Model 979 Series Helium Mass Spectrometer Leak Detector
3-6
DRAFT 9/15/03
3.1.2.4 Ion Voltage
Touch the ION VOLTAGE box to display the current ion voltage value of the Ion Source in
the spectrometer tube. This value can also be manually adjusted. The ion voltage parameter
is used to tune the leak detector, maximizing the leak detector output for a peak helium sig-
nal. The ion voltage parameter is adjusted before the leak detector is calibrated to helium.
Typical ion voltage values range from 230 VDC to 270 VDC. The ion voltage value is auto-
matically adjusted and set during the Calibration routine.
3.1.2.5 Variable Focus Voltage
The VAR FOCUS Voltage adjustment box displays the current Variable Focus Voltage value
of the ion source in the spectrometer tube and allows for the adjustment of this parameter.
The variable focus voltage parameter is used to tune the leak detector, maximizing the leak
detector output for a peak helium signal. The variable focus voltage parameter is adjusted
before the leak detector is calibrated to helium.
Typical Variable Focus Voltage values range from 180 VDC to 200 VDC.
3.1.2.6 Suppressor Voltage
The SUPPRESSOR indicator displays the current Suppressor Voltage value in the
preamplifier in the spectrometer tube. The suppressor voltage parameter is not variable.
This parameter cannot be changed by the operator.
3.1.2.7 Fixed Focus Voltage
The FIXED FOCUS Voltage indicator displays the current Fixed Focus Voltage value of the
ion source in the spectrometer tube. The fixed focus voltage parameter is not variable and
cannot be changed by the operator.
3.1.2.8 Filament Selection
The Filament Selection box switches between FIL 1 ACTIVE and FIL 2 ACTIVE. The filament
selection can be performed manually, or it will occur automatically in the event that the
current operating filament burns out. Execute a calibration routine each time the operating
filament is changed.
FILAMENT
SELECTION
In the event that the current operating filament burns out, the 979
automatically switches over to the next available filament. The
change is indicated on the touch screen display and the leak rate
exponent display flashes a C, indicating that calibration is required.
NOTE
We recommended that you replace the ion source as soon as it
is convenient after the spare filament has been put into use. See
Section 4.4 “Ion Source Replacement Outside of Annual
Maintenance” on page 4-20.
Summary of Contents for 979 Series
Page 139: ......