4.4 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).
NOTICE
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 4-1 and Equation 4-2.
Chord Gas Velocity Equation 4-1:
ℎ
=
ℎ
2
2
ℎ
1
2
1
2
and
Chord Sound Velocity Equation 4-2:
ℎ,
=
ℎ
2
1
+
2
1
2
ℎ
=
ℎ,
×
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,
Equation 4-3
= 1 + 0.5 •
ℎ
2
ℎ,
2
•
ℎ
2
ℎ
2
• tan
2
60°
For 75 degree port angles,
Measurement
Operations manual 21
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