Agilent VacIon Plus 800 Bedienungsanleitung Seite 216

Technical Information
Figures 38 to 39 show the typical pumping speed vs. pressure diagrams for
saturated and unsaturated pumps and the pressure vs. current diagrams.
Please notice that the current-pressure curves in Figure 40 refer to the pump
equipped with one feedthrough.
Unsaturated curves are given as reference, since the measurement of the pumping
speed in the unsaturated state is not described in the norms and may be strongly
influenced by the testing conditions.
The pumping speed of a new or newly regenerated (i.e. baked) sputter ion pump is
typically higher (for nitrogen about 180-190%, depending on the pressure range)
than its nominal pumping speed; it decreases during operation until it reaches a
stabilized level known as "saturation" (corresponding to the nominal pumping
speed). Saturation does not correspond to the end of the pump life.
For further explanation on the physics of this phenomenon, please refer to the
section "VacIon Plus Pumping Speed" of the ion pump general catalogue. It is worth
noticing that to saturate the VacIon Plus 800 pumps, it normally requires an
amount of gas of about 23 mbar-liters (in the case of nitrogen).
Consequently, pumps can operate for extended periods of time at low pressures in
the non-saturated state, if they are properly conditioned.
Moreover, we point out that for the unsaturated curves only the first part of the
curve is shown, since during the measurement (carried out from low pressure
towards high pressure) the pump starts to move from the unsaturated to the
saturated condition, so that in the transient phase it cannot be clearly be classified
as unsaturated or saturated.
It is also worth noticing that the shown current versus pressure curves are typical
and may appear different in the presence of a leakage current. A small deviation
from the reported curve may also be due to the intrinsic uncertainty of the gauge
reading.
216 Agilent VacIon Plus 800 User Manual