Shock Calibration Research Articles

A Method for Synchronous Shock Calibration of Triaxial High-g Accelerometers Based on Modified Hopkinson Bar Technique

Since the width of the excitation pulse is generally in the order of microseconds to milliseconds, the key technique in the shock calibration of triaxial high-g accelerometer is how to achieve the synchronous loadings with high-g amplitude along the three orthogonal axes. Given this background, this paper developed a synchronous calibration method for the triaxial high-g accelerometers by modifying the conventional Hopkinson bar method. Using this newly developed method, three-dimensional reference acceleration pulses with amplitude range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> g-10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> g and width range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> μs-10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> μs can be generated and imposed on the triaxial high-g accelerometers synchronously. Then, calibration experiments on a typical triaxial high-g accelerometer were carried out by using both the synchronous calibration method and the conventional Hopkinson bar method, respectively. The sensitivity of the triaxial accelerometer was characterized by a matrix, the so-called sensitivity matrix, containing 3 main sensitivity coefficients and 6 transverse sensitivity coefficients. Least squares method (LSM) was used to calculate the sensitivity matrix. Generalization error was employed to evaluate the measurement accuracy of the accelerometer. The results show that the measurement accuracy of the triaxial high-g accelerometer calibrated by the synchronous method is higher than that calibrated by the conventional asynchronous method. Therefore, the developed synchronous method is recommended to ensure and improve the measurement accuracy of the triaxial high-g accelerometers. Finally, the validity and the calibration ability of the newly developed method were numerically investigated and discussed in detail.

Primary Low-g Shock Acceleration Calibration Using Laser Interferometry

The current situation of low g shock is introduced with three types of shock exciters described. The measuring theory and system set-up using laser interferometry is explained in accordance with ISO 16063-13 with the emphasis on key technology of signal demodulation algorithm and air-bearing shock exciter based on collision. According to calibration results, the primary shock calibration system can achieve expanded uncertainty of 1%,k=2, in the acceleration range from 20m/s2 to 10000m/s2 and pulse duration from 0.5ms to 10ms.

Primary shock calibration with fast linear motor drive

This paper describes the implementation of a new, fast and precise linear motor drive for PTB’s primary shock calibration device. This device is used for monopole shock calibrations of accelerometers using the “hammer-anvil” principle according to ISO 16063-13:2001 and operates in a peak acceleration range from 50 m/s² to 5000 m/s². &lt;br /&gt;The main challenge of implementing this kind of shock generator is accelerating a hammer to velocities up to 5 m/s within distances of less than 70 mm. &lt;br /&gt;In this paper, a few helpful improvements are described which lead to an enhanced repeatability of pulse generation over the full shock intensity range as well as a substantial decrease of harmonic disturbing signals.

Detonation shock dynamics modeling and calibration of the HMX-based conventional high explosive PBX 9501 with application to the two-dimensional circular arc geometry

A surface evolution model is developed for the detonation propagation dynamics of the HMX-based conventional high explosive PBX 9501, which relates the normal surface speed Dn to its local surface curvature κ. Such surface evolution models are important for the understanding and modification of engineering design calculations for high explosive applications. We describe a series of unconfined PBX 9501 slab geometry experiments of varying thickness, and detail how the steady axial detonation speed and detonation front shape data are obtained. A merit-function based calibration process is then described that uses both the PBX 9501 thickness effect and front shape data to parametrize the Dn−κ propagation law. The time-dependent PBX 9501 Dn−κ surface evolution law is then applied to detonation wave propagation in two-dimensional circular arc geometries, systematically examining the effect of arc thickness, inner radius, relaxation dynamics to steady-state propagation and confinement.

Sovereign Risk in Macroprudential Solvency Stress Testing

This paper explains the treatment of sovereign risk in macroprudential solvency stress testing, based on the experiences in the Financial Sector Assessment Program (FSAP). We discuss four essential steps in assessing the system-wide impact of sovereign risk: scope, loss estimation, shock calibration, and capital impact calculation. Most importantly, a market-consistent valuation approach lies at the heart of assessing the resilience of the financial sector in a tail risk scenario with sovereign distress. We present a flexible, closed-form approach to calibrating haircuts based on changes in expected sovereign defaults affecting bank solvency during adverse macroeconomic conditions. This paper demonstrates the effectiveness of using extreme value theory (EVT) in this context, with empirical examples from past FSAPs.

