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
17
©2000-2008
DH Instruments, a Fluke Company
If you are using molbox1 manually, press
[TARE]
and select
<2purge>
. Set the desired purge time then press
[ENTER]
. The time you will need to fully purge out the system depends on the flow rate you have set. If your flow rate
is greater than 1 slm, one minute is usually sufficient. If you are flowing less than 100 sccm, you may need to purge for up
to 5 minutes.
If you are using COMPASS software, there are two ways to execute a purge. When in
[RUN DUT]
or
[RUN molbox]
,
select the
[Purge molbox]
icon, then enter the desired purge time. If you are running a test, an automatic purge can be
scripted into the beginning of the test, with a selectable purge time and purge flow rate.
See the COMPASS for molbox User’s Manual Version 4.00 for further instruction on purging within COMPASS.
When to purge:
Whenever the gas in the flowpath or molbloc to molbox pneumatic lines is unknown or is different from the
calibration gas to be used, a purge should be performed. Since there is no flow through the molbloc to molbox lines during
normal operation, they will not purge out by the gas movement through the flowpath. The molbox1 or COMPASS purge
function must be performed. The molbloc to molbox pneumatic lines have quick connectors with check valves, so the last gas
used will remain in the lines when they are disconnected.
Tare
This procedure zeros the molbox1 differential pressure measurement. The tare should always be performed with the normal
operating pressure supplied to the molbloc. The DUT does not need to be connected to perform the tare.
Open the molstic shut off valve allowing the gas supply to reach the molbloc.
Make sure that the flow rate is less than the molbloc’s full scale flow. Taring can be performed with or without flow
through the molbloc but it is usually easier to achieve pressure stability with a non-zero flow rate.
If you are using molbox1 manually, press
[TARE]
and select
<1tare>
and
<1upstream>
. Wait for stability and press
[ENTER]
when ready.
If you are using COMPASS software, there are two ways to execute a tare. When in
[RUN DUT]
or
[RUN molbox]
,
select the
[Tare molbox]
icon, then select the
<upstream pressure>
button. If you are running a test, a fully automatic
or manual tare can be scripted into the test on any flow point.
See the COMPASS for molbox User’s Manual Version 4.00 for further instruction on taring within COMPASS.
When to tare:
A tare should be performed at the beginning of each day that the molbox is used. This allows the user to track any
changes in the molbox pressure transducers. When taring, the previous tare value is displayed and can be compared to the new
tare value that is saved. These values should not differ by more than 10 Pa if the molbox was tared recently. The molbox
should also be tared each time that the molbloc inlet pressure is changed significantly, but the inlet pressure should
remain constant for AFMETCAL systems.
