4. OPERATION
Page 55
© 2007 DH Instruments, a Fluke Company
4.4.4.1
LEAK TEST OPTION IN A TEST DEFINITION
This leak test option checks for leaks in the Reference Gas Cylinder, though the
catenary tube, and up to the isolation valve in the GFS enclosure sidewall
column.
Once an acceptable limit in flow has been established as described above with a
minimum time for a valid result, these values can be entered on the Pre-Test tab
of a Test Definition as detailed in Section 5.5.2.4. The leak test will occur based
upon the options selected as defined in that section.
4.4.4.2
SEMI-AUTOMATED LEAK TEST
This operation is similar to 4.4.4.1 in that it checks for leaks in the Reference Gas
Cylinder, though the catenary tube, and up to the isolation valve in the GFS
enclosure sidewall column, but it is run outside of a test definition in manual
mode.
The user must still establish an acceptable leak limit and minimum time, but
these values could be determined at any time up to the point where the user is
ready to end the test.
The semi-automated leak test is performed as follows:
A manual test is run as outlined in Section 5.6.2, steps 1 to 6. If the user
wishes to record the leak test data then a data file is opened as in Section
5.6.2, step 7.
In order to keep the isolation valve closed, a flow point should
NOT
be set as
in Section 5.6.2, step 8.
An accumulation is started per Section 5.6.2, step 9, but in the accumulation
setup window a large starting tolerance (~5%) that results in a short starting
time, a flow value, and a mass to deplete greater than 1 gram are all entered.
The flow and mass values actually entered are irrelevant as the system will
ideally be neither flowing nor depleting mass, but the setup will not continue
with zero or null values. The “OK” button is selected to continue.
The test is allowed to continue for the minimum time established to get an
accurate result. If the data is being recorded to a data file, the “Take Point”
options as in Section 5.6.2, Step 10 need to be defined.
Once the minimum time has elapsed, the user must judge the significance of the
“Depleted Mass/Time”
calculated flow value reported in mg/s on the GFS
Diagnostics run screen (see Section 5.1.5.3) against the minimum test flow in mg/s.
The leak test can be aborted at any time by using the “Stop” icon.
4.4.4.3
SEMI-AUTOMATED LEAK TEST TO MANUAL ISOLATION
POINT
This leak test is nearly identical to Section 4.4.4.2 except a flow point will be
requested, which will open the isolation valve and pressurize the flow path to the
point where the user has chosen to install a manual isolation valve. Other than
the regulators on the Reference Gas Cylinder, the flow path for the leak test
should not include a regulator or the regulator needs to be bypassed as it has the
potential to continue to bleed pressure through and cause a false leak indication.
If an MFC is in the flow path included in the leak check then the user must
ensure that the setpoint is high enough to fully open the MFC valve and allow the
pressure to equalize across the MFC or a leak could be falsely indicated. An