3. OPERATION
Page 41
© 1995 - 2010 Fluke Corporation, DH Instruments Division
3.4
Direct Function Keys
3.4.1
[K]
PURPOSE
To cause the flow value calculated by 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
). This may be
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
. The
calibration gas
that simulates the
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:
SF6 flow x 0.970 = equivalent SiH4 flow for the MFC
The K function in allows a gas conversion factor to be entered by which flow values
measured by will be multiplied. In this example,
0.970
would be entered as K so
that the values indicated by when SF6 is flowing through the molbloc simulate the
flow of SiH4 for that manufacturer's MFC.
When the K function is active, 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 which is displayed in the upper right corner of the
display should always be the gas that is actually flowing through the molbloc.
Note
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. molbox/molbloc does not use factors or
conversion coefficients between gases. Flow is calculated from molbloc
characteristics and specific gas properties for each gas supported by
. The gas selected on (see Section 3.4.2) which is
displayed in the upper right corner of the 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:
K Factor?
1on 2off
If
<2off>
is selected, no conversion factor will
be applied. If
<1on>
is selected, the next screen is:
K Factor:
1.00000
