IMS Radar Width Measuring System

Whitepaper
Radar
Width Measuring System
Online radar width measurement in
hot mills and plate mills

CONTENTS
01
Introduction
02
Task
02
03
04
Development of a
Radar Width Measuring System
4.1 Measuring principle
4.2 Design and properties
of the radar sensors
06 - 07
08 - 09
4.3 Design of the overall system
10 - 11
06
Measuring results
6.1 Test bay measurements
07
Summary
16 - 17
6.2 Operating measurements
18 - 21
22 - 23
03
User benefits
05
Integration into
production
08
References
04 - 05
12 - 15
24 - 25

01
02
Introduction
Task
When rolling steel and other metals, knowing
and controlling the width of the rolling
stock is crucial for the product quality and
efficiency of the entire rolling process. In
some of the process steps, however, the
conditions of the production environment
and of the installation can make it difficult
to use conventional measuring systems –
and therefore also to effectively control the
width.
In hot strip mills, for example, the width of
the rolling stock is largely set at the roughing
stand. Correction of the width in the
subsequent process steps is hardly possible.
However, descaling, which is essential
on the roughing stand, leads to a high
volume of vapour and spray water as well
as falling scale.
As a result, stable use of measuring systems
based on optical measuring principles
or requiring components below the roller
table is usually only possible with a great
deal of mechanical effort and involves
intensive maintenance. The often very limited
space available in the production lines as
well as the heavy vibrations at the roll stand
make the integration of suitable measuring
hardware even more difficult.
In rolling mills, insufficient knowledge of
the actual width of the material being
measured means that control processes
are based solely on model-based calculations
of the width, which significantly
reduces their effectiveness.
Width control based on real measurement
data, on the other hand, offers the
possibility of optimising width performance
and, as a result, increasing resource
efficiency and stabilising the rolling
process.
In order to enable reliable width measurement
with real measurement data under
the harsh environmental conditions in hot
mills, a radar-based Width Measuring
System was developed by IMS Messsysteme
GmbH in cooperation with Fraunhofer
FHR.
Radar technology is particularly suitable as
a measuring method in this area of application,
as it is insensitive to vapour and spray
water. Another advantage is the compact
design of the components, which can be
integrated into existing mill lines without
major conversion work, even where space
is limited.
The measuring principle of the newly developed
Radar Width Measuring System is
based on the use of two radar units, which
are installed on both sides of the roller
table and measure the exact distance to
the edge of the material. The actual width
of the measured stock is determined from
the two distance values on the basis of a
suitable calibration.
The objective for this development was a
radar-based online measuring system that
is suitable for the challenging conditions
on the roughing stand of hot mills and
enables stable and precise width measurement
in the long term. In addition to the
mechanical design and easy integration of
the measuring system into existing production
lines, the optimisation of the sensor
and data processing technology to achieve
high measuring accuracy were also of crucial
importance.
02 INTRODUCTION TASK 03

03
User benefits
Several years of experience of use in hot
mills in the metal industry have now proven
that the Radar Width Measuring System
from IMS Messsysteme GmbH guarantees
reliable and accurate width measurement
even under the most adverse ambient
conditions.
The Radar Width Measuring System is
therefore stable and precise even in the
presence of high levels of vapour and spray
water, as several successful installations
have confirmed. Since the measurement is
performed on metallic surfaces in reflection,
the temperature of the measured stock,
whether red-hot or cold, has no effect on the
measuring accuracy.
The two compact radar units can be integrated
into existing plants without major effort,
even where space is limited. As the two
measuring units do not need to be mechanically
connected to one another and can
therefore be positioned at a greater distance
from each other, the system has also
proven to be effective for use in plate mills.
By installing the two radar units to the side
of the roller table, the measurement is not
impaired by the vibrations occurring on the
roll stand or any falling scale. The maintenance
effort is correspondingly low – in
most cases, cleaning the measuring windows
during the usual maintenance downtime
is sufficient.
Another advantage of radar measurement
is that no further safety precautions are
necessary due to the low transmission
power. The radiation frequencies lie entirely
in the free frequency band between 57 and
64 GHz, meaning that the system can be
used safely in most countries without the
need for authorisation. At the same time,
the high bandwidth of 7 GHz enables a
high resolution and a width measurement
accuracy of < 1 mm.
04 USER BENEFITS USER BENEFITS 05

