Gas] - Fluke MOLBOX RFM Operation And Maintenance Manual

When the K function is ON, as indicated by a <K> following the current flow unit in the
first line of the MAIN run screen, the current molbox RFM flow indication equals:
(flow as calculated by molbox RFM for the selected gas) x (the current K factor)
So the indicated flow is actually in error (biased) relative to the true flow through the
molbloc by the value of the K factor. Care should be taken to ensure that the correct
molbloc range is selected for tests when a K factor is used, since the actual flow rate
through the molbloc is different from the device under test range in the process gas.
3.4.2

[GAS]

PURPOSE
To specify the gas that is currently flowing through the molbloc so that molbox RFM uses the
correct gas property values in its flow calculations.
PRINCIPLE
molbox RFM calculates the flow through a molbloc from:
•
molbloc geometric characteristics
•
gas pressures
•
gas temperature
•
specific characteristics of the flowing gas
The gas characteristics include:
•
gas density under standard conditions
•
change in gas density with pressure and temperature
•
gas viscosity under standard conditions (when needed)
•
changes in gas viscosity with pressure and temperature
Proprietary algorithms are used to calculate gas density and viscosity (when needed) under
the actual flowing pressure and temperature conditions from density and viscosity under
standard conditions.
The characteristics of molbox RFM supported gases and corresponding algorithms are
stored in molbox RFM memory. To correctly calculate the flow of a gas, the correct
information for that gas must be used. The molbox RFM GAS function allows the user to
specify the flowing gas so that molbox RFM will use the correct gas information in calculating
the flow through the molbloc.
The set of available calibration gases that can be used is not the same with molbloc-L and
molbloc-S, and the operation of the GAS function is different. They are described separately below.
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3. OPERATION