26 Average weighted flow velocity using chord proportions
Section 4: Flow measurement 3410 Series Gas Ultrasonic Meters Operations Manual
January 2018 3-9000-777 Rev E
4.4.4 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) an indicator that the value is still the default
(
Is[Fwd/Rev]Prop[A..D]DfltBin[1..10]). A chord proportion value is the ratio of the chord velocity
to the average weighted flow velocity as shown in Equation 4-5 below. The default 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 default indicators are initialized to
TRUE. The
bin data is stored in non-volatile memory.
Equation 4-5 Chord proportion calculation
where
= chord proportion (dimensionless)
= chord velocity (m/s) (FlowVelA ... FlowVelD)
= average weighted gas flow velocity (m/s) (AvgWtdFlowVel)
Prop
chord
V
chord
V
AvgWtd
---------------------------=
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