990 CLD Autoline™ Leak Detector
4-14
DRAFT 2/2/04
Residual Background Check
Once testing is complete and helium is no longer entering the leak detector through a leak,
the vacuum system rapidly removes the remaining helium. However, a small residual
amount, called background, is usually present. Normally, this background is steady and can
be cancelled by zeroing the leak-rate display. It is sometimes useful to measure background
as an indication of a dirty system which needs cleaning or overhaul.
To run a residual background check:
1. Start and run the leak detector.
2. Verify that the leak detector is tuned and calibrated.
3.
Valve-off
the test chamber.
4. Place the RESIDUAL BACKGROUND switch in the CHECK position to make the leak
detector almost completely insensitive to all gases, including helium.
5. Select the most sensitive RANGE.
6. Adjust the fine and course ZERO controls until the leak rate display indicates zero, then
set the RESIDUAL BACKGROUND switch to the RUN position. The resulting reading is
background.
7. Re-zero the leak rate display before using the leak detector.
If the background reading is more than one-half scale in the second most sensitive
range, the vacuum system may be contaminated or it may have a leak.
Subassembly Replacement
If a problem is isolated to a subassembly, replace the entire subassembly so that leak testing
can continue without prolonged interruption. Refer to 5“Parts List” for a list of replacement
subassemblies and their corresponding Vacuum Technologies part numbers.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
