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Appendix A Series 820 Instruction Manual
A-2 IM-82-C
Calculating For a Single Gas
The following tables provide K-factors and thermodynamic proper-
ties of gases commonly used with mass flow meters and controllers.
The purpose of these tables is two-fold:
1. Calibrating an ÒactualÓ gas with a reference gas. This is particu-
larly useful if the actual gas is not a common gas or if it is toxic,
flammable, corrosive, etc.
2. Interpreting the reading of a flow meter or flow controller which
has been calibrated with a gas other than the actual gas.
In applying the tables, the following fundamental relationship is used:
Q
1
/Q
2
= K
1
/K
2
(1)
Where:
Q = The volumetric flow rate of the gas referenced to standard
conditions of 0°C and 760 mm Hg (sccm or slm),
K = The K-factor defined in equation (6),
( )
1
= Refers to the ÒactualÓ gas, and
( )
2
= Refers to the ÒreferenceÓ gas.
The K-factor is derived from the first law of thermodynamics ap-
plied to the sensor tube, as described in Chapter 1:
H =
mC DT
¥
N
p
(2)