LEFM 3xxCi User Manual
IB1406 Rev 12
Section 5
Page 37
August 2017
T
T
T
-
T
C o s
2
U
D
D
U
P
•
=
θ
V
Using this method, the velocity measurement V is independent of the velocity of sound. Consequently, the
velocity measurement is unaffected by variations in flow, temperature, density, chemical composition, etc.
Measuring Flow Rate
LEFM Ultrasonic Flowmeters can measure velocities along multiple acoustical paths arranged across the
flow pattern in the pipe. The accuracy and repeatability of the flow measurement increases with the number
of paths. The acoustic paths of the 380Ci are arranged into two planes. The plane is oriented at an angle
(path angle) with respect to the centerline of the pipe. Refer to Figure 5.2 for the acoustical path
configuration.
Figure 5.2 Acoustical Path Configuration
During manufacturing, precision measurements of inside diameter (ID), path lengths and path angles are
taken and inserted into the equation for volume flow rate. For maximum accuracy, the LEFM 3xxCi
automatically compensates for pipe thermal expansion and contraction.
Gross Flow Rate to Net Flow Rate Conversion (Hydrocarbon Gas)
The calculation of volumetric flow rate and total at standard (base) conditions is done externally by a flow
computer which meets the current API/AGA/ISO standards for calculation of gas volumes from linear pulse
output meters (AGA-7 & AGA-8). The LEFM 380Ci measures and outputs flow rate and volume at “as
measured” (actual) conditions. The output from the LEFM must be sent to a suitable flow computer to
calculate the volume at “base” conditions; the values upon which custody transfer or allocation transactions
are typically based. The Cameron Scanner family of EFM/RTU flow computers may be used for this
function.
