An Accurate Mercury Manometer for the NBS Gas Thermometer

Abstract

A mercury manometer using capacitance sensing of meniscus positions has been refined to give an accuracy within 2 parts in 108 of the pressure in the range from 1 x lo4 to 1.3 x 105 N/ma. The determination of pressure ratios is accurate within 1.5 parts in 1 0 6 for pressures in the same range.

Deviation of international practical temperatures from thermodynamic temperatures in the temperature range from 273.16 K to 730 K

“…H ydrogen diffu ses through pure Pt at the rate of 0.1 3 Pa-liter per cm 2 per min per mm thickness of the metal , with a hy drogen pressure of 10 5 Pa on one sid e and a vacuum on the other (the " permeation rate"). Platinum immersed in hydrogen at a pressure of 10 5 Pa absorbs 0.34 Pa-liters of the gas per cm 2 per mm thickness.…”

“…The National Bureau of Standards' gas thermometer has been described in numerous papers [1][2][3][4][5][6][7][8][9][10]1 t hat give details of many of the impor tant parts of the equipment and of some of the special measurements required. The last two of these papers also give the results of measurements with the gas thermometer from 0 to 142°C .…”

Practical uncertainty limits to the mass determination of a piston-gage weight

“…The results are shown in table 5. (1) There are several striking discrepancies in the results at the level of about 0.3 ppm in the mass of Xl or T. Perhaps the most interesting of these is that, when the same standard weights were used with Bal-2, the mass value computed for T depended on whether T was suspended from the hook or was placed flat on the pan. As seen in table 4, the difference in these two results is 188 J.Lg, more than seven times greater than the combined standard deviation based on the random errors of each measurement.…”

“…The hook is at sufficient height so that the suspended weight clears the pan. Based on considerations in section 3, minimum errors should be obtained 1 Brand names are used solely to identify the apparatus used. Such identification neither implies endorsement by the National Bureau of Standards, nor does it imply that the particular product or equipment is necessarily the best available for the purpose.…”

“…This level of accuracy is motivated by research underway at NBS which seeks to achieve unprecedented levels of accuracy in the calibration of selected piston gages. The standard used in these measurements is a mercury manome-565 ter which has an error of the order of 1 ppm in the pressure range from 10 to 130 kPa [1].…”