990 CLD Autoline™ Leak Detector
3-10
DRAFT 2/2/04
RANGE SELECT Switch
The RANGE SELECT switch determines the lowest exponent digit that appears. The switch
setting does not affect the electrical sensitivity of the leak detector. This setting is used to
match the displayed exponent to the exponent on a calibrated leak at the end of the
Calibration Procedure. See Table 3-3 on page 3-12 for information on switch setting.
Auto Filament Toggle Switch
The 990 Controller includes circuitry that allows the filament to be lighted automatically
once the spectrometer tube reaches an acceptable pressure. If the FILAMENT toggle switch
is in the:
❑
OFF position prior to reaching the critical spectrometer tube pressure, light the
manually by moving the switch to the ON/AUTO position.
❑
ON/AUTO position prior to reaching the critical spectrometer tube pressure, the
filament lights automatically.
The filament can be turned off at any time by switching the FILAMENT toggle switch to the
OFF position.
Some hysteresis is included in the filament control circuit. The filament control circuit lights
the filament when the needle of the cold cathode gauge meter is two-thirds of the way
down the green band (from right to left). The filament extinguishes when the needle rises to
the upper edge of the green band. This hysteretic pressure margin eliminates oscillations in
spectrometer tube pressure due to the transient outgassing of the filament as it lights.
Remote Filament Control
The 990 CLD leak detector includes a remote filament control feature. The OPTO-22
modules must be inserted into the back panel connectors of the 990 Controller (refer to
Table 2-2 on page 2-6). When jumper
J11
on the main electronics board is in the:
❑
LOCAL position, it activates the front panel FILAMENT toggle switch.
❑
REMOTE position, the momentary actuation of the FILAMENT ON line turns the
filament on if or once the spectrometer tube critical pressure is reached. A
momentary actuation of FILAMENT OFF turns off the filament
The FILAMENT ON and FILAMENT OFF lines are accessed viaJ10 on the 990 Controller
back panel.
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