Jevatec JEVAmet, Инструкция по эксплуатации

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BA_IOM_02.2018_EN 9
3.
Technical Product Description
3.1 Function
The JEVAmet
®
IOM is a hot cathode ionisation gauge by Bayard-Alpert. It has been
designed for vacuum measurement of gases in the pressure range of 5·10
-10
– 5·10
-2
mbar.
The vacuum gauge has a flange connection DN16KF or DN25KF and can thus to suitable
flange connections be attached.
NOTE: Field of Application
On the basis of the following information, please check whether the instrument
is appropriate for your application.
3.2 Measuring Principle
The Bayard-Alpert ionisation gauge utilizes the ionisation by electron impact of gas particles.
The electrons are emitted from a heated cathode (filament), are then accelerated to the
anode grid, ionizing the gas on their way. The ions which are being created inside the grid
are accelerated to the collector and are generating the measurement current. The collector
current is proportional to the gas pressure over a wide pressure range, in addition being
dependent on the ionisation probability of the gas. At lower pressures the measurement
range is primarily limited by the geometry of the sensor. For the JEVAmet
®
IOM sensor the
low-pressure limit is in the range of < 5
∙10
-10
mbar whereas the high-pressure limit is in the
range of 10
-1
mbar.
Increase and fluctuations of the pressure reading of the Bayard-Alpert ionisation vacuum
gauge are being produced by contaminations (increased outgassing inside the tube). In this
case it is advisable to clean the sensor by degassing at pressures

1
∙10
-4
mbar during
which the sensor is heated by means of electron bombardment. During the degassing the
pressure reading serves as an orientation about the cleaning procedure but is beyond the
accuracy specifications of the JEVAmet
®
IOM. By degassing of the sensor, the
contaminations are removed to a large extent.
Considerable falsifications of the measured value can occur if electrons or ions are emitted
from the vacuum system. This effect is being reduced by the application of a protective
adapter (baffle).
Strong magnetic fields (e.g. from ion getter pumps) cause the deflection of electron
trajectories and therefore possibly induce measurement errors. In this case an increase of
the distance between the JEVAmet
®
IOM and the magnet is advisable.