5 Definition of Terms
Autoranging The range of the preamplifier and
the vacuum ranges are selected
automatically.
The autoranging feature of the
UL 200 covers the entire range or
leak rates depending on the sel-
ected operating mode: „2: Mode
Vacuum“, „2: Mode Sniff N/QT“ or
„2:Mode Partial normal/oil-free“.
Not only the leak rate signal, but
also the pressure in the test sam-
ple (inlet pressure PE) and the
forevacuum pressure (PV) are
used for control purposes. Range
switching between the main ran-
ges is performed via valves. Fine
range switching within the main
ranges is implemented by swit-
ching over the gain factor of the
preamplifier.
Autotune,
mass alignment This function automatically aligns
the mass spectrometer so that a
maximum leak rate is displayed.
The control computer changes
the voltage which accelerates the
ions in the selected mass range
until a maximum ion current is
detected by the ion detector.
During each calibration the mass
alignment is run automatically.
Autozero Determination and compensation
of the helium background.
With this function, the internal
Zero level of the leak rate signal
is determined in order to avoid a
readout of the internal helium
background and mistaking it as a
proper measured value.
This function is run automatically
each time when pressing STOP
to enter Standby or Vent, or when
entering the CAL mode.The Zero
measurement is only run in the
most sensitive preamplifier range
and it is calculated for the other
ranges. The Zero values which
have been determined in this way
for the various measurement ran-
ges are stored and are used to
correct all leak rates which are
determined later on.
If subsequently negative leak ra-
tes are obtained due to this cor-
rection, the stored offset values
are changed so that Zero will be
the lowest value which can be
obtained. In this way the values
adapt automatically to a decaying
background (adaptive backgro-
und correction).
The entire measurement process
may take up to 10 s after opera-
ting STOP. However, this process
is interrupted automatically when
operating the START push-button
in the mean time.
Basic menu Comprises menu lines 1 to 9.
This part of the menu is not pro-
tected by a password. For details
please refer to Chapter 2.5 and
2.5.4 (menu line 14).
CONTROL Control connection on the rear of
the instrument.
Default condition Status of the UL 200 when sup-
plied by the factory.
Extended menu Comprises menu lines 10 to 49.
Access to this part of the menu
can be restricted / or enabled by
entering the first password (see
also Chapter 2.5).
FINE Valves V2a and V4 are open;
PE < 0.2 mbar; the turbomolecu-
lar pump with its high pumping
speed is connected to the inlet
flange.
GROSS Valves V2a and V2b are open; PE
= 0.2 ... 3 mbar.
Internal helium
background The existing helium partial pres-
sure in the measurement system.
The level of the internal helium
background is measured in the
Standby mode and subtracted
from the measured signal.
Measure,
measurement mode The UL 200 measures the leak
rate of the test sample.
Menu item Menu lines numbered from
1 ... 99.
Standby Mode which is attained by opera-
ting the STOP push-button; the
START LED on the hand unit is
turned off. The LCD display (3/2)
indicates the message Standby.
All valves leading to the test
connection are closed. The mea-
surement system is internally dis-
connected from the test connec-
tion.
42
TH 10.211/8.02 - 12/97
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