Appendix F Calculations and theory
Page F.4
Equation F.1#3b:V.O.S. of the measured gas (pure of composition) for S.G. method
Using:

()

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=
C
G
G
G
C
K
C
CK
C
*
1
*
1
1
τ
τ
Where:
G
C = V.O.S. of the measured gas (in m/s)
C
C = V.O.S. of the calibration gas (in m/s)……………………..……..{See Equation F.1#2}

τ

= Periodic time of density transducer output signal (in μs)
K = Density transducer VOS constant
= 2.10 * 104for a 7812 Gas density transducer
= (1.35 * 104 for a 7810 Gas density transducer)
= (2.62 * 104 for a 7811 Gas density transducer)
And:
1G
C =
()
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gc t
SGSG
K
K
273*293*
*1
004
3
λλρ
Where: t = Calibration temperature
SG = Specific gravi ty
[ ] c = For calibration gas
[ ] g = For measured gas
0
γ
= Low pressure ratio of specific heats (or ‘Gamma’)……………… (See notes below)
And:
3
K and 4
K are constants that must be SET into the 795x……….………(See notes below)
Notes:
•K3 and K4 are normally taken from the calibration certificate that was issued with the gas density transducer.
Alternatively, the following table has typical values that can be used.
• ‘Ideal’ values for Specific Gravity can be taken from Table F.2. In practice, the live Specific Gravity
measurements may be more appropriate.
• For a measured pure gas, a value for 0
γ can be taken from Table F.2.
• For a measured composition of gas, a value for 0
γcan be taken from Table F.2 but needs to modified in
proportion to the volumetric fraction (percentage) of each gas component.
Table F.3: K3 and K4 Values
Gas Composition Density K3K4
Nitrogen-Methane 10 to 60 kg/m3 830.222 59.006
Nitrogen-Methane 60 to 200 kg/m3 1389.4 205.455
Argon-Methane 60 to 200 kg/m3 2186.01 310.079