TECHNICAL DESCRIPTION flowIQ® 3100
26
Kamstrup
A/S • Technical Description •
5512-1242_N
1_GB •
10.2019
12.3
Transit time method
The transit time method used in flowIQ® 3100 utilizes the fact that it takes an ultrasonic signal sent in the opposite
direction of the flow longer to travel from sender to receiver than a signal sent in the same direction as the flow.
The transit time difference in a flow sensor is very small (nanoseconds). Therefore, the time difference is measured
as a phase difference between the two 1 MHz sound signals in order to obtain the necessary accuracy.
Illustrated on the diagram below.
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
S
IG
N
A
L
PHASE DIFFERENCE
T
Against flow
With flow
t