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The spectral emissivities of refractory transition metals have been measured from about 2 500 K up to temperatures above the melting point T_m. The experimental method adopted is based on multiwavelength pyrometric measurements, where the determination of the spectral emissivity is implicitly related to the evaluation of temperature through the radiation emission law and an assumed relationship between the spectral emissivity ε and the wavelength λ. Heating was produced with a pulsed laser in times of order 100 ms. A specially constructed pyrometer was used which enabled measurements at six different wavelengths to be carried out at time intervals of order 0,1 ms. A model for the evaluation of temperature and spectral emissivities has been developed and its limitations arising from statistical and systematic errors are discussed. Our experiments on the refractory transition metals Hf, Mo, Nb, Re, Rh, Ta, W, V and Zr: (i) confirm the existence of a unique wavelength, λ_x, for each metal (already well established in the solid state where ∂ε_λ/∂λ ⩽ 0) to which different ε_λ-isotherms converge for λ < λ_x, from which they diverge for λ>λ_x and at which ε_λ is independent of T, and thus equal, in particular, to its value at T_m; (ii) indicate that λ_x is preserved through T_m; and (iii) reveal that at T_m these metals are effectively "grey", i.e. their emissivity, within the measurement uncertainty, is independent of λ (∂ε_λ/∂λ = 0), while for T > T_m is ∂ε_λ/∂λ > 0, that is, opposite to its behaviour at T<T_m.

In order to evaluate the agreement among representations of the ohm based on the quantum Hall effect and to establish a firm basis for international traceability among the laboratories concerned, the BIPM, at the request of the CCE, organized and carried out an international comparison of 1 Ω and 10 kΩ resistance standards from eighteen national laboratories and from the BIPM. The weighted means of the results obtained by the ten national laboratories which, like the BIPM, based their measurements on their own QHE resistance standard differ from the BIPM results by (-0,032±0,024) parts in 10⁶ at the 1 Ω level and by (0,009±0,022) parts in 10⁶ at the 10 kΩ level.

An analytic approach, based on thin-wall theory, to analysis of the "controlled clearance" method of restricting the gap between a shaft and a surrounding cylinder is presented. A modified form of thin-wall theory allows this analysis to be extended to seals with outside to inside diameter ratios up to 2.3. The effects of (a) the supply pressure, the jacket pressure, the pressure dependence of the viscosity of the oil and the geometry of the system on (b) the deformation of the cylinder, the pressure profile in the gap between the shaft and the cylinder and the flow of oil are illustrated. A path using this information is given for the design of a controlled clearance seal. It is shown that when the jacket pressure and the supply pressure are equal (reentrant cylinder condition) the supply pressure needed to close the gap is infinite. The difference between this result and that for a cylinder with a built-in end, for which the supply pressure for closure is finite, is discussed. Experimental tests are described and the results are shown to agree with computed figures based on the theory. This work is of particular relevance to hydraulically actuated standards of pressure and force, where "simple" piston-cylinder assemblies suffer excessive deformations at pressures beyond 50 MPa.

An international neutron-dosimetry comparison has been organized by the Bureau International des Poids et Mesures by circulating a set of transfer instruments supplied by the BIPM. Eight laboratories participated in this comparison. Its purpose was to compare, free in air, the kerma values in A-150 plastic for the neutron and gamma components, K_N and K_G, per unit of reference monitor in the local (d + T) mixed (n + γ) field, when measured with the BIPM equipment and with the local dosimetry systems. The results of the comparison are given and discussed.

