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Dirk Röske
KEY COMPARISONS IN THE FIELD OF TORQUE MEASUREMENT

One of the main tasks of the National Metrology Institutes (NMIs), besides the realization and improvement of standards for the different physical and other quantities, is to carry out comparisons between their own standards and those of other NMIs. At the highest level, the CIPM key comparisons involve at least the standards with the smallest uncertainties of measurement in the world and should cover - if possible - all geographical regions through the corresponding Regional Metrological Organizations (RMOs). It is also intended to compare different realization techniques of the given quantity and to make a statement of equivalence for the different calibration capabilities. This document deals with the recently agreed CIPM key comparisons in the field of torque measurement.

Andreas Brüge, Rudolf Konya
INVESTIGATIONS ON TRANSDUCERS FOR TRANSFER OR REFERENCE IN CONTINUOUS TORQUE CALIBRATION

The highest level of torque calibration is achieved by direct loading and, due to the use of mass stacks, is associated with the step-by-step method. In order to fit the demand of applications especially in industry, calibration devices with the ability of performing continuous loading were developed which are working as reference machines. A benefit of continuous methods is that the time for a loading-unloading cycle can be ten times or more shorter than using the step method. This fast change in torque leads to conditions of use that cannot be represented in the national torque standards. Therefore the appointed reference- and transfer-transducers should have negligible sensitivity to fast loading effects. With such transducers the results of slow absolute calibrations in the national torque standards are valid also in the fast continuous-working machines. In Germany a guideline treating this problems of continuous calibration is in preparation at a working group of the German Calibration Service (DKD). In this guideline special qualification-tests are proposed which can be performed in existing direct loading machines and which can deliver information about the suitability of transducers as reference or transfer for continuous working machines. In this paper we describe these qualification-tests, discuss the results of the tests in comparison to the behaviour of the tested transducers in continuous measurements and recommendations for the selection of transducers for continuous use are given.

Aimo Pusa, Dirk Röske, Michael Sachs
COMPARISON MEASUREMENTS OF MIKES-RAUTE 20 kN·m TORQUE REFERENCE DEVICE WITH THE PTB

This article deals with the vertical 20 kN·m torque reference calibration device newly built by MIKES- RAUTE. It widens the possibilities of the MIKES-RAUTE Mass and Force Laboratory in the field of torque calibrations from 2 kN·m up to 20 kN·m. A brief overview about the construction and setup of the device is included in this report. Also some information about the applied calibration process is given. The main part of this article describes comparison measurements with the PTB, Germany, from summer 2004 and presents their results. They show that the device will attain an uncertainty level of 5·10-4 or better over the entire measurement range.

Dan-Mihai Stefanescu, Dae-Im Kang
AXISYMMETRICAL ELASTIC ELEMENTS FOR VERY LARGE FORCE TRANSDUCERS

Measuring of large forces up to 10 MN with high accuracy is a complex subject, blending theory, practice and applications, with a special accent in the field of Metrology. It is simply to generate complex shapes of mono-block elastic structures starting from simple shapes of strain gage measuring sections, the axisymmetrical ones being the best suited in this respect. The body of the force transducer is easy to design by 2D axisymmetric FEM and easy to manufacture. The paper have in view a unified approach of square (type A) and rectangle (type B). Square section is among the few with an analytical but complicated formula, having two strain gauges tangentially located on the outside of the ring torsion and the other two strain gauges, which complete the Wheatstone bridge, being diametrically opposed. The rectangular section (with different ratios between the two sides but without analytical formula), is obtained by a minimum modification of the previous one (making two slots), the strain gauges being circumferentially located on the upper and the lower faces. We formulate a standard FEA procedure for axisymmetrical elastic elements of strain gauged force transducers using ANSYS Mechanical program. The starting model is very “flexible”, so that, changing one by one different parameters (e.g. modifying the keypoints coordinates), a lot of variants could be studied. A special attention is necessary to obtain proper strain diagrams on the superior, lateral and inferior sides of the elastic element measuring section, because it is essential to compare these diagrams in order to establish the best strain gauges positioning. In this respect, appropriate paths were conceived and plotted each time on graph, more precise and suggestive than plotting on geometry. An original grouping of all kinds of strain diagrams on the same plot of the deformed and undeformed bodies is presented. A lot of interpretations are possible based on the multitude of data and having in view: the influence of the axisymmetrical elastic element shape (varying different parameters) on the strain gauge sensitivity; the best combination of conflicting design criteria: strain, stress (determining the overload) and displacement (determining the stiffness); the possible correlation between the nominal load and the dimensions of a particular variant, e.g. with square measuring section. In the next stages will be very useful to unite FEM and CAD, following the elastic elements parametric modeling for their best constructive optimization.

