Description of the Menu 57
iina70e 06.fm technical handbook(1408)
6.2.5 Background in Stand-by
• Main Menu > View > Background in Stand-by
The internal background leak rate can be displayed in Stand-by mode (ON) or not
(OFF).The default setting is OFF.
The internal background is generated by residual gas (e. g. helium) that has not been
pumped away yet. Sources for residual
gas are air or absorbed gases from the inner
surfaces of the leak detector. This internal background will never disappear totally.
Very clean systems which have been pumped for a long time will show a background
in the 10
-11
mbar l/s range. Under normal conditions the background level is in the
10
-10
mbar l/s or low 10
-9
mbar l/s range.
When pressing START the current internal background is subtracted from all further
measured signals automatically. Thus it is made sure that only the net leak rate from
the part under test is measured.
When switched to Stand-by / Vent again a new internal background is calculated
after 25 s. The updated value is underlined. This means that if you press START
when the value is underlined, the actual background signal will be subtracted. If you
press START when the value is not underlined, the old background signal from the
last Stand-by will be subtracted.
6.2.6 Decimal places
• Main Menu > View > Decimal places
The number of the decimal places of the displayed leak rate can be choosen. The
default setting is 1.
Two decimals are especially usefull, when the I•CAL leak rate filter (
Please refer to
Chapter
6.6.5.3) is used.
Softkey 3: Off
The background leak rate will not be shown.
Softkey 5: ?
Help
Softkey 7: ON
The background leak rate will be shown.
Softkey 3: 1
The leak rate will be displayed with one decimal place.
Softkey 7: 2
The leak rate will be displayed with two decimal places.
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