of a glass substrate. Light, passing through the substrate, reaches an array of amorphous silicon differential structure deposited on the opposite side of the glass substrate. The structure is designed to perform differential current measurements between a light- shielded diode, whose current is sensitive only to temperature, and a photosensor, sensitive to both incident light and temperature. The device therefore balances the thermal variations of the photodiode current and reduces the dark-current noise. These features make the presented system very appealing as highly miniaturized micro-analytical devices for biosensing applications.

Self-sensing control of piezoelectric positioning stage by detecting permittivity

Piezoelectric displacement contains hysteresis and creep properties. Therefore, a displacement sensor is indispensable in precise positioning devices; however, the additional space and cost are problems. On the other hand, self-sensing methods that utilize the piezoelectric actuator itself as the displacement sensor have been proposed. With these self-sensing methods, precise positioning becomes possible without an additional displacement sensor. We developed a self-sensing method utilizing the non-hysteresis relationship between the permittivity change and the piezoelectric displacement. Furthermore, a differential current measurement method using two piezoelectric elements with a bimorph actuator could improve the positioning accuracy. In this study, we examine the control of a positioning stage using two multilayered piezoelectric actuators by applying the differential current measurement method for self-sensing control. The results indicate that the differential current measurement method is effective for precise positioning control. The positioning errors due to hysteresis decreased from 0.8μm to 0.1μm for a 10μm displacement range. In addition, permittivity feedback control could compensate for the creep property.

On-chip detection performed by amorphous silicon balanced photosensor for lab-on chip application

In this paper we have integrated a two-channel microfluidic network, fabricated by molding two polydimethilsiloxane channels, with a balanced photodiode constituted by two series-connected amorphous silicon/silicon carbide n-i-p stacked junctions, deposited by Plasma Enhanced Chemical Vapor Deposition on a glass substrate. The structure takes advantage of the differential current measurement to reveal very small variations of photocurrent in a large background current signal suitable for biomedical application. The microfluidic network has been fabricated with dimensions of 3cm×2mm×150μm (L×W×H) for each channel.The experiments have been carried out measuring the differential current in several conditions. All the experiments have been executed under a large background light intensity to reproduce realistic operating conditions in biomedical applications. We have found that the proposed device is able to detect the presence or absence of water flow in the channel and the presence of fluorescent marker. In particular, under identical channel conditions the differential current is at least a factor 60 lower that the current flowing in each diode.

High-Speed Differential Protection for Smart DC Distribution Systems

This paper presents a high speed current differential implementation approach for smart dc distribution systems capable of sub-millisecond fault detection. The approach utilizes the natural characteristics of dc differential current measurements to significantly reduce fault detection times compared to standard applications and hence meet requirements for dc converter protection (around 2 ms). Analysis is first developed to help quantify protection implementation challenges for a given dc system. Options for implementing the proposed technique are then illustrated. Results of scaled hardware testing are presented which validate the overall protection operating times in a low voltage environment. These results show the implementation approach can consistently achieve protection system operating within the order of a few microseconds .

Eddy Current Sensing of Torque in Rotating Shafts

The noncontact torque sensing in machine shafts is addressed based on the stress induced in a press-fitted magnetoelastic sleeve on the shaft and eddy current sensing of the changes of electrical conductivity and magnetic permeability due to the presence of stress. The eddy current probe uses dual drive, dual sensing coils whose purpose is increased sensitivity to torque and decreased sensitivity to variations in distance between probe and shaft (liftoff). A mechanism of keeping the distance constant is also employed. Both the probe and the magnetoelastic sleeve are evaluated for performance using a standard eddy current instrument. An eddy current instrument is also used to drive the coils and analyze the torque data. The method and sensor described are general and adaptable to a variety of applications. The sensor is suitable for static and rotating shafts, is independent of shaft diameter and operational over a large range of torques. The torque sensor uses a differential eddy current measurement resulting in cancellation of common mode effects including temperature and vibrations.

Reduced leakage current of multiferroic BiFeO3 ceramics with microwave synthesis

Preparation of multiferroic BiFeO3(BFO) is reported using microwave heating. The prepared sample is characterized using x-ray diffraction, scanning electron microscopy, differential scanning calorimetry and leakage current measurements. It is observed that the BFO can be prepared with microwave heating at a fast heating rate, consisting of more homogeneous microstructure and better electrical properties. Phase purity of the sample is confirmed from x-ray diffraction measurements. Uniform grain size distribution is observed for the sample prepared with microwave heating. More than an order of magnitude reduction in the leakage current is observed for the sample prepared with microwave heating as compared to conventional radiant heating.

High-precision positioning using a self-sensing piezoelectric actuator control with a differential detection method

We present a self-sensing control method for piezoelectric actuators, which enables high-resolution positioning without an external positioning sensor. One of the present authors previously proposed a self-sensing piezoelectric actuator control system (Kawamata et al. (2008) [1] and Ishikiriyama and Morita (2010) [2]). In the previous studies, a linear relationship between piezoelectric displacement and permittivity change was discovered, and this linear relationship was applied for positioning control. To detect permittivity changes, a high frequency voltage signal (permittivity detection voltage), in addition to the driving voltage signal, was applied to the actuator. The permittivity change was monitored as the amplitude of the current at the same frequency as the permittivity detection voltage. From this current amplitude, the permittivity change was easily calculated in real time. However, the positioning resolution was insufficient compared to that of traditional external positioning sensors, such as a strain gage sensor. In this study, we improved the positioning resolution by introducing a differential current measurement using two piezoelectric elements, one on each side of a bimorph actuator. The phase of the detected current signal was taken into consideration using a lock-in amplifier. In other words, the conductivity-related current and the permittivity-related current were measured separately. With these improvements, the permittivity change related to the piezoelectric displacement could be measured precisely, and self-sensing feedback control with a positioning error of less than 0.4 μm over a movement range of 80 μm was demonstrated.

