UM353-1 Function Blocks
March 2003
3-13
3.2.5 AG7 - AGA 7 Measurement of Gas by Turbine Meters
AG7 function blocks, which can be used on a one per loop
basis, are available in firmware 1.30 and higher, This block
uses the AGA 7 (American Gas Association Report #7)
calculation to accurately measure the volume flow of gas at
base conditions using a turbine meter. The basic equations
calculated by this block in accordance with AGA Turbine
Meter Report No. 7, 1985 (AGA Catalog No. XQ0585) are:
Q
b
= Q
f
(T
b
/T
f
)(P
f
/P
b
)(Z
b
/Z
f
)
where:
Q
f
= volume flow at standard conditions
Q
b
= volume flow rate at base conditions
P
f
= flowing pressure (psia)
T
f
= flowing temperature)
Z
f
= compressibility at flowing conditions
P
b
= base pressure (psia)
T
b
= base temperature (°F)
Z
b
= compressibility at base conditions
Block output Q
b
is updated continuously and is the volume flow rate at base conditions in the same units as input
Q
f
. T
b
and T
f
are converted within the block from °F to °R (adds 459.67 to the °F input value) for the actual
calculation. Compressibility factors (
Z
f
, Z
b
) can be entered manually using HLD (Hold) function blocks, computed
and downloaded from a host device, or calculated in the controller using the AG8 (AGA 8 Compressibility Factors
of Natural Gas) function block.
Input
Qf
AGA 7
Qb
Output
Qb
AGA 7
AG7 ESN =
000
Qf
E
xec.
S
eq.
N
o. ..................... 000 to 250 (000)
Input
Pf
Pf
INPUT Zb
.............
loop tag.block tag.output (null)
Input
Tf
Tf
Input
Zf
Zf
Input
Zb
Zb
TU
P
N
I
P
f
TUP
N
I
TUP
N
I
T
U
P
N
I
P
b
f
T
Tb
fZ
Z
b
S
E
N
INPUT Zf
..............
loop tag.block tag.output (null)
INPUT Tf
..............
loop tag.block tag.output (null)
INPUT Pf
..............
loop tag.block tag.output (null)
b
ase
P
ressure (psia)
.............................. Real
(14.73)
b
ase
T
emperature (deg F)
................... Real
(60.0)
T
U
P
N
I
Q
f
INPUT Qf
..............
loop tag.block tag.output (null)
Q
f
P
f
T
f
Z
f,b
Q
b
AGA 7
Application Diagram
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