Kamstrup MULTICAL 21 - Page 56

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:
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 by
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 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
FCFC
LT






As
FC
,
2
F
can be omitted and the formula reduced as follows:
2
2



L
CT
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