F. Tegtmeier, M. Peters
ENCAPSULATION AND UNCERTAINTIES OF STRAIN-GAUGE SENSORS FOR STRESS-MONITORING OF CONSTRUCTIONS

Strain gauges are an important tool in measuring techniques applied to determine loads and detect damages. Due to their high signal-resolving power, they are also suitable for stress analysis in building constructions. Without specific encapsulation, they are, however, suitable only for short-term measurements. Therefore, a completely new encapsulation type was developed at PTB. The strain gauges were placed in a sensor housing which protects the sensitive technology - similar to common force transducers - and is fitted into a small measurement borehole of the structure. These applied investigations were part of the work of a collaborative research center of the German Research Foundation. Based on these investigations, the measurement uncertainty of the sensor will be analyzed and the final design for commercial production and calibration of this new sensor type presented. An additional impor- tant result of this research project was the development of a new type of plastic encapsulation for the strain gauges inside that sensor. The encapsulation was tested in thermostatic hot water baths, in climatic chambers similar to those of DIN IEC 68 2-30 and in outdoor tests.

Richard Davis, Josette Coarasa
ERRORS DUE TO MAGNETIC EFFECTS IN 1 kg PRIMARY MASS COMPARATORS

A revised draft of OIML R111 has been approved recently. Among the many notable changes to the previous edition are specific requirements for both the magnetic susceptibility and residual magnetization of weights used in legal metrology. The highest class of such weights is E1, for which a 1 kg weight has a manufacturing tolerance of ± 0.5 mg. It therefore follows that better magnetic properties might be needed for weights having mass uncertainties substantially better than E1 tolerances. The work presented below shows how this problem was approached at the BIPM and supports our conclusion that alloys meeting the new Class E1 specifications for 1 kg weights have magnetic properties sufficient for the needs of the BIPM.

Oliver Mack
INVESTIGATIONS OF PIEZOELECTRIC FORCE MEASURING DEVICES FOR USE IN LEGAL WEIGHING METROLOGY

In conjunction with low-drift charge amplifiers static force and weighing measurements get more and more important for piezoelectric force transducers if the measuring time and time of load change are in the range of a few minutes. The presented investigations according to the international recommendation OIML R60 [7] point out, that piezoelectric sensors can be used for static applications with low accuracy requirements (e.g. class D for ordinary accuracy weighing instruments). With suitable methods for compensation or adjustment the sensors even meet the higher requirements of medium accuracy class C (e.g. commercial scales). Especially for high nominal loads the piezoelectric measurement technology offer unused potentials also for static precision measurements.

J. W. Chung, M. Borys, M. Firlus, W. G. Lee, R. Schwartz
BILATERAL COMPARISON OF BUOYANCY ARTEFACTS BETWEEN PTB AND KRISS

Buoyancy artefacts (BAs) are used for the experimental determination of air density. The artefacts used for this comparison were manufactured at the PTB and the KRISS respectively and consist of one hollow cylinder and one bobbin. Mass differences of the PTB and the KRISS BAs in vacuum and in air are measured simultaneously by using the PTB prototype mass comparator. Results of the bilateral comparison including uncertainty budgets and the deviation between air densities obtained by the BAs and those calculated by the CIPM formula are presented. Additionally, a comparison with a correction of the CIPM formula based on recently measured values for the air composition is given.

M. S. Kim, I. M. Choi, Y. K. Park, D.I. Kang
ATOMIC FORCE MICROSCOPE PROBE CALIBRATION BY USE OF A COMMERCIAL PRECISION BALANCE

In this paper, we investigate the characteristics of commercial AFM cantilevers and force calibration cantilevers in the range of 10 nN ~ 1000 µN by use of a high precision balance with resolution of 1 nN and 1-D fine positioning stage. This document is a guideline to the authors of papers to be presented at the TC3 2005 conference. These directions are written in the format required for papers. We advise you to download these directions as a MS Word document and use it as the template for your paper because it contains all necessary formats and styles. Papers should be submitted before October 30, 2004. The paper must be written in English, and length is limited to 6 pages, including graphs, figures, reference list.

S. Niehe
NEW EXPERIENCES WITH A FORCE MEASURING FACILITY FROM THE RANGE FROM 1 mN TO 5 N

In this contribution new experiences with a force measuring facility [1] for the range from 1 mN to 5 N consisting of a piezoelectric positioning unit for force generation and a precision compensation balance for force measuring are presented. The enhancement of the facility by means of a rotational table allows to rotate the force transducer under test around its axis and to measure the sensitivity of the transducer at different positions. By averaging the measured sensitivities of a complete rotation cycle the rotation effect can be taken into account and the deviation from the calibration of the investigated force transducer in a deadweight force standard machine is then of the order of 10-4 in relative terms. This improves the deviation of earlier results [1] without consideration of rotation effects about a factor of 8.

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