User Manual Reference -
This technical bulletin
complements the
information contained in
Volume 3, applicable to
Revision 23.74/27.74. and
replaces original document
TB-970804
.

Natural Gas Net Volume
and Energy Calculation -
Natural gas net volume and
energy calculations apply to
all gas flow computers,
These calculations are
considered using a gas
chromatograph, product
overrides, or live 4-20 mA
analyzer inputs of specific
gravity (SG) and heating
value (HV).
Scope ................................................................................................................... 1
Abstract ............................................................................................................... 2
Basic Calculations.............................................................................................. 2
Critical Configuration Entries Which Affect the Calculation of Net Volume
and Energy .......................................................................................................... 2
Density of Air at Base Conditions .................................................................................. 2
Gas Relative Density (SG) ............................................................................................ 3
Gas Heating Value (HV)................................................................................................ 3
Key Analyzer Setup Menu Entries Needed ................................................................... 4
No Gas Chromatograph Used - Manual Overrides Required ..................................................... 4
Component Analysis Data Obtained From a Gas Chromatograph............................................. 5
Using Manual Overrides for Component Analysis Data.............................................................. 5
Component Analysis Data via a Serial Data Link ....................................................................... 5
Using Live Inputs for Heating Value, Specific Gravity, Nitrogen or Carbon Dioxide ................... 5

Scope
Firmware Revisions 23.74 and 27.74 of Omni 6000/3000 Flow Computers have
the feature of Natural Gas Net Volume and Energy Calculation. This feature
applies to Orifice/Turbine Gas Flow Metering Systems. This bulletin covers
natural gas net volume and energy calculations using a gas chromatograph,
product overrides, or live 4-20 mA analyzer inputs of specific gravity (SG) and
heating value (HV).
TB-970804 23/27.71+


1 Omni 6000 / Omni 3000 Flow Computers
Technical Bulletin
Abstract
Getting Tech Support -
Technical support is
available at:
(281) 240-6161
Email should be sent via
the WEB Page at:
www.omniflow.com

or email to:
techsupport@omniflow.com

Gas compositional data needed by the flow computer to calculate flowing
density, mass flow and energy flow of natural gas can be obtained from various
sources. The following describes how the flow computer should be configured
for each possible scenario.
Basic Calculations
The basic calculations are:

Net Volume = Mass Flow / Density @ Base Conditions
(1)

Energy = Net Volume x Heating Value
(2)
Density at Base Conditions can be obtained by one of the following methods:

(GC Relative Density) x (Density of Air @ Base Conditions)
(3)

(Override Relative Density) x (Density of Air @ Base Conditions)
(4)

(Live 4-20mA Relative Density) x (Density of Air @ Base Conditions) (5)

Calculated using Detailed Method of AGA 8
(6)
Heating Value is obtained using one of the following methods:

GC Analysis Heating Value
(7)

Manual Override Heating Value
(8)

Live 4-20mA Heating Value
(9)

Calculated using AGA 5, GPA 2172 or ISO 6976
(component analysis required)
(10)
Component Analysis Data is obtained from one of the following sources:

Online Danalyzer or Applied Automation Gas Chromatograph
(11)

Manual Overrides in the Fluid Data Analysis menu
(12)

Serial Communication Link
(13)

Live 4-20mA SG, HV, N2 and CO2
(AGA 8 gross calculation methods only)
(14)
Critical Configuration Entries Which Affect the
Calculation of Net Volume and Energy
Density of Air at Base Conditions
This entry is in the Factor Setup menu. Setting this entry to 0 ensures that gas
density at base conditions is calculated using AGA 8. (method (6) previous
page). Entering the density of air at base conditions assuming a valid gas
relative density (SG) is available (see next paragraph) will override the AGA 8
calculation of gas density at base conditions. In this case gas density at base
conditions is calculated using either method (3), (4) or (5) (previous page).
2

