Cirrus SP101013.111 – 10 October 2012
MKS Instruments UK Ltd., Spectra Products
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8. Analyser Maintenance (PVD and Open Source)
Before carrying out ANY operations that involve the analyser, take precautions to prevent
contact with any hazardous substances that may have been sampled.
Allow all parts of the inlet and oven to cool before commencing.
8.1 Overview
The quadrupole analyser is the front end of your mass-spectrometer, it produces electrical signals
which, when presented to your electronics, display the contents of your vacuum chamber in a
meaningful fashion.
The analyser can be broken down into four separate areas by virtue of their function.
1. The ion source or ioniser
This is located at the top (furthest from the flange) of your analyser and its function is to take a
representative sample of molecules and atoms from your vacuum chamber, convert them into ions and
present them to the quadrupole filter.
2. The quadrupole filter
This is the centre section of your analyser. Its function is to take the ion beam generated in the source
and separate the various ions by their mass to charge ratio (m/e) and present the single selected m/e
to the collector.
3. The detector
This area of your quadrupole analyser is "hidden" inside the flanged housing. Its function is simply to
convert the filtered ion beam presented by the quadrupole filter into a small electrical current, which
can be passed to the electronics for amplification and subsequent display to the outside world.
4. The flanged housing
This is the only part of your analyser that you will see under normal operating conditions. Comprising
of an industry standard 2.75" Conflat® flange with an electrical feedthrough, which carries the various
supplies and signals to and from the quadrupole analyser.
All quadrupole analysers require periodic maintenance, the regularity of which is determined by its use.
The cleanliness of the vacuum, hours of operation and the type of sample being analysed all have an
effect on the analyser’s performance.
Apart from these considerations there are times when the analyser will require maintenance and these
are when accidents happen i.e. the vacuum is vented with the filaments on, or someone forgets to
turn on the water cooling for the oil diffusion pump.
Routinely there is only one area of the analyser that requires any maintenance, this is the ion source.
The ion source contains two filaments, only one of which will be in use at any one time. The filament is
heated to approximately 2000 deg K at which temperature it emits electrons, which are used to
produce the ions required by the quadrupole filter. At this high temperature, there are two deleterious
effects.
The filament material slowly evaporates and condenses upon the surrounding surfaces. This effect is
extremely slow but would require, from time to time, the cleaning of the surrounding source plates and
ceramics and the replacement of the filaments.
The second effect is similar to the first except that the vacuum, under which the source is operating,
has either a high oxygen or water content. Then instead of metal being deposited upon the