04
Development of a
Radar Width Measuring System
4.1. Measuring principle
Radar sensors generate electromagnetic
waves that are emitted by an antenna.
During radar width measurement, these
waves are focussed in the direction of
the roller table and hit the edge of the
material. From there, they are reflected
and received by two receiving antennas of
the same system unit. Based on the distance
travelled, there is a delay between
the signal being transmitted and it being
received.
The radar sensors used here transmit signals
that are linearly modulated in time (FMCW
radar), which means that the time delay can
be precisely determined by analysing the difference
frequency between the signal being
transmitted and received.
Since the waves travel at the speed of light,
the distance to the edge of the material can
be precisely calculated from this in correlation
with the time delay. In addition, the additional
use of a signal processing
algorithm increases the accuracy of the
distance measurement.
To determine the width, two radar units
are installed opposite each other on both
sides of the roller table (Figure 1). Each unit
measures the distance to the respective
edge of the material. After calibrating the
measuring range, the exact width of the
passing material can be determined from
the two independently determined distance
values.
Figure 1: Schematic representation
of the measuring principle
06 DEVELOPMENT OF A RADAR WIDTH MEASURING SYSTEM DEVELOPMENT OF A RADAR WIDTH MEASURING SYSTEM 07

04
Measured
Simulated
Development of a
Radar Width Measuring System
Amplitude (dBm)
Figure 3: Antenna emission characteristics
4.2. Design and properties
of the radar sensors
Angle (degrees)
The design of the radar sensors used in
the Width Measuring System is shown
in Figure 2. The generation of the radar
waves and the determination of the distance
take place in the electronics of the
respective radar sensor, which is integrated
into a protective housing (protection class
IP67). The connections for the power supply
(24 V) and data transmission are located
on the back of the housing.
Three Teflon antennas are attached to
the front of the housing. The antenna in
the centre emits the radar waves outwards
towards the edge of the material and focuses
them like a lens. The waves reflected
by the strip edge are in turn received by
the identical antennas above and below
the transmitting antenna. The separated
arrangement of the transmitting and receiving
antennas increases the usable dynamic
range of the system. Furthermore, the use
of two receiving antennas enables the
measurement of two distance values at
different heights, which is advantageous in
the case of large variations in the thickness
of the measured stock (e.g. heavy plate).
Figure 2: Radar sensor with
three Teflon antennas
In addition, this enables measurements with
low angular error even with vertical strip
roaming or a ski-shaped bend in the strip.
The emission characteristics of the radar
antennas are shown in Figure 3.
The majority of the power is emitted or
received within the radar beam, which has
an aperture angle 1 of approx. 4°. The radar
beam is rotationally symmetrical and has a
Gaussian radiation profile.
Following the laws of geometry, the size
of the beam on the strip edge depends on
the aperture angle and the distance to the
measured stock.
In this way, the measuring signal is averaged
over a certain range, making it less
sensitive to slight unevenness or edge
cracks.
As already mentioned, the frequency of
the emitted waves is linearly modulated
between 57 GHz and 64 GHz. The radiant
power is below 10 mW, so that no further
safety measures 2 are required for ongoing
operation.
1 Drop in output of 3 dB at approx. ± 2°.
2 Individuals with active implants should not stand directly
in front of the antennas.
08 DEVELOPMENT OF A RADAR WIDTH MEASURING SYSTEM DEVELOPMENT OF A RADAR WIDTH MEASURING SYSTEM 09

04
Development of a
Radar Width Measuring System
4.3. Design of the overall system
The distance values determined by the
radar sensors are sent at a data rate of
> 1 kHz via a UDP connection to an
industrial computer, in which the width of
the measured stock is calculated by applying
the stored calibration data. The width
values are determined in this way at a
data rate of 1 kHz and forwarded to the
customer via a suitable interface. The type
of data transmission is always customised
to the customer’s requirements.
The industrial computer is also used to
control the entire system and to visualise
and store the measurement data. In addition
to the distance and width measurement
values, the time and frequency spectra are
also displayed in the visualisation, allowing
suitable parameters and threshold values to
be set in order to suppress interference signals
(e.g. from other reflections in the roller
table) and control the measuring cycle.
This computer is also used to control the
calibration unit and record the calibration
parameters with the aid of the visualisation.
For this purpose, a calibration body
is moved through the linear unit and the
distances measured by the radar sensors
at each position of the body are recorded.
The calibration parameters are determined
from this data, which in turn are used to
optimise the distance accuracies and relate
the distance values to each other for width
determination.
Calibration is carried out both in the
IMS Messsysteme GmbH test bay before
delivery of the system and during commissioning
in the factory itself.
Recalibration is usually only necessary if
changes are made to the system, e.g. in
the case of realignment, replacement of
components or changes to the measuring
range.
10 DEVELOPMENT OF A RADAR WIDTH MEASURING SYSTEM DEVELOPMENT OF A RADAR WIDTH MEASURING SYSTEM 11

