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
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11
©2000-2008
DH Instruments, a Fluke Company
The RPM3 test port must be pneumatically connected to the flow path at the point
where the pressure is to be measured. Whether the pressure and temperature need to
be measured at the inlet or outlet of the DUT, or simply estimated from some
measurement of surrounding pressure and temperature, depends on Air Force
procedures and the type of DUT being calibrated. For instance, fittings 4 or 7 in
Figure 2 may be replaced by tees or other fittings which allow the RPM3 and a
temperature measuring device to be connected to and inserted in to the flow path.
Frequently, pressure is measured at the outlet of the DUT, which is open to
atmosphere when no DUT back pressure is required. In this case, the RPM3 can
also be left open to atmosphere to effectively measure the outlet pressure of the
DUT. When back pressure is to be applied to the DUT and measured, the RPM3
can either be pneumatically connected to the gauge port of the back pressure
regulator or connected to a tee in place of fitting 7 as described above.
Temperature is usually measured near the same location that pressure is measured.
The temperature measurement probe may create a flow restriction where it is inserted
into the flow path and create a pressure drop which can affect the DUT
pressure measurement. Make sure to either position the pressure measurement
connection closer to the DUT than the temperature measurement connection, or
avoid a temperature measurement connection that is significantly restrictive to flow.
Also, when the temperature and pressure devices are connected between the molbloc
and the DUT, care must be taken to make a leak-free connection.
Figure 3 shows an example of temperature and pressure connections made at the
outlet of the DUT, when back pressure is applied to the DUT.
Figure 3.
Connection of RPM3 and Temperature Measurement Device
for DUT with Back Pressure
TEMPER ATURE
F
1
FL O W D I R EC TI ON
2
4
5
3
m o ls t i c
REFERENCE PRESSURE MONITO R
8
9
G
6
MEASUREMENT DEVICE
