LengthProfiler – Slab, bloom, billet and section laser length measurement

There is no doubt that the best method of measuring length in a caster or steel mill is by using a Doppler gauge. For accurate measurement, the object must pass the laser at the reference distance ±100 mm and for some applications this is not possible. Typically this problem arises on slab casters where there is a large difference between the narrowest and widest slab or wide roller tables where bars are passing and are not in a fixed location but can wander left or right. LIMAB have developed a turn-key solution to solve this measurement application and it is suitable for use on billet/bloom or slab casters or any roller table transporting hot or cold bars. The Doppler is mounted on a servo driven positioning mechanism that automatically tracks the position of the bar placing the Doppler at the optimum distance. The information about the slab position comes from a separate laser distance sensor. The system is protected by a special forced air cooled housing which keeps the equipment clean and cool.


Basic Specification

Measuring objectLength accuracyPositioning travelPositioning speed
Hot or cold slabs, blooms, billets or sections< ± 0.03%800 mm / 31 inch256 mm/s / 10 inch/s

Operating Principle

The length is measured using the principle of dual beam laser Doppler velocimetry which ensures highly accurate measurement without contact. However for this technique to function, the material must pass at the reference distance ±100 mm. The Doppler gauge is mounted on a servo operated positioning mechanism that automatically tracks the slab position using a separate laser distance sensor. This ensures the Doppler gauge is at the correct distance for optimum measurement.


  • Speed measurement on slab continuous casters
  • Length measurement on slab continuous casters for cut-to-length control
  • Hot rolled section length control at hot saws
  • Run-out length of hot rolled sections
  • Slab length prior to reheat furnace

Accurate length measurement
The correct positioning of the doppler will ensure an accurate length measurement.

Automatical positioning of the doppler
The doppler will automatically be positioned to the optimum distance from the measuring object. This is done by reading the actual distance by a separate laser sensor.

Air cooling
The system is cooled by an air blower.

Several different output interfaces are available such as RS232, RS422, Ethernet, Quadrature Pulse.

Mounting stand
The mounting stand for the doppler housing is adopted to each installation.

Hot to cold conversion
A pyrometer will provide the actual measuring object temperature at the point of measurement enabling a hot to cold correction.

Proven technology

Doppler gauges were introduced to the metals industry more than 30 years ago and are proven technology with thousands of installations worldwide.  Measuring length or speed with Doppler ensures the best accuracy and reliable measurement for all types of applications.

Complete solution

The LengthProfiler system allows applications that would have once been difficult or impossible to accomplish reliably to be done with ease. LIMAB provide a complete turn-key solution including all hardware and software.

Replace water-cooled contact rollers on casters

With accuracy better than ± 0.03%, irrespective of the material grade, temperature, surface condition the LengthProfiler is ideal for replacing traditional water-cooled contact rollers found on continuous casters.  The measurement is more accurate, reliable and due to non-contact technology much less costly to maintain.

Eliminate the need for multiple hot metal detectors or photocells

Traditionally sections lengths are measured with banks of HMD’s or photocells together with a tachometer driven by a contact roller. In the harsh steel mill environment, the position and alignment of the photocells are difficult to maintain resulting in poor reliability and accuracy. The LenghtProfiler eliminates all these problems.

Side mounting

Measuring hot slabs from the side is the most accurate method as the heat shimmer in the surrounding air is much reduced when compared with mounting above the slab. Furthermore the ambient temperature and heat transfer is much lower, this reduces the installation cost and makes the operation more reliable.

Slab Length Measurement

Speed range0… ±19,000 m/min for 1.5 m stand off
AccuracyBetter than ±0.03%
Measuring objectAll metals up to 1200 +C°
Stand off distance1.0, 1.5, 2.0, 2.5 or 3.0 m
Laser classLaser Class 3B according to EN 60825-1:2014 and 21 CFR 1040.10 and 1040.11 except for deviations pursuant to Laser Notice No. 50, dated June 24, 2007.
OutputsRS232, RS422, Ethernet, Quadrature Pulse
Servo travel800 mm
Servo speed256 mm/sec
Distance laser typeLIMAB XLR30
PLC typeSiemens
CoolingAir blower & filter assembly
Cooling air volume2000 m³ / h
Dimensions of housing (typical)1800 x 600 x 300 mm
Adjustable mounting standProvided to suit application