Level webs may run faster and with less waste. Level profiles are so vital that they are often rejectable specifications set by either the supplier or the customer or both.

Almost everyone measures profile, which usually refers to the variation of gage (thickness) or basis weight (areal density) across the width. Measurements can be done online with scanners, offline in the test lab, or on the wound roll. Since gage uniformity is so important, you must ask which measurement methods are cheapest, easiest, fastest and most sensitive for your application.

Online scanners are brought to the highest levels of technology in papermaking. For several decades, they have measured basis weight, caliper and moisture on most of the thousands of paper machines throughout the world. These multi-million dollar devices are demanding. It is not unusual for the instrument supplier to provide a full-time service engineer to be dedicated to scanners at a single mill.

Even so, only in the last two decades have these instruments become trustworthy enough to be given control of profile adjusters. Even now, it is not unheard of for mills to shut off the controls and allow the operator to manually adjust them, because humans can do a better job. In not a few cases, profile has been improved by shutting off the controller and simply leveling the actuators.

The problem is usually not, as many think, with the profile adjustment or the control algorithm. Rather, it is more basic. The measurement is not sufficiently sensitive for the purpose of avoiding defects. I will illustrate with a common situation where there is a gage band in the wound roll. You can see the bulge with your eyes. You can feel the bulge with your hand. You can hear the bulge by striking it with a stick.

When you look at the scanner, however, it shows no resemblance to the shape of the wound roll. It may look like the EKG of a heart patient ready to expire. The gage defect may be so pronounced that the roll may be stretched into bagginess or corrugate there, and the scanner still might not see it. It is interesting to observe the cultural reactions to this information discrepancy. In paper, operators trust the scanners because they've been around so long. In film, the operators usually ignore them as they seldom seem to relate. In any case, if you can see, feel and hear a bulge, you don't need a scanner. You know you HAVE a gage band no matter what other instruments may say.

Lab measurements of caliper have been around so long that few question their integrity. Test standards and instruments conforming to these standards are older than we are. However, the fundamental issue is still present. Gage variations too small to be picked up by bench instruments may cause rejectable-sized problems during winding. Further complicating the lab is sample size, something like trying to characterize a truckload of peas by sampling a handful. Also, the test lab results may be delayed by minutes to hours from the time of production. This is something like housebreaking a dog. If you don't push their nose into it within minutes, they will not figure out what they have done wrong.

I will make a long story short with two general conclusions. First, the most sensitive measure of caliper variation is usually the wound roll. Here, we might use hardness or diameter variation as a judge of manufacturing uniformity. Second, the fussiest customer for caliper is not the one you sell to. It is the winder. In fact, if you pay closer attention to your customer's language you will note that they don't usually complain of excessive gage variations. Instead, they complain of poor wound-roll appearance. That is, assuming you don't reject it internally first, due to bagginess, corrugations, telescopes, wrinkling or other gage-related problems.