Varian 959D, Operation Manual

Page: 42 / 82

959D Leak Detector
2-14
DRAFT
9/13/02
6. The leak rate should drop to zero with just one bar lit on the display.
A change in one adjustment may affect the others. Therefore, it may be necessary to
repeat step 2 through step 7 until no significant change occurs in the leak rate reading.
The 959D is now tuned to helium.
NOTE
If tuning cannot be achieved, system service may be necessary.
Contact Varian Vacuum Technologies Customer Service at
1-800-8VARIAN for further instruction.
7. Calibrate the leak detector (see Section 2.5.1 “Calibrating with a Calibrated Leak” on
page 2-11).
8. Press VENT and remove the calibrated leak.
CAUTION
To prevent a build-up of helium and to minimize deterioration
of the calibrated leak, always store the calibrated leak with its
valve open.
2.5.4 Tuning the Spectrometer Tube Using a Tuning Leak
The tuning leak is a specially designed adjustable needle valve in an adapter to fit the test
port. When the needle valve is opened such that test port pressure is 100 mTorr, helium nat-
urally present in the atmosphere (5 parts per million), enters the leak detector, giving a leak
rate reading of approximately 10
−
6
atm cc/sec. Since this reading is about 10 times as large
as with the reservoir type of calibrated leak, tuning the spectrometer tube is easier. The con-
trols referred to in the procedure are shown in Figure 2-2 on page 2-2 and Figure 2-4 on
page 2-4.
1. Verify that start up has taken place, that the pumps are up to speed, and that the leak
detector is ready to test (see Section 2.2 “959D Startup Procedure” on page 2-7).
2. Press VENT .
3. Set
RESIDUAL BACKGROUND
to
RUN
.
4. Loosen the test port tightening nut and unplug the test port.
5. Place the tuning leak onto the test port and hand-tighten it to compress the O-ring and
establish a vacuum-tight seal.