Emerson Daniel 3415

Average weighted gas flow velocity Equation 4-6:


= 
ℎ

ℎ

ℎ
where
Equation 4-6
V
AvgWtd
=
average weighted gas flow velocity (m/s) (AvgWtdFlowVel)
Wtd
chord
=
chord weight (dimensionless) (WtA ... WtD)
V
chord
=
chord average gas velocity (m/s) (FlowVelA ... FlowVelD)
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 .
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 4-7 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.
Chord proportion calculation Equation 4-7:
Pr
ℎ


ℎ


where
Equation 4-7
Prop
chord
=
chord proportion (dimensionless)
V
chord
=
chord velocity (m/s) (FlowVelA ... FlowVelD)
V
AvgWtd
=
average weighted gas flow velocity (m/s) (AvgWtdFlowVel)
Measurement
24 3410 Series Gas Ultrasonic Flow meters