Running webs well with very low tension is a problem for the drive system.
Typical tensions run about 1.5 PLI (263 N/m). Low tension would be below 0.5 PLI (121 N/m). This may apply to some fabrics, nonwovens and laminated webs.
A few of the problems are measuring the tension when it is very low. Load cells are known for reading incorrectly with low tension. Check your tension indicators just after a web break. They should read zero. If we can’t measure it, it is difficult to control.
The friction due to bearings and friction and windage doesn’t care that the web wants to see low tension. We still have two bearings for each roller. It may take more torque to overcome friction than to establish tension. The friction will certainly change with temperature and so cannot be properly modeled and compensated.
For lines running low tension, I suggest using premium bearings and the widest web possible. Pay particular attention to the load cell selection and mounting.