MULTICAL® 62
TECHNICAL DESCRIPTION
Ka st up A/“ •
Technical
Des iptio •
5512-1036-GB_
D •
.2016
49
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 phase difference can be expressed as:
2
1
1
1
V
V
L
T
In connection with ultrasonic flow sensors the velocities up- and downstream,
1
V
and
2
V
respectively, can be stated as:
F
C
V
1
and
F
C
V
2
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
2
F
and the formula is reduced as follows:
2
2
L
C
T
F
To minimize the influence from variations of the velocity of sound in water, the latter 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.