Sovereign Risk in Macroprudential Solvency Stress Testing

This paper explains the treatment of sovereign risk in macroprudential solvency stress testing, based on the experiences in the Financial Sector Assessment Program (FSAP). We discuss four essential steps in assessing the system-wide impact of sovereign risk: scope, loss estimation, shock calibration, and capital impact calculation. Most importantly, a market-consistent valuation approach lies at the heart of assessing the resilience of the financial sector in a tail risk scenario with sovereign distress. We present a flexible, closed-form approach to calibrating haircuts based on changes in expected sovereign defaults affecting bank solvency during adverse macroeconomic conditions. This paper demonstrates the effectiveness of using extreme value theory (EVT) in this context, with empirical examples from past FSAPs.

On the formation of diaplectic glass: Shock and thermal experiments with plagioclase of different chemical compositions

AbstractThis contribution addresses the role of chemical composition, pressure, temperature, and time during the shock transformation of plagioclase into diaplectic glass—i.e., maskelynite. Plagioclase of An50‐57 and An94 was recovered as almost fully isotropic maskelynite from room temperature shock experiments at 28 and 24 GPa. The refractive index (RI) decreased to values of a quenched mineral glass for An50‐57 plagioclase shocked to 45 GPa and shows a maximum in An94 plagioclase shocked to 41.5 GPa. The An94 plagioclase experiments can serve as shock thermobarometer for lunar highland rocks and howardite, eucrite, and diogenite meteorites. Shock experiments at 28, 32, 36, and 45 GPa and initial temperatures of 77 and 293 K on plagioclase (An50‐57) produced materials with identical optical and Raman spectroscopic properties. In the low temperature (&lt;540 K) region, the formation of maskelynite is entirely controlled by shock pressure. The RI of maskelynite decreased in heating experiments of 5 min at temperatures of &gt;770 K, thus, providing a conservative upper limit for the postshock temperature history of the rock. Although shock recovery experiments and static pressure experiments differ by nine orders of magnitude in typical time scale (microseconds versus hours), the amorphization of plagioclase occurs at similar pressure and temperature conditions with both methods. The experimental shock calibration of plagioclase can, together with other minerals, be used as shock thermobarometer for naturally shocked rocks.

A two-DOF model-based input prediction for high-shock accelerometer calibration

This article describes a two-degree-of-freedom (two-DOF) model-based input prediction method in the frequency domain for the comparison of high-shock acceleration calibration facilities. The current measurand for transferring the unit is the shock sensitivity as the relationship between the peak values of the accelerometer output quantity and the acceleration. The common transfer standards applied in shock calibration facilities in the range up to 100 km s−2 are piezoelectric-based transducers with a first resonance close to, or within, the spectrum of the exciting shock. This leads to the effect that the provided is, technically speaking, only valid for shocks of the same spectral composition, resulting in unpleasantly high uncertainties in high-shock measurements. This is thus not feasible if applied to shocks of differing spectral composition.A parametrized two-DOF model is capable of describing the transfer standard and allows the prediction of the applied input excitation with unprecedented accuracy. A method for the parameter identification and input prediction in the frequency domain and the results for two transfer standards are presented.

Sovereign Risk in Macroprudential Solvency Stress Testing

This paper explains the treatment of sovereign risk in macroprudential solvency stress testing, based on the experiences in the Financial Sector Assessment Program (FSAP). We discuss four essential steps in assessing the system-wide impact of sovereign risk: scope, loss estimation, shock calibration, and capital impact calculation. Most importantly, a market-consistent valuation approach lies at the heart of assessing the resilience of the financial sector in a tail risk scenario with sovereign distress. We present a flexible, closed-form approach to calibrating haircuts based on changes in expected sovereign defaults affecting bank solvency during adverse macroeconomic conditions. This paper demonstrates the effectiveness of using extreme value theory (EVT) in this context, with empirical examples from past FSAPs.

