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The Automation Division of Tata Steel Limited has developed a Vision Based Width Measurment System using state of the art image processing techniques.

TrueSpan has been developed for online width measurement of strip in Hot and Cold Rolling Mills. TrueSpan can be configured for stereoscopic measurement of strip with varying HOP and TILT on the roller table. TrueSpan is developed to provide a very high-speed width output maintaining high precision measurement accuracy under all mill conditions.



Principle of Working

TrueSpan senses the strip edges with two very high-resolution linear array CCD cameras used to snap at about 20 MHz placed on the top of the rolling table. For width measurement at same point with respect to the strip, a common clock controller synchronizes the cameras. TrueSpan uses sophisticated image processing algorithms for noise filtering and edge detection. Triangulation principles are used to estimate the width incase of HOP or TILT of the strip on the roll table. For measuring width of cold strip same principle is applied with appropriate back light arrangement.



  • High-resolution line-scan CCD cameras with environmental enclosure (for long & maintenance free life).
  • High-speed image processing on digital signal processors for real-time width measurement.
  • Image processing computer.
  • Flat screen color graphic display.
  • Measurement accuracy.



  • Measuring the width of slabs at the entry of a roughing stand.
  • Transfer bar width after roughing mill.
  • Strip width after finishing mill.
  • Measuring cold strip width with appropriate back light arrangement


System Specification

  • Stereoscopic width measurement
  • Material width 500 mm to 1800 mm
  • Temp above 600° C without backlight
  • In case of cold strip (temperature less than 600° C), a backlight is required under the roller table and object of interest will be the dark portion instead of white one. The backlight needs to be protected from temperature and scales.
  • Hot width and cold width display.
  • Analog output for width deviation and centre-line deviation.
  • Width display in engineer terminal and operators terminal.
  • RS232/Ethernet communication with mill computers.
  • Alarm display and reset facility.
  • History.
  • Calibration & diagnostic software.