A Noncontacting Method for Measuring Paper Sheet Grammage and Thickness Using Acoustic Tone Bursts

The grammage, ie., mass per unit area, is one of the most important quality factors in paper industry. The grammage of the paper web is constantly monitored during the paper manufacturing, and the ever rising pulling speeds and wider reels demand more accurate and faster methods to monitor the grammage changes in both the cross direction and in the machine direction. Nowadays, the standard method is to use radioactive beta rays, which method was invented in 1950s. The beta radiation is attenuated as a function of sample grammage, but the temperature of surrounding air, and the atomic number of the sample also affect the measured intensity of the beta rays. These effects can be conquered by calibration and by monitoring the temperature. But one technical difficulty remains, though. Only one measuring head is traversing across the paper web, which is quite a slow method to achieve the cross profile of the paper web [1–2].