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Q
O2
= Q
a
= Q
r
X K = 1000 X 0.9926 = 992.6 sccm
where K = relative K factor to reference gas (oxygen to nitrogen)
1
d X C
p
where d = gas density (gram/liter)
C
p
= coefficient of specific heat (cal/gram)
Q
a
K
a
Q
r
K
r
where Q
a
= mass flow rate of an actual gas (sccm)
Q
r
= mass flow rate of a reference gas (sccm)
K
a
= K factor of an actual gas
K
r
= K factor of a reference gas
23
=
9. CALIBRATION CONVERSIONS FROM
REFERENCE GASES
The calibration conversion incorporates the K factor. The K factor is derived from
gas density and coefficient of specific heat. For diatomic gases:
= K
=
K
gas
Note in the above relationship that d and Cp are usually chosen at the same con-
ditions (standard, normal or other).
If the flow range of a Mass Flow Meter remains unchanged, a relative K factor is
used to relate the calibration of the actual gas to the reference gas.
For example, if we want to know the flow rate of oxygen and wish to calibrate
with nitrogen at 1000 SCCM, the flow rate of oxygen is: