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Installation and Configuration Manual 51
Performance Optimization
Principles of Operation Certified System DrawingsReturn PolicyPerformance Optimization
Compressibility factor
The normal or base density (
ρ
s
) is given by the equation:
The basic operation of the instrument allows the pressure/temperature ratio to be considered constant,
hence equation A5 reduces to:
The Z factor for gases or gas mixtures may be obtained from reference sources or may be derived
from:
For Nitrogen at 20°C:
For a methane-based gas mixture at 20°C:
A5
where P
s
, t
s
, Z
s
= Values of pressure, temperature, and compressibility at
standard conditions
ρ, P, t, Z = Values of density, pressure, temperature, and
compressibility at measurement conditions
ρ
s
ρ
P
s
P
------
×
t
t
s
----
×
Z
Z
s
------
×=
A6
where K = Calibration constant
Z
F
= Compressibility factor
ρ
s
ρK
Z
Z
s
------
=
ρ
s
ρKZ
F
=
A7
where P = The gas pressure in bar absolute
Z1.0P2.38
4–
×10()–=
A8
where P = The gas pressure in bar absolute
M = The mean molecular weight of gas
I = Volume/mole fraction of inerts (for example, N
2
and CO
2
Z 1.0 P 1.7
4–
×10 6
5–
×10 M()1.13
5–
×10 M
2
()– 7.2
3–
×10 I()++[]+=