6. TROUBLESHOOTING
Page 159
© 1995 - 2010 Fluke Corporation, DH Instruments Division
SYMPTOM
PROBABLE CAUSE
SOLUTION
Pressure indicated by
never becomes stable.
There is a leak in the and/or
in the system to which it and the
molbloc are connected.
Find and correct leak. Consider using
LEAK CHECK functions. 3.4.4.3
Flow indication appears to be
grossly incorrect.
Your assumption of flow in the system
is grossly incorrect.
Check and adjust flow in the system.
Flow indication appears to be
grossly incorrect.
The molbloc connected to
has been swapped without
reinitialization so is still using
characteristics from a previous molbloc.
Reinitialize molbloc using
[SETUP]
,
<1molbloc>.
3.5.1
In molbloc-S mode, there is no
flow through the molbloc but
is indicating a large flow
value.
is in BPR OFF mode and
flow is being calculated from upstream
absolute pressure without knowledge of
downstream pressure.
Behavior is normal. Consider BPR when
evaluating flow measurements when using
molbloc-S. Also consider changing BPR
mode to Auto or ON. 3.1.5, 3.6.9, 3.4.4.5
Flow indication appears to be
incorrect.
molbox/molbloc and/or the device you
are comparing it to are in tolerance but
you have not properly evaluated the
tolerance limits.
Determine flow measurement tolerance of
molbloc/molbox and device you are
comparing with. Evaluate “correctness”
relative to the combined tolerance of the two.
1.2.5.
Flow indication appears to be
incorrect.
Reference pressure transducer(s)
(RPTs) are inoperable or out of
calibration.
Use
[P&T]
to view pressure indications.
Recalibrate RPTs if necessary. 3.4.5, 5.2
Flow indication appears to be
incorrect.
The gas selected is not the gas flowing
through the molbloc.
Select the correct gas. 3.4.2
Flow indication appears to be
incorrect while using molbloc-S to
measure air flow
Incorrect humidity ratio is being used.
Reselect Air as the test gas and make sure
the humidity ratio W is entered properly. W
should be zero for dry air and should be
calculated from ambient conditions when
measuring ambient air. 3.4.2.2.
Flow indication appears to be
incorrect.
The gas selected is the gas flowing
through the molbloc but the molbloc
has not been calibrated for that gas.
Verify that the molbloc has calibration
coefficients for the flowing gas, have the
molbloc calibrated for the flowing gas if
necessary or accept higher measurement
uncertainty in the flow measurements. 3.5.1,
1.2.5
Flow indication appears to be
incorrect.
Gas flowing through molbloc is not
pure.
Check purity rating of gas used; purge
molbox/molbloc if flowing gas was just
changed. If gas is a known mix, use the flow
adder
and
multiplier
to correct for the mix.
3.4.4.2, 3.5.3
Flow indication appears to be
incorrect.
The molbloc is not being used at the
correct pressure for its pressure
dependent calibration type.
Check molbloc Calibration Report for
pressure dependent calibration type and
check operating pressure. 1.2.5, 3.2.5
Flow indication appears to be
incorrect.
pressure and/or Reynolds
numbers are outside of limits.
Observe pressure and Reynolds numbers
and adjust pressure/flow to be inside of
limits. 1.2.5, 3.4.5
Flow indication appears to be
incorrect.
Flow through molbloc is in wrong
direction.
Check that flow through molbloc is in
direction of arrow on molbloc. Switch if
necessary.
Flow indication appears to be
incorrect.
Leak in pressure lines from molbloc to
.
Check lines for leaks and correct if
necessary. 3.4.4.3
Flow indication appears to be
incorrect.
A flow adder or multiplier has been
incorrectly or inadvertently applied.
Check and correct if necessary. 3.5.3
Flow indication appears to be
incorrect.
molbloc calibration has changed due to
contamination.
Check molbloc for contamination. Contact
your
DHI
Authorized Service Provider if liquid
or particulate contamination is detected. 7.4
Flow indication appears to be
incorrect by a constant offset
amount.
needs to be correctly
“zeroed” (
tared
) at the current operating
pressure.
Tare
. Be sure to
tare
upstream if
the upstream pressure is constant and
downstream if the downstream pressure is
constant. 3.4.4.1
