Table of contents

An algorithm of the Monte Carlo method is described which allows evaluation of the effective emissivities of isothermal and nonisothermal specular-diffuse black-body cavities for use in radiometry, photometry and optical pyrometry. The calculation provides estimates of normal spectral effective emissivity for black-body cavities, formed by cone surfaces and a cylinder. It does this for an isothermal cavity and for a cavity having an arbitrary variation of temperature along the cavity length.

Comparison calibration designs are rank insufficient to permit a purely batch estimation of parameters, and require the input of some a priori knowledge. The estimator commonly used, which is based on Restrained Least Squares, is shown to be inappropriate because of its inability to take account of uncertainty in the a priori knowledge. A model in which the parameters represent the state of a dynamic stochastic system is proposed together with the appropriate recursive estimator, namely the Kalman filter-predictor. This estimator is less affected than Restrained Least Squares by errors in the a priori knowledge. Its application in mass comparisons in conjunction with a fully recursive approach, i.e. with use of all the available a priori knowledge, is discussed.

Theoretical analyses of the effects of quantization, differential and integral non-linearities on digital correlators measuring noise power are reviewed. The theoretical results are then applied to the measurement and modelling of errors in two 15-bit analogue-to-digital converters (ADCs) used in a high-accuracy Johnson noise thermometer. The experimental results support the theory and show that a significant fraction of the correlator error can be modelled by an error in the sign bit of the ADCs. This error cannot be modelled by a truncated Taylor series. For the ADCs tested, the model fits the observed non-linearities with an accuracy of 10 ppm relative to the noise variance.

The second and third dielectric virial coefficients of ⁴He have been measured by the symmetrical gas-expansion technique of Buckingham, Cole and Sutter for six isotherms between 3,00 K and 17,68 K. The effects of helium adsorption are important, and are considered in detail. No temperature dependence of the second coefficient is seen at a level of δb=±0,008 cm³ mol^-1, and average values of the second and third coefficients are b = 0,006 (10) cm³ mol^-1 and c = -5 (4) cm⁶ mol^-2, respectively. The uncertainty for b is relatively large because it has a systematic dependence on c: reanalysis of all the existing data shows that a more probable value of the third coefficient is c = -2 (1) cm⁶ mol^-2, which when combined with our data gives b (3 K - 18 K) = -0,001 (4) cm^-3 mol^-1. The very small value suggests that theoretical calculations of the excess polarizability of the helium diatom need to be reconsidered. The small value and the small uncertainty of b indicate that future work to improve experimental values of the second density virial coefficient of ⁴He for this temperature range may without ambiguity make use of the methods of dielectric constant gas thermometry.

The experimental procedure described here in detail enables the heat defect of water caused by electron radiation in the energy range from 1 MeV to 5 MeV to be determined with an overall uncertainty of less than 0,5% for the correction factor. The principle of measurement is based on a comparison of the temperature increase caused by the radiation energy of electrons totally absorbed in water with that caused by an ohmic heating of the water. In measuring the radiant energy of the electrons, corrections are needed for backscatter of the electrons entering the water and for bremsstrahlung energy loss during electron slowing down. Precise knowledge of the heat defect is a prerequisite for the establishment of the water absorbed-dose calorimeter as a primary standard of absorbed dose to water.

Design considerations for the NRC sealed cryogenic triple point cells are discussed, together with their filling system. The versatility of the filling system is illustrated by the purification of CO₂. Finally, it is shown that the effects of residual impurities upon the realized liquidus points of high-purity cryogenic substances may be demonstrated by observing the dependence of the liquidus points on the fraction of sample condensed.

10–14 May 1993, Helsinki Fair Centre, Finland

Scope of the Conference

The Conference reports and reviews the state of the art and future trends in force and mass measurements in science and industry. Emphasis is on the applications of new methods, current problems in calibration and quality control, as well as on advancements in new sensor technologies and industrial application of force and mass measurements.

Main Themes and Topics

1. The state of the art and development trends in force and mass measurements

1. Development and stability of high level mass standards

2. Mass comparators and force standard machine

3. New research topics in mass and force

2. Calibration and quality control

1. Calibration methods

2. Estimation of uncertainties and classification of accuracies

3. Relations between calibration, testing and quality control

4. Requirements for quality control

5. Verification of weighing instruments and their main devices

3. Application of force and mass measurements

1. Automatic weighing

2. Mass flow measurements

3. Quality control in process industry

4. Sensor technologies

5. Practical applications

6. Special applications in industry, trade, etc.

Deadline for submission of abstracts: 30 June 1992.

For further information please contact: Finnish Society of Automation, Asemapäällikönkatu 12C, SF-00520 HELSINKI, Finland Phone: Int. +3580 1461 644, Fax: Int. +3580 1461 650