The accurate scan averages and high-resolution CD profiles measured by Valmet IQ Pulp Weight Measurement (IQ Pulp Weight) provide a solid foundation for Valmet’s machine-direction and cross-direction basis weight (grammage) controls for heavy board or pulp machines.
Beta radiation provided by an enriched Sr90 nuclear source is absorbed by the mass in a paper or board sheet. As mass increases, transmitted radiation that is captured by the ion chamber type detector is reduced. IQ Pulp Weight uses this basic principle and refines it, by using special sensor design techniques and measurement diagnostics, to provide the stable, high-resolution measurements needed for precise MD and CD controls.
The digital measurement resolution of IQ Pulp Weight is automatically optimized for specific grades by using 7 internal calibration verification standards, custom selected for the required range of measurements. The resolution of the sensor is always maximal despite the non-linear nature of the physics of nuclear absorption. The internal standards also compensate for any dirt buildup and source decay on the sensor’s windows during scheduled standardization sequences.
In addition to the head internal temperature stabilization common to all Metso IQ sensors, the temperature of the source and the detector head air gaps is actively regulated. The temperature of all the internal and external air gaps is measured using high-speed sensors. The effect of air density changes is incorporated into the temperature compensation algorithm.