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A. Brüge
Mathematical representation of reference torque transducers in partial-range regimes

Investigations with regard to the mathematical description of reference torque transducers used in comparison calibration facilities are described. A method is presented which uses only the direct loading calibration data of a torque transducer in the full range in order to calculate its behaviour in any reasonable partial range. Examinations of typical reference torque transducers demonstrate how to find transducers which are qualified for this calculation method and provide estimations of the possible effects on the measurement uncertainty caused by the calculation of the partial-range behaviour.

P. Averlant, A. Gosset
Development of the new LNE 50 N·m deadweight torque standard machine

This paper describes the new LNE 50 N·m deadweight torque standard machine. Informations on the design, development, and commissioning of this standard are given. Its design is described focusing on mechanical and metrological characteristics in particular of the structure, the deadweight, the air bearing and the lever arm.

L. C. Cabral-de Freitas, S. R. Reis-da Costa, R. Soares-de Oliveira, C. A. Koch
The torque metrology management in Brazil

In 2001, in order to improve the confidence level and the accuracy of the torque calibration systems in Brazil, the Force, Torque and Hardness Laboratory (Lafor/Inmetro) acquired a Torque Primary Standard Machine from 20 N·m up to 3000 N·m of nominal range, in clockwise and in anti-clockwise, where it was qualified by PTB/Germany in 2004. Since them, some steps have been done to disseminate the improved torque results to the users. The present work has the objective to demonstrate how Inmetro/Lafor is preparing to manage the torque metrology in Brazil due to the best measurement capabilities obtained and the increasing of the demand by the accredited laboratories and industries which are upgrading their torque equipment in order to get better uncertainties together with decreasing measurement costs.

T. Licht, S. E. Salboel
Primary vibration calibration by laser interferometry and mechanical shortcomings

Primary vibration calibration by laser interferometry using quadrature outputs has been used for the last 10-15 years. The ISO 16063-11 was published in 1999 and this has increased the interest further.
With new compact laser interferometers the difficulties of optical alignment and adjustment has been practically eliminated and dedicated software has made the process automatic, permitting to gather much more data.
Furthermore the advancement in electronic measurement capabilities, especially in high precision A/D converters, has made the electrical parts of the error budget very small.
Therefore today the dominating error sources are of mechanical nature. The problem that the laser beam not always can be directed towards the point or surface to which it ideally should be directed, introduces errors that can be quite significant and often will dominate the final error budget.
At low frequencies this is often due to non-ideal exciter motion, at high frequencies due to relative motion between points on apparently rigid mechanical structures. The ISO standards and other published material do not treat these problems in detail; only very general comments are given.
To help the calibration laboratories to a better understanding and agreement of uncertainties some practical examples, finite element modelling and corresponding measurements will be given. Examples of solutions to these problems including uncertainty calculations will be presented.

J. Setina, J. Tesar, Z. Krajicek
Validation of a variable bell jar pressure as a method for primary generation of absolute pressure in the range from 100 Pa to 5 kPa

Generation of absolute pressure with a pressure balance is commonly done by enclosing the space above weights with a bell jar and evacuating it with a vacuum pump. Residual pressure in a bell jar is usually of the order of few tens of Pa to few Pa, depending on the effective pumping speed. Its value is added to a calculated pressure of the gravitational force of the piston and weights to obtain the generated absolute pressure. By connecting to the absolute pressure balance a precise and stable pressure gauge with sufficient resolution it is easy to observe that small changes of residual pressure in a bell jar generate a corresponding change in a pressure reading of the gauge. Unfortunately the lowest absolute pressure which can be generated by a pressure balance of conventional design is determined by the tare weight of the piston and some small additional weights necessary for sufficient minimum free rotation time and it is in the pressure range starting at 3 kPa and up to 5 kPa.

J. C. Torres-Guzmán, L. H. Paraguassú, P. R. G. Couto, I. L. Bezerra
SIM vacuum comparison from 133.3 Pa to 13.33 kPa

This comparison constitutes the second part of the first vacuum comparison among National Metrology Institutes (NMI) within the Interamerican Metrology System (SIM). Each laboratory used its national standards for the compared range. The Centro Nacional de Metrología (CENAM, Mexico) used a reference standard (comparison system type) and the Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO, Brazil) used a similar reference standard (comparison system type). The comparison started in December 2004 and finished in March 2005. The objective of the comparison was to estimate the level of agreement for the realization of the quantity and the uncertainty associated to its measurement.
One transducer (Capacitive Diaphragm Gauge) was used as transfer standard; the comparison range was selected from 133.3 Pa up to 13.33 kPa. The relevant aspects of the measurement protocol are summarized in the paper but were widely developed in the comparison reference documents. The gas used for the comparison was nitrogen. The measurements started at the lowest pressure and the pressure was increased up to the maximum range. The analysis of measurements comparability between the laboratories is included here. This bilateral comparison has been entered within the SIM data base as a pilot comparison SIM.7.26 P.

