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S. Lorefice, A. Malengo
HYDROSTATIC WEIGHING SYSTEM AT THE INRiM FOR CALIBRATING HYDROMETERS

Hydrometers are simple but effective instruments for measuring the density of liquids. In this work, we present the new hydrostatic weighing system developed at the INRiM, formerly IMGC – CNR, for the calibration of hydrometers in the range 500 kg·m-3 to 2000 kg·m-3.
The apparatus which uses a method to automatically align specific scale-marks for the calibration of hydrometers, makes easy the whole calibration procedure and allows to reduce the former uncertainty declared by laboratory. It consists of a vision system, a stepping motor, and software to control the system. The vision system, composed of a CCD camera and a frame grabber, is used to acquire images. The overall performance of the apparatus is illustrated by the assessment of the uncertainty for some usual kinds of hydrometers sent to the Institute for calibration.

Koji Ohgushi, Takashi Ota, Kazunaga Ueda, Diedert Peschel, Andreas Brüge
INTER-LABORATORIES COMPARISON OF REFERENCE TORQUE WRENCH CALIBRATION BETWEEN NMIJ AND PTB

Inter-laboratories comparison of reference torque wrench calibration was conducted between the NMIJ and the PTB using a torque transducer with the form of torque wrench, TTS/100Nm, the rated capacity of which was 100 N·m, as a transfer device. Under various calibration conditions, the calibration results obtained by both laboratories were coincided within the range of uncertainties of measurement.

Kenichi Fujii, Naoki Kuramoto, Yohei Kayukawa
EFFECT OF COVARIANCES IN A DENSITY MEASUREMENT OF SILICON SAMPLES BY HYDROSTATIC WEIGHING

A density standard realized by 1 kg silicon spheres has been used for measuring the density of solid samples by hydrostatic weighing. Details are given for the structure of the measurement system, procedure for the solid density measurement, and uncertainty evaluation. The density of a 1 kg silicon sample has been measured with a relative combined standard uncertainty of 1.2 parts in 107. When the effect of covariances in input quantities is taken into account, the relative combined uncertainty in measuring the density difference between the silicon spheres and the silicon sample may be reduced to 3.6 parts in 108. Uncertainty sources in the hydrostatic weighing and the effect of covariance in the input quantities are discussed.

Jon R. Pratt, John A. Kramar
SI REALIZATION OF SMALL FORCES USING AN ELECTROSTATIC FORCE BALANCE

We describe the realization of micronewton forces in a fashion traceable to the International System of Units (SI) using the National Institute of Standards and Technology (NIST) electrostatic force balance. A comparison between deadweight and electrostatic force is presented at a force level of approximately 200 µN. Our results demonstrate agreement between these two independent measurements at a level consistent with the uncertainties in 20 mg mass artifacts. We provide a brief description of our balance and its measurement principles, and then outline the procedures and the data analysis used to derive our results. As part of the paper, we also present a table that summarizes the uncertainties associated with realizing a 200 µN force via an electrode suspended in a measured electrostatic field. We compare this with the uncertainties associated with realizing the same force via a mass artifact in a measured gravitational field.

Jens Illemann, Rolf Kumme
RESEARCH FOR A NATIONAL FORCE STANDARD MACHINE IN THE RANGE FROM MICRO NEWTON TO NEWTON RELYING ON FORCE COMPENSATION

Electromagnetically compensated balances (ECB) are reliable and well-established weighing instruments. As completely electromagnetically compensated types they are commercially available with mass ranges from two grams to several kilograms. They also represent a highly stable and linear scale for force. In this publication it will be shown how ECBs can be used for force standard machines (FSM) having a range of a few Newtons and a feed-back stabilized resolution of single micro Newtons. Moreover, such FSMs conform to the future requirements of continuous calibration.

Jeah-Sheng Wu, Hsien-Chi Yeh, Sheau-shi Pan
MEASUREMENT OF PHOTON PRESSURE

Center for Measurement Standards has established a system to probe micro force down to nano Newton. Based on a very stable torsion strip pendulum with restoring torque constant 5.25·10-6 N·m/rad. Light beam of a high power Nd:YAG laser was reflected by the mirror attached on pendulum frame. Result in angular deflection of the pendulum. The deflection was measured by an angular interferometer with resolution 1.95·10-7 rad. Modulation signal, generated by varying power of laser, shift the pendulum from its standing position. The angular deflection equivalent torque is the same as photon generating torque to within 22%.

Günther Haucke, Daniel Schwind, Rolf Kumme
INVESTIGATION OF FORCE TRANSDUCERS WITH DIFFERENT LOADING PROCEDURES ON JOCKEY-WEIGHT AND DEADWEIGHT MACHINES

Force transducers used as transfer standards are usually calibrated according to ISO 376. Industrially applied force transducers can be calibrated according to more simplified procedures, however with extended measurement uncertainty. The main purpose of this paper is to point out the different values of the characteristic parameters which are due to varied loading procedures.

A.Capelli, G.D’Agostino, S.Desogus, A.Germak, C. Origlia, D. Quagliotti
A TRANSPORTABLE ABSOLUTE GRAVITY METER ADOPTING THE SYMMETRIC RISE AND FALLING METHOD

The Gravimetry Group of the Institute of Metrology “G. Colonnetti” (IMGC-CNR), nowadays National Institute of Research in Metrology (INRIM), developed a new version of a transportable absolute gravimeter, the IMGC-02. The instrument presents several improvements mainly concerning the transportability, the measurement automation and the user-interface programs. According to the ISO-GUM (Guide to the Expression of Uncertainty in Measurements), an extensive analysis concerning the contributors to the uncertainty budget has been conducted. At present the instrumental expanded uncertainty (p = 95%) is believed to be about 8 parts in 109 of the surface gravity value. The detailed description of the IMGC-02 apparatus and an outline of its metrological characterization is the subject of this paper.

Jae-Hyuk Choi, Mahn-Soo Choi, Min-Seok Kim, Yon-Kyu Park, Jin-Hoon Sohn
NEW CONCEPT OF FORCE REALIZATION BASED ON MACROSCOPIC QUANTUM EFFECT

We present a new concept of force realization, flux quantum-based mechanism in the sub-pico-Newton range. By controlling the number of flux quantum in a superconducting ring, a force can be generated as an integer multiple of a constant force step. For a 50 nm-thick Nb annulus with the inner and outer radii of 5 µm and 10 µm, respectively, and the field gradient of 10 T/m the force step is estimated to be 184 fN. Realization procedure, feasibility, and the stability against thermal fluctuations are also addressed.

Dirk Röske, Dietmar Mauersberger
ON THE STABILITY OF MEASURING DEVICES FOR TORQUE KEY COMPARISONS

Key comparisons are an important approach for the national metrological institutes to ensure that the units of the different physical, chemical and other quantities are realized and disseminated according to the stated uncertainties. In May 2005, the first world-wide CIPM torque key comparison (CCM.T-K1) has been started. The main purpose of this paper is to compare the stability of the torque standard machine, the travelling standard (torque transfer standard) and the amplifier DMP40 of the pilot laboratory with the combination of the bridge standard BN100 and the same amplifier.

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