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2910 Essen,
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DOCUMENT TITLE
ULTRASONIC FLOWMETER SERIES 6, MODELS Q.SONIC
PLUS
SUBTITLE
QUICK START MANUAL
DOCUMENT NUMBER
22.100.200.000.02/2
REVISION
B
REVISION DATE
2013-02-22
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detrimental to our interests and that all copies will be returned immediately on demand
PAGE
8 OF 29
22.100.200.000.02_2_B ULTRASONIC FLOWMETER SERIES 6.DOC
3 Theory of operation
An ultrasonic flow meter is an inferential measurement device that consists of ultrasonic
transducers that are typically located along a pipe's wall. The transducers are inserted into the
piping using a gas tight mechanism. Ultrasonic pulses are alternately transmitted by one
transducer and received by the other one. Figure 3 shows a simple geometry of two transducers,
‘A’ and ‘B’, at a sharp angle “
ϕ
” with respect to the axis of a straight cylindrical pipe with diameter
“D”. The Q.Sonic Series 6 employs reflection paths, where the acoustic pulses reflect one or more
times off the pipe wall.
v
B
A
L
D
ϕ
Figure 3: Ultrasonic measuring line
3.1
Flow velocity measurement
The acoustic pulses are crossing the pipe like a ferryman crossing a river. Without flow,
they propagate with the same speed in both directions. If the gas in the pipe has a flow
velocity different from zero, pulses travelling downstream with the flow will move faster,
while those travelling upstream against the flow will move slower. Thus, the downstream
travel times “
t
ab
“ will be shorter, while the upstream ones “
t
ba
“ will be longer as compared
when the gas is not moving. Equation 1 illustrates the computation of these times:
( )
−
⋅
⋅
=
n
n
n
n
raw
tba
tab
L
VoG
n
1
1
cos
2
ϕ
Equation 1: raw gas velocity
where:
t
abn
the downstream travel time of path n.
t
ban
the upstream travel time of path n.
L
n
the straight line length of the acoustic path between the two transducers.
VoGraw
is the average uncorrected (raw) gas velocity.
ϕ
n
the angle between the gas flow and ultrasonic signal.
The raw gas velocity is corrected by a Reynolds flow profile correction. This correction is
depending on the path type. Also the contribution of the gas velocity of each path to the
combined gas velocity is depending on the path type.