3 AND A HALF CENTURIES LATER - THE MODERN-ART OF LIQUID-COLUMN MANOMETRY

After three and a half centuries the Torricellian mercury manometer re mains the most accurate pressure standard. State-of-the-art manometers achieve parts-per-million total uncertainties near atmospheric pressu res and imprecisions as low as 0,01 Pa. The total uncertainty is deter mined primarily by uncertainties in the measurement of the height of t he mercury surfaces and the average mercury density. The latter is lim ited generally by the uncertainty of the average temperature of the me rcury. The techniques used to locate the mercury surfaces and determin e their heights not only determine the imprecision and accuracy of the height measurement, but can also have a significant effect on the mai ntenance of a stable and uniform mercury temperature. This review disc usses the factors important in high-accuracy manometers with particula r emphasis on surface detection and height measurement techniques. Spe cifically discussed are capacitance detection, white-light fringes, op tical interferometry, with and without floats, and ultrasonic measurem ents.