Effect of Nano-Sized ZnO on the Physical Properties of (Cu0.5Tl0.25Pb0.25)Ba2Ca2Cu3O10−δ

High-temperature superconductor phase of (Cu0.5Tl0.25Pb0.25)-1223 was synthesized by solid-state reaction technique and characterized using X-ray powder diffraction (XRD). XRD analysis revealed that the prepared sample was nearly monophase and exhibited tetragonal structure with space group P4/mmm. Nano-zinc-oxide, prepared by Co-precipitation method, was added to the sample. ZnO-concentrations y varied from 0.0 to 2.0 wt.% of the sample’s mass. The prepared samples were investigated through XRD, scanning electron microscope (SEM), energy dispersive X-ray (EDX), particle size analyzer (PSA), differential scanning calorimeter (DSC), electrical resistivity and transport critical current density measurement. X-ray data analysis showed that the nano-Zn addition does not affect the tetragonal structure of (Cu0.5Tl0.25Pb0.25)-1223 phase, whereas the lattice parameters showed an insignificant variation. The results of the superconducting transition temperature, the transport critical current density and melting point of the prepared samples were found to depend on nano-ZnO concentrations.

Superconducting resistive transition in coupled arrays of4Åcarbon nanotubes

We report superconducting resistive transition characteristics for array(s) of coupled $4\text{ }\text{\AA{}}$ single wall carbon nanotubes embedded in aluminophosphate-five zeolite. The transition was observed to initiate at 15 K with a slow resistance decrease switching to a sharp, order of magnitude drop at $\ensuremath{\sim}7.5\text{ }\text{K}$. The latter exhibits anisotropic magnetic field dependence, and the differential resistance versus current (voltage) measurements show a rich variety of details that are consistent with the establishment of coherence, in stages, as the temperature is lowered below 15 K. In particular, the resistance drop that starts at 7.5 K exhibits attributes that are consistent with the manifestations of a Berezinskii-Kosterlitz-Thouless transition that establishes quasi-long-range order in the plane transverse to the $c$ axis of the aligned nanotubes.

Amorphous silicon twin photodiode structure for differential current measurements

In this paper we present a new amorphous silicon structure called “twin photodiode” constituted by two p–i–n series connected photodiodes biased at the same reverse voltage. The structure takes advantage of the differential current measurement to reveal very small variations of photocurrent in a large background current signal. The removal of the background allows us to increase the dynamic range of the input signal and the sensitivity of the detection system. In addition, the differential approach allows us to reduce the common mode signal due to the effect of temperature variations and instability of light source intensity. We have fabricated several twin structures for detection of ultraviolet radiation with different geometries utilizing a four mask-step process. Experimental results have demonstrated the ability of our structure to detect differential currents three orders of magnitude lower than the current of each sensor. The achieved common mode rejection ratio keeps constant with reverse bias voltage and increases with increasing wavelengths, varying from 30 dB nm at 254 nm to 42 dB at 365 nm.

Differential current measurement in the BNL energy recovery linac test facility

An energy recovery linac (ERL) test facility is presently under construction at BNL [V.N. Litvinenko, et al., High current energy recovery linac at BNL, PAC, 2005; I. Ben-Zvi, et al., Extremely high current, high brightness energy recovery linac, PAC, 2005]. The goal of this test facility is to demonstrate CW operation with an average beam current greater than 100 mA, and with greater than 99.95% efficiency of current recovery. This facility will serve as a test bed for the novel high current CW photo-cathode [A. Burrill, et al., Multi-alkali photocathode development at BNL, PAC, 2005; A. Murray, et al., State-of-the-art electron guns and injector designs for energy recovery linacs, PAC, 2005], the superconducting RF cavity with HOM dampers [R. Calaga, et al., High current superconducting cavities at RHIC, EPAC, 2004; R. Calaga, et al., in: Proceedings of the 11th workshop on RF superconductivity, Lubeck, Germany, 2003], and the lattice [D. Kayran, V. Litvinenko, Novel method of emittance preservation in ERL merging system in presence of strong space charge forces, PAC, 2005; D. Kayran, et al., Optics for high brightness and high current ERL project at BNL, PAC, 2005] and feedback systems needed to insure the specified beam parameters. It is an important stepping stone for electron cooling in RHIC [I. Ben-Zvi, et al., Electron cooling of RHIC, PAC, 2005], and essential to meet the luminosity specifications of RHICII [T. Hallman, et al., RHICII/eRHIC white paper, available at http://www.bnl.gov/henp/docs/NSAC_RHICII-eRHIC_2-15-03.pdf]. The expertise and experience gained in this effort might also extend forward into a 10–20 GeV ERL for the electron-ion collider eRHIC [ http://www.agsrhichome.bnl.gov/eRHIC/, Appendix A, The linac-ring option, 2005]. We report here on the use of a technique of differential current measurement to monitor the efficiency of current recovery in the test facility, and investigate the possibility of using such a monitor in the machine protection system.

Development of Differential Current Measurement System with Optical Intensity Modulation Using Flint Glass Fiber Type Optical Current Transducers

Development of Differential Current Measurement System with Optical Intensity Modulation Using Flint Glass Fiber Type Optical Current Transducers