Fluke MOLBOX RFM Operation And Maintenance Manual page 79

PRINCIPLE
Use of the microrange feature improves molbox RFM flow measurements while using
molbloc-L only. Microrange has no effect and is disabled during molbloc-S operation.
The molbox RFM microrange option (if present) improves molbox RFM flow measurements
when using a molbloc-L element below 10 % FS of its measurement range. Flow measurement
resolution and accuracy are enhanced by implementing a low differential pressure RPT which
improves the resolution and accuracy of differential pressure measurement when differential
pressure is below 12.5 kPa (1.8 psi). See Section 3.1.5 for microrange operational principles
and Section 1.2.4.1.1 for microrange specifications.
In automatic microrange mode, use of the microrange option to improve flow measurement is
optimized in a manner that is transparent to the user. In particular, the transition between the two
different types of differential pressure measurement is smoothed out by weighted averaging of
the differential values in a transition zone between 10 and 12.5 kPa differentials (1.5 to 1.8 psi).
The MICRO function turns ON and OFF the microrange option's automatic mode.
With automatic microrange
measurements are not used at all (unless manual microrange is ON, see Section 3.6.7). With
automatic microrange option ON, the differential pressure value used to calculate mass flow
can come from the difference between the upstream and downstream RPTs, the microrange
differential RPT or a combination of the two during the transition from one method to the other.
The microrange option can also be operated in a manual mode (see Section 3.6.7).
OPERATION
The MICRO function can be operated at any time from the main run screen.
Pressing [MICRO] causes automatic microrange to turn ON if it is OFF and to turn OFF if it is
ON. When [MICRO] is pressed, the molbox RFM displays a 3 second message indicating
whether it is turning automatic microrange ON or OFF and then returns to the main run
screen in the new condition. Automatic microrange ON is indicated by an <m> in the
microrange status character of the main run screen. If molbox RFM is not equipped with the
microrange option, a 5 second message indicates that the microrange option is not installed.
Don't confuse this message with <Access denied> which displays when the security level
setting restricts [MICRO] key access (see Section 3.6.2).
Turning microrange OFF may reduce the accuracy of flow measurements below 10 % of the
molbloc flow measurement range and lead to unexpected results.
Automatic microrange option ON is indicated by an "m" in the microrange option
designator character of the main run screen (top line, 6
Microrange option OFF is indicated by a blank designator (see Section3.2).
Use of the MICRO function overrides the current setting of manual microrange option made
by pressing [SPECIAL] and selecting <7micro> (see Section 3.6.7). If manual microrange is
ON, pressing [MICRO] turns OFF manual microrange and turns ON automatic microrange.
OFF, the microrange
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3. OPERATION
option differential pressure
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character from the right).
© 1998-2007 DH Instruments, a Fluke Company
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