Reference, Installation, and Operations Manual

Section 6: Meter operation

3-9000-743 Rev S

June 2013

 

 

 

6.1.5Chord 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 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.

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 Equation 6-1and Equation 6-2.

Equation 6-1 Chord Gas Velocity

Vchord =

Lchord2

 

t1 t2

 

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

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

 

2Xchord

 

t1 t2

 

 

Equation 6-2 Chord Sound Velocity

Cchord,classic =

Lchord

 

t1 + t2

 

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

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

 

2

 

t1 t2

 

 

Cchord = Cchord,classic PortAngleFactor

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,

 

V2

 

X2

 

2

 

 

 

 

 

 

 

 

PortAngleFactor = ⎜1 +

 

0.5 ⋅ ⎜

------------------------------chord

⋅ ⎜

chord

⋅ tan

(60

°)

 

 

 

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

 

 

Cchord2

,classic

Lchord2

 

 

 

 

 

for 75 degree port angles,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

V2

 

X2

 

2

 

 

 

 

 

 

 

 

 

PortAngleFactor = ⎜1 +

 

0.5 ⋅ ⎜

------------------------------chord

⋅ ⎜

chord

⋅ tan

(75

°)

 

 

 

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

 

 

Cchord2

,classic

Lchord2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chord gas and sound velocity measurements

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