Primary shock calibration of accelerometers at Inmetro

This paper presents the primary shock calibration system developed at Inmetro to obtain the shock sensitivity of accelerometers and acceleration measuring chains. The shock exciter employs a pneumatic driver and is based on the mechanical shock between two rigid bodies guided by air bearings. The system follows the ISO standard 16063-13. The shock acceleration is measured by laser interferometry. Details of the calibration system, including the shock machine, data acquisition and signals processing are presented and some measurement results are discussed by the authors.

Determination of Pulse Width and Pulse Amplitude Characteristics of Materials Used in Pendulum Type Shock Calibration Device

Determination of Pulse Width and Pulse Amplitude Characteristics of Materials Used in Pendulum Type Shock Calibration Device

Study on several key problems in shock calibration of high-g accelerometers using Hopkinson bar

In this paper, we studied several key problems in the shock calibration of high-g accelerometers, in which the Hopkinson bar system was employed as the loading and testing device. Firstly, in order to generate a strain pulse (the excitation signal in shock calibration) with high amplitude and a wide frequency bandwidth, the pulse shaping techniques by adjusting the geometry of projectile were numerically investigated. It was found that a smaller degree of taper at the front end of the projectile causes lower amplitude and wider duration of the acceleration pulse. The findings in studying pulse shaping technique could guide the choice of the projectile's geometry in the dynamic linearity calibration of accelerometers. Second, a novel method of the dynamic linearity calibration for accelerometers was proposed and verified by experimental tests. In the calibration process, we employed a single-barrel gun instead of the double-barrel gun (proposed in earlier studies) to launch two coaxial cylindrical projectiles, such that the synchronous impact of the two projectiles can be easily achieved in practice. Lastly, the efficiency of this developed calibration method was discussed in details. The calibration system used in this study is able to achieve a testing range from thousands of g to nearly 300,000g.

Implementations and pilot comparison of primary low intensity shock calibration

&lt;p class="Abstract"&gt;This paper first presents two main technical concerns for a possible low intensity shock comparison: variety of primary shock calibration systems and feasibility of comparison artifact. For the primary calibration system, the mechanical excitation includes hammer-anvil collision, pneumatic driven projectile impact and Hopkinson bar. The shock pulses generated are smooth monopole shape by the first two types with air bearings, but dipole shape by the third type. For the comparison artifact, a standard accelerometer of single-ended type with a charge amplifier consists of an accelerometer measuring chain whose nonlinearity of amplitude and phase frequency responses is investigated. Based on the nonlinear fact of comparison artifact at frequency domain and the spectrum range difference of mechanical excitations of the calibration system, strict comparison conditions had to be laid down for measurement of shock sensitivity at specific acceleration levels and pulse durations.&lt;/p&gt;The pilot comparison, coded as APMP.AUV.V-P1, is successfully organized by Asia Pacific Metrology Programme. Some comparison results of both monopole excitation and dipole excitation are shown with the expanded uncertainty. The completion of this pilot comparison can serve as part of the basis for a planned key comparison targeted at a low intensity shock range at Consultative Committee level.

An enhanced primary shock calibration procedure to reduce the zero shift effect of piezoelectric transducers by using a virtual amplifier

The low-frequency response of a charge amplifier induces an accelerometer (a combination of a piezoelectric transducer and a charge amplifier) output voltage with zero shift. Hence, a virtual amplifier with same input–output characteristics as the charge amplifier was designed to reduce the zero shift effect. The charge shock sensitivities of a piezoelectric transducer were evaluated by applying the input acceleration to the virtual amplifier. The results of the study indicated that the charge shock sensitivities were comparable to the vibration calibration results.

Dispersion analysis of accelerometer shock calibrations by comparison using a new exciter developed at Inmetro

The applicability of a new mechanical shock exciter developed at the Vibration Laboratory of Inmetro for primary calibrations was analysed for calibrations of accelerometers by the comparison method. Using two back-to-back reference transducers and a single-ended general purpose accelerometer as device under test (DUT), calibrations were performed using the exciter developed at Inmetro, and the results were compared with those obtained with a commercial shock exciter. Two shock amplitudes and two pulse durations were applied to evaluate the dispersion of the DUT shock sensitivity. This analysis shows that the new exciter provides appropriate repeatability for shock sensitivity measurements, indicating a powerful system for generation of shock pulses.

