Vern E. Bean

Dynamic Pressure Metrology

According to the ANSI MC88.1-1972 standard A Guide for the Dynamic Calibration of Pressure Transducers, the properties to be determined when calibrating a dynamic pressure transducer are sensitivity, amplitude as a function of frequency, phase as a function of frequency, resonant frequency, damping ratio, rise time and overshoot. A static calibration yields only the sensitivity. The properties of dynamic pressure transducers and various methods for determining them are reviewed.

The dual melting curves and metastability of carbon tetrachloride

Carbon tetrachloride has three known solid phases at atmospheric pressure: Ia (face‐centered cubic), Ib (rhombohedral), and II (monoclinic). Both Ia and Ib melt directly at temperatures some 5 K apart. These phase changes have been traced as a function of hydrostatic pressure up to 350 MPa. Between atmospheric pressure and 100 MPa, CCl4 has dual melting curves; one for Ia, and a few degrees higher, one for Ib. The two curves diverge with increasing pressure. Above 100 MPa it was not possible to detect the Ia phase. There appears to be no Ia–Ib‐liquid triple point. The metastability associated with these phases is discussed.

The Mercury Melting Line Up to 1200 MPa

The mercury melting line has been determined for pressures up to 1200 MPa. The change of electrical resistance in the mercury sample was used for detecting the equilibrium between the solid and liquid phases. Pressure measurements were made with highly stable manganin gages calibrated against two controlled clearance piston gages. Temperature measurements were made in the constant temperature bath by means of platinum resistance thermometry. Systematic errors in pressure and temperature were evaluated for all the measurements as well as the scatter due to the resolution of the equilibrium determination between the two phases of mercury. The mercury melting point at 0 °C is 756.84 ± 0.16 MPa which is in close agreement with the value obtained by Dadson and Greig. The experimental results are compared with previous melting lines. There are systematic differences when compared to Bogdanovs equation up to 1200 MPa but there is very close agreement with recent data obtained by Houck and Morris over the pressure range they covered. The experimental data were fitted to a third order polynomial; this equation fits the melting line data much more closely than the Simon type heretofore recommended and can be used up to 1200 MPa to increase the accuracy of a practical pressure scale based on the melting line of mercury.

Development of a Primary Standard for the Measurement of Dynamic Pressure and Temperature

The National Institute of Standards and Technology is developing a primary standard for the measurement of dynamic pressure and temperature. Our method requires a dynamic source and a technique for calibrating it. The source is a shock tube; the calibration technique is based on the properties of diatomic gas molecules measured by laser spectroscopic methods.

Effects of viscosity, temperature, and rate of rotation on pressure generated by a controlled‐clearance piston gauge

The calculation of the pressure generated by a controlled‐clearance piston gauge depends upon the jacket pressure corresponding to zero clearance between the piston and cylinder Pz. The dependence of Pz on the viscosity of the pressure transmitting fluid, the temperature, and the rate of piston rotation have been measured. The four fluids used in this study have viscosities ranging from 0.7 to more than 10 000 cP. The value of Pz is nearly independent of viscosity below 60 cP. Above 60 cP, Pz depends strongly upon viscosity. Variations of Pz with temperature and rate of rotation are more severe at higher viscosities. The results suggest that the best choice of fluid is the one having the lowest viscosity at the operating pressure. Such a fluid can be selected on the basis of having the most nearly linear plot of Pz as a function of pressure of the candidate fluids. These results are also a clear indication that, for the most accurate pressure measurements, a controlled‐clearance piston gauge must be chara...

Optical windows for a flow cell to contain aqueous solutions at high pressure and temperature

A flow cell to contain aqueous solutions at pressures up to 40 MPa and temperatures up to 600 °C that is equipped with sapphire windows for the transmission of visible light is described. There are four windows, two for the entrance and exit of a laser beam, and two located at 90° that feature f/1 (53° included angle) collection apertures with a 9 mm diameter unobstructed view for Raman spectroscopy, absorption measurements, or studies using full‐field back illumination. The window‐to‐metal seals are gold o‐rings; the metal‐to‐metal seals are gaskets prepared by pressing a gold o‐ring onto a gold foil washer. This cell has been used for two years for Raman studies of aqueous solutions at high pressures and temperatures both below and above the supercritical point of water.

Hydrometer calibration by hydrostatic weighing with automated liquid surface positioning

We describe an automated apparatus for calibrating hydrometers by hydrostatic weighing (Cuckows method) in tridecane, a liquid of known, stable density, and with a relatively low surface tension and contact angle against glass. The apparatus uses a laser light sheet and a laser power meter to position the tridecane surface at the hydrometer scale mark to be calibrated with an uncertainty of 0.08 mm. The calibration results have an expanded uncertainty (with a coverage factor of 2) of 100 parts in 106 or less of the liquid density. We validated the apparatus by comparisons using water, toluene, tridecane and trichloroethylene, and found agreement within 40 parts in 106 or less. The new calibration method is consistent with earlier, manual calibrations performed by NIST. When customers use calibrated hydrometers, they may encounter uncertainties of 370 parts in 106 or larger due to surface tension, contact angle and temperature effects.

Pressure variation of the low‐frequency dielectric constants of some anisotropic crystals

The low‐frequency dielectric constant for quartz, sapphire, calcite, and magnesium fluoride has been measured both parallel and perpendicular to the optic axis at several temperatures over the pressure range 0–0.3 GPa. The results, when compared with the reported values for the effect of pressure on the high‐frequency dielectric constant, indicate that pressure decreases the infrared contribution to the dielectric constant for all materials except calcite. Consequently, the infrared polarizability decreases with pressure for all but calcite. Further, it is found that the infrared polarizability decreases with pressure for calcite perpendicular to the optic axis, but increases with pressure parallel to the optic axis. In addition, it is shown that the volume‐independent temperature derivative of the low‐frequency dielectric constant is positive for sapphire, calcite, and magnesium fluoride showing that cubic terms in the lattice potential energy dominate, while for quartz, the derivative is negative implyi...

Pressure and temperature measurements in the annulus between the piston and cylinder of a simple dead‐weight piston gauge

Precise and accurate pressure measurements are obtained using appropriately designed and operated piston gauges. Elastic distortion of the piston and cylinder is the leading cause of inaccuracy in measurement of higher pressures. The distortion depends upon the ratio of the pressure in the annulus between the piston and the cylinder to the pressure under the piston. Heretofore, as the proper value of this ratio or a method to determine it was unknown, the practice has been to assume a value of 0.5 when calculating distortion effects. In this work, the pressure and temperature of the fluid in the annulus have been measured along the working length of the piston and the cylinder. The model for the pressure ratio proposed by Bass on the basis of the clearance between the piston and cylinder is in excellent agreement with the pressure measurements. The appropriate value of the pressure ratio for the calculation of the distortion is marked by a sharp decrease in the slope of the pressure ratio curve. The corre...

Tracking, pulsed ultrasonic interferometer

A pulsed ultrasonic interferometer was designed and constructed that has the ability to track changes in transit time as the ambient pressure and temperature of the sample are changed. The stability over 17 h approached one part in 107. This instrumentation will be incorporated into an automated high pressure transfer standard calibration system.