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How to Maintain Optimal Production with a Defective Tension Load Cell

by Bassam Dib, B.ing, Senior Analyst

Challenges

Detection

Solution

To control tension, most paper winders make use of multiple load cells feeding a closed loop system. This control requires that all load cells are calibrated periodically to correct for developing drifts in their measurements. However, load cell measurements can shift or the load cell can fail at any given time. Anticipating this failure or detecting it in a timely manner is a challenging task, mostly because the closed loop control will always match the tension feedback signal to the tension reference on the operator’s station.

This was the case at one of our customers where the mill experienced a complete failure of one load cell causing an increase of the effective tension by 40 % for the same set point.

Our analysis modules continuously monitoring individual tension load cell signals and comparing them with the estimated tension calculated from electrical measurements detected the deficiency of the load cell on time.

load cell signal

Our engineers promptly sent the mill a detailed report with supporting graphs and recommendations. To avoid interrupting production, a recommendation was issued to temporarily bypass the faulty load cell in the control until corrective actions can be taken during the upcoming shutdown.

When the mill’s technician completed the intervention of bypassing the faulty load cell, we confirmed with supporting data that his implementation was done correctly.

 

Four weeks later, the faulty load cell was replaced during a planned shutdown. Once again, we confirmed to the mill that the tension measurement and calibration were successfully restored.

Web tension is a key parameter in insuring good roll quality. However, many components can fail in this control system leading to major issues. For instance, higher tension can result in an increased number of sheet breaks or bursts in paper rolls, leading to major downtime. In contrast, low tension can create a web movement resulting in wrinkles or rings on roll edges. Even in the absence of such defects, an uneven tension can lead to registration issues at the press. All of which represent significant profit margin reduction.

Our intervention allowed the mill to maintain the winder productivity and avoid quality issues with minimum interventions, both of which prevented significant losses to the mill.

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