3410 Series Gas Ultrasonic Meters Operations Manual
Section 4: Flow measurement
3-9000-777 Rev E
January 2018
Average weighted gas flow velocity
25
Every five seconds the meter updates the AGA10-calculated sound velocity. This value is
readable via the
AGA10SndVel
data point and the calculation status value is readable via the
AGA10SndVelStatus
data point. The status values are as listed in the table below:
Over the course of an hour (starting from the top of the hour), the meter calculates the average
measured sound velocity (the average of the average weighted sound velocity) and the average
AGA10-calculated sound velocity. At the end of the hour, the two averages are compared; the
comparison error (%) is readable via the
SndVelCompErr
data point.
Note that the comparison error is only calculated at the end of the hour if during the hour all of
the following are true:
•
no AGA10 sound velocity calculation errors occurred (i.e.,
AGA10SndVelStatus
always
equal to 0),
•
the measured flow velocity was always above the minimum sound-speed-check flow
velocity (specified via the
SndSpdChkMinVel
data point which has a default value of 1 m/
s), and
•
the measured sound velocity was always valid (as indicated by the
QMeterValidity
data
point).
4.4.3
Average weighted gas flow velocity
When all active chords are non-failed, the average weighted gas flow velocity is a weighted sum
of the chord velocity measurements as shown in
Equation 4-4
where the chord weights are
determined by the meter geometry.
Equation 4-4 Average weighted gas flow velocity
where
Table 4-2 AGA10 calculation status
AGA10SndVelStatus
value
Description
0
Calculation OK (no errors).
1
Calculation not performed as the feature is not enabled
(
see Section 3.2
).
AGA10SndVel
is set to zero.
2
Calculation not performed as the selected AGA8 method is not the Detailed
method (
HCH_Method
not set to Detailed Method(3)).
AGA10SndVel
is set to
zero.
3
Calculation not performed due to invalid AGA8 calculation results.
AGA10SndVel
is set to zero.
4
Calculation error due to division by zero.
AGA10SndVel
is set to zero.
=
average weighted gas flow velocity (m/s) (AvgWtdFlowVel)
=
chord weight (dimensionless) (WtA ... WtD)
=
chord average gas velocity (m/s) (FlowVelA ... FlowVelD)
VAvgWtd
WtchordVchord
ActiveChords
=
VAvgWtd
Wtchord
Vchord
