TECHNICAL DESCRIPTION
ULTRAFLOW
®
54 and 34
5512-385 GB/02.2014/Rev. H1
36
In principle, flow is determined by measuring the flow velocity and multiplying it by the area of the measuring
pipe:
A
F
Q
×
=
where:
Q
is the flow
F
is the flow velocity
A
Is the area of the measuring pipe
The area and the length, which the signal travels in the sensor, are well-known factors. The length which the signal
travels can be expressed as
V
T
L
×
=
, which can also be written as:
V
L
T
=
where:
L
is the measuring distance
V
is the sound propagation velocity
T
is the time
The time can be expressed as the difference between the signal sent with the flow and the signal sent against the
flow.
−
×
=
∆
2
1
1
1
V
V
L
T
In connection with ultrasonic flow sensors the velocities
1
V
and
2
V
can be stated as:
F
C
V
−
=
1
And
F
C
V
+
=
2
respectively
where:
C
is the velocity of sound in water
Using the above formula you get:
F
C
F
C
L
T
+
−
−
×
=
∆
1
1
which can also be written as:
2
2
2
)
(
)
(
)
(
)
(
F
C
F
L
T
F
C
F
C
F
C
F
C
L
T
−
×
=
∆
⇒
+
×
−
−
−
+
×
=
∆
As
2
2
F
C
〉〉
,
2
F
can be omitted and the formula reduced as follows:
2
2
×
×
∆
=
L
C
T
F
In order to minimize the influence from variations of the velocity of sound in water, the velocity is measured via a
number of absolute time measurements between the two transducers. These measurements are subsequently, in
the built-in ASIC, converted into the current velocity of sound which is used in connection with flow calculations.
