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A 200
About leak detection
GB 03302 - Edition 03 - July 12
The iridium filament allows a good performance at high pressures and
a small overheating.
These ionized particles are accelerated by an electrical field.
They arrive in a zone subjected to a magnetic field which has the
property of deflecting the trajectories of the ions along different curves
according to the masses of those ions (to be more precised, according
to their m/e ratios). Thus the ions beam, which contained ions with
different masses, is divided into several beams, each containing only
ions with the same m/e ratio. For example, the helium ions (m/e = 4)
are separated from the lighter (H
2+
or H
1+
, smaller beams) or heavier
ions (N
2+
or O
2+
, bigger beam).
The triode electrode 1 collects the ions which the mass is higher than
the tracer gas mass. The electronic current measured in this way
allows to calculate the total pressure in the analyzer cell.
Because there is a constant magnetic field (permanent magnet), the
accelerator electrical field is adjusted so that the tracer gas ions follow
a pre-determined trajectory (passing through diaphragm 2) and arrive
on the target at the input to a direct current amplifier.
In order to separate the helium ions from "noise" caused by other
ions, an electrode located in front of the target eliminates them. This
electrode 3 is called the "braking electrode".
The current of ions of the tracer gas is proportional to the partial
pressure this one in the installation and by measuring it we can find
the flow rate of the leak that has been detected.
It is essential that the total pressure in the analyzer cell is less than
10
-3
mbar, so that the trajectories of the electrons and the ions are not
disturbed by residual molecules.
There is a spare iridium filament 6 in the analyzer cell.
adixen Vacuum Products - ASM 310 Operating instructions
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