INFICON UL5000 Dry Helium Leak Detector - Manual (Page 40)

40
Description and Working Principle
iina
74
e 0
4
.f
m
te
chn
ica
l ha
nd
boo
k
(1
40
8)
Now the lower part of the turbo pump further evacuates the sample and after the
pressure p
1
has reduced below 0.4 mbar the UL5000 switches into ULTRA mode, i.e.
V1a and V4a close and V4b opens. The entrance into the turbo pump is on a higher
level now. The pumping speed at the inlet port is now 20 l/s, the detection limit is
<5×10
-12
mbar l/s.
Tipp A special set up of the UL5000 stopps the autoranging procedure as
described above. With the mode Gross only (See Chapter
6.3 Mode ) the
unit will stay in GROSS Mode Fig. 4-7 (right) regardless the inlet pressure.
4.3.2 Sniffer Mode
In sniff mode a sniffer line (preferably the INFICON standard sniffer line 14005) is
connected to the inlet port. When pressing the
START Button the system starts to
pump air through the sniffer line. Due to the constant gas flow through the sniffer line
the software will range through GROSS into FINE mode and stay there. The inlet
pressure will not drop further down. By measuring the inlet pressure the system
software makes sure that the flow through the sniffer line is at the right level.
Otherwise warning messages are generated. The detection limit in sniff mode is
<1×10
-7
mbar l/s.
INFICON’s sniffersystem QT100 may also be used to sniff. Since the QT100
provides a lower inlet pressure it is recommended to keep the system in vacuum
mode to avoid a wrong generation of pressure warnings.
Fig. 4-8: left: FINE Mode, right: ULTRA Mode