TECHNICAL DESCRIPTION MULTICAL® 21 & flowIQ® 2101 /..02 /..03
56
Kamstrup A/S •Technical Description • 5512-897_J1_GB • 06.2016
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 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
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 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
To minimize the influence from variations of the velocity of sound in water, the latter is measured via
absolute time measurements between the two transducers. These measurements are subsequently in the