Overview

An alphatron is a type of barometric sensor that uses ionizing radiation to accurately estimate barometric pressure.

Functionality

The alphatron is a cold-cathode ionization gauge. It can detect both density and composition of a gas in between it's source and detector down to very low pressures. The device works by using the alpha source to ionize particles in the chamber surrounding the collector. As long as the dimensions of the chamber are smaller than the range of the alpha particle the number of ions present in the chamber will only depend on the source and the density of the medium in the chamber. The collector will provides the path for the generated ions, dissipating current through a resistor. A voltage can be measured across the resistor by a high input impedance output meter. This type of gauge is appropriate only once the pressure drops below 0.15 atmosphere.

Schematic

Sources:

http://www.instrumentationtoday.com/alphatron-vacuum-gauge/2011/10/