MEASUREMENT & MONITORING
WORLD SMALLEST CORIOLIS
KOBOLD
THE WORLD’S SMALLEST DUAL-TUBE CORIOLIS MASS
FLOW METER: HIGH PRECISION MEASUREMENTS
WITHIN 150 MM
Due to the weight influence of sensor coils,
for the measurement of very small flow-rates
it is common practice to use single tube
Coriolis flow meters. The sensor coils of dual-
tube Coriolis sensors are mounted onto one
of the two measuring tubes, thus having,
by very small tube diameters, a significant
weight influence on the tube on which they
are mounted.
Therefore, the influence of the sensor coils
on the measurement results increases by
decreasing tube diameter. For this reason
single tubes are often favoured for the
measurement of very small flow rates, where
the coils are mounted to the chassis and
not on the tube. However, with the use of
just one measuring tube the influence of
external interferences increases dramatically.
To reduce this sensitivity and at the same
time delivering accurate measurements at
very small flow rates, Heinrichs Messtechnik
has developed the dual-tube Coriolis
principle to a new level.
In this new state-of-the-art technologie,
the sensor coils are no longer mounted
onto the tubes, but rather between them,
thus freeing the measuring tubes from the
influence of the coils weight allowing for
extremly small tube diameters in dual-tube
design. The result is the world’s smallest
dual-tube Coriolis Mass flow-meter: The
high Performance Coriolis (HPC). With
an installation length of just 150 mm it
is now possible to achieve high accuracy
measurements with deviations of just ± 0.1
percent. Furthermore, the sensor shows
insensitivity to temperatures of up to 180
°C, to pressures of up to 600 bar as well as to
strong vibrations.
“Market observations have revealed an
open gap in the measurement of small
flow rates”, explains Frank Schramm, the
managing director of Heinrichs Messtechnik
GmbH. The current problem is that the
state-of-the-art stipulates the use of
dual-tube technology, where the magnets
are mounted to one tube, the exciter and
sensor coils to the other. However, for very
small flow rates this principal has a decisive
limit. For example, where extremely small
flow rates demands a tube diameter of just
1 mm, the vibrating behavior of the coils
weight can influence the measurement
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results significantly. “Therefore it is common
practice to use one tube systems for these
applications, in which the coils are mounted
to the chassis of the sensor. This system has
the decisive disadvantage in that the second
tube, which also serves as a measurement
reference, is omitted, requiring that the
sensor coils be mounted on to the chassis
of the enclosure making the sensor
more susceptible to vibrations and other
disturbances.
For this reason, Heinrichs Messtechnik
GmbH has set as its objective, the
development of a high precision, shock
resistant Coriolis Mass Flow Meter. Emerged
is the High Precision Coriolis – short HPC –
with its installation length of just 150 mm
the smallest Coriolis mass flow meter in
dual-tube design.
Reducing disturbance
influences by positioning
the sensor coils between the
measuring tubes
“Due to the sensitivity single tube Coriolis
sensors, a costly mechanical decoupling
is often required, rendering them
inappropriate for many applications. Our
quest was therefore to find a means of
unifying a dual tube design with very small
diameter tubes”, explained Schramm. Since
the fundamental problem lies in the weight
of the coils, which when compared with
tube diameters of 1.5 mm or less present a
significant weight, Heinrichs Messtechnik
adopted the following solution: The
conventional approach of mounting the
coils onto the tubes was abandoned in
favour their mounting on a printed circuit
board mounted between the tubes. This
method also enables the use of four sensor
coils instead of two, as is usually the case
with dual-tube Coriolis, providing a higher
resolution.
On the measuring tubes themselves only
very light magnets are mounted, which,
with a weight of only 0.08g, have little to no
influence on the vibrating behavior of the
tubes. Instead of conventional brazing, the
magnet holders are mounted onto the tubes
using a special laser-welding technology.
Utilizing this method, Heinrichs Messtechnik
aims at keeping the production costs of
the sensor to an absolute minimum, it not
only allows for a stress free connection, but
also eliminates the time-consuming and
elaborate process of brazing in a vacuum
oven.
Insensiti