High Current Measurement Research Articles

Accuracy assessment of high frequency radar current measurements in the Strait of Gibraltar

An assessment of accuracy of a three site short-range (27 MHz) CODAR SeaSonde HF radar network deployed in the Strait of Gibraltar is attempted by comparing its surface current estimates with measurements from a moored point current meter. Radial and total current vectors are compared for a 47 day period from 19 October to 4 December 2013, yielding angular offsets, root mean square errors and correlations in the range 2ͦ–30ͦ, 8–22 cm s-1 and 0.31–0.81, respectively. Statistics improve when the measured antenna pattern is used, except at one radar site. A self-consistency check in overwater baseline reveals that the dominant source of velocity differences is HF radar variance error.

Pulsed voltage driven organic field-effect transistors for high stability transient current measurements

In this article, we propose the usage of gate voltage pulses of alternating polarity, to effectively suppress the hysteresis in organic field effect transistors (OFETs). The hysteretic behaviour of poly(3-hexylthiophene-2,5-diyl) (P3HT) based OFETs is systematically investigated by using continuous and pulsed sweep voltage mode. On the basis of the experimental results, both time settings and mode of gate bias voltage influence the carrier transport in the semiconductor channel. Hysteresis-free transfer characteristic curves are obtained by applying diametrically opposed gate pulses of a few milliseconds in duration. Stable on-current transient measurements are also achieved by implementing the pulse mode, thus allowing on-line gas sensing measurements to be successfully performed. Finally, the response of the sensor upon exposure to different concentrations of analyte vapours is found to be in good agreement with the Langmuir adsorption isotherm model.

Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet.

We present the designs of probes for making critical current density (Jc) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ~0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J(c) measurements, made by uniformly ramping the current up to a maximum current (I(max)) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b'), and the maximum safe temperature for the critical-current leads (T(max)). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI(max)/A = [1.46D(-0.18)L(0.4)(T(max) - 300)(0.25D(-0.09)) + 750(b'/I(max))D(10(-3)I(max)-2.87b') × 10⁶ A m⁻¹ where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm(2) is obtained when I(max) = 1000 A, T(max) = 400 K, D = 0.2, b' = 0.3 l h(-1) and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h(-1). When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I(max) ≈ (1.35 × 10(-3))D(0.41) l h(‑1) A(-1). A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of -1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder.

Electrospray pulsation: A diagnostic to understand cone-jet stability and minimum flow

Detailed current and flow rate measurements obtained during pulsation mode nano-electrospray of ethylene glycol solutions are presented. High temporal resolution current measurements reveal for the first time that current is observed at the electrode immersed in the electrospray fluid, even when there is no observed spray. This current, believed to be the charging current associated with electrode and meniscus polarization, is dependent upon the voltage applied to the electrospray system. Quantitatively, the total charge transfer that is observed during the non-spray period of the pulsation approximates to that required to obtain electrostatic equilibrium in the conical meniscus, and is relatively independent of the fluid conductivity. A linear relationship exists between this charging current and the observed pulsation frequency. Pulse shape, indicated by the parameters of spray current rise time, fall time, and spray current pulse duration, are observed to be independent of frequency for a given solution. The total charge lost during a single pulsation event is significantly larger than the charge transfer observed during the meniscus replenishment phase of the pulsation. For the solvent tested, the rate at which meniscus charging takes place is linearly dependent upon solution conductivity, and thus appears to scale directly with the electrical relaxation time.

Novel designs of wideband Rogowski coils for high pulsed current measurement

This study presents design, calibration and testing of six novel flat-spiral self-integrating Rogowski coils wound in two layers. These coils are two varnished-wire wound coils with air and ferrite cores (RC1 and RC2, respectively), two flat-twin wire wound coils with air and ferrite cores (RC3 and RC4, respectively) and two coaxial-cable wound coils with and without the insulating jacket and with ferrite core and RC5 and RC6, respectively. All coil parameters are calculated and good agreement is found between these values and the corresponding measured ones. Coil sensitivity decreases as coil-to-wire separation increases and so does mutual inductance between the coil and the current-carrying wire. Linearity of all coil sensitivities are checked for different separations and waveforms, and good agreement is found. Designed coils with ferrite core give better response than those with air core because the low cutoff frequency decreases. On the contrary, the droop effect is slightly observed for coils wound on wooden core, where RC4 and RC6 give the best response. Finally, the frequency response analysis for all coils shows that the percentage relative errors of the measured and the calculated coil sensitivities are within ±0.1%.

