An interferometric oil micromanometer

Describes an absolute U-tube micromanometer using silicon oil for measuring pressures from 0.3 to 6 Pa with an uncertainty of less than +or-.05%. A novel polarising interferometer using a helium-neon laser and fringe-counting electronics is used on each limb to measure the movement of the oil surfaces to the nearest quarter-fringe. Oil vibrations are damped over the measurement area by reducing the oil depth to 0.5 mm. The various sources of uncertainty are discussed in detail, and the results of a comparison between the micromanometer and a capacitance manometer, previously calibrated by the series expansion technique, given.