Instruction manual

ControlWave Gas Flow Computer (GFC Plus) Instruction Manual (CI-ControlWave GFC Plus)
1-10 Introduction Revised Feb-2013
 AGA7/NX-19
 AGA7 with selectable AGA8 Gross or AGA8 Detail
 Auto-adjust AGA7/NX-19
 Auto-adjust AGA7 with selectable AGA8 Gross or AGA8 Detail
The application performs a complete flow calculation using the process
variables every second. Each calculation includes instantaneous rate
according to API 14.3, compressibility according to AGA 8 Detail or
Gross method, and updates of all volumes, totals, and archive averages.
1.7.3 Flow Rate and Flow Time Calculations (AGA3)
For orifice flow measurement, the application compares the differential
pressure value to a low flow cutoff value every second. If the
differential pressure falls below the low flow cutoff value, flow is
considered to be zero for that second. Hourly and daily flow time is
defined to be the number of seconds for which the differential pressure
exceeded the cutoff value for the period.
The values for static and differential pressure and temperature are used
as inputs to the flow equations. You can select API 14.3 (AGA3, 1992)
and AGA8 calculations, with compressibility calculations according to
AGA Report No. 8, 1992 (with 1993 errata). The application supports
both the detail method and the two gross methods of characterization
described in AGA 8. Users may also select the AGA3, 1995 and NX-19
flow equations to calculate the rate of flow.
1.7.4 Flow Rate and Flow Time Calculations (AGA7)
When using PD meters, turbine meters or ultrasonic meters, the
application calculates flow rate by applying the correction factor
computed by the AGA7 calculations to the frequency of the input
pulses. When the frequency drops below 1 Hz, the application sets the
flow rate estimate to zero; however, volume calculations still
accumulate. The flow time recorded is the time for which the flow rate
is non-zero.
1.7.5 Extension Calculation and Analog Averaging
For orifice meters, the application calculates the flow extension every
second. The extension is the square root of the product of the absolute
upstream static pressure times the differential pressure. This extension is
used in the flow rate calculation. When there is no flow, the application
reports the arithmetic averages of static pressure and temperature. This
allows you to monitor static pressure and temperature during shut-in
periods.