Kamstrup MULTICAL 402, Техническое описание, Страница: 60 / 113

MULTICAL® 402
60
Kamstrup A/S · Technical Description · 5512-742_M1_GB_01.2016
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






− × = ∆
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
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 of sound in water
is measured by means of the built-in ASIC. For this purpose a number of absolute time measurements between
the two transducers are made. These measurements are subsequently converted into the current velocity of
sound, which is used in connection with flow calculations.