Kazunaga Ueda

Characterization of Shock Accelerometers Using Davies Bar and strain-gages

This paper proposes a novel method for evaluating the dynamic characteristics of shock accelerometers under high acceleration levels and a wide frequency bandwidth. High accelerations of 103∼105m/s2 can be generated by the reflection of an elastic wave pulse propagating in a metal bar known as the Davies bar. The elastic wave pulse is produced by the collision of a projectile against one end of the bar, and is detected by straingages. The accelerometer to be characterized is attached to the other end of the bar. The one-dimensional theory of elastic waves enables the derivation of an input acceleration to the accelerometer from the measured strain. The dispersion of the elastic waves caused by the lateral inertia of the bar is compensated for by using a two-dimensional analytical solution. This method was validated by an experiment characterizing a piezoelectric-type accelerometer within the frequency band approximately 1 kHz∼70 kHz.

A Proficiency Testing of Weight Calibration Laboratories in the Milligram Range

A proficiency testing on the mass calibration of standard weights was carried out among 16 laboratories under the JCSS accreditation scheme run by the NITE. The NMIJ/AIST which act as the reference laboratory, has prepared 3 sets of stainless steel weights with nominal values of 200 mg, 20 mg and 2 mg. To evaluate the mass stability of the traveling standard weights, the calibrations of the 18 weights have been made 13 times in the course of the testing. The performance of the participating laboratories is evaluated using En numbers. It has been confirmed that 15 laboratories have sufficient measurement capability in the milligram range. Only one outlier was a calibration result of a 200 mg weight reported by a participating laboratory

Uncertainty evaluation on the fully-automated sub-multiple calibration in the milligram range

The National Metrology Institute of Japan, AIST establishes the mass standards from 1 mg to 5000 kg, referring to the Japanese prototype kilogram, and these standards are disseminated to the weight-calibration laboratories. In this service, calibration of standard weights in the mass range of 1 mg to 500 mg has been performed by using a sub-multiple calibration method. The mass comparisons of standard weights are made by a fully-automatic mass comparator with a capacity of 5.1 g and a readability of 0.1 mug. A new weighing scheme for sub-multiple calibration is presented in order to operate the fully-automatic mass comparator more efficiently. The expanded uncertainty of the mass of the 500 mg weight measured by the sub-multiple calibration method has been estimated to be 1.7 mug. This paper describes the measuring procedure of the sub-multiple calibration by using the fully-automatic mass comparator. The measured results of the sub-multiple calibration of 100 mg decade are also presented.

Improvement of novel NRLM method for accelerometer characterization to the range 102 m s−2

Abstract This report presents a novel method for characterizing accelerometers under medium and high accelerations ranging from 2 × 10 2 to 1 × 10 6 m s −2 . The reflection of longitudinal elastic waves in a thin circular bar is used for the excitation of a test accelerometer that is attached to the end of the bar. A newly designed laser interferometer can determine the input acceleration accurately. By improving the resolution of the interferometer, the lower acceleration limit of this method can be extended from 2000 m s −2 , the previous limit, to 200 m s −2 . The effectiveness of the method is confirmed through an experiment in which a piezoelectric-type accelerometer is characterized.

Improved working efficiency of force standard machine by separating alternative weight stacks

Renovation work has been carried out to separate the 3 kN/500 N dead-weight type force standard machine (DWM) at the National Metrology Institute of Japan. Two loading frames and a common structural frame were newly manufactured. No significant changes were observed in the calibration results of several force transducers before and after the renovation; in some cases, there has even been improvement in terms of repeatability and reproducibility of the calibration results. The renovation has made it possible to operate the two weight stacks simultaneously and to improve the working efficiency of calibration, while maintaining the reliability of the DWMs as the National Force Standards.

Determination of the amount of physical adsorption of water vapour on platinum–iridium surfaces

This paper presents the measurement of the physical adsorption of water vapour on platinum–iridium surfaces using a vacuum mass comparator. This value is of importance for redefining the kilogram, which will be realized under vacuum in the near future. Mirror-polished artefacts, consisting of a reference artefact and a test artefact, were manufactured for this experiment. The surface area difference between the reference and test artefacts was 226.2 cm2. This surface area difference was approximately 3.2 times the geometric surface area of the prototype of the kilogram made of platinum–iridium (71.7 cm2). The measurement results indicate that the amount of physical adsorption at a relative humidity of 50% is 0.0129 μg cm, with a standard uncertainty of 0.0016 μg cm. This value is 0.03 to 0.16 times that observed in other studies.

Characterization of shock accelerometers using Davies bar and laser interferometer

In this paper, we propose a novel method for evaluating the frequency response of shock accelerometers using Davies bar and interferometry. The method adopts elastic wave pulses propagating in a thin circular bar for the generation of high accelerations. The accelerometer to be examined is attached to one end of the bar and experiences high accelerations of the order of 103∼105 m/s2. A laser interferometer system is newly designed for the absolute measurement of the bar end motion. It can measure the motion of a diffuse surface specimen at a speed of 10−3 ∼100 m/s. Uncertainty of the velocity measurement is estimated to be±6×10−4 m/s, proving a high potential for use in the primary calibration of shock accelerometers. Frequency characteristics of the accelerometer are determined by comparing the accelerometers output with velocity data of the interferometry in the frequency domain. Two piezoelectric-type accelerometers are tested in the experiment, and their frequency characteristics are obtained over a wide frequency range up to several ten kilohertz. It is also shown that the results obtained using strain gages are consistent with those by this new method.

Mass Measurement of 1-kg Silicon Spheres for Determination of the Avogadro and Planck Constants

For the accurate determination of the Avogadro and Planck constants by the X-ray crystal density method, the mass of 1-kg silicon spheres must be measured precisely. This paper describes the mass measurement method and the evaluation of its uncertainty at the National Metrology Institute of Japan (NMIJ). For the precise mass measurement, the amount of the physical adsorption of water vapor on the surface of the silicon spheres, which could be a relative amount of about 10-8 of the total mass, was evaluated by comparison weighings both in nitrogen gas and in water vapor at a pressure of about 1200 Pa. In addition, we compare the results of seven 1-kg mass measurements conducted at the NMIJ and the International Bureau of Weights and Measures from 1996 to 2011 to confirm the reliability of our mass measurement.

Mass measurement of 1-kg silicon spheres for the precise determination of the Avogadro constant at the NMIJ

Mass measurement of 1-kg single-crystal silicon spheres is important for precise determination of the Avogadro constant. We describe the mass measurement method and its uncertainty evaluation at the NMIJ. In addition, we report the measurement of the physical adsorption of water vapor on the surface of the silicon sphere. We also report the comparative results of 1-kg mass measurement carried out six times at the NMIJ and the BIPM from 1996 to 2006 to confirm the reliability of our mass measurement.

Enabling one step loading operation using linkage-weight system of 20 kN force standard machine

The loading frame lifting mechanism of the 20 kN dead-weight type force standard machine was improved to enable the one step loading operation at the first force step. This modification was achieved by adding a reduction gear to amplify the output torque of the motor driving the loading frame. The one step loading operation allows the evaluation of the time-dependent characteristics of force transducers, and also improves the working efficiency. Some force measuring devices showed a little change of sensitivity upon applying the one step loading operation. It was found that the degree of time dependence in the characteristics of the three force measuring devices examined in this study had only a small impact on the measurement uncertainty.