Originally Posted by ESjaavik Al, I think the moiré effect is also used by having a graticule with a slightly different spacing than the disk. If you have 2 disks, one with 1000 lines/rev, and one with 1001 lines. When viewing through both one side will be completely dark 0% light, the other side 50% dark. In between you will have 0-50% dark. |
Evidentally it will also work with gratings of the same spacing as shown in this technical paper, where you can copy two exact gratings for demonstration purposes.
http://claymore.engineer.gvsu.edu/~j.../cont_sens.pdf
Also the shutter effect can be seen if a 'dead' encoder with the disc exposed but the head still present is held up to reflective light and the shaft is turned.
I still remember working on old linear scales by Ferranti that had a 15watt incandescant lamp in them and every time you changed a lamp the sine/cosine relationship between the heads had to be adjusted using a 'scope.
Al