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AGA #7: Turbine Meter Gas Volume Calculation for Pulse, Frequency and Analog Input (2002) standard
Function Description
This function is used to calculate Turbine Meter Gas Volumes for Pulse, Frequency and Analog types of inputs. It uses
the AGA Report #7 (2002) standard. The calculation block also requires a list of input constants and provides the
required outputs to meet the reporting standard. Some of the input constants can be created from other function blocks,
such as from AGA#8, while others can be manually entered or downloaded from a host SCADA system. See below for
examples and the list of inputs and outputs:
The additional parameters EN and ENO can be configured.
Complementary Functions
Other function blocks complement this function when used in conjunction with the AGA#7 block.:
The AGA#8 can be used to calculate the Compressibility Factor of Natural Gas and Related Hydrocarbon Gases.
The Totalizer function can be used to total the volume flow rate output from AGA#7.
Representation in FBD
Representation: This is an example of using AGA#7 Turbine Meter Gas Calculation with AGA#8 and the Totalizer
function block.
Representation in LD
Representation:
Representation in IL
Representation: CAL AGA7_Instance
(METER, TFLOW, PFLOW, TBASE, PBASE, PARA, ZFLOW, ZBASE, UNITS,
 TIMEBASE, QF, QB, PMR, TMR, ZMR)
Representation in ST
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Representation: AGA7_Instance (METER, TFLOW, PFLOW, TBASE, PBASE, PARA, ZFLOW, ZBASE, UNITS,
 TIMEBASE, QF, QB, PMR, TMR, ZMR)
Parameter Description
For a definition of each parameters units, refer to the "Unit Conversion Constants and Universal Constants" section
below.
Note: The defined (Default) value will be used, if the input constant is configured with a wrong value.
The following table describes the AGA#7 input parameters:
Parameter Type Comment
Units
USC Metric
METER REAL Meter Input (Pulse, Freq or Analog)
TFLOW REAL Flowing Temperature meter °F °C
PFLOW REAL Flowing Pressure meter psig kPag
TBASE REAL Base Temperature °F °C
PBASE REAL Base Pressure psia kPaa
PARA Para_AGA7 AGA#7 input attributes (see Para_AGA7 table below for moredetail)
ZFLOW REAL Z Flow (from AGA#8)
ZBASE REAL Z Base (from AGA#8)
UNITS INT Units (0=SI Metric, 1=US(Default))
TIMEBASE UINT Timebase for Output (0=Hourly, 1=Daily(Default))
The following table describes the AGA#7 input attributes for [Para_AGA7]:
Parameter Type Comment
Units
USC Metric
MTRTYP REAL Meter Type (1=Pulse,2=Freq,3=Analog(Default))
MCF REAL Meter Correction Factor
KFAC REAL K Factor, pulses/unit volume
PATMOS REAL Atmospheric Pressure psia kPaa
The following table describes the AGA#7 output parameters:
Parameter Type Comment
Units
USC Metric
QF REAL Flow Rate Instantaneous ft3/hr m3/hr
QB REAL Flow Rate @ base T&P conditions ft3/hr m3/hr
PMR REAL Pressure Multiplier Ratio
TMR REAL Temperature Multiplier Ratio
ZMR REAL Compressibility Multiplier Ratio
Definition of Terms
kPaa kilopascals atmospheric
kPag kilopascals gauge
psia pounds-force/sq.in atmospheric
psig pounds-force/sq.in gauge
Turbine Meter Calculation Theory for
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AGA Report #7 - 2002
PURPOSE
This document contains the proposed calculations for turbine meters or any other linear meter i.e.; (positive
displacement, ultrasonic, coriolus, vortex shedding meter) used in natural gas applications.
TERMS OF REFERENCE
All equations are based on American Gas Association Report No. 7.
This AGA 7 handles the volume and mass flow calculations for a natural gas fluid. For a gas turbine meter AGA 7
calculates the flow rate of natural gas determined at flowing and base temperature/pressure conditions.
