5.2 Application notes
When selecting and installing vacuum gauges their properties and
the particularities of vacuum measurement must be taken into account:
- Appropriate selection of the installation location due to
potential pressure gradients occurring in vacuum chambers.
- Surfaces and sealing materials exhibit outgassing. The vacuum
gauge could therefore indicate a higher pressure than that in the
vacuum chamber. Connection flanges should therefore be a short as
possible and the number of seals reduced to a minimum.
- Ionization vacuum gauges can have a pumping effect and as a
result indicate a lower pressure than the actual pressure in the
- Cold cathode gauges have an inherent sputter effect which is
particularly pronounced when operated with heavy gases (such as
argon) in the medium vacuum range. This can result in inconsistent
and inaccurate readings.
- When hydrocarbons are present, ionization gauges become
contaminated with decomposition products of the organic molecules. In
the same way as the sputter effect, readings can be distorted or
- Switching points for ionization gauges must be selected to
avoid contamination due to the phenomena described above.
- Strong magnetic fields and electrical fields can impair the
function of vacuum gauges. This applies particularly for ionization
- To enable ultra-high vacuum to be generated, the vacuum
equipment, including the vacuum gauges, must be baked out. The
maximum bakeout temperature and the conditions specified in the
technical data must be adhered to.
Cold cathode gauges can be easily dismantled and cleaned in the
event of contamination. With other measuring principles, it is usually
possible to replace the sensor. It should always be borne in mind that
vacuum gauges are subject to a certain degree of wear and
contamination and therefore require to be replaced every so often. The
wide range of operating conditions makes it impossible to make a
general recommendation for the replacement interval.