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3098 Technical Manual Performance Optimisation
A-5
TOTAL FACTOR CALCULATIONS
Total factors when using calibration gases as reference:
[]
E
Xx
A
AXY y X x
AY X
a1
1
1
11
= −
−
−
−−−−
−
()
()()()
()
A10
E
b1
= As in equation A10 but substituting B for A
E
c1
= As in equation A10 but substituting C for A
Total factors when using methane and sample gas C as reference:
[]
E
Xx
Y
YXC c X x
YC X
y2
1
1
11
= −
−
−
−−−−
−
()
()()()
()
A11
E
a2
= As in equation A11 but substituting A for Y.
E
b2
=
As in equation A11 but substituting B for Y.
Note: If sample B was used as the calibration gas the equation as in A11 would be used with B substituted for C and b
substituted for c.
Legend for Table A1
Column Description of Column Contents
1
Gas type and use i.e. function - calibration or sample.
2
M
Molecular weight of gas.
3
γ
Ratio of specific heats.
4
Z
s
Compressibility factor at base conditions.
5
ρ
s
true
Base density of gas.
6
V
F
Velocity of sound factor.
7
Z
Compressibility factor at reference chamber pressure.
8
Z
F
Compressibility correction factor.
9
E
F
Total factor
()
VxZ
FF
.
10
Δ
F
%
The value
()
1 100%− Ex
F
.
11
E
1
Calculated total factor using calibration gases as reference.
12
Δ
1
%
The value
()
EEx
F1
100%− which is the anticipated error which results from a
simple methane/nitrogen calibration. In general these errors are mainly defined by the
compressibility factors and in consequence will be reduced in relation to the reference
chamber pressure.
13
E
2
Calculated total factor using methane and sample gas as reference.
14
Δ
2
%
The value
()
EEx
F2
100%− which is the anticipated error which results from a
methane/sample gas C calibration. This is directly equivalent to a methane/nitrogen
calibration in which the nitrogen base density Y’ is used in place of the true base density,
i.e. an offset has been added. Once again the errors can normally be reduced by
reducing the reference chamber pressure.
15
ρ
s
ind .
Values of
ρ
s
which are anticipated in order to obtain zero error for methane and sample
gas C.