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Functional Description
In general, the ion gauge exhibits good repeatability. However, the ion gauge
response depends on gas composition. A certain pressure of air and water will
give a different reading than that of Helium. The Ion Gauge is meant to be a
rough indicator of vacuum conditions. It is not a precise quantitative tool.
The gauge uses thoria-coated iridium (ThO-Ir) filaments. These filaments are
burnout resistant, and therefore exhibit high tolerance to air and water in the
vacuum manifold. There is a time delay associated with heating the filament.
This delay translates to a delay in determining whether a filament is open. From
15 to 20 seconds are usually required after you turn the filament on to obtain a
stable reading.
The ion gauge will measure pressures between 10
-6
and 10
-2
Torr. A logarithmic
amplifier amplifies the collector current, and the data system interprets this
current as measured vacuum.
Foreline Pump
A foreline pump has two purposes. The first is reducing the vacuum system
pressure to a level that will allow the operation of high vacuum pumps such as
turbomolecular pumps and diffusion pumps. The second is maintaining the
vacuum system pressure by removing the high vacuum pump’s exhaust gases.
The foreline pump is connected to the high vacuum pump by a 2.1m (84 in.)
length of 1.9 cm (0.75 in.) ID vacuum tubing. The pump plugs into the rear panel
outlet labeled “J2 - LINE VOLTAGE - PUMP ONLY” on the rear of the MS.
Power is supplied through this outlet and is controlled by the power switch on the
rear panel.
The foreline pump used on the Saturn GC/MS is a two-stage rotary vane pump
with a pumping speed of 90
µ
L/min. and a vacuum potential of 1.5 x 10
-3
Torr
(2 x 10
-1
Pa).
If you use the Saturn GC/MS to analyze hazardous materials, be sure to affix
the foreline pump exhaust to an exhaust system that complies with applicable
safety regulations.
Electronic Assemblies
The electronic assemblies consist of the following:
•
Power input subsystem and turbomolecular (or diffusion) pump controller
(See Diffusion Pump Controller).
•
Power board
•
Scan acquisition processor/waveform (SAP/Wave) board
•
Manifold electronics assembly
•
RF generator board
