Measurement Adjustment
Control algorithms designed to adjust measurement readings based on the actual temperature of a moving material web are critical for maintaining accuracy in high-speed manufacturing lines. By executing web temperature compensation, the control system corrects the readings from moisture and thickness sensors that are influenced by the heat of the paper sheet. Since paper webs are measured while still hot from the drying section, their temperature can vary by dozens of degrees during a production run.
This correction ensures that the reported moisture and thickness values represent the properties of the sheet at room temperature, which is the baseline used by customers.
Sensor Sensitivity
The physical properties of paper, such as electrical conductivity and infrared absorption, shift as the temperature of the web changes. For example, a hot paper sheet will appear to have a higher moisture content to an uncompensated capacitive sensor than the same sheet when cold. This occurs because heat increases the mobility of water molecules and ions within the fibrous network, changing the dielectric constant.
By using a non-contact infrared thermometer to measure the web temperature simultaneously, the system can apply a mathematical correction to the sensor signal, neutralizing the temperature effect.
Quality Control
Applying the correction prevents false adjustments to the drying section of the paper machine. When the compensation is disabled, the automated control system might over-dry the sheet, wasting energy and creating brittle paper. The resulting uniform sheet possesses consistent strength and moisture, which are critical for trouble-free printing and converting.
