Measuring Linear feet of paper

I Guess they may be doing somthing like this.

This method is used typically for process control and is sufficient for most needs. However there is always slippage whether it is a idler roll or a driven roll.

How consistent is the density/thickness?

Is there any reason not to just weigh it? You just need to accurately measure and weigh say 100'. Weigh the empty bobbin, then, weigh the bobbin as the paper spools onto it.

I'd be surprised if the consistency caused more than the 0.35% inaccuracy you've got to play with.

I doubt that mean thickness can be controlled with in that tolerance on batch to batch basis. If we take a +/- 1% for a .2mm paper, it is +/- 2Micron, it looks too tight.

What do you think?

A roller with a good wrap around it powering a high-count encoder with at least twice the resolution and accuracy you require from your process. The measurement of the roll circumference must also be very precise, and a doctor blade to keep it clean is also a possiblility.

The conversion of pulses to engineering units can be performed on a PC to give length, in whatever units you require, or even to pounds, if your needs change.