Granville-Phillips Micro-Ion 354 E Series, Инструкция по эксплуатации, Страница: 47 / 54

Micro-Ion E Module Instruction Manual 354011, Rev. A
47
Appendix B Theory of Operation
B.1 Module Operation
The Micro-Ion E vacuum gauge module houses a Micro-Ion gauge
(Bayard-Alpert type ionization gauge).
B.2 Micro-Ion E Gauge
Operation
The functional parts of the Micro-Ion E gauge are the filament (cathode),
grid (anode), and ion collector. Figure B-1 is a schematic diagram of the
Micro-Ion E gauge. The electrodes are maintained by the controller at +30,
+180, and 0 volts, relative to ground, respectively.
Figure B-1 Micro-Ion E Gauge Schematic Diagram
The filament is heated to such a temperature that electrons are emitted and
accelerated toward the grid by the potential difference between the grid and
filament. All of the electrons eventually collide with the grid, but many first
traverse the region inside the grid many times.
When an electron collides with a gas molecule, an electron is dislodged
from the molecule, leaving the molecule with a positive charge, thereby
transforming the molecule into a positive ion. Most ions then accelerate to
the ion collectors. The rate at which electrons collide with the ion collectors
is proportional to the density of the gas molecules; therefore, ion current is
proportional to gas density (or pressure, at constant temperature).
filament (+30 V)
Ion collector (0 V)
Grid (+180 V)