.Mass Filter Options.
Single Mass Filter. (Fitted as Standard) A Low cost single stage mass filter using cylindrical rods for low mass applications.
Saddle mounted Filter. A high precision saddle mounted mass filter is
available as an option on our range of instruments. It is easily de-mounted for cleaning. This enclosed filter offers improved sensitivity, resolution and abundance sensitivity.
Dual & Triple filters. These are available based on saddle mounted mass filters, and are normally chosen for
special applications or when the highest performance/resolution is
required.. Available on the AX800 instrument only.
Faraday Only. A Faraday plate detector for ion collection. Used mainly for higher pressure applications when greater ion currents are available for collection.
Dual Faraday/Channeltron. The Channeltron (SEM) provides a high level of amplification of the ion beam and therefore provides detection of much lower ion currents.
When in SEM mode the pre-amplifier can be operated at a lower gain and faster
scanning speeds are possible.
Discreet SEM. A
discreet dynode Electron multiplier is available on the AX800 as an alternative
to the Channeltron Electron Multiplier. This has much larger surface area of
secondary electron electrodes and therefore offers much longer life when
operating on continuous high signal levels over prolonged periods of time. The
Faraday option is not available when this device is fitted.
Pulse Counting. Provides the ultimate in detection by counting individual ions arriving at the detector.. Normally used in trace gas analysis applications where the lowest level of detection is required. A special version of the electronics is available that includes a counting pre-amplifier, system clock, counter, and interface for transferring the accumulated ion count to the quadrupole software for display.
Thermal Extender. Allows
operation of the quadrupole whilst the analyser is at high temperature This
option is available on most of our RGA instruments and has to be fitted to the
analyser at the time of manufacture. It extends the back of the analyser
by approx 24 cms so the plug-on electronics is now separated from the analyser
The majority of our competitors use a twin filament
assembly. That means that when one of the filaments blows the customer has a
difficult decision. Does he replace the filament assembly throwing the remaining
good filament away, or does he run on the second filament and hope it does not
blow during a critical measurement when there is no back-up.
All ASI/Larimax RGA’s are fitted with two filaments. The
filaments are individually replaceable. Therefore if one filament blows, that
filament can be changed at a convenient time. And the other good filament
remains on the analyser
|Operating temperature for
Pure Tungsten approx 2200C
||A good low cost general purpose filament.
||Life is reduced in oxidising atmospheres above 5x 10e-6mBar
|Operating temperature for
Thoriated Tungsten (1% Thoria) approx 1950C
||Under high vacuum, below 10e-6mBar filaments will last many
months and sometimes many years.
||Life is reduced in high partial pressures of water vapour
(10e-5mBar) due to filament erosion.
||Can be used at high pressure in inert atmospheres.
||Tungsten filaments usually produce background peaks at mass
28 (CO) and 44(CO2).
||Can be used in Hydrogen or reducing atmospheres.
||Sudden exposure to high pressure above 10-2mBar of oxidising
atmosphere can cause instant oxidation and burn out of filament.
||Safe to handle filaments.
||Will burn out instantly if switched on at atmospheric
||Can produce a catalytic action with some chemicals.
Slow evaporation of filament will
cause the filament to become thinner over a very long period of time, with
a reduction of operating current eventually leading to failure.
Normally recommended in medium and
high vacuum systems for general-purpose residual gas analysis.
||Life typically 12 months or more.
||More expensive than tungsten filaments.
|Operating temperature approx 1400C.
||Runs at lower temperature and therefore lower out gassing
from Ion Source.
||Poisonous and mildly Radio-Active. Disposable gloves and
mask should be worn when handling filaments.
||Does not produce CO or CO2 and therefore these background
peaks are much lower.
||High levels of hydrogen can cause reduction of the oxide
coating with an increase in water background, and a consequent reduction
in filament life.
||Can be used at high pressures in oxidising atmospheres.
||Severe Shock or vibration can dislodge the coating.
||Will tolerate high pressure burst.
||Cannot be chemically cleaned.
Normally recommended for gas
analysis applications and for use at high operating pressures, especially
if oxidising gases are present. Also may be preferred in UHV conditions
when the lowest possible background is important.