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Bob Hardy
TRUST BUT VERIFY – PRACTICAL APPROACHES TO HUMIDITY GENERATION AND MEASUREMENT

Construction of humidity generators is a common undertaking in many of today's national metrology institutes and commercial calibration laboratories. A generator based on theoretical methods and statistical uncertainty expectations is often trusted as a laboratories primary humidity reference. While it is important to follow sound design theory, and compute statistical estimates of the output from a generator, verification is an equally powerful tool that can help to make even the weakest of designs more trustworthy. Generator designs will be reviewed in an effort to avoid common obstacles while capitalizing on a few simple and practical improvements. Testing and verification will also be considered with a focus on condensation hygrometry.

Howard W. Yoon, Charles E. Gibson, David W. Allen, Robert D. Saunders, Maritoni Litorja, Steven W. Brown, George P. Eppeldauer, Keith R. Lykke
THE REALIZATION AND THE DISSEMINATION OF THE DETECTOR-BASED KELVIN

In the International Temperature Scale of 1990 (ITS-90), temperatures above the freezing temperature of silver are determined with radiation thermometers calibrated using spectral radiance ratios to one of the Ag-, Au- or Cu-freezing temperature blackbodies and the Planck radiance law. However, due to the use of spectral radiance rats, the temperature uncertainties of the ITS-90 increase as the square of the temperature ratios. Recent acoustic- gas thermometry measurements have also shown that the underlying thermodynamic temperatures used in the radiance ratios in determining the Ag- and Au-fixed point temperatures could be in error. Since the establishment of ITS-90, much progress has been made in the development of radiation thermometers and blackbody sources. Cryogenic electrical-substitution radiometry is widely used in detector and radiometer calibrations, and stable, high-temperature metal-carbon eutectic blackbodies are under development. Radiation thermometers can be calibrated for absolute radiance responsivity, and blackbody temperatures determined from measurement of optical power without the use of any fixed points thus making possible direct dissemination of thermodynamic temperatures. We show that these temperatures can be measured with lower final uncertainties than the ITS-90 derived temperatures. We have shown that these “Absolute Pyrometers” can be used to determine the thermodynamic temperatures of the ITS-90 fixed points as well as also being used in bilateral comparisons of temperature scales. Many leading national measurement institutes are already utilizing detector- based temperatures in establishing spectroradiometric source scales. We believe, that due to these developments, the international temperature scale should be revised so that a thermodynamic temperature scale can be directly disseminated.

P. Marcarino, G. Bonnier
TEMPERATURE AMPLIFIER BY MEANS OF COUPLED GAS-CONTROLLED HEAT-PIPES

BNM-INM and IMGC-CNR have been working during many years in the field of Gas-Controlled Heat-Pipes (GCHPs). These devices have been specifically developed for accurate temperature measurements, with ever improving thermal characteristics during the last 30 years. A GCHP is based on the thermodynamic properties of the liquid-vapor transition of a given working fluid under a controlled pressure. The measuring zones of the more recent GCHPs, connected to an accurate pressure controlled line, present a temperature uniformity and stability at the millikelvin level in a very large range of temperature. The basic principles of GCHPs are reviewed and the most important results achieved by using this device in thermometry are presented. By applying the same pressure to several GCHPs using different working fluids, the temperature in one GCHP is thermodynamically related to the temperature in another GCHP. It means that any temperature of a given working fluid, i.e. between 240 °C and 400 °C for a mercury GCHP, is able to be "amplified" in order to establish an unique and very reproducible higher temperature in another working fluid, i.e. between 660 °C and 962 °C for a sodium GCHP. This instrument, called “Temperature Amplifier” (TA), allows a considerable improvement in the calibration process of SPRTs at high temperature. Indeed, the operating temperature of the reference SPRT in the low temperature GCHP can be limited to 400 °C, and, consequently, the stability and reproducibility in the high temperature GCHP are largely improved. The experimental results lead to the possibility to use the TA above the Aluminum point as a possible alternative instrument in a future temperature scale.

Joachim Fischer, Bernd Fellmuth, Joachim Seidel, Wolfgang Buck
TOWARDS A NEW DEFINITION OF THE KELVIN: WAYS TO GO

The present definition of the kelvin links the unit of temperature with a material property. It would be more consistent with the current approaches to other base units to fix the value of the Boltzmann constant k, in- stead. For this purpose, k must first be determined with distinctly lower uncertainty. This paper considers ex- perimental methods having potential to contribute to the determination of k.

Shang Wei Lu, Li Tao, Cheng Yong Pei, Wang Yan, Qian Zhao Jun
50 kNm TORQUE STANDARD MACHINE

The paper introduces the working principle of dead-weight balance type 50kNm torque standard machine , which was developed recently. The paper describes in detail the key technique , etc. such as the knife edge supporting technique with high load , the force magnifing technique , the alignment technique and the computer control automatic loading technique , etc. The paper analyses the uncertainty of the machine and the compared and verifyed data with LNE . The uncertainty of the 50kNm torque standard machine arrives at 0.023%(tp=3.1).

M. Peters, D. Peschel, R. Kumme, D. Mauersberger
PTB's 'new' 2 MN Deadweight Force Standard Machine

In this contribution, the new 2 MN deadweight force standard machine of PTB, which was moved from Berlin to Braunschweig and has been completely modernised, is presented. The determination of the mass of the deadweights with a special mass comparator is described. The uncertainty of the machine is theoretically analysed and experimentally verified by force measurement procedures.

Liron Anavy, Boris Katz
UNCERTAINTY AND INTERPOLATION

This article deals with interpolation methods, ways to determine which method is required and ways to check the results’ fitness.

Boris Katz, Liron Anavy, Itamar Nehary
The calibration system of force measurement devices - conceptions and principles

Developed, put into practice and used the universal automatic system MABA-2000 for calibration of force measurement devices in accordance to ISO 376-1999, ISO 7500-1999 and manufacturer requirements. The system includes a set of load cells from 1 kN to 5 MN, amplifier DMP-40 (HBM), computer and accessories. Mathematically proved the possibility of calibration in points, which vary from series to series, proved, and confirmed the application of calculation of formulas accuracy deviation and repeatability in accordance to ISO 7500-1999. This approach increases the productivity and simplifies the calibration process. Software MABA-2000 permits to communicate the measurement line “load cell-amplifier-computer” and to perform calibration process on mode ON-LINE: input of the measurement data, indications of the deviations in real time, calculations of the uncertainties, calculations of the calibration results and output of certificate. For calibration by method of Dead Weight a computer automatically selects a set of standard weights as a function of the True Force and value of gravity acceleration. The strict and precise method of the measurement results’ rounding optimizes the value of uncertainty. Calculation of interpolation polynoms of 1st, 2nd, 3rd degree is done automatically too, and does not require additional resources or time. The software MABA-2000 includes also the subroutine for the measurement load rate and calculates uncertainty in accordance to customer requirements.

Jorge C. Torres-Guzmán, Daniel A. Ramírez-Ahedo
SIM FORCE STANDARDS COMPARISON UP TO 10 kN

A comparison in the quantity of force was carried out among the SIM national laboratories in order to estimate the level of agreement for the realization of the quantity and the uncertainty associated to its measurement. This comparison was carried out up to 10 kN. The equipment used consisted on two force transducers (load cells); both with the same measuring range (10 kN). With the purpose of obtaining maximum accuracy on the transducers, the comparison range was selected from 4 kN up to 10 kN. This comparison provides a link to CIPM Key Comparisons. The results obtained, as well as the reference values selected for the comparison are included in this document. Two different methods were used to analyze the level of agreement and to state the conformity declaration.

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