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molbox™ RFM™ OPERATION AND MAINTENANCE MANUAL
Close an isolation valve downstream or plug the exhaust of the flow system that
is being tested (downstream of the molbloc and the DUT if the molbloc/molbox is
being used to test another device).
Using the molbox RFM display to read the pressure set the pressure to the
normal operating pressure.
Next, close an isolation valve upstream of
the molbloc so the gas supply is no longer
open to the system being checked. Once
the
[ENTER]. The display is:
The molbox RFM is checking:
•
•
© 1998-2007 DH Instruments, a Fluke Company
Internal Pneumatic Schematic
– SYSTEM LEAK CHECK – CHECKING OFFSET AND STABILITY
FOR SYSTEMS WITH MASS FLOW CONTROLLERS (MFCs):
Keep in mind that the valves in most MFCs are not intended to provide a
complete gas shutoff and so they may not be suitable to close off the test
system. If an MFC is downstream of the molbloc and its downstream port
is open to atmosphere, it is best to close the system by connecting a cap to
the MFC outlet fitting or by connecting a shutoff valve downstream. If the
MFC valve is closed (most MFCs have normally closed valves) when the
operating pressure is applied from the upstream side, most of the gas will
be stopped by the MFC valve and will not immediately fill the volume between
the MFC valve and the downstream cap or valve. If this happens, the gas
may leak by the MFC valve to fill this volume during the test and cause a
pressure decay and an apparent system leak. The solution is to send a
setpoint signal to the MFC to open the MFC valve while pressurizing the system.
Then close the MFC valve (remove the setpoint signal) after the system is
pressurized to avoid heating of the test gas by the energized valve.
pressure
has
stabilized,
For pressure and temperature stability before running the system leak test
That the disagreement between the two RPTs is not excessive
Page 50
1. Channel A High Isolation: Open
2. Channel A Low Isolation: Open
3. Bypass:
4. Microrange Bypass:
Figure 9. molbox RFM
molbloc-L operation
347.587 kPaa
press
Open
Open
347.583
WAIT:
30
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