Valmet IQ Basis Weight Measurement
The accurate scan averages and high-resolution CD profiles measured by Valmet IQ Basis Weight Measurement (IQ Basis Weight) provide a solid foundation for Valmet’s machine-direction and cross-direction basis weight (grammage) controls.
Digital signal processing, internal 7-point calibration verification and sensitive high-speed air density temperature compensation ensure superior measurement accuracy even in hot, humid and unclean papermaking environments.
Beta radiation provided by an enriched Kr85 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 Basis 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 Basis 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 measurement 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.
The calibration of IQ Basis Weight is consistent from grade to grade despite changes in sheet filler content or coating weights. In addition to the head internal temperature stabilization common to all sensors, the temperature of the source head air gap is stabilized and the detector head air gap 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.
- More accurate and stable onsheet measurements for more precise control of MD and CD properties under even the harshest environments.
- Precise streak control using 5 mm resolution profiles, available after the very first sheet scan.
- Faster on-spec quality and reduced startup waste.
- Ash-independent measurement for varying compositions.
- Produces a reading with a superior signal to noise and therefore a better measurement resolution.