Fault Diagnosis
Filament Failure
9-8
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
Thermo Fisher Scientific
A good test for system integrity is to introduce helium, which will
typically give the following pressure readings:
70 micron pinhole leak
ca. 2 x 10
-6
mbar
50 micron pinhole leak
ca. 1 x 10
-6
mbar
30 micron pinhole leak
ca. 5 x 10
-7
mbar
The above is only a rough guide but can be used to establish if the
micro capillary is blocked, significantly lower readings, or there is a
gross leak, significantly higher readings.
If the capillary is blocked or the ion source is contaminated, the
linearity factors obtained during calibration will depart greatly from
unity; typically they are close to 1 (e.g. 0.7 to 1.3) but in the event of
a blockage or contamination, could be as low as 0.3 or as high as 3.0.
After prolonged operation of the unit (typically between six months
and two years) a build-up of contamination may occur on the ion
source electrodes, the magnet pole pieces, and Z-restrictor. This can
result in the build-up of insulating films on metal surfaces, which in
turn can charge up and disturb the local field potentials. This usually
results in a reduction in sensitivity and / or a distorted peak shape. In
this event, it will be necessary to clean the source, pole pieces, and
the Z-restrictor. Refer to
procedures.
Typical filament lifetime is six months to two years. The instrument
status flags indicate filament failure. Filament current, trap current,
and source current will all be zero. Filament failure can be checked
(after setting the ion energy and focus voltages to zero), by testing
the source flange plug for continuity between pins 7 and 9 for the
case of filament 1 or pins 16 and 17 for the case of filament 2 on the
source plug. However, since the source is the dual filament type then,
provided one filament is still intact, one can simply switch operation
to the other filament. Filament replacement can then be carried out at
any convenient time, such as during a routine preventive
maintenance service.
Note:
The filament current will be switched off if the Penning
pressure rises above its set point. This should be checked before
dismantling the system to change the filament.
Ion Source and
Magnet Pole
Pieces Assembly
Filament
Failure
