Impulse Calibration Research Articles

First demonstration of a fiber optic bolometer on a tokamak plasma (invited).

A fiber optic bolometer (FOB) was demonstrated observing a fusion plasma for the first time at the DIII-D tokamak. A FOB uses a fiber optics-based interferometric technique that is designed to have a high sensitivity to temperature changes [75 mK/(W/m2) responsivity in high vacuum with 0.38 mK noise level] with a negligible susceptibility to electromagnetic interference (EMI) that can be problematic for resistive bolometers in a tokamak environment. A single-channel test apparatus was installed on DIII-D consisting of a measurement FOB and shielded reference FOB. The single-channel FOB showed a negligible increase in the noise level during typical plasma operations (0.39 mK) compared to the benchtop results (0.38 mK), confirming an insignificant EMI impact to the FOB. Comparisons to DIII-D resistive bolometers showed good agreement with the single-channel FOB, indicating that the FOB is comparable to a resistive bolometer when the impulse calibration is applied. The noise-equivalent power density of the calibrated FOB during a plasma operation was 0.55 W/m2 with an average sampling time of 20ms. The major potential effect of ionizing radiation on the FOB would be the radiation-induced attenuation, which can be efficiently compensated for by adjusting the probing light power.

Long‐Term Stability of Reference Measuring System for Impulse High Voltage

Long‐term stabilities of shielded resistive voltage dividers for lightning and switching impulse, employed as the reference dividers of Japan High‐voltage Impulse testing Laboratory Liaison (JHILL) are investigated. The DC scale factors and the step‐response parameters have been annually measured for 20 years. Annual variations of impulse parameters, namely the peak value, the front time, and the time to half value of the calculated waveform from the step‐response waveforms by the convolution algorithm are investigated. Furthermore, long‐term stabilities of reference low‐voltage impulse calibrators are investigated. The parameters of circuit elements of the calibrators have been annually measured for 18 years. The impulse parameters of the output waveforms of the calibrators are calculated, and the annual variations of them are investigated. After the detailed evaluation, it can be expected that the measurement system employing the voltage dividers and the calibrators, including the analytical method of the data, has the similar performance to those of NMIs of developed countries. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A Proposed Resistance-to-Time Converter with Switching Impulse Calibrators for Application in Resistive Bridge Sensors

This paper presents a simple resistance-to-time converter. It consists of two voltage comparators, a ramp voltage generator, two logic gates and impulse voltage calibrators. A square-wave generator circuit is suggested in this paper. The design is simple and independent of the OPAMP offset issues. The resulting square-wave is rectified to get its DC equivalent and to a triangular output; the two outputs are applied to a comparator for generating a digital output with a duty cycle proportional to a change in resistance upon which is dependent the DC.

Electromagnetic impulse calibration in V-shaped parts

In this study, a 2D finite-element model of electromagnetic impulse calibration was established to understand the mechanistic of springback correction. According to the results both in experiment and simulation, the springback angle after the coil discharging sharply decreases in comparison with quasi-static stamping, and the springback angle decreases gradually with the increasement in discharging energy. Finally, negative springback under the 6-KJ condition both occur in experimental and simulation results. It was found the sheet corner moves far away from punch by magnetic force and the inertial effect caused by magnetic force firstly. When the sheet peak reaches the maximum position, the sheet corner immediately reverse bending and moves closer to the punch. The phenomenon of reverse bending generates additional tangential stress in opposite direction, which decreases the original tangential stress on sheet corner and even makes the sheet corner undergo plastic deformation in high discharge energy. The discoveries showed in this paper will provide theoretical basis for controlling the springback of complex parts in the future.

Reduction of springback in V-shaped parts using electromagnetic impulse calibration

Abstract Many studies reported that a pulsed magnetic force acting on the bending area can significantly reduce and even eliminate the springback. However, a detailed mechanistic understanding of springback correction has not been reported. In this study, a finite-element model of electromagnetic impulse calibration was established to understand the mechanistic of springback correction. It was found that the springback angle after the coil discharging sharply decreased in comparison with quasi-static stamping. This shows that the simulation and experimental results are consistent. By analyzing the changes in displacement, plastic strain, and principal with time, we found that the sheet corner moves far away from punch by magnetic force firstly, and then the sheet corner immediately moves closer to the punch due to the sheet impact with die. Thus, the reverse bending appears at the sheet corner, generating additional tangential stress and then changing the tangential stress at sheet corner.

