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3.4
Direct Function Keys
3.4.1
[K]
PURPOSE
To cause the flow value calculated by molbox1+ to be multiplied by a factor, K. Generally used
to apply a test device's gas correction factor used when a test device is calibrated with a gas
other than its normal gas.
PRINCIPLE
Frequently, when testing or calibrating a flow measuring device, it is not possible to flow the
gas with which that device will normally be operated (the process gas).
because the process gas is toxic or corrosive or simply because it is not available. When the
process gas cannot be used for calibration, it is common to use a different gas for testing or
calibrating (the calibration gas). In this case, a factor representing the relationship between
the calibration gas and the process gas for the test device may be applied so that the
calibration gas simulates the process gas.
process gas is often called a surrogate gas for the process gas.
The relationship between a test device's process gas and calibration gas is frequently
called a K factor or gas conversion factor. The factor's value depends on specific properties
of the test device and determining the value is the responsibility of the device manufacturer.
For example, Silane (SiH4) is a frequently used gas in semiconductor processing. SiH4 is
highly toxic and requires extensive handling precautions so it is not practical for use in
calibration and testing. A major manufacturer of Mass Flow Controllers (MFCs) recommends
that MFCs that are to be used with Silane be tested with Sulfur Hexafluoride (SF6), a non-
toxic, non-flammable gas, using a conversion factor of 0.970. In other words:
The K function in molbox1+ allows a gas conversion factor to be entered by which flow values
measured by molbox1+ will be multiplied. In this example, 0.970 would be entered as K so
that the values indicated by molbox1+ when SF6 is flowing through the molbloc simulate the
flow of SiH4 for that manufacturer's MFC.
When the K function is active, molbox1+ performs all of its flow calculations normally but
multiplies the current flow value by the value of the K factor prior to displaying it.
The gas selected on molbox1+ which is displayed in the upper right corner of the molbox1+
display should always be the gas that is actually flowing through the molbloc.
K factors or gas conversion factors are based on the properties of the
device being tested. Their availability and validity are the responsibility of
that device's manufacturer.
conversion coefficients between gases. Flow is calculated from molbloc
characteristics and specific gas properties for each gas supported by
molbox1+. The gas selected on molbox1+ (see Section 3.4.2) which is
displayed in the upper right corner of the molbox1+ display should always
be the gas that is actually flowing through the molbloc.
OPERATION
To enable a gas conversion factor press [K] from any
run screen. The display is:
If <2off> is selected, no conversion factor will
be applied. If <1on> is selected, the next screen is:
SF6 flow x 0.970 = equivalent SiH4 flow for the MFC
Note
molbox/molbloc does not use factors or
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The calibration gas that simulates the
K Factor?
1on 2off
K Factor:
1.00000
© 1995 - 2010 Fluke Corporation, DH Instruments Division
3. OPERATION
This may be
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