Both codestrip and encoder must have exactly the same
window sizes and distances between windows in order to work
properly. Movement of the encoder with respect to the codestrip
changes resulting window size gradually as a function of the
displacement. When both windows match each other, light can
pass from the light source in the encoder through the codestrip,
through the windows of the encoder onto the photocells in
the encoder.( sometimes the photocells are made just the same
size(s) and distances as the windows resulting the same effect
). When the windows don't match at all, and as the bar ratio
equals the window size, no light can reach the photocells.
The number of the dark/light transitions for a given displacement
gives relative position