Adaptive Acquisition of Power IGBT Transients With Discrimination Circuit

The frequency spectrum of the power insulated gate bipolar transistor (IGBT) circuit originates mostly from high gradient switching and low rate conduction components. High gradient transients are captured with direct probes. Switching losses are represented with 3-D surfaces acquired with Delaunay triangulation processing. Interpolation functions are introduced, allowing the prediction of the switching loss in the entire 3-D space. A chopper circuit is introduced for the acquisition of the IGBT low rate transients in the conductive stage of operation. A Zener discriminator enhances the measurement accuracy by two orders of magnitude. The experimental results are presented for a half-bridge converter. Measurement uncertainties are acquired with dc and impulse calibration apparatuses.

Precision electromagnetic calibration technique for micro-Newton thrust stands

This paper introduces a new direct non-contact electromagnetic calibration technique for high precision measurements of micro-thrust and impulse. A ring-shaped electromagnet with an air gap is used in the calibration. The calibration force is produced by the interaction of a uniform magnetic field with a copper wire current in the air gap. This force depends linearly on this current as well as the steady angular displacement of the torsion arm of the thrust stand. The range of calibration force is very large and the calibration force is easy to generate and insensitive to the arm displacement. The calibration uncertainty for a 150-μN force is 4.17 μN. The more influential factor on the calibration uncertainty is the magnetization of the electromagnet core due to the copper wire current. In the impulse calibration, the exerted impulse is linearly dependent on the maximal angular displacement of the torsion arm. The uncertainty in the impulse calibration is determined by uncertainties in both the force calibration and the pulse time.

High-Accuracy Comparison of Lightning and Switching Impulse Calibrators

This paper summarizes the results of a comparison on two calculable impulse voltage calibrators and one commercial calibrator between Helsinki University of Technology, Finland (MIKES-TKK), Nippon Institute of Technology, Japan (NIT), and Physikalisch-Technische Bundesanstalt, Germany (PTB). The peak voltage levels of the comparison ranged from 10 to 300 V. Both lightning and switching impulse voltage calibrators were studied using both positive and negative polarity impulses. The comparison was performed by applying impulses from the calibrators to a 12-b digitizer and then comparing the reported digitizer errors. For the switching impulse peak value, the agreement between the two calculable calibrators was better than 0.02% for all the measured voltages and better than 0.4% for the time parameters. For the lightning impulse peak value, the disagreement between the same two calibrators was smaller than 0.05% for all voltages examined and smaller than 1% for the time parameters

Comparisons between impulse voltage calibrators and digitizers

AbstractComparisons between impulse calibrators and digitizers are useful in determining the uncertainties of the instruments, especially when multiple devices are being cross compared. In this paper, comparisons between calibrators and digitizers from NIT, Japan and NMI, Australia are reported. Comparisons of full lightning impulse and switching impulse waveforms were performed. The results of the comparisons are reported with an analysis of the sources of the uncertainties. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Comparisons between impulse voltage calibrators and digitizers

AbstractImpulse voltage calibrators are important instruments for the calibration of impulse voltage digitizers and other measurement devices. The impulse digitizers, on the other hand, are often sufficiently accurate for checking the performance of impulse voltage calibrators. Comparisons between impulse calibrators and digitizers are useful in determining the uncertainties of the instruments, especially when multiple devices are being cross compared.In this paper, comparisons among calibrators and digitizers from Nippon Institute of Technology (NIT), Japan, National Measurement Institute (NMI), Australia, and Korea Electrotechnology Research Institute (KERI), Korea, are reported. Comparisons of full lightning impulse and switching impulse waveforms were performed. The results of the comparisons are reported with an analysis of the sources of the uncertainties. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Comparison of Two Impulse Calibrators With a High-Resolution Digitizer

The lightning impulse voltage calibrators, developed at National Measurement Laboratory (NML) and MIKES-HUT, and a recently developed commercial digitizer were compared. With this three-way comparison, not only the accuracies of the devices were compared, but also the linearity of measurement of both peak voltage and time parameters was investigated. The results demonstrated that the linearity of the calibrators is superior to that of the digitizer.

