Справочник Пользователя для Emerson Process Management 3420

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 

 where the chord weights are 

determined by the meter geometry.

where

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 

 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)



=