Emerson Process Management 3410 Manual Do Utilizador

3-9000-743 Rev S

June 2013

6.1.5

Chord gas and sound velocity measurements

At each batch update period, each firing path's transit time measurements are averaged. The 
average (mean) value for each path is available via data points 

MeanTmA1 ... MeanTmD2 (as 

appropriate for the meter type).   

The difference between a chord's average upstream transit time and average downstream 
transit time is the average delta time. The chord's average times and the chord “X” and “L” 
dimensions are used to calculate the gas velocity and sound velocity measured by the chord as 
shown in 

 and 

.

where the PortAngleFactor is a dimensionless factor that is dependent upon the chord port angle 
with respect to the meter body:

For 60 degree port angles,

 

for 75 degree port angles,

 

The data point names often use a “short-hand” way of identifying the receiving transducer. 
The last two characters identify the chord (A...D) and the transducer (1=upstream, 
2=downstream). For example, MeanTmA1 is the mean transit time for the chord A upstream 
transducer.

2

2X

------------------

1

2

–

1

2

--------------

=

,

2

---------------

1

2

+

1

2

--------------

=

,

×

=

1

0.5

2

,

2

-------------------------------













×

2

2

---------------













×

60

°

(

)

2

tan

×

+













=

1

0.5

2

,

2

-------------------------------













×

2

2

---------------













×

75

°

(

)

2

tan

×

+













=