High accuracy current measurement in the main power converters of the large hadron collider: tutorial 53

In the Large Hadron Collider (LHC) at CERN, the powering of the main dipole and quadrupole circuits is divided into eight separate powering sub sectors due to the very high magnetic energy stored in these circuits and to protection constraints of the superconducting magnets [1]. As a consequence, individual sector currents must be controlled with very high accuracy in amplitude and time to ensure that the beam of particles sees the same magnetic field in all sectors. This results in a requirement for current tracking between the different sectors of better than ± 5 ppm and short term stability of better than ± 2 ppm [1], at 13 kA currents.

A high-current calibration system based on indirect comparison of current transformer and Rogowski coil

The calibration of the protective current transformer (CT) is of particular importance, since its accuracy at high currents is crucial to the correct operation of the subsequent relay protection devices. Conventional calibration methods have been using an electromagnetic CT which contains an iron core as the standard CT. The iron core is big and difficult to manufacture for high-current measurement, and the serious residual magnetism of the iron core at high currents can lead to excessive measurement errors. This paper proposes a calibration system based on indirect comparison of CT and Rogowski coil, i.e. using an iron-core CT to correct the error of the Rogowski coil at low currents, which may be caused by the position of the current-carrying conductor and so on, and then using the calibrated Rogowski coil as the standard transformer at high currents for its good linearity and wide dynamic range, and there is no magnetic saturation. Since the output of the Rogowski coil needs to be integrated, an improved digital integrator based on direct current (dc) negative feedback is adopted, which can effectively eliminate the influences of temperature drift, time drift and dc offset caused by the analogue circuit. The measurement errors of each part of the calibration system have also been discussed, and the test results show that the accuracy of the system can reach up to the 0.05S Class and the uncertainties are 0.038% for ratio and 0.68′ for phase in the range 500 A to 50 kA.

Modeling the Failure Mechanism of Electrical Vias Manufactured in Thick-Film Technology

Hybrid-thick-film circuits consist of many different components, like screen-printed passive elements (conductors, resistors, and electrical vias), SMDs, and active elements like transistors or ICs. Whereas most of passive components are well investigated and described, the electrical vias often remain unattended. Resistive heating caused by high current pulses might lead to the destruction of the vias. In previous work, we set up a 3d FEM model and investigated the influence of non-radial-symmetric contacting and geometric irregularities of the vias on the occurring maximum temperatures. The present contribution deals with the modeling of a failure mechanism of an electrical via caused by high current pulses. When the local temperature exceeds a defined melting temperature, the metallization layer melts and is not available for conduction any more. The current density rises as a consequence of the decreased cross section area of the vias and leads to a higher heat production in a smaller area. This conducts further melting of the metallization layer and results in a positive feedback that accelerates the destruction of the via. The approach of this contribution is to model the described failure mechanism in a 2d-radial-symmetric FEM model. The modeling results were validated using high current measurements of electrical vias. Modeling and measurement of the voltage drop during a constant current pulse agree very well, from very low current density pulses up to pulses that lead to the destruction of the vias.

Test of Time Reversal Invariance and COSY

Test of Time Reversal Invariance in pd scattering is planned at the COoler-SYnchrotron COSY-Jülich using the PAX internal target station. Feasibility test, performed in September 2012, have shown possibility to perform such an experiment using COSY and PAX. In parallel to the PAX upgrade a new high precision beam current measurement system will be constructed by the end of 2014. After these modifications, it will be possible to improve the current upper limit on a strength of T-odd P-even NN potential by an order of magnitude.

