Varian 959D, Руководство по эксплуатации

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959D Leak Detector
2-10
DRAFT
9/13/02
2.4.2 Out-of-Range Situations
The testing range of the 959D is set by the RANGE switch and the leak rate within the set
range is displayed as a 0 to 10 vertical illumination on the primary front control panel of
Figure 2-2. Either the
OVER
or
UNDER
LED will light up if the measured leak rate is
out-of-range for the particular setting of the RANGE switch.
OVER range If the OVER LED is steadily ON and the vertical bar graph is at
maximum, rotate the RANGE switch clockwise until the vertical
display falls within its operating range. If the Range switch arrives
at its highest setting of 4 bars and the display is still stuck at its high-
est point, you can assume that a gross leak exists associated with
the object under test.
UNDER range If the UNDER LED is steadily ON and the vertical bar graph is at
minimum, rotate the RANGE switch counter-clockwise until the
vertical display falls within its operating range. If the Range switch
arrives at its lowest setting of 1 bar and the display is still stuck at its
lowest point, you can assume that the system background is actu-
ally
below any previously set zero value. Refer to section 2.6.1 to
re-zero the leak detector.
2.4.3 Testing above 200 mTorr
The 959D is designed to detect very small leaks at very low pressures. But, the system
can detect leaks at relatively high pressures (gross leaks) by placing a throttle valve,
p/n 626603345, between the test object and the test port. The throttle valve maintains toler-
able foreline pressure of less than 250 mTorr.
To measure a leak at a test port pressure above 200 mTorr, first attach the throttle valve and
then proceed with the measurement.
1. Press VENT to vent the test port to atmosphere.
2. Loosen the tightening nut and remove the test object.
3. Place the throttle valve in the test port and tighten the nut to compress the O-ring and
establish a vacuum-tight seal.
4. Connect the object on the throttle valve at the test port.
5. Press START and follow the procedure described in the previous section.
6. Adjust the throttle valve for a pressure less than 250 mTorr or allow the leak detector to
transfer into TEST .