Operation & Installation Manual V12-V6 2010-05-31.doc
31/05/2010
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This component increases or decreases the speed of the sound wave as it moves from one
transducer to the other transducer.
The transit time from Trd A to Trd B (t
AB
) is:
(1)
In opposite direction (from Trd B to Trd A) the transit time (t
BA
) becomes:
(2)
The velocity of gas is derived from formula (1) and (2) as :
(3)
An important feature of this method is that the calculated gas velocity does not depend on
the speed of sound in the gas or gas properties in general. The gas velocity as calculated is
only a function of the measured transit times t
AB
and t
BA
; the length of the chord and the
angle of intersection of the measuring chord are supposed to be known from the design of
the flow meter.
As a “bonus” the speed of sound in the gas can also be derived from formula (1) and (2) as :
(4)
This gives a measured speed of sound value, a valuable tool for diagnostic purposes, as it
can be compared with data from other sources.
2.1.2. Swirl compensation.
Symmetrical swirl.
Figure 2-2: Symmetrical swirl
ϕ
cos
⋅
+
=
v
c
L
t
AB
ϕ
cos
⋅
−
=
v
c
L
t
BA
−
⋅
⋅
=
BA
AB
t
t
L
v
1
1
cos
2
ϕ
+
⋅
=
BA
AB
t
t
L
c
1
1
2