Searching for momentum enhancement in hypervelocity impacts

In conjunction with the Los Alamos National Laboratory hypervelocity microparticle impact (HMI) team effort to produce higher impact velocities and to understand the physics of crater formation and momentum transfer, we have implemented a low noise microphone as a momentum detector on both the 6 MV Van de Graaff and 85 KV “test stand” particle accelerators. Calculations are presented showing that the impulse response of a circular membrane. When used as a momentum impulse detector, the microphone theoretically may detect impulses as small as 8.8 × 10 −15 N s. Sensitivity of the microphone in this application is limited by the noise threshold of the electronic amplifiers and the ambient microphonic vibration of the system. Calculations lead us to anticipate detection of particles over the full range of the Van de Graaff acceleration capability and up to 7 km/s on the test stand. We present momentum enhancement data in the velocity range between 10 km/s and 20 km/s. Preliminary work is presented on momentum impulse calibration of the microphone using laser-pulse photon momentum as an impulse source.

High-amplitude/low-frequency impulse calibration of microphones; a new method

This paper describes a new method to measure the peak amplitude response and the step-function decay (low-frequency response) of a microphone and its associated amplifiers. The requirements for the new method were that it be simple, inexpensive, and accurate. An acoustic ’’step function’’ would be an ideal source for testing the large-amplitude and low-frequency response of microphones, especially for measurements of impulsive noise. Unfortunately, a positive going acoustical step-function source is difficult to obtain. This method involves the use of a negative step-function input which is applied by enclosing a microphone inside a thin membrane which is inflated and then burst. The sudden decrease in pressure represents a negative going step-function input to the microphone. The peak output voltage produced by the microphone must be proportional to the initial static pressure within the membrane, and the return (decay) of the voltage output of the the microphone to zero directly represents the decay of the microphone and system. The low-frequency cutoff of the system is easily calculated from the time constant of the decay curve.

High-amplitude/low-frequency impulse calibration of microphones: A new method

This paper describes a new method to measure the peak amplitude response and the droop (low-frequency response) of a microphone and its associated amplifiers. The requirements for the new method was that it be simple, inexpensive, and accurate. An acoustic “step function” would be an ideal source for testing the large-amplitude and low-frequency response of microphones, especially for measurements of impulsive noise. Unfortunately, a positive-going acoustical step-function source is difficult to obtain. This method involves the use of a negative step-function input which is applied by closing a microphone inside a thin membrane which is inflated and then burst. The sudden decrease in pressure represents a negative-going step-function input to the microphone. The peak output voltage produced by the microphone must be proportional to the initial static pressure within the membrane and the return (decay) of the voltage output of the microphone to zero directly represents the droop of the microphone and system. The low-frequency cutoff of the system is easily calculated from the time constant of the decay curve.

Amplifier improves vibration data analysis

In conjunction with the Los Alamos National Laboratory hypervelocity microparticle impact (HMI) team effort to produce higher impact velocities and to understand the physics of crater formation and momentum transfer, we have implemented a low noise microphone as a momentum detector on both the 6 MV Van de Graaff and 85 KV “test stand” particle accelerators. Calculations are presented showing that the impulse response of a circular membrane. When used as a momentum impulse detector, the microphone theoretically may detect impulses as small as 8.8 × 10−15 N s. Sensitivity of the microphone in this application is limited by the noise threshold of the electronic amplifiers and the ambient microphonic vibration of the system. Calculations lead us to anticipate detection of particles over the full range of the Van de Graaff acceleration capability and up to 7 km/s on the test stand. We present momentum enhancement data in the velocity range between 10 km/s and 20 km/s. Preliminary work is presented on momentum impulse calibration of the microphone using laser-pulse photon momentum as an impulse source.

Polarity Limits of the Sphere Gap

It is found that (10-cycle polarity characteristics correlate with the positive and negative impulse calibration curves for grounded sphere gaps sufficiently well to use them for determining the polarity limits for sphere gaps. The available data show that the maximum spacing at which a grounded sphere gap has equal positive and negative spark-over is a linear function of the size of the spheres. From this relation, it follows that the maximum sparking distance for equal positive and negative sparkover, expressed as a per cent of the diameter of the spheres, is not constant for all sphere diameters. Therefore, arbitrary polarity limits expressed in terms of the diameter of the sphere cannot apply to all sizes of sphere gaps.