When a load cell does not report zero properly the first time, such as when the web is off, an attentive maintenance department will re-zero and recalibrate the tension system. If it happens a second time, maintenance may be inclined to repeat the recalibration. If it happens a third time, it is probably best to redesign the system. Re-zeroing load cells are like trying to fix a flat tire by putting air in it. You know what is going to happen, what is guaranteed to happen, it will leak and go flat again. Time to find out where the leak is and fix it. Load cells should be stable for months if not years unless they are damaged (may be a application error in not using mechanically overload protect cells) or the electronics drifts (may be a design error by the manufacturer). This does not mean you should not regularly check calibration, only that the adjustments to zero and gain should be only minor tweaks.
A problem that occurs more than a couple times is nearly guaranteed to occur again, and again, and again. It is field proven to f__k up. Fool me once, shame on you. Fool me twice, shame on me.
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Dr. Roisum is a well-known authority in the area of web handling and converting. He has authored seven books, including Winding, Rollers and Web-Handling and has coauthored or edited several others. He was a technical editor for Converting Magazine with a monthly column entitled "Web Works." An accomplished professional speaker and instructor, Roisum has been praised for his skill at translating highly technical information into a common sense practical reference. Dave has been honored by TAPPI with their Finishing & Converting Division Award, Thomas W. Busch Prize and Finest Faculty awards and is a TAPPI Fellow. Dave received his Ph.D. from the Web Handling Research Center where he later became an Industrial Advisory Board member.
Dave has worked for the Beloit Corporation as a designer of winding machinery and later as a manager of research, and for Kimberly-Clark as a converting expert serving all business units. He is now a principal of Finishing Technologies Inc., providing consulting services to more than 300 clients who convert or manufacture: paper, film, foil, nonwovens, textiles and many other materials. He has accumulated much practical experience working in nearly 1,000 plants over the course of more than three decades.
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