Thanks for the ideas guys. I will investigate the use of ultrasonic, because the final stage had a number of rollers on which this could work. I am also interested in the 10GHz meter because it provides other interesting measurements. Will keep you all posted on progress as it forges on. Regards John ----- Original Message ----- From: "Alan B. Pearce" To: "Microcontroller discussion list - Public." Sent: Tuesday, September 26, 2006 8:01 AM Subject: Re: [EE]: High Speed Thickness Measurement > >> This a stupid (maybe) idea (long way out of my field) > >> > >No Idea is stupid Steve, thanks for the suggestion > > So here is my suggestion. Assuming the paper can be run over a rounded > surface (it could be an existing guide roller) so that you know it is flat > against the surface (i.e. under some tension), then my thought was to use > ultrasonic sensors to measure the thickness difference between the paper > height and the roller. You could have a number of sensors across the width > of the paper if necessary. > > >> Light permeability > >> For a lamp of given intensity the translucence of the sheet > >> could be used as a thickness measurement > >> This could work if the light source is self calibrating, > >> allowing for the gradual degradation of the lamp. > > > >Anyone know how well this could be used to measure a change > >of fractions of a micron? > > Yes. The way I would do it, taking the roller arrangement I suggested above, > is to shine the light so it is shining along the tangent of roller onto a > linear CCD. The roller will cause a shadow, which you use as reference, and > the paper will increase the shadow height. Readout speed will probably be > limited to the clockout rate of the CCD. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist