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52 Micro Motion 3098 Gas Specific Gravity Meter
Performance Optimization
The Z factors of the calibration gases and the sample gases should be calculated at both base and
operating conditions in order to establish the compressibility factor V
F
and then tabulated as shown
by
the example in
Table A-2
.
Combination of
V
F
and
Z
F
By combining equations A4 and A6, gives:
The combination of V
F
and
Z
F
should also be tabulated as shown in Table A-2. The combined factor
E
F
can then be used to determine the anticipated measurement errors on sample gases when using the
two selected calibration gases. Furthermore, the tabulated results can be plotted to show the error
trends and uncover the most suitable calibration gas selection and/or calibration offset to give
minimum measurement error on the sample gases (see Figure A-1).
Table A-1 is provided to identify the variables used in equations A10 and A11.
Total factor calculations
Total factors when using calibration gases as reference:
Total factors when using methane and sample gas C as reference:
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.
A9
ρ
s
Kρ
i
V
F
Z
F
=
A10
E
1B
= As in equation A10 but substituting B for A
E
1C
= As in equation A10 but substituting C for A
E
1a
1
X1 x–()
A
---------------------–
AX–()Y1 y–()X1 x–()–[]
AY X–()
-------------------------------------------------------------------------–=
A11
E
2a
= As in equation A11 but substituting A for Y
E
2b
= As in equation A11 but substituting B for Y
E
2y
1
X1 x–()
Y
---------------------–
YX–()C1 c–()X1 x–()–[]
YC X–()
-------------------------------------------------------------------------–=