An Absolute Micromanometer Using Diamagnetic Levitation

A friction-free suspension in vacuo is provided for a graphite disk by magnetic induction. The disk rotates round a vertical line of force inside a properly designed stator; when the stator is cooled, a thermomolecular torque is developed and the acceleration thus given to the disk is measured by an automatic device. It is shown that this acceleration depends only on the geometrical design of the manometer and on the pressure, to which it is proportional. The manometer unit is passive, very small, and insensitive to vibrations and shocks affecting the vacuum setup. The lower limit of its range of measurement is less than 10−10 Torr. When stator cooling is removed, the disk is influenced only by a (smaller) molecular damping torque. This depends on the composition of the residual atmosphere; provided this is known, the magnitude of the damping can be computed a priori with good precision so that the instrument becomes a useful standard manometer for calibration in the 10−3 to 10−7 Torr range.