BASE CONDITIONS (Pb, Tb)
The base conditions for the flow measurement of natural gases are defined in the United States in customary (USC)
units is a pressure of 14.73 pounds per square inch absolute (101.560 kilopascals) at a temperature 60.0°F (15.56 °C
). According to the International Standards Organization, base conditions are defined as a pressure of 14.696
(101.325 kilopascals) at a temperature of 59°F (15.0°C)
FLOW MEASUREMENT EQUATION
Flow Rate at Flowing Conditions
The volumetric flow rate at flowing conditions can be calculated using the following equation:
Case – Meter with pulse output
Case – Meter with frequency output
Case – Meter with analog output
Case – Meter with volume output
Where:
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Qf = flow rate at flowing conditions
 KF = meter K factor in pulses per unit volume
 Cuf = units conversion factor
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Flow Rate at Base Conditions
The volumetric flow rate at base (standard) conditions can be calculated using the following equation:
Where:
Qf = flow rate at flowing conditions
Pf = absolute pressure at flowing conditions
Pb = absolute pressure at base conditions
Tb = absolute temperature at base conditions
 Tf = absolute temperature at flowing conditions
 Zf = Compressibility of gas at flowing conditions.
Zb = Compressibility of gas at base conditions
Pressure Multiplier
The pressure multiplier can be calculated using the following equation:
Where:
Pf = Static gauge pressure of the fluid at flowing conditions.
Pbar = Atmospheric pressure
Pb = Base or reference pressure
Temperature Multiplier
The temperature multiplier can be calculated using the following equation:
Where:
Tf = Absolute temperature of the fluid at flowing conditions.
Tb = Absolute base temperature
Compressibility Multiplier
The compressibility multiplier can be calculated using the following equation:
Where:
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Zf = Compressibility of gas at flowing conditions.
Zb = Compressibility of gas at base conditions
 These gas compressibility values may be determined from the AGA 8 calculations.
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Mass Flow Rate
The mass flow rate at base (standard) conditions can be calculated using the following equation:
The mass flow rate at flowing conditions can be calculated using the following equation:
Where:
Qf = flow rate at flowing conditions
 Qb = flow rate at base conditions
 b = density at base conditions
t,p = density at flowing conditions
Unit Conversion Constants and Universal Constants
Variable(s) U.S.IP Metric SI
P1, P2, Pf, Pb psia psia bar Pa
t,p, b lbm/ft3 lbm/ft3 kg/m3 kg/m3
qm lbm/hr lbm/hr kg/hr kg/s
qv, Qb ft3/hr ft3/hr m3/hr m3/s
Tf, Tb, Tr °F °F °C °K
R 10.7316 10.7316 0.0831451 8314.51
psia-ft3/lbmol-°F psia-ft3/lbmol-°F bar-m3/kmol-°C J/kmol-°K
Mrair 28.9625 28.9625 28.9625 28.9625
CALCULATION BLOCK MAPPING
Meter Run Configuration Inputs
1) Selected units for the calculation
· USC Units
· Metric Units
2) Pressure Base (Pb)
3) Temperature Base (Tb)
4) Atmospheric pressure (Pbar)
5) K Factor (KF)
6) Meter Factor (MF)
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Variable Inputs
7) Flowing Temperature (Tf)
8) Flowing Static Pressure (Pf)
9) Compressibility Factor at base conditions (Zb)
10) Compressibility Factor at flowing conditions (Zf)
11) Density at base conditions ( b)
12) Density at flowing conditions ( t,p)
Calculated Outputs
1) Volume flow rate at base conditions (Qv)
2) Mass flow rate (qm)
CALCULATION APPROACH
The general outline of the solution procedure for linear meters is as follows:
A. Calculate the volume flow rate at flowing conditions - Qf
B. Calculate absolute flowing pressure - Pf
C. Calculate pressure multiplier
D. Calculate temperature multiplier
E. Calculate compressibility multiplier
F. Calculate volume flow rate at base conditions - Qb
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