J.O. Bangi, S.M. Maranga, S.P. Nganga, S. M. Mutuli
TORQUE WRENCH CALIBRATION AND UNCERTAINTY OF MEASUREMENT

Torque wrenches (TW) are widely used in the automotive, aviation and building industry. TW are used to control torque in assembly and fastening operations. Regular calibration of torque tools guarantees traceability to international standards. At KEBS, a torque wrench calibrator with four interchangeable torque transducers and torque meters are used to calibrate both type I and type II torque wrenches as per ISO 6789:2003. In compliance to “Guide for evaluation of uncertainty in measurement” (GUM), it is a requirement that a complete measurement result should include its uncertainty, a proposed method with an example on how to estimate measurement uncertainties for torque wrenches is presented after taking into account the various influencing quantities. Uncertainty values of ± 2.54 N·m, ±1.15 N·m, and ±1.33 N·m are estimated at 20%, 60% and 100% respectively of a type II class A torque wrench with a nominal value of 1000 N·m. The paper aims to provide guideline information for TW calibration and uncertainty evaluation.

R. Kumme, F. Koehler
PTB´S 16.5 MN HYDRAULIC AMPLIFICATION MACHINE AFTER MODERNIZATION

This paper describes the 16.5 MN hydraulic amplification machine of PTB after modernization. The control system of the hydraulic amplification machine is described. The amplification factor and the temperature influence of the machine are determined by comparisons with deadweight machines.

M. Borys, M. Mecke, U. Kuetgens, I. Busch, M. Krumrey, P. Fuchs, K. Marti, H. Bettin
THE GROWTH OF THE OXIDE LAYER ON SILICON SPHERES AND ITS INFLUENCE ON THEIR MASS STABILITY

The first results of gravimetric measurements of the growth of the oxide layer on single-crystal silicon spheres are presented and compared with a theoretical model and with measurements of the surface layer based on X-ray and ellipsometric methods. From the results, conclusions can be drawn about the quantitative influence of the growth of the oxide layer on the mass stability of silicon spheres.

Marco M. Schäck
HIGH-PRECISION MEASUREMENT OF STRAIN GAUGE TRANSDUCERS AT THE PHYSICAL LIMIT WITHOUT ANY CALIBRATION INTERRUPTIONS

The maximum resolution when measuring transducers, which operate on the strain gage principle, is physically limited. Possible sources of errors and their compensation to achieve the high accuracy class of 0.0005 (5 ppm) are shown. In addition to the actual extraordinary high measuring accuracy and long term stability, for the new precision instrument DMP41 the autocalibration cycles could also have been omitted. An innovative method allows to measure for the first time in this accuracy class without any interruptions caused by an auto-calibration.

Y. Kayukawa, Y. Fujita
PRECISE MASS AND VOLUME DETERMINATION OF THE SILICON SINKER FOR SEA WATER DENSIMETRY

In order to improve measurement performance in sea water densimetry which is important in global environmental monitoring, a hydrostatic weighing system is under development in the NMIJ. A 100 g silicon sinker is used as a density reference and it is required to calibrate its mass and volume with higher accuracy that the conventional calibration procedures. In the present study, sub multiple mass measurement was conducted by using 1 kg silicon sphere and newly designed silicon disc weight set. The mass uncertainty was decreased to less than 0.01 mg for the silicon sinker. The volume of the sinker was measured by using a pressure-of-floatation method (PFM) to realize the relative uncertainty of the volume being 0.17 ppm.