A. Navarro-Nateras, J. C. Torres-Guzman, P. Olvera-Arana
Measurement systems development for the calibration of leaks and holes in dynamic pressure (microflow) at CENAM, Mexico

The pressure and vacuum group of the Force and Pressure Division, at the Centro Nacional de Metrologia (CENAM, Mexico) has developed two measurement systems for calibration, one for leaks and another for holes in dynamic pressure.
The leaks calibration system is based on the method of pressure increment at constant volume (and constant temperature) within the measurement range starting at 1 x 10-6 Pa·m³·s-1 up to 5 Pa·m3·s-1 with volumes of 0.5 L or 1 L (according to the leak range to be calibrated), with an operation pressure from 1 x 10-5 Pa up to 130 kPa, using helium, nitrogen or air as manometric fluids.
For the calibration of holes in dynamic pressure, the method PVTt is used. This is, pressure increments at constant volume and constant temperature during a given time. The volume used is 3.75 L with a gas flow up to 20 cm³·min-1 using nitrogen as operation fluid.
The procedure of holes calibration consists on measuring the flow through a small hole by measuring the pressure increment due to the gas accumulation in a known volume during a period of time with controlled temperature conditions. The PVTt system is formed by pressure gauges, a gas collection tank with a known volume, temperature sensors, a chronometer for time measurement, a vacuum pump, a set of valves to control the gas flow direction and the hole which will be calibrated.

J. Galvan-Mancilla, J. C. Torres-Guzman, D. Ramirez-Ahedo
Torque proficiency test among accredited laboratories in Mexico

A torque proficiency test among accredited laboratories in Mexico was performed starting in January 2007. The main objectives of this exercise were to estimate the level of agreement for the dissemination of the quantity among laboratories and to evaluate the compatibility, including the uncertainty associated to its measurements, of the laboratories results with the set references values. The Centro Nacional de Metrologia, CENAM (Mexico) was the pilot laboratory and responsible for the coordination of this program. The maximum torque measurement for this proficiency test was 800 N·m. The torque standard TS used for the proficiency test was a torque wrench with a range up to 800 N·m. In this torque proficiency test 5 Mexican torque accredited laboratories participated. The results of the test showed good agreement among the laboratories and also with the reference values set by the national metrology institute (CENAM).

D. Ramirez-Ahedo, J. C. Torres-Guzman, F. Martinez-Juarez
Hybrid torque standard machine for 1 kN·m developed in CENAM

The torque laboratory at the Centro Nacional de Metrología in Mexico (CENAM) started operations in 1997 with the design, built up and set up of a torque transfer standard machine for 2 kN·m (TTSM-2kN·m). Since that time, a total of five torque standards have been developed at CENAM. Two of them realize the quantity via the primary method (dead weights applied in a lever arm of a well known length) in the measuring ranges of 2 kN·m and 1 kN·m. The other three transfer standard machines are in the ranges from 20 N·m and 2 kN·m, and the last one is a TTS machine which is in the set up stage, with a range up to 20 kN·m.
This paper gives general information about the design, build up and set up of the torque standard machine up to 1 kN·m which has a dual function, this is, realizing the quantity with a primary torque standard method (PTSMe) and/or disseminating it with a torque transfer standard method (TTSMe); depending on the type of calibration one wishes to perform.

S. Martínez-Sanchez, F. M. C. Laguna-Aguilar, J. C. Torres-Guzman
Metrology impact in Technological Universities, Mexico

The Universidades Tecnológicas (Technological Universities) in Mexico have as a mission to offer a high quality education model which has been in operation for more than 50 years in countries where it has proven to be a success. In 1998, the Centro Nacional de Metrología (CENAM) collaborated with the Technological Universities by means of an indepth technical training in Metrology. The objective was to disseminate the metrological knowledge among the academic members and stimulate them to establish secondary calibration laboratories in their institutions.

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