05
Integration into production
For use in rolling mills, each individual
radar sensor is integrated into a compact
metal housing with a Teflon measuring
window to protect it from the harsh environmental
conditions prevailing there (Figure 4).
The housing can be double-walled and
cooled with water if required to protect it
from the high ambient temperatures at the
roughing stand. Depending on the installation
situation, the housings are mounted
on suitable stands in order to set and
guarantee the ideal height of the radar sensors
in relation to the measured stock.
Product data
Strip thickness:
Distance from
antennas to material
edge:
≥ 5 mm
750 mm–3,000 mm
Performance data
Width accuracy (2σ):
Measurement rate:
≤ ± 1.0 mm
1 kHz
Figure 4: Protective hood with Teflon window
12 INTEGRATION INTO PRODUCTION INTEGRATION INTO PRODUCTION 13

The sensors are themselves attached to a
specially designed bracket with corresponding
adjustment options for fine adjustment
of the height, antenna alignment and to
compensate for eventual unevenness.
The supplied calibration unit also serves as
an alignment aid, which is fixed to the roller
table in the measuring area and enables
the sensors to be aligned with each other
and with the roller table.
To ensure optimum measurement performance,
the calibration unit is usually
equipped with a linear unit and a motor as
standard, so that the calibration body can
be moved automatically within the measuring
range (Figure 5). In principle, however,
simplified calibration is also possible without
a travelling device.
The prerequisite for successful integration
and optimum performance of the Radar
Width Measuring System is a sufficiently
large, unrestricted line of sight on both
sides of the roller table through which the
radar waves can reach the respective edge
of the material.
Depending on the installation situation,
suitable measuring openings may have to
be provided on the sides of the roller table
(e.g. in the case of existing protective walls
or side guards). The optimum size of this
measuring opening depends on the sensor
spacing, which is adapted to the specific
conditions at the factory.
As described above, the radar sensors
used in this Width Measuring System
provide stable, precise measurements even
with a high volume of vapour and spray
water. A closed film of water, on the other
hand, cannot be penetrated by the radar
waves. Flowing water at the edges of the
strip or a strong flow of water in the measuring
area should therefore be avoided or
eliminated, e.g. by blowing off.
Figure 5: Radar sensor with adjustment unit
14 INTEGRATION INTO PRODUCTION
INTEGRATION INTO PRODUCTION
15

06
Measuring results
6.1. Test bay measurements
In order to be able to test the performance
of the Radar Width Measuring System
during the development phase, a specially
equipped test rig was installed in the
IMS Messsysteme GmbH test bay. This
consists of a support device with a linear
unit, which is driven by a step motor. The
two radar units are each positioned at the
ends of the support, on which the test and
calibration bodies can be moved along
the axis between the two radar sensors.
Three certified test pieces with flat edges,
a thickness of 50 mm each and widths
of 800 mm, 1,300 mm and 1,800 mm are
used to check the measuring accuracy and
cover typical width values in hot strip mills.
For the test measurements shown below,
the test pieces described were aligned in
the centre between the radar units, which
were placed opposite each other at a
distance of approx. 6 m.
The radar beams were aligned at right
angles to the test piece on both sides
and the height of the measuring spot was
aligned with the centre of the test piece
edge to avoid angular errors. The test
pieces were moved step by step 3 by
± 200 mm from the centre in order to simulate
the horizontal strip roaming that is
common in factory conditions.
Width: 800 mm
Width: 1,300 mm
Width: 1,800 mm
Centreline displacement (mm)
Figure 6: Measuring results with certified test pieces
Figure 6 shows the deviations between the ation is less than ± 0.5 mm. The low
measured and certified width values for all standard deviation (error bar) shows the
three test pieces, each averaged over three high reproducibility of the measurement.
measurement repetitions. For all widths and
over the entire travel range, the width devi-
16 MEASURING RESULTS
MEASURING RESULTS
17

