TH 10.211/8.02 - 12/97
Normal: Standard partial flow operating mode
Oil-free Avoids possibly occurring backstreaming of
oil vapour from the partial flow pump.
Note
Switch off the FINE MODE lock (menu item 31) „Only
GROSS mode off“.
03: Gas ballast closed Remove helium background
with the gas ballast facility
The gas ballast is employed to reduce a helium back-
ground in the UL 200 which is too high. For this, the built
in gas ballast valve of the forevacuum pump must be
opened in the Standby mode („Gas ballast OPEN“).
After 20 minutes the valve closes automatically. But the
gas ballast valve may also be closed manually by selec-
ting „Gas ballast CLOSED“.
The gas ballast valve will also closed after having selec-
ted „START“ (start of the measurement process).
The gas ballast valve may also be opened automatically.
This is done in the setting „Gas ballast AUTO“. Here the
internal helium background is monitored for the first time
after 30 s have elapsed in the Standby mode. If a helium
background in excess of 1/10th of the entered trigger
level for triggers 1, 2 or 3 is detected, the gas ballast
valve on the forevacuum pump will open automatically.
The gas ballast valve also opens automatically when the
helium signal is so great that measurements in the most
sensitive range are not possible.
(Q ~ 1E-6 mbar·l·s
-1
)
The internal helium background can be displayed in the
Standby mode through the function „21: System BG dis-
play“.
04:Test <enter> Check the measurement signal
for helium
In this mode, the UL 200 checks whether or not the sig-
nal is generated by helium or by a high water vapour
background, for example. For this, tuning of the mass
spectrometer in the UL 200 is briefly shifted by 1/2 of a
mass unit, i.e. it is adjusted to the masses 3.5 amu and
4.5 amu. The corresponding intensities which are then
measured must reduce by at least 50 % compared to the
measurement signal for mass 4.
The message „Test OK“ indicates that the measurement
signal is being caused by helium.
The message „Test failed“ means that there is no clear
peak on mass 4.
Possible causes:
- The sensitivity cure of a neighbouring mass, mass 2,
for example, extends over to mass 4, superimposing
this mass.
- There is no helium signal present (during Standby or
Vent, for example).
18
The same applies correspondingly when the UL 200 has
been set to M = 2 amu (H
2
) or M = 3 amu.
05: to 08: not assigned
09: Password locked Enter password for access to
the extended menu.
See Chapter 2.5.2.
10: Evac Time 1 30 s Monitoring of gross leaks.
This menu item is used to define when the gross leak
message is to occur. The gross leak detection process
operates in two steps and the limits can be adapted as
required.
This menu item is particularly useful in series testing
under the same conditions at all times.
After pressing the Start push-button the test sample is
evacuated. If the pressure conditions are not attained, or
if the pressure does not drop low enough within the peri-
ods of time specified here, the pumpdown process is ter-
minated and the display (4/2) will indicate one of the
messages „EVAC Stopped Time 1“ or „EVAC Stopped
Time 2“.
Within the period of Time 1, the inlet pressure at the test
flange (3/2) must have dropped below 100 mbar. The
duration may be selected freely between 1 second and 9
minutes or can be set to endless. The default is 30 s.
Within the period of Time 2 the status of measurement
readiness must have been attained, i.e. the inlet pressu-
re must have dropped below 2 mbar. The duration may
be freely selected between 1 minute and 10 minutes or
can be set to endless. The default is 10 minutes.
The periods which are selected in each case depend
firstly on the desired reaction time for the gross leak
message, and secondly on the volume of the test sam-
ple and the effective pumping speed.
Caution If the evacuation time was set to endless
the oil level of the mechanical pump
should be checked more often.
11: Sensitivity normal Select sensitivity
normal: The output of leak rates to the hand unit and the
control panel is restricted.
For both hand unit and control panel „-9“ is the
lowest exponent for the unit mbar·l·s
-1
. Software
filtering is performed over 8 measured values at
intervals of 20 ms.
high: The sensitivity of the leak detector is increased.
The detection limit is Q < 5·10
-11
mbar·l·s
-1
.The
reaction time of the UL 200 is now longer since
software filtering is performed over 512 measu-
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