Calibration Conversions From Reference Gases - Omega FMA1700A User Manual

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:
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.
where Q
Q
r
K
a
K
r
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:
Q
O2
where K = relative K factor to reference gas (oxygen to nitrogen)
K
gas
where d = gas density (gram/liter)
C = coefficient of specific heat (cal/gram)
p
K =
= mass flow rate of an actual gas (sccm)
a
= mass flow rate of a reference gas (sccm)
= K factor of an actual gas
= K factor of a reference gas
= Q = Q X K = 1000 X 0.9926 = 992.6 sccm
a r
1
=
d X C
p
Q K
a a
=
Q K
r r
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