MULTICAL®
403
92
Kamstrup
A/S
∙
Technical
description
∙
5512
‐
1689_B1_GB_03.2017
For
calculation
of
the
transit
time
difference
we
only
view
a
simple
example
with
a
sound
patch
parallel
to
the
measuring
pipe.
The
signal
path
along
the
flow
is
crucial
and
the
transit
time
to
the
measuring
distance
l
is
calculated
as:
v
c
l
t
where:
t
is
the
transit
time
from
sender
to
receiver
of
the
sound
signal
along
the
measuring
distance
l
[s]
l
is
the
measuring
distance
[m]
c
is
the
sound
propagation
velocity
in
stagnant
water
[m/s]
v
is
the
average
flow
velocity
of
water
[m/s]
The
transit
time
difference
can
be
expressed
as
the
difference
between
the
absolute
time
of
the
signal
sent
against
the
flow
(
‐
)
and
the
signal
sent
with
the
flow
(+).
v
c
l
v
c
l
t
which
can
also
be
written
as:
2
2
2
)
)(
(
)
(
)
(
v
c
v
l
t
v
c
v
c
v
c
v
c
l
t
As
2
2
v
c
,
2
v
can
be
omitted
and
the
formula
reduced
as
follows:
l
c
t
v
2
2
Thus,
we
know
the
basic
connection
between
the
average
flow
velocity
and
the
transit
time
difference.
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.
Furthermore,
MULTICAL®
403
takes
the
influence
of
the
temperature
of
the
water
into
account
i.e.
the
built
‐
in
ASIC
uses
the
sound
velocity
at
the
water’s
current
temperature
in
connection
with
the
flow
calculations.
The
flow
(volume
flow
rate)
is
then
determined
by
measuring
the
transit
time
difference,
calculate
the
average
flow
velocity
and
multiply
it
by
the
area
of
the
measuring
tube:
A
v
q
where:
q
is
the
flow
(volume
flow
rate)
h
m
3
A
Is
the
area
of
the
measuring
pipe
2
m
The
volume
V
passing
through
is
finally
calculated
as
a
time
integration
over
the
flow
(multiplication
of
(cross
section
constant)
flow
by
time).
