INFICON UL1000 Helium leak detector - Manual (Page 46)

46
Description and Working Principle
iina
70
e 0
4
.f
m
te
chn
ica
l ha
nd
boo
k
(1
40
8)
Since the scroll pump continues to evacuate the test sample the inlet pressure p
1
will
continue to drop. Below 2 mbar the UL1000 and UL1000 Fab will switch to FINE
mode, i.e. V4a will open and V1b will close. The gas stream enters the turbo pump
at an intermediate level. The sensitivity of the system now is higher, the detection
limit is 1×10
-10
mbar l/s.
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 UL1000 and UL1000 Fab 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 2.5 l/s, the
detection limit is 5×10
-12
mbar l/s.
Tipp A special set up of the UL1000 and UL1000 Fab stopps the autoranging
procedure as described above. With the mode FINE ONLY (Please refer to
Chapter
6.3 Mode ) the unit will stay in FINE Mode Fig. 4-7 (left) regardless
the inlet pressure. The valve V1a is closed.
Fig. 4-7: left: FINE Mode, right: ULTRA Mode
V4a
V4b
p
2
V2
MS
V6
V7
p
1
V1b
V1a
V5
TL
V8
V4a
V4b
p
2
V2
MS
V6
V7
p
1
V1b
V1a
V5
TL
V8