P&T] (Pressure And Temperature) - Fluke MOLBOX RFM Operation And Maintenance Manual

OPERATION
Select [TARE], <5BPR>. The display is:
1. The current pressure read by the upstream
(left) and downstream (right) RPTs without
taking into account the current tare value.
These are untared readings in the current
pressure unit of measure.
2. The current BPR (ratio of downstream to
upstream absolute pressure).
Press [ENTER] or [ESCAPE] to exit the BPR function and return to the previous
RUN screen and BPR mode.
3.4.5 [P&T] (PRESSURE AND TEMPERATURE)
PURPOSE
To provide continuous display of the pressures measured by molbox RFM, the Reynolds
number of the flow through the molbloc, the temperature of the molbloc and other pressure
measurement information depending on whether a molbloc-L or molbloc-S is connected to
molbox RFM.
PRINCIPLE
molbox RFM continuously measures pressures and molbloc temperature and uses these
measurements to calculate flow.
The pressure at the molbloc upstream and downstream ports is read by two absolute
Reference Pressure Transducers (RPTs). In molbloc-L operation, the flow is calculated from
the differential pressure across the molbloc. The differential pressure is calculated as the
difference between the two absolute RPT measurements (upstream - downstream) and is
displayed in the pressure screen. If the molbox RFM is equipped with the microrange option,
differential pressure below 12.5 kPa (1.8 psi) is measured by the microrange option's low
differential pressure RPT.
In molbloc-S operation, the flow is calculated from the molbloc-S upstream pressure. The
upstream pressure may be read by either one or both of the RPTs, depending on which BPR
mode is used (see Section 3.6.9). When molbox RFM is in a valve state called BPR OFF,
the molbloc-S downstream pressure is not measured and both RPTs are used to measure
the molbloc-S upstream pressure. Their readings are averaged to reduce the uncertainty of
the molbloc-S upstream pressure measurement. An indicator is used next to the "downstream"
RPT value to show whether the RPT is currently measuring the molbloc downstream or
upstream pressure. Whenever the molbloc-S downstream pressure is measured, the BPR is
calculated and shown in the P&T pressure screen. When both RPTs measure the upstream
pressure (BPR OFF mode), the indicated pressure for both RPTs is adjusted to equal the
average of the two using the dynamic tare and BPR is no longer displayed.
Since the displays and operation of the P&T pressure screen are different for molbloc-L and
molbloc-S operation, they are described separately in the
For temperature measurement, two Platinum Resistance Thermometers (PRTs) are embedded
in each molbloc. These are connected to the molbox RFM by the molbox to molbloc cable.
The molbox RFM ohmic measurement system reads the resistance of the PRTs and
calculates molbloc temperature.
molbox RFM continuously calculates the Reynolds number of the flow through the molbloc.
molbox RFM's current pressure and temperature readings as well as the Reynolds number of
the current flow can be displayed using the P&T function.
259.312 kPa ↓99.5769
BPR 0.38
OPERATION sections below.
Page 59 © 1998-2007 DH Instruments, a Fluke Company
3. OPERATION