Performance Improvement of Slow-Wave Rogowski Coils for High Impulse Current Measurement

This paper presents the operating principles, design, and performance improvement and limitations of three slow-wave air-core Rogowski coils that enable plateau bandwidths up to 11 MHz and sensitivities of less than 0.25 V/kA to be achieved. The frequency response for these coils is examined to optimize the coil termination resistance in order to achieve the suitable transit time, minimize the droop effect, and achieve desired bandwidth. In the present design, the coil inductance is increased to compensate for the resulting reduction in the sensitivity due to the coil termination resistance. Oscillatory and overdamped unidirectional current waveforms up to 10 kA peak value are generated by using different linear and nonlinear loads, and impulse current generator configurations. These high impulse currents are measured by different methods, namely, a commercial impulse current transformer (ICT), a commercial Rogowski coil (CRC), and the three newly designed self-integrating Rogowski coils. Distortion of the measured current pulses is studied by using the lumped-element model of Rogowski coil and its termination resistance, and the signal cable and its matching resistance. The optimal coil termination resistance is obtained under these impulses, and the linearity of all newly designed self-integrating Rogowski coils' output voltages are also investigated. Calibration results and a comparison between ICT, CRC, and the developed three coils for measurements of different high impulse currents demonstrate that the developed coils can accurately reproduce the actual waveform with a constant sensitivity over the desired bandwidth.

High-current measurement of the grain resistivity in zinc oxide varistor ceramics

Abstract A new pulse technique for grain resistivity measurement in varistor ceramics is suggested. Such technique allows obtaining more precise value of the grain resistivity due to the use of the concept of differential electrical resistance. This technique can be used in the current density range where the overheating of varistor sample is insignificant. The technique was verified using commercial ZnO varistors. Grain resistivities of 0.60±0.02 Ω cm at 293 K and of 3.40±0.13 Ω cm at 77 K were obtained. This result indicates the negative temperature coefficient of grain resistance in ZnO varistor in the range (77–293) K. The contribution of the grain boundaries to the current–voltage characteristic of ZnO varistor is estimated on the basis of the measured grain resistivity and the current–voltage data. It is shown that the electrical conduction in ZnO varistor is controlled by grains if the current density exceeds approximately 1000 А сm −2 .

Positional Error Analysis of PCB Rogowski Coil for High Accuracy Current Measurement

Geometrical, physical, and electrical parameters have influences on the precision of printed circuit board Rogowski coils (PCBRCs). This paper outlined operating principles and properties of PCBRCs. Two kinds of positional sensitivities between current conductor and PCBRC are analyzed, and mathematical models and formulas for error computing are established and derived. The roles of some critical geometrical parameters are characterized and verified by experiment. These methods can be used to define structure parameters of PCBRC for precise current measurement applications.

A High Precision Pico-Amperes Scale Current Measurement System in Radiation Detection

A weak current measurement system is developed. It is mainly used in the accurate measurement of weak current in radiation detection. The principle of the measurement system is introduced. The interference protection measures of current to voltage (I-V) conversion and amplification unit, the technology of ∑-△ ADC and the program design of micro-programmed control unit are described. The system is able to communicate with the computer controlled platform by the USB interface, which has the functions of storage, range selection, data display, data plotting and so on. The measuring range is from 0.1pA to 2.1mA, and the resolution is 5½ bits. The system has been successfully used in the detection of radiation.

Robust digital control approach for high performance tunneling current measurement system

This paper is devoted to the digital control system design for high performance measurement of tunneling current. A common approach for such applications is to use a conventional Proportional Integral (PI) control. In this paper, a robust digital design method is instead considered, based on combined pole placement with sensitivity function shaping, and allowing for better performance tuning in terms of precision, robustness and disturbance rejection. The resulting control scheme looks like some enhanced PID controller, and is validated over an experimental setup, developed in GIPSA-lab (Grenoble Image Parole Signal Automatique) research center. The corresponding simulation and experimental results show improved performances with respect to those obtained with the more conventional PI control technique.