06
Measuring results
6.2. Operating measurements
The measurement results shown below
were obtained in the hot strip mill at
Salzgitter Flachstahl GmbH. There, the
measurement performance was initially
tested with a first prototype at the exit
of the roughing stand by means of a concrete
comparison with an optical width
measurement, whereby the desired accuracy
of approx. 1 mm and a high degree of
stability were achieved [1].
The Radar Width Measuring System was
then moved to its final location at the
entry of the roughing stand and has been
successfully in use in this configuration
since 2017 (Figure 7). In this specific application,
the radar units are set up at a
distance of ~ 5 m on the sides of the roller
table and measure the strips, which are up
to around 2 m wide.
On both side guards, which align the strips
so that they are straight and centre them
on the roller table, there is an opening
through which the radar beams are
projected and hit the edges of the material
to be measured. The flowing water falling
from the strip surface when descaling is
switched off is blown off at both measuring
windows using an air nozzle.
For some strips that were no longer
processed in the last pass through the
roughing stand, it was possible to make a
concrete comparison between the finalised
Radar Width Measuring System and an
optical measurement.
Figure 8 shows an example of the width
profile of such a strip, measured with the
Radar Width Measuring System in direct
comparison with an optical system.
The slight shifts in the length scale result
from inaccuracies in the measurement of
the strip speed.
The actual width profiles of both measuring
methods and their characteristics are
therefore almost identical.
Measuring
opening
Radar
Figure 7: Radar width measurement at the roughing
stand entry at Salzgitter-Flachstahl GmbH.
18 MEASURING RESULTS
MEASURING RESULTS
19

In the lower image of Figure 8, you can see
the results of a test in which an approx.
7 m long piece was cut out of a cooled
pre-strip, placed on the roller table and run
through the Radar Measuring System several
times [2].
The measuring results are shown in comparison
to the results of a manual sliding
gauge measurement of the test piece. Here,
too, there is very good agreement between
the radar measurement and the manual
reference measurement as well as between
the individual measurement repetitions.
Extensive long-term analyses [3] also demonstrated
that the Radar Width Measuring
System at Salzgitter Flachstahl GmbH has
an availability of more than 99% and is well
suited for measures to improve the width
performance. Thanks to more homogenous
input conditions, the Radar Measuring System
enabled a more stable rolling process in
the finishing mill.
Width (m)
Radar measurement
Optical measurement
Length (m)
Width (m)
Length (m)
Figure 8: Top: Comparison of the radar measurement on the roughing stand with the optical measurement.
Bottom: Comparison of the radar measurement with a manual measurement (red dots)
20 MEASURING RESULTS
MEASURING RESULTS
21

07
Summary
With the development of the Radar Width
Measuring System presented here, stable
and precise width measurement could be
achieved even under the adverse ambient
conditions that prevail on the roughing
stand in hot strip mills.
The measurement itself is not dependent
on the composition of the metallic material
being measured and its temperature. The
Radar Width Measuring System also offers
real advantages for other applications,
such as in the aluminium industry.
The system developed by IMS Messsysteme
GmbH in cooperation with Fraunhofer
FHR is low-maintenance and, thanks to
its compact design, can be integrated into
existing production lines even in confined
spaces without major structural changes.
The frequency range of the radar sensors is
in a free frequency band and can therefore
be operated without the need for authorisation
or further safety measures.
The high long-term stability and availability
of the Radar Width Measuring System
were demonstrated in live operation at
Salzgitter Flachstahl GmbH. To summarise,
customers have confirmed that the system
is suitable for improving width performance
and contributes to a more stable rolling
process.
Radar width measurement has also proven
its worth for use in plate mills , as the two
separate, easy-to-place radar units eliminate
the need for a complex superstructure.
22 SUMMARY SUMMARY 23

08
References
[1] Fischer, B., Krauthäuser, H., Krebs, C., Gütgemann, S., Nüßler, D., Pohl, N., & Antoine, C. P.: Radar
width measurement system for hot rolling mills. In 10th International Rolling Conference
and the 7th European Rolling Conference, (2016).
[2] Fischer, B.; Krauthäuser, H.; Krebs, C.; Gütgemann, S., and Antoine, C. P.: Radar Solutions
for Harsh Environmental Conditions; BHM Berg- und Hüttenmännische Monatshefte,
163 (2018), P. 84–89.
[3] Haschke, T.; Huge, Th.; Lipowski, M.; Mengel, Ch.; Fischer, B.; Krauthäuser, H.: Increased
width performance due to use of a radar width measurement in the roughing mill; ESTAD proceedings.
ESTAD 6th, (2023).
24 REFERENCES REFERENCES 25

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42579 Heiligenhaus
Phone: +49 (0) 2056 / 975 – 0
Fax: +49 (0) 2056 / 975 – 140
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