Hideaki Nozato

Calibration of vibration pick-ups with laser interferometry: part IV. Development of a shock acceleration exciter and calibration system

Measuring shock acceleration with peak accelerations ranging from 200 to 5000 m s?2 is a significant concern for mechanical or electrical applications in industries. To precisely calibrate accelerometers using shock acceleration, we developed a shock acceleration calibration system at the National Metrology Institute of Japan. In the calibration system, the shock acceleration exciter generates shock acceleration using rigid-body collisions between three metallic bars inside an air bearing. The pick-up to be calibrated is fixed on an edge surface of the third metallic bar so that the pick-up moves together with the metallic bar. The displacement of the pick-up is measured by a He?Ne laser interferometer with traceable voltage, length and time standards. The sensitivity of the pick-up is evaluated by analysing signals from the accelerometer and laser interferometer. We describe the calibration procedure, the specification of the shock acceleration calibration system and the uncertainty in the shock-acceleration calibration. The shock acceleration calibration result has the expanded uncertainty of roughly 1.0% with a coverage factor 2 and is comparable to the vibration acceleration calibration result with an En value below 0.3.

The methods for the calibration of vibration pick-ups by laser interferometry: part V. Uncertainty evaluation on the ratio of transducer's peak output value to peak input acceleration in shock calibration

This study describes the uncertainty of measurement about accelerometer sensitivity in shock calibration based on ISO 16063-13. The typical shock approximates to a sine-squared waveform with peak acceleration in the range from 200 to 5000 m s−2 and a pulse width of several milliseconds. The shocks are generated by a transient collision motion on contact with a rubber surface between two rigid bodies. A laser interferometer with a He–Ne laser measures the displacement change that is input to the accelerometer to be calibrated. The accelerometer sensitivity is evaluated in the time domain and defined by the ratio of the accelerometers output peak value to the input acceleration peak value. The individual uncertainty components are assessed to formulate an uncertainty budget that includes an expanded uncertainty with a coverage factor of k = 2 at approximately 6.5 × 10−3.

Spectroscopic Studies on Impurity Transport of Core and Edge Plasmas in LHD

Spectroscopic diagnostics have been extensively developed for studies of impurity and neutral particle transports at core and edge plasmas in LHD. Diagnostics of core plasmas are similar to a tokamak case, i.e., Zeff from visible bremsstrahlung, K-x-ray measurements from x-ray spectroscopy using Si(Li) detectors and a compact crystal spectrometer, and high-Z impurity diagnostics from VUV spectroscopy using a flat-field EUV spectrometer. A combination of impurity pellet injection and visible bremsstrahlung is an active tool for determination of the diffusion coefficient D and convective velocity V. Using this tool the spatial structures of D and V are obtained and discussed with a neoclassical effect. On the other hand, the spectroscopic method for edge diagnostics is considerably different from the tokamak case because of the existence of a thick ergodic layer in addition to the x-points necessarily included into the diagnostic chord view. In order to break this negative situation, Zeeman and polarization spectroscopy are adopted to LHD edge plasmas. As a result, 2-dimensional emission contours of HeI and Hα are successfully obtained. Laser absorption spectroscopy is tried to measure hydrogen neutrals directly. Radial profiles of edge impurities are also measured with a mirror-assembled 3 m VUV spectrometer. Recent results of and progress in LHD spectroscopy are briefly reviewed.

Simple digital phase-measuring algorithm for low-noise heterodyne interferometry

We present a digital algorithm for measuring the phase difference between two sinusoidal signals that combines the modified fringe-counting method with two-sample zero crossing to enable sequential signal processing. This technique can be applied to a phase meter for measuring dynamic phase differences with high resolution, particularly for heterodyne interferometry. The floor noise obtained from a demonstration with an electrical apparatus is

Effect of demodulator unit on laser vibrometer calibration

5\times10^{-8} \mathrm{rad/\sqrt{Hz}}

Preliminary implementation of primary calibration system for laser vibrometer

at frequencies above approximately 0.1 Hz. In addition, by applying this method to a commercial heterodyne interferometer, the floor-noise level is confirmed to be

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

7\times10^{-14} \mathrm{m/\sqrt{Hz}}

Shock Calibration with Zero Shift Using a Digital Filter Technique

from 4 kHz to 1 MHz. We also confirm the validity of the algorithm by comparing its results with those from a standard homodyne interferometer for measuring shock-motion peak acceleration greater than 5000 m/s^2 and a 10 mm stroke.

Measurement of angle error of gyroscopes using a rotary table enhanced by self-calibratable rotary encoder

In this study, the effect of demodulator unit characteristics on the calibration of a laser vibrometer is investigated. For this purpose, two commercial available laser vibrometers with analogue demodulator units are used in the experiments. The demodulator units are electrically calibrated using simulated frequency-modulated signals, which are equivalent to output signals obtained from laser optics during laser vibrometer calibration. The calibration results of the demodulator units show extremely similar characteristics to laser vibrometer calibration results carried out in accordance with the new proposed draft (ISO16063-41). Although both calibration results had a large deviation of more than 0.5 % from the nominal sensitivity, a smaller deviation within 0.5 % was obtained by correction on the basis of the demodulator calibration results. The calibration results for both commercially availbale laser vibrometers indicate same amount of deviation after correction.. Most of the large deviation in the laser vibrometer calibration is due to the demodulator characteristics. In ISO16063-41 draft, laser vibrometer calibration is carried out by applying actual vibration to the laser vibrometer. However, the acceleration amplitude range applicable for calibration is limited due to the capability of the vibration exciter. Therefore, the measurable dynamic range of the laser vibrometer is not always sufficiently covered in the calibration. To overcome this problem, our investigation suggests the applicability of a combination of individual component calibrations.

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

In this paper, we outline a preliminary implementation of primary calibration for a laser vibrometer (LV) on the basis of newly proposed first ISO draft. The sine approximation method is applied to our calibration system. Under some different measurement conditions, primary calibration is preliminarily carried out for achieving reliable measurements. From these results, the effects of acceleration amplitude stability, mechanical distortion, position of measuring beam, and spot diameter of measuring beam have been discussed. Some conditions required for achieving the reliable calibration is indicated on the basis of the discussion. Additionally, the strict regulations of the distance between spots and such amount of mechanical distortion would be indispensable for guaranteeing a higher reliability of such calibration within an expanded uncertainty (k = 2) of less than 0.5 %.