Development of high speed continuous transport critical current measurement system for long piece of HTS conductor

In case of long pieces of HTS conductor, their critical current measurement is an important process for the conductor manufacturer and the customer, however, it is very time consuming process. Conventional critical current measurement is carried out by ‘four probe method’, which increase the transport current and measure the voltage between the fixed voltage taps. Therefore, it consists of conductor moving and measuring process. To speed up the measuring process, longer distance between voltage taps is required. In this case, the measured critical current is averaged and small defects, which can be very crucial for thermal stability, cannot be found. Therefore, the limitation of the voltage tap length should be carefully decided considering the cooling environment. Another non-contact or indirect method is to measure the screening effect of magnetic field and converting the field signal to the critical current, which is called as hall probe method. This process is known as a very efficient way to find local defects and estimate the distribution of the critical current, however, it contains inevitable error and noise because it should measure the small magnetic field signals.This paper describes a new critical current measurement system, which have similar hardware structure of conventional ‘four probe method’. However, it is much faster than other systems using fast feedback control of the transport current while the conductor is continuously moving with high speed. The measured results are compared with the conventional method and hall probe method.

Direct measurements and numerical simulations of gas charging in microelectromechanical system capacitive switches

Gas breakdown in microelectromechanical system capacitive switches is demonstrated using high resolution current measurements and by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. Measurements show an electric current through a 3 μm air gap increasing exponentially with voltage, starting at 60 V. PIC/MCC simulations with Fowler-Nordheim [Proc. R. Soc. London, Ser. A 119, 173 (1928)] field emission reveal self-sustained discharges with significant ion enhancement and a positive space charge. The effective ion-enhanced field emission coefficient increases with voltage up to about 0.3 with an electron avalanche occurring at 159 V. The measurements and simulations demonstrate a charging mechanism for microswitches consistent with earlier observations of gas pressure and composition effects on lifetime.

Characteristic analysis of shunt for high voltage direct current measurement

The resistive shunt is generally used as a sensor in the high voltage direct current (HVDC) system. The high frequency alternating current has an impact on the performance of the shunt owing to the skin effect and proximity effect causing DC measuring errors and even leading to protective system false operation. The impact of skin and proximity effects on the squirrel cage shunt is discussed in the paper. Numerical evaluation of the two effects is applied. The calculation results show that the value of the shunt resistance is dependent on the current frequency. Adequate selection of the radius of the conductors and the distances between conductors can greatly reduce the influence of the two effects on DC measurement accuracy. The field data of practical shunts during nominal operation and transient process confirm the results.

Design of a Low-Consumption Fluxgate Transducer for High-Current Measurement Applications

This paper presents the design and final realization of a transducer system for the measurement of high dc and ac currents. This transducer is based on the magnetic flux compensation technique, also called fluxgate principle. The transducer designed can measure currents of around 1 kA of peak value with a 170-kHz small-signal bandwidth. This functionality can be achieved with low power consumption if the designed system is compared with other fluxgate transducers available on the market and with similar functional specifications. Improvement in consumption was achieved by the inclusion in the design of a switching power supply (based on flyback topology) and a switched amplifier for generating magnetic flux compensation current (based on half-bridge inverter topology).

OPTIMIZING METHODS TO MEASURE HYDRODYNAMICS IN COASTAL WETLANDS: EVALUATING THE USE AND POSITIONING OF ADV, ADCP AND HR-ADCP

Hydrodynamic impacts of vegetation in the intertidal zone are highly important to coastal protection. However, most studies on hydrodynamic impacts of vegetation in the intertidal zone are carried out in flumes. This results in a lack of field data for validating models that describe short-term hydrodynamic impacts of vegetation. The current research focuses on field measurements of flow patterns and waves in vegetated intertidal areas. Ample measurement devices are available to measure hydrodynamic processes in the field. Examples are: acoustic Doppler current profilers (ADCP), high resolution acoustic Doppler current profilers (HR-ADCP) and acoustic Doppler velocity meters (ADV). This study focuses on the differences in the performance of these devices, to determine which of them can be best deployed in a future fieldwork campaign in mangroves. Major points of attention in this comparison are the accuracy of the data and the potential disturbance of the measurements by the presence of vegetation. It is concluded that ADV's perform very well in vegetated intertidal areas, while (HR-)ADCP's show difficulties when deployed upward looking. Furthermore, ADV's are preferred over (HR-)ADCP's due to their ability of combining high frequent wave and current measurements and their convenient deployment.

测量低频大电流的自积分罗氏线圈设计

测量低频大电流的自积分罗氏线圈设计