Specifications

3. OPERATION
Page 47 © 1998-2007 DH Instruments, a Fluke Company
3.4.4.3.1 Leak Check molbox
 PURPOSE
To check the internal molbox RFM pneumatic circuit for leaks.
 PRINCIPAL
It is normally not necessary to run the MOLBOX LEAK CHECK procedure
frequently. It is intended for troubleshooting purposes when there appears to be
a leak or other molbox RFM measurement problem whose source cannot be
identified by the SYSTEM LEAK CHECK or other troubleshooting means. It is
recommended to run the MOLBOX LEAK CHECK after it has been shipped or if it
is suspected that the molbox has been exposed to a large shock or liquid or
particulate contamination.
 OPERATION
Press [TARE] and select <3leak check>, <1molbox>. If the molbox RFM has a
microrange option, microrange RPT <1active> or <2bypassed> must be
selected to proceed (see Section 3.1.5). The next display is:
1. The pressure read by the upstream transducer
(left), the downstream transducer (right) and
the pressure unit of measure (middle).
2. Indicator that the figure that follows is
differential pressure.
3. Differential pressure across the molbloc in
current pressure unit of measure.
4. Prompt for the action to take when ready.
347.458 kPaa 307.455
DP 40.003 <ENTER>
The molbox RFM internal valving is in its normal measuring configuration (see
Figure 3). This display is intended to assist the operator in setting the leak
check pressure.
Apply the maximum differential pressure across the molbloc that is normally
encountered during flow measurement while working at your typical absolute
working pressure. Neither pressure should be less than atmosphere. Use the
<DP> indication on the molbox RFM display to set the absolute and differential
pressure.
Once the pressure setting is correct,
press [ENTER]. The molbox RFM
actuates its internal valves to isolate itself
from the molbloc and trap the upstream
and downstream pressures on its RPTs
(see Figure 8). The display is:
Vent molbloc ports
<ENTER>
Assure that both molbox RFM rear panel pressure connections are vented.
Since the pressure quick connections on the molbox RFM and the quick-
connectors on the molbloc pressure connection tubes seal when disconnected,
they cannot be vented by simply disconnecting them. The easiest way to assure
that the connections are vented is to maintain the normal connections to the
molbloc, shut off the molbloc gas source and open one or both ends of the
molbloc so it can vent to atmospheric pressure. Another alternative is to install the
non-sealing quick connectors (P/N 101889) provided in the molbox accessories (see
Section 2.1.2) into the molbox quick connectors.