The paper deals with He-Ne lasers at 633 nm, frequency-stabilized by saturated absorption in ¹²⁷I₂. The procedure of iodine cell cleaning and filling is presented in detail. This technology provides long-term reproducibility of laser frequency as may be seen from measurements taken over a four-year period. The paper shows the hyperfine spectrum of a fused silica laser with eighteen hyperfine components obtained by a third-harmonic detection technique and mean frequency differences resulting from comparisons with the standards of the PTB (Braunschweig) and the BIPM (Paris). The frequencies of the line centres of hyperfine structure (hfs) components o, p, q, r of the R (127) 11-5 absorption line of ¹²⁷I₂ measured directly by beat frequency measurement are presented. Taking into consideration that the measured laser has a mean frequency offset of -22 kHz for hfs components (a-n), the following frequency differences of the components o, p, q, r with reference to the component i of the reference laser INVAR 1 have been obtained: δν_oi = (-263,187 ± 0,01) MHz δν_qi = (-292,689 ± 0,05) MHz δν_pi = (-290,271 ± 0,05) MHz δν_ri = (-320,720 ± 0,01) MHz. The He-Ne/I₂ lasers have been used for testing the single-frequency-stabilized lasers.

Soviet and Australian photometric and radiometric standards have been intercompared. Luminous intensity and luminous flux values were compared using lamps, and illuminance, irradiance and spectral responsivity using detectors. Agreement at the 1% level or better was found for these values as determined by the two national laboratories.

A new way to realize the ampere by the method of superconducting mass levitation is proposed. The approach promises to simplify the measurement procedure because it substitutes the "mechnical" joule realization by measurements in the levitation mode of the periods of small vertical oscillations of the mass. One has to measure the period value, with constant current flowing in the levitating coil, and again with the mass in the same position but with the coil short-circuited to maintain the magnetic flux constant.

The Edlén equation has become the standard method of relating the index of refraction of air to the air temperature, pressure and humidity. The recent suggestion for improvements in the humidity dependence by Birch and Downs has been verified at the 0,633 μm He-Ne laser wavelength using the line scale interferometer at the National Institute of Standards and Technology (NIST).

The seminar will be held from 2 to 4 June 1993, preceding the next meeting of the CCM, at the Laboratoire National d'Essais (LNE), 1 rue Gaston Boissier, 75015 Paris, France.

Scope of the Seminar

The purpose of the seminar is to review the state of the art of pressure measurements in the 1 kPa to 1 GPa range and to present original and innovative contributions from standards laboratories and industry.

Main Topics

The seminar will be organized in six sessions as follows:

• Liquid-column manometers

• Piston gauge pressure standards

• Properties of liquids and gases relevant to pressure metrology

• Pressure transducers and transfer standards

• Pressure standard comparison (methods and results)

• Dynamic pressure measurements.

Each topic will be introduced by a review paper presented by a session chairman. A final session, coordinated by Dr G F Molinar (IMGC), Chairman of the CCM High Pressure Working Group, and Dr P Stuart (NPL), Chairman of the CCM Medium Pressure Working Group, will deal with:

• Actual limits of accuracy of static pressure measurements in fluid media

• Fundamental problems in pressure metrology between I kPa and 1 GPa.

Call for Papers

Papers should be prepared for oral presentation and will be refereed by the session chairmen. The Proceedings will be published as a special issue of Metrologia. Papers should be written according to the instructions for authors printed on the inside back cover of this journal. A one-page abstract should be sent to Dr Molinar at the IMGC, to arrive before 31 January 1993.

A participation fee of 900 FFr (175 US$) will be charged. This will cover general expenses and a copy of the Proceedings. Hotel reservations, meals and transport are not included.

Organizers

For further information please contact: 1993 CCM Pressure Seminar, Dr G F Molinar, Istituto di Metrologia "G Colonnetti", Strada delle Cacce 73, 1-10135 Torino, Italy telephone (39) 11 39771; telex 212209 IMGCTO-I; fax (39) 11 346761.

Contact at the LNE: J C Legras, telephone (33) 1 40433700; fax (33) 1 40433737.

Scientific Committee

The following are responsible for the preparation of the seminar programme: J Bonhoure, BIPM, France V Borovkov, VNIIFTRI, Russia C Ehrlich, NIST, USA J Jäger, PTB, Germany J C Legras, LNE, France G F Molinar, IMGC, Italy P Stuart, NPL, UK C Tilford, NIST, USA S Yamamoto, NRLM, Japan R Wisniewski, Warsaw Univ. of Tech., Poland