There is no app, just a statement about the trade-offs necessary when you want cross-web measurement of thickness.
What we all want is total knowledge of coating thickness at every position on the web. What we generally pay for is some compromise.
- Spot measurements. This is the lowest-cost option. The user hopes that the position chosen for the spot measurement is representative of the coating as a whole.
- Variable Spot measurements. This is slightly more sophisticated but much more powerful. The position of the spot measurement can rapidly be adjusted, allowing, for example, a quick "left, middle, right" measurement before setting the spot to its default position, usually the middle. Although this can be done via some automated system, a manual movement is often highly satisfactory and keeps things low-cost. There is an obvious problem with the beta and gamma gauges - unless you are confident that the variation in substrate thickness is smaller than your coating variation
- Multi-spot measurements. If the measurement heads are relatively low-cost then installing 3 of them for left, middle, right, provides obvious benefits. Again, for beta and gamma gauges the problem is the need to install 3 upstream gauges - unless, again, you are confident of your substrate uniformity.
- Scanning gauges. Why do you want a scanning gauge? Is your coating technology so poor that you are worried about constantly shifting coatweights? Maybe you should get a better coating system. Or do you want to detect glitches such as coating misses or lines? Arguably a defect scanner will do a better job as it is generally able (through laser scanning or multiple cameras) to cover essentially 100% of the web all the time. But if you want a scanning head just to keep a good overall view of the coating there are a few questions:
- How fast should it go?
- How do you visualise and store the data?
- How do you adjust the scan width for different coatings?
- How do you synchronise the scans for beta and gamma gauges?
This is a pretty simple set of considerations, but it's surprising how often these questions aren't properly thought through - giving a system that is either over-priced or under-performing.