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Next, close the isolation valve upstream of the molbloc so the gas supply is no
longer open to the system being checked. Once the pressure has had time to
stabilize, press [ENTER].
The next display is:
Press [ENTER] to begin the test
The next display is:
1.
The average pressure from the two molbox
RFM absolute RPTs.
2.
Current absolute pressure measurement in
active pressure unit of measure.
3.
SYSTEM LEAK CHECK count down in
seconds.
Press [ESCAPE] to abort the leak test.
Pressing [ENTER] while the test is in progress restarts the test and reset the leak
test timer.
When the test is complete, a test results screen is displayed:
1.
The total change in average pressure over the
test interval.
2.
The currently selected pressure unit of measure.
3.
Average rate of pressure change, per second,
during the test.
Since flow systems using molbloc-S will may use widely varying flow rates and
tubing sizes, and test volumes may be quite large, it is difficult to predict what
size pressure rate of change is acceptable to avoid significant flow errors. Your
best guide may be to run the SYSTEM LEAK CHECK often with your hardware,
find a typical rate of change which represents a sound setup, and attempt to
match that rate each time. In any case, you should be able to achieve a rate of
change smaller than 0.01 % / second of the absolute line pressure.
If you observe a relatively large leak rate and are unable to locate a leak in the
flowpath components, check or replace the upstream and downstream molbloc
to molbox pressure tubes and their connectors and retry the test. They are a
critical part of the pneumatic system and if a significant leak is present in these
tubes, it will cause an error in flow measurement.
3.4.4.4
<4AutoZ>
PURPOSE
To offset the molbox RFM absolute reference pressure transducers (RPTs)
relative to a reference value in order to compensate for possible changes in RPT
zero between full recalibrations.
Improper use of the AutoZ function can cause out of tolerance pressure
measurements. AutoZ should be used only by qualified personnel for the
purpose of rezeroing the molbox RFM reference pressure transducer
absolute pressure measurement function.
ENTER to start
60 s leak check
199.16 kPa a
leak testing
ΔP –0.0720 kPa
Rate –0.0012 kPa/s
Page 53
© 1998-2007 DH Instruments, a Fluke Company
3. OPERATION
60s
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