990 CLD Autoline™ Leak Detector
3-6
DRAFT 2/2/04
Tuning the Spectrometer Tube Using a Helium Reservoir Leak
The calibrated leak can be used for two functions:
❑
Tuning the spectrometer tube
❑
Calibrating the leak detector
These functions are normally performed at the same time, in the sequence indicated.
To tune the spectrometer tube:
1. Place the calibrated leak in the vacuum system as close as possible to the test chamber.
2. Open the valve on the calibrated leak and operate the vacuum system.
3. Start and run the leak detector.
4. Observe the leak rate indication on the LEAK RATE bar graph.
It is probably less than that of the calibrated leak. If necessary, use the RANGE
pushbuttons to set the largest reading without lighting the OVER SCALE LED.
5. Close the valve on the calibrated leak and check for a decrease in the displayed
leak rate.
6. If required:
❑
Carefully rotate the FINE ZERO adjustment to obtain a zero reading on the
LEAK RATE display.
❑
Move the COARSE ZERO adjustment on the secondary controls panel to obtain a
zero reading on the LEAK RATE display.
7. Re-open the valve on the calibrated leak and observe the LEAK RATE display.
8. Use the RANGE pushbuttons to position the reading between 1 and 9 on the display.
9. Gently adjust the FOCUS control for a maximum reading on the LEAK RATE display,
then adjust the ION control for a maximum peak on the LEAK RATE display.
NOTE
The ION control is a 10-turn potentiometer that normally only
requires a slight adjustment for a maximum reading on the
display. The detector is tuned to helium at the factory. When
tuned to helium, the number on the outer dial at the 12 o'clock
position should be between 2 and 8.
If enhancement magnets have been disturbed or if extensive repair work was performed
on the spectrometer tube, it might be necessary to adjust the enhancement magnets or
reset the ion source emission current on the spectrometer tube. Refer to 6“Fundamentals
of Leak Detection” on page 6-1 for enhancement magnet and emission current
readjustment.
10. Repeat steps 5 through 9, as a change in one adjustment may affect others.
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