Valmet IQ Optical Caliper Measurement

The accurate scan averages and high-resolution CD profiles measured by Valmet IQ Optical Caliper Measurement (IQ Optical Caliper) provide a solid foundation for Valmet’s cross direction caliper controls. The paper web is stabilized to the reference plate and there is none of the sheet pinching effect experienced with conventional contacting caliper measurements. These results in improved runnability as there are no contacting parts that could interact with sheet impurities in a way that would lead to holes or sheet breaks.

Valmet IQ Optical Caliper Measuruments


IQ Optical Caliper combines two accurate measurement techniques. The magnetic principle is used to measure the distance of the laser to a reference plate while the non-contacting laser triangulation optical principle measures the distance to the paper surface. Paper thickness is reached by subtracting these individual measurements from each other. The combination of the two principles in this design eliminates errors introduced by normal mechanical tolerances involved in scanning the sensor across the sheet.

The paper web is stabilized to the reference plate using the Coanda effect. This prevents passline variations and aerodynamical effects from disturbing the accuracy even for the highest machine speeds.
An automatic standardization and calibration procedure periodically adapts the sensor’s calibration parameters to the environmental conditions and, in that way, guarantees long term accuracy and reliability.


  • Sub-micron caliper measurement accuracy at the highest resolution and scanning speed lead to more accurate and stable onsheet measurement and more precise control of MD and CD properties.
  • There is no pinching effect to cause holes, sheet breaks or marking due to sheet impurities or high nip force. This leads to improved production line runnability and reduced waste.
  • Passline handling combined with the simple and robust measurement principle leads to improved profile accuracy over a wide range of paper grades. These include highly calendered and very fast machines where conventional contacting caliper measurement has been challenging.
  • Even caliper improves reel build and winder and press room runnability.