Kamstrup MULTICAL 402 - Page 60

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:
AFQ ×=
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
VTL ×=
, 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








−×=∆
21
11
VV
LT
In connection with ultrasonic flow sensors the velocities
1
V
and
2
V
can be stated as:
FCV −=
1
and
FCV +=
2
respectively
where:
C
is the velocity of sound in water
Using the above formula you get:
FCFC
LT
+
−
−
×=∆
11
which can also be written as:
22
2
)()(
)()(
FC
F
LT
FCFC
FC
FC
LT
−
×=∆
⇓
+×−
−−+
×=∆
As
FC〉〉
,
2
F
can be omitted and the formula reduced as follows:
2
2
×
×∆
=
L
CT
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.