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TB-970804
Calculation of Natural Gas Net Volume and Energy
Gas Relative Density (SG)
This entry is located in the Fluid Analysis Data menu. One entry per active
product is required. It is mandatory that this field contain a valid value of SG for
all AGA 8 gross calculation methods except for 1985 method #4. The data in
this field can be manually entered or, automatically overwritten by a live 4-20mA
input of SG if it exists. This entry also serves as the GC SG override if a GC is
providing gas relative density (SG) and a GC failure occurs.
Entering a minus value in this field will force the flow computer to calculate gas
density at base conditions using AGA 8. (method (6) previous page). Entering
the gas relative density (SG) assuming a non zero Density of Air @ Base
Conditions is entered (see above) will override the AGA 8 calculation of gas
density at base conditions. In this case gas density at base conditions is
calculated using either method (3), (4) or (5) (previous page).
When an AGA 8 detailed method is selected and a GC is used to provide gas
relative density (SG), this entry field is ignored unless a GC failure occurs and
the GC Fail Code entry is set to Use Override on GC Failure.
Gas Heating Value (HV)
Heating Value Calculation
- The flow computer always
calculates Heating Value
using one of the mentioned
standards, even if it is
instructed not to use it.
These calculated values are
stored in the data base and
can be used to compare
against the values obtained
from the GC or calorimeter.
7629=Mtr #1 calculated HV
7630=Mtr #2 calculated HV
7631=Mtr #3 calculated HV
7632=Mtr #4 calculated HV


Additional Modbus address:
7142=Mtr #1 AGA8 HV
7242=Mtr #2 AGA8 HV
7342=Mtr #3 AGA8 HV
7442=Mtr #4 AGA8 HV


Heating Value in Use:

8568=Mtr #1 HV in use
8668=Mtr #2 HV in use
8768=Mtr #3 HV in use
8868=Mtr #4 HV in use


Product Data Heating
Value in Btu/Ft3 or MJ/m3
17253=Prd #1 Heating Vaue
17283=Prd #2 Heating Vaue
17313=Prd #3 Heating Vaue
17343=Prd #4 Heating Vaue


This entry is located in the Fluid Analysis Data menu. One entry per active
product is required. It is mandatory that this field contain a valid value of HV for
AGA 8 gross calculation method #1 and also AGA 8 1985 methods #2 and #4.
The data in this field can be manually entered or, automatically overwritten by a
live 4-20mA input of HV if it exists. This entry also serves as the GC HV
override if a GC is providing gas heating value (HV) and a GC failure occurs.
Entering a minus value in this field will force the flow computer to use a
calculated gas heating value (HV) calculated using either AGA 5, GPA 2172 or
ISO 6976 ( method (10) previous page).
Entering a positive value into the gas heating value (HV) entry will override the
AGA 5, GPA 2172 or ISO 6976 calculation of gas heating value (HV). When an
AGA 8 detailed method is selected and a GC is used to provide gas heating
value (HV), this entry field is ignored unless a GC failure occurs and the GC
Fail Code entry is set to Use Override on GC Failure.

Heating Value calculations for AGA5:
Calculate the gas energy Btu per cubic gfoot, 14.73 psi, 60 deg f. using the
following equation: (wet or dry depending on the contents of water of the gas
analysis)
Ev = Vg (Vcd + Vn + Vo + Vhe + Vcm + Vhs + Vw-Vhy)
Vg = (1571.5 x specific Gravity) +144
The result will be converted to Metric units for Revision 27.






TB-970804 23/27.74


3 Omni 6000 / Omni 3000 Flow Computers
Technical Bulletin
Heating Value calculation for GPA2172
Calculates the gross heating value at base temperature and pressure. (wet or
dry depending on the contents of water of the gas analysis)
To match the examples on GPA2172-96 @ 60Deg F and 14.696 psia, the
precalculated tables of constants will be used as shown in the examples with
rounding and resolution effects when base temperature 60F and pressure
14.696 psia are entered into an Omni. The precalculated tables are on dry
basis.

Heating value calculation for ISO6976:
Calculates the real superior calorific value at 15 Deg C and 1.01325 bar (wet or
dry depending on the contents of water of the gas analysis)
Key Analyzer Setup Menu Entries Needed
The following text discusses only those key entries that must be made to ensure
that the right values for component analysis are used in the calculation of Net
Volume and Energy Flow.
No Gas Chromatograph Used - Manual Overrides Required
Select Always Use Fluid Data Overrides for GC Fail Code in the Analyzer
Setup menu. No other entries are needed.
4

TB-970804 23/27.74
TB-970804
Calculation of Natural Gas Net Volume and Energy
Component Analysis Dat