MULTICAL®
403
Kamstrup
A/S
∙
Technical
description
∙
5512
‐
1689_B1_GB_03.2017
91
8
Flow
sensor
Throughout
more
than
25
years
ultrasonic
measurement
has
proved
accurate
and
the
most
long
‐
term
stable
measuring
principle
for
heat
measurement.
Experience
from
repeated
reliability
tests
carried
out
in
Kamstrup’s
accredited
long
‐
term
test
equipment
and
at
AGFW
in
Germany
as
well
as
from
ultrasonic
meters
in
operation
has
documented
the
long
‐
term
stability
of
ultrasonic
meters.
(see
e.g.
report
on
random
sampling
of
flow
sensors,
Kamstrup
A/S
doc.
No.
5811
‐
060)
8.1
Measuring
principles
Within
ultrasonic
flow
measuring
there
are
two
main
principles:
the
transit
time
method
and
the
Doppler
method.
The
Doppler
method
is
based
on
the
frequency
change
which
occurs
when
sound
is
reflected
by
a
moving
particle.
This
is
the
effect
you
experience
when
a
car
passes
you.
The
sound
(the
frequency)
decreases
when
the
car
passes
by.
The
transit
time
method
used
in
MULTICAL®
403
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.
A
piezo
‐
ceramic
element
is
used
for
transmitting
and
receiving
ultrasound.
The
thickness
of
the
element
changes
when
exposed
to
an
electric
field
(voltage)
and
thereby
it
functions
as
a
transmitter
of
ultrasound.
When
the
element
is
mechanically
influenced,
it
generates
a
corresponding
electric
voltage,
and
thus
functions
as
a
receiver
of
ultrasound.
8.2
Signal
path
and
flow
calculation
The
most
important
elements
of
the
signal
path
in
MULTICAL®
403
are
shown
in
Figure 6
:
Piezo
‐
electric
elements
transmit
and
receive
the
ultrasound
signal,
which
is
reflected
into
and
through
the
measuring
tube
to
the
receiver
via
reflectors.
Due
to
superposition
of
velocities
of
water
and
sound
signal,
ultrasound
spreads
faster
with
the
flow
than
against
the
flow.
As
it
is
proven
by
the
calculations
below,
the
average
flow
velocity
is
directly
proportional
to
the
transit
time
difference
of
ultrasound
signals
which
are
sent
with
or
against
the
flow.
In
small
meters
(q
p
0.6…2.5
m³/h)
a
construction
with
a
sound
path
parallel
to
the
pipe
axis
is
used.
The
emitted
sound
waves
cover
the
pipe
area
of
these
meters
reasonably
well
and
thus
the
measuring
signal
is
stable
enough
towards
flow
variations
along
the
pipe
diameter.
In
big
meters
(q
p
3.5…15
m³/h)
a
construction
with
a
triangular
sound
path
is
used
to
make
sure
that
flow
variations
along
the
pipe
diameter
are
covered
too
in
these
meters.
The
measuring
signal
here
results
in
a
linear
integration
along
the
sound
path,
which
levels
possible
dissymmetry
of
the
flow
profile
in
the
meter.
q
p
0.6…2.5
m³/h
Parallel
measurement
q
p
3.5…15
m³/h
Triangular
measurement
Figure 6: Signal paths in MULTICAL® 403.
Sound
signals are sent from the transducers via 2 or 4 reflectors, depending
on the construction. For small meters (q
p
0.6…2.5 m³/h) a parallel sound path is sufficient. To cover flow
variations
along the pipe diameter (flow profile) in the flow sensor a triangular sound path is used in big
meters
q
p
3.5…15
m³/h). In both constructions the transit times of the signal with and against the flow vary.