A Round Robin Test of Piezoresistive Shock Accelerometers between Shock and Centrifuge Calibrations

A Round Robin Test of Piezoresistive Shock Accelerometers between Shock and Centrifuge Calibrations

Final report on pilot comparison of low intensity shock APMP.AUV.V-P1

This is the final report for pilot comparison APMP.AUV.V-P1 in the area of low-intensity 'shock', which in this case means monopole and dipole shock acceleration. The aim of this comparison was to measure the shock voltage sensitivity of one Accelerometer Chain with primary means under monopole shock excitation in the acceleration range from 500 m/s2 to 5 000 m/s2, and under dipole shock excitation with the reference acceleration of 1000 m/s2 and pulse duration from 0.03 ms to 2.0 ms. Four laboratories with primary shock calibration capability have participated in the comparison with National Institute of Metrology, P R China as pilot lab. One standard accelerometer of back-to-back type with a charge amplifier (Accelerometer Chain) was circulated among the participants. The pilot comparison reference values have been calculated using the weighted mean value of the results. The degrees of equivalence calculated from the data submitted by the four laboratories, support the uncertainty of measurement reported by them for the calibration of the shock sensitivities of accelerometer. At the reference acceleration of 1 000 m/s2 and pulse duration of 2 ms (specified in ISO 16063-13:2001), the participating laboratories calibrated the Accelerometer Chain with their claimed relative expanded uncertainty (k = 2), the smallest of which equal to 0.5%, i.e. smaller than the limit specified by the ISO standard. The completion of APMP.AUV.V-P1 can serve as part of the basis for a planned key comparison targeted at low intensity shock range at CC level.Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCAUV.

A primary standard for low-g shock calibration by laser interferometry

This paper presents a novel implementation of a primary standard for low-g shock acceleration calibration by laser interferometry based on rigid body collision at National Institute of Metrology, China. The mechanical structure of the standard device and working principles involved in the shock acceleration exciter, laser interferometers and virtual instruments are described. The novel combination of an electromagnetic exciter and a pneumatic exciter as the mechanical power supply of the standard device can deliver a wide range of shock acceleration levels. In addition to polyurethane rubber, two other types of material are investigated to ensure a wide selection of cushioning pads for shock pulse generation, with pulse shapes and data displayed. A heterodyne He–Ne laser interferometer is preferred for its precise and reliable measurement of shock acceleration while a homodyne one serves as a check standard. Some calibration results of a standard acceleration measuring chain are shown in company with the uncertainty evaluation budget. The expanded calibration uncertainty of shock sensitivity of the acceleration measuring chain is 0.8%, k = 2, with the peak acceleration range from 20 to 10 000 m s−2 and pulse duration from 0.5 to 10 ms. This primary shock standard can meet the traceability requirements of shock acceleration from various applications of industries from automobile to civil engineering and therefore is used for piloting the ongoing shock comparison of Technical Committee of Acoustics, Ultrasound and Vibration (TCAUV) of Asia Pacific Metrology Program (APMP), coded as APMP.AUV.V-P1.

Implementing a Shock Calibration System Using a Vibration Exciter and Pendulum

As the custodian of the National Measurement Standards (NMS), the vibration laboratory of the National Metrology Institute of South Africa (NMISA) has developed a mechanical shock calibration syste...

Digital filter design with zero shift on charge amplifiers for low shock calibration

Zero shift caused by the low frequency response of charge amplifiers is one of the most significant factors in shock measurements with long duration, such as low shock calibration of accelerometers. In order to reproduce the same zero shift as the charge amplifier, infinite impulse response (IIR) filters were developed by applying a second order transfer function to the high pass characteristic in the low frequency part of the measured frequency response of charge amplifiers. For the experimental verification of the zero shift using the IIR filter, input/output signals of the charge amplifier were investigated by using rectangular waveforms with a peak voltage of 2 V and pulse width of 10 ms and 5 ms, respectively. As indicated by the results, the IIR filter succeeds in following the same zero shift as the charge amplifier.