New optical moisture meter for paper

Measuring speed increased by 40-fold


Metso Automation, a global engineering and technology corporation in the pulp and paper industry, and Technical Research Centre Finland (VTT) have developed an optical meter to measure paper moisture Thanks to the increased speed, the system’s traverse speed during full-sheet measurement is higher and the process control process becomes faster. The improved diagnostic features of this meter allow the paper manufacturers to access the interference sources of the paper machine better than before. This measurement device covers large basis weight areas of paper and board ranging from 10 grams of paper to 500 grams of board. Metso Automation began production of these meters in 2006.

Based on infrared light absorption

The moisture meter functions are based on the infrared light absorption by the water and fibre components of the sheet when the light passes through the sheet. The device measures all light wavelengths required for moisture measurement at the same time. This improves the precision and measuring speed of the paper quality information and thus reduces the noise produced by the inhomogeneous features of the sheet. The optical output is measured from the other end of the sheet using a multi-channel infrared detector.

Utilization of measurement information

The paper machine sheet passes the quality control system at a maximum speed of 33 metres per second. The PaperIQ system developed by Metso Automation uses meters that are located in a carrier, which laterally measures the paper quality of the sheet. Quality measurement is connected to a closed-loop control where the measurement information is utilized online by the paper machine’s control system. The most important quality factors to measure are the basis weight, moisture and thickness of the paper.

The even moisture profile of the sheet and moisture control are key factors in controlling paper quality, production capacity and costs. The moisture of the sheet also affects the runnability of the machine and the distribution of the coating on the paper’s surface. It also affects paper curling and the tightness of the roll.

VTT was in charge of designing the measurement principle and structure of the moisture meter. This includes optical surfaces and mirrors that enable efficient lighting of the paper sheet and gathering of light that has passed through the sheet. One of VTT’s tasks was to optimize the wavelengths and improve calibration.


Additional information

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