Vacuum Technology Know How - Triumf

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Pirani thermal conductivity vacuum gauges are used between 1 and 10 - 4 mbar. It is also
possible to use special „high-pressure“ hot cathode ionization vacuum gauges at pressures
p of less than 10 - 2 mbar.
Direct
(gas-independent)
pressure
measurement
Cold Cathode
Hot Cathode
Capacitative
Indirect
(gas-dependent)
pressure
measurement 1 . 10 -13 1 . 10 -7 1 . 10 -3 1 1,000
mbar
Figure 3.8: Pressure measurement ranges and measurement principles
Either cold cathode ionization vacuum gauges, or ionization vacuum gauges after Bayard-
Alpert in the case of clean conditions and rigorous accuracy requirements, are used for
pressures of less than 10 - 3 mbar. It is always meaningful to use a combination of measuring
sensors that covers the entire pressure range in use.
In the case of diaphragm vacuum gauges and Pirani vacuum gauges, pressure switch points
are generated in order to not activate ionization vacuum gauges until sufficiently low pressure
prevails, thus protecting them against contamination or burn-out of the heated cathode. Consequently,
combination sensors are also offered, which are described below.
3.2.2 Transmitters
Transmitters are measuring sensors that output the measured pressure either in the form of an
analog measurement signal (0 - 10 V) or a digital signal to a standardized interface. They must
be supplied with a direct-current voltage (e.g. 24 V). Power supplies that display the measured
values are also offered for the transmitters.
3.2.3 Vacuum gauges
Vacuum gauges are connected to control units via cables; the control units afford power
supply, analysis and display of the measured data. These devices usually also have analog
voltage outputs.
Pirani
Piezo
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Vacuum
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