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190 Average weighted gas flow velocity
Section 6: Meter operation Reference, Installation, and Operations Manual
June 2013 3-9000-743 Rev S
6.1.7 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 6-4 where the chord weights are
determined by the meter geometry.
Equation 6-4 Average weighted gas flow velocity
where
Average weighted flow velocity using chord proportions
In the event of one or more chord failure(s), the meter operation is dependent upon the number
of non-failed chords. If there is at least one operating chord, then the meter uses a velocity
estimation method described in the following paragraphs. If all chords fail, then the meter re-
enters the Acquisition mode as described in the “Re-Acquisition” section below.
The meter partitions the velocity range (for forward and reverse flow) into ten consecutive, non-
overlapping “bins” (where the velocity range is as specified via the MeterMaxVel data point).
The meter maintains a set of bins for each active chord where each bin contain three data
values: (1) the chord’s average velocity (within the bin’s velocity range), (2) the chord’s average
proportion value, and (3) a “trained” indicator. A chord proportion value is the ratio of the chord
velocity to the average weighted flow velocity as shown in Equation 6-5 below. The “trained”
indicator is used to determine if a bin’s velocity and proportion data values have been updated
from their initialized values. The bins are initialized with the average velocity over the bin’s range
and meter-geometry-dependent proportion values. All “trained” indicators are initialized to
FALSE. The bin data is stored in non-volatile memory.
=
average weighted gas flow velocity (m/s)
(AvgWtdFlowVel)
=
chord weight (dimensionless) (WtA ... WtD)
=
chord average gas velocity (m/s) (FlowVelA ... FlowVelD)
V
AvgWtd
Wt
chord
V
chord
ActiveChords
=
V
AvgWtd
Wt
chord
V
chord