M O L B L O C / M O L B O X ™ L O W M A S S F L O W C A L I B R A T I O N S Y S T E M A F M E T C A L
C O N F I G U R A T I O N S
I N S T A L L A T I O N A N D O P E R A T I O N M A N U A L S U P P L E M E N T
Page
19
©2000-2008
DH Instruments, a Fluke Company
Wait a short time for pressure stability and press
[ENTER]
on the molbox front panel, or
[OK]
in COMPASS. In
manual molbox1 operation, you must follow the prompts on the molbox screen. Specific leak check steps and
explanation of the on-screen messages during manual operation leak test are found in the molbox1 molbloc Terminal
(Ver. 5.00 and higher) Operation and Maintenance Manual.
If you are running COMPASS, the leak test will proceed automatically, and the remaining test time is displayed. A
pass/fail message will display briefly in the COMPASS status bar after the test has ended, before proceeding to the next
part of the test. A COMPASS option will allow you to force the test to abort if the system leak test fails.
When to run leak check:
Run a leak check whenever any components included in the leak check closed system are disconnected
and reconnected. Typically, this only includes the molbloc.
When more than one molbloc is required within a single COMPASS test, a test option may be selected to run a
molbox purge and/or system leak check after each molbloc change in addition to the beginning of the test.
setting DUT back pressure
Once the system is setup and the procedures described in Section 3.2.2 have been performed, the user can begin setting flows,
establishing steady-state (stable) flow conditions and taking data. If the DUT is to be calibrated with back pressure (outlet pressure
above atmospheric pressure), then the back pressure regulator must be adjusted on a non-zero flow point in addition to adjusting the
flow. Follow these steps to set DUT back pressure.
Begin with the back pressure regulator handle turned fully counter-clockwise (regulator wide open).
Set the flow roughly to the desired flow setpoint.
Adjust the back pressure regulator slowly clockwise to bring the pressure indicated by the DUT pressure measurement device
(typically RPM3) to the desired level. This is likely to change the flow rate.
Reset the flow rate using the metering valve. The back pressure should remain steady when the flow is changed by small
amounts.
To set the next point, adjust the metering valve to the desired flow. Once the desired flow is reached, check the DUT pressure
measurement device. The back pressure may need small adjustments at each point depending on the magnitude of the change
in flow and the level of precision needed on back pressure.
