Справочник Пользователя для Emerson Process Management - Emerson Electric Co. Ventilation Hood 7951
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:
(
)
¸
¸
¹
¹
·
¨
¨
©
©
§
+
−
=
C
G
G
G
C
K
C
C
K
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 * 10
4
for a 7812 Gas density transducer
= (1.35 * 10
4
for a 7810 Gas density transducer)
= (2.62 * 10
4
for a 7811 Gas density transducer)
And:
1
G
C
=
(
)
»
»
»
¼
º
«
«
«
¬
ª
¸¸
¸
¹
·
¨¨
¨
©
§
»
¼
º
«
¬
ª
+
−
»
¼
º
«
¬
ª
¸
¸
¹
¹
·
¨
¨
©
©
§
+
+
g
c
t
SG
SG
K
K
273
*
293
*
*
1
0
0
4
3
λ
λ
ρ
Where:
t
= Calibration temperature
SG
= Specific gravity
[ ]
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:
• K
3
and K
4
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
γ can 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
K
3
K
4
Nitrogen-Methane
10 to 60 kg/m
3
830.222
59.006
Nitrogen-Methane
60 to 200 kg/m
3
1389.4 205.455
Argon-Methane
60 to 200 kg/m
3
2186.01
310.079