KROHNE ALTOSONIC V12 EN - Manual (Page 100)

9
TECHNICAL DATA
100
ALTOSONIC V12
www.krohne.com 04/2013 - 4002643502 - MA ALTOSONIC V12 R02 en
Swirl can disturb the gas velocity measurement as the tangential velocity component adds up
with the gas velocity measured along one chord. However chords can be arranged in a way to
compensate for swirl effects. Two chords arranged in the same plane intersect the flow at
opposite angles (cross configuration). These chords respond to the tangential velocity
component with the same magnitude but with the opposite sign.
This allows cancellation of the swirl effect by adding or averaging the measured velocity value of
both chords. An acoustic path with two chords in a V-shape, with a reflecting signal, has the
same effect. The measured flow velocity is increased by the tangential component on one chord
and decreased by the same value on the other chord.
9.4 Multipath ultrasonic flowmeters
With an ultrasonic measuring system the measured gas velocity value is the average velocity
sampled across the length of the acoustic path. Due to distortion of the gas velocity profile in the
pipe this value may not be representative for the average gas velocity across the whole of the
pipe cross section. In order to obtain a high accuracy the flow is sampled using a number of
measuring chords intersecting the flow in different planes, as shown in the figure below.
The total volume flow is calculated by means of an integration algorithm using the results from
the individual paths.
As swirl components are already compensated for in each individual measuring plane, the
integration method using data from multiple paths makes the flowmeter highly insensitive for
any kind of distortion of the flow profile.
The average speed of sound is the average of the speed of sound values measured on each of
the chords. Normally these values are very close to each other.
Figure 9-3: Swirl pattern after a single bend
Figure 9-4: Path configuration with multiple acoustic paths