For an unwind zone (on a web press or converting machinery) under closed-loop tension control, tension can be controlled by a pneumatic brake, an electric brake or a regenerative drive.
During machine operation the measurement signal from the tension transducers is input to an automatic tension controller. The controller compares the actual tension to a desired tension set point input by the operator. The controller works by sending a compensated electric or pneumatic signal output to the control device.
The output signal decreases as the material roll decreases in diameter to maintain constant tension going into the next tension zone.