Kamstrup ULTRAFLOW 54 DN150-250, Техническое описание, Страница: 30 / 64

TECHNICAL DESCRIPTION ULTRAFLOW
®
54 DN150-250
5512-876 GB/04-2012/Rev. F1
30
2
F
In principle, the 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 by
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
〉〉
it is reasonable to omit and the formula is 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
converted in the built-in ASIC into the current velocity of sound which is used in connection with flow calculations.