Friction for rotating machinery is measured as the torque needed to overcome it. Many aspects of friction can be measured in a very simple way. Without the web, run the equipment at various RPMs. I suggest measurements at 1% RPM, 2%, 5% 10%, 20%, 30% to 100%. The measurement is the drive torque required to run the equipment at that RPM. This friction measurement considers many factors contributing to friction, but not all of them. For instance, the windage friction associated with the web is not measured in this way.
Apply friction compensation as determined by these measurements. This will require the help of a skilled drive technician. This will compensate for about 90% of friction effects.
The next step in setting friction correctly requires running the line with the web. The tension regulator will overcome the remaining friction in the system. By looking at the output (CV) of the tension regulator, askilled drive technician can determine the remaining friction as a function of line speed and roll diameter. Expensive, time-consuming work, but tension improvements can be made.