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In this paper, the aspects of gas-operated pressure balances that affect their performance are discussed. These aspects include both the features that make gas-operated pressure balances suitable for use as pressure standards and the factors that must be managed to achieve good performance. As key features, gas-operated pressure balances are pressure generators, have excellent relative short-term stability (~5 × 10−9) and long-term stability (~1 × 10−6), and can be used as primary standards. Factors to manage include harmonic oscillation of the piston in the cylinder, pressure balance temperature and operating height, and geometric imperfections. Three applications are used to illustrate the performance aspects of gas-operated pressure balances: a primary standard, a standard for differential pressure from 1000 Pa and a standard for absolute pressure from

We present a method of analysis for cross-floats between pressure balances. This analysis relates to the residual mass method of treating cross-float data in which the residual mass Me of one pressure balance is an unknown in the analysis, along with the effective area and the elastic distortion coefficient. Me is the effective mass of any unweighed parts of the piston and load and may include an equivalent mass for other forces on the piston such as oil surface tension. Two models for the analysis with the Me method are presented in a form suitable for linear least squares analysis: one for the calibration of a pressure balance and the other for the comparison of two reference pressure balances. This analysis is equivalent to the p-method when Me is known to be zero. Linear generalized least-squares estimation is shown to be convenient for the calculations. A pressure balance calibration is used to illustrate the analysis and the associated uncertainty evaluation.

This paper describes a pressure comparison, covering the range 25 MPa to 260 MPa, carried out between the CSIRO National Measurement Laboratory (NML, Australia) and the Measurement Standards Laboratory of New Zealand (MSL) in 1997 and 1999. A feature of each part of the comparison was the high-resolution Digiquartz pressure transducer used as the transfer standard. This small and relatively inexpensive transducer is easier to transport between countries than a bulky and heavy pressure balance. The measured performance of the transducer demonstrates that it can compare the pressure scales of each laboratory to a standard uncertainty of 2.3 kPa, which is much smaller than the uncertainties specified for each pressure scale. The results of both comparisons show that the two pressure scales agree to within their respective uncertainties, although the 1999 comparison produced a larger difference than the 1997 comparison. This may indicate a change in the pressure balance parameters or that the transducer performance is not yet fully characterized. An analysis is presented to show the relationship between the measured pressure difference and the parameters of each pressure balance.

This paper describes the improvements that have been made to our measurement of the Newtonian gravitational constant (G) since our last published value of G in 1995. As a result of a new measurement of G made with the improved apparatus, we have discovered some second-order corrections that were omitted from the previous measurement. New values for G are presented; both from the latest measurement and a recalculated value from our previous measurement. Our latest values are G = 6.6742(7) × 10-11 m3 kg-1 s-2 for the most recent measurement and G = 6.6746(10) × 10-11 m3 kg-1 s-2 for the recalculated 1995 value. These two values agree to within their uncertainties.

A high resolution gauge is used to determine the change in effective area of a 250 MPa piston–cylinder unit as a function of jacket pressure. These changes are compared with values calculated using a finite element method. The results of the comparison revealed that the jacket pressure seals were applying unexpected forces to the cylinder outer diameter. These forces were modelled in the finite element calculations giving reasonable agreement. Further measurements were made after modifying the jacket seal mounting. The new results showed reasonable agreement at low operating pressures but large disagreement between theory and experiment as the operating pressure approached 250 MPa.

An analytic approach, based on thin-wall theory, to the analysis of simple piston-cylinder systems is presented. The deformation of the cylinder, the pressure profile in the gap between the piston and the cylinder and the flow of oil are determined. The theory is extended further to calculate the effective areas of both the simple and the controlled clearance piston-cylinder systems, taking into account the distortion of the piston. The application of this work to thick-walled systems is discussed.

This paper describes the design and testing of a method to measure the Newtonian gravitational constant G. The method uses a torsion balance in which a small cylindrical mass is suspended from a slender fibre. Two large cylindrical masses produce a gravitationally induced torque on the small mass. This induced torque is balanced by the electrostatic torque produced by an electrometer. A servo-control system adjusts the electrostatically induced torque so that the fibre does not twist during the measurement. The torque produced by the electrometer is calibrated by an acceleration method that uses torques much larger than those produced by the gravitational attraction of the large masses. Other features of the method include a reduction in sensitivity of the measurement to density variations in the suspended mass, a measurement strategy which reduces the effect of drift in the measurement and computer control of the measurement. Preliminary measurements of the terms used to calculate G showing an uncertainty of 2,5 parts in 104 can currently be achieved. The limiting factor at present is the variation in the gravitational potential seen as the apparatus accelerates. Indications are that further modifications and measurements will provide a value of G with an uncertainty of about 1 part in 104.

The design and construction of a small compact autocollimator based on the laser head of a compact disc player is described. The instrument provides a cheap and simple means of measuring angles over a total angular range of 1200 mu rad ( approximately 200 arcsec) with a resolution of better than +or-0.006 mu rad. The 100 mu rad central region of the measurement range is linear to better than 2%. The autocollimator head is compact and can operate over long distances and with high ambient lighting. The unit described can, with a single measurement head, be used to simultaneously measure angles in two orthogonal directions.

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.

A key comparison of low differential pressure standards, organized under the auspices of the Consultative Committee for Mass and Related Quantities (CCM), was carried out at four national metrology institutes (NMIs) between July 1998 and May 1999 in order to determine the degrees of equivalence of the standards at pressures in the range 1 Pa to 1000 Pa. The differential pressures were superimposed on a line pressure of nominally 100 kPa. The primary standards, which represent two principal measurement methods, included three liquid-column manometers and one double pressure balance. The transfer standard package consisted of four high-precision pressure transducers: two capacitance diaphragm gauges to provide high resolution at low differential pressures, and two resonant silicon gauges to provide the required calibration stability. Two nominally identical transfer packages were used to reduce the time required for the measurements, with Package A being circulated among laboratories in the European region (Istituto di Metrologia G. Colonnetti, Italy; National Physical Laboratory, UK) and Package B in the Asia-Pacific region (Measurement Standards Laboratory of New Zealand). The results obtained were normalized using data obtained from simultaneous calibrations of the two packages at the pilot laboratory (National Institute of Standards and Technology, USA). The degrees of equivalence of the measurement standards were determined in two ways: deviations from key comparison reference values and pairwise differences between these deviations. The differential pressure standards of the participants were generally found to be equivalent and the results revealed no significant relative bias between the two principal methods tested.

A determination is made of the spectroscopic parallax of Stock 14 on the basis of an MK classification of the 14 brighter stars. Of these, it is noted that two are spectroscopic nonmembers and one is the supergiant V810 Cen. The mean color excess is found to be E(B-V) = 2.26 m + or - 0.12 kpc (s.e. mean for 11 stars); this is fully consistent with Turner (1982), whose results are based mainly on UBV photometry, and conforms to the slightly evolved main sequences of NGC 3293. The independent determination made here confirms Turner's result, in particular with regard to the absolute magnitude and probable membership of the pseudo-cepheid V810 Cen. The nature of the star as a small-amplitude cepheid, however, is by no means certain.

We show that all of the primary and secondary images of photoelectrically measured stars on plates exposed with a Pickering-Racine prism can be used to simultaneously determine the plate calibration and primary-secondary magnitude difference Δ. The uncertainty in Δ so determined is found to he significantly smaller than that determined using only those secondary images brighter than the faintest photoelectrically measured primary image. The technique is useful only if the precautions outlined by Christian and Racine (1983) are closely observed.

The 15.4-day cepheid AV Sgr has been suggested as a possible member of the open cluster NGC 6546. In order to investigate this possibility, we obtained new spectroscopic, radial velocity, and photometric data at Cerro Tololo Inter-American Observatory. From these data we find a distance to the cluster of 1.20 :1: 0.12 kpc, considerable differential reddening with a mean color excess = 0.72 :1: 0.14 (s.d.), and earliest spectral type B2. This places it on the outer edge of the - I spiral arm. From similar data for AV 8gr we find a distance of 2.20 :1: 0.25 kpc and excess = 1.37 s.d. :1: 0.03, leading us to conclude that it cannot be a member. Key words: cepheid-open cluster- UB V photometry-spectra-radial velocity

The reduction of photoelectric photometry data is examined, and a reduction method which differs significantly from Hardie's (1966) traditional approach is reviewed. Consisting of a multilinear solution for all transformation model parameters, the technique is suitable for modern computing facilities. Programs for broad-band and intermediate-band systems, mathematical solutions, and generalizations are presented, with the most general situation being photometry on different telescopes on different nights. Sample results are given to illustrate the multinight reduction method, and are compared to results of single-night reduction. Practical aspects and advantages are also discussed, and the reduction algorithm is found to be sufficiently powerful and applicable to many general situations, allowing judgments about the data to be made more easily and effectively.

Star counts to a B magnitude of 18 show each cluster to have a central projected star number density 2-3 times that of the surrounding field. With radii approximately 2-arcmin and centers separated by only 3.2 arcmin, the clusters overlap in the sky. However, photographic UBV photometry to V equals 15.1 indicates the clusters to have different ages (approximately 60 million years for Cz 29 and 200 million years for Haf 10). Cz 29 is located 2.9 plus or minus 0.5 kpc from the sun at galactic longitude approximately 231 deg, galactic latitude approximately plus 1 deg where previous work has already shown the existence of a weak concentration of stars in the galactic disk. Haf 10 has significantly fainter stars but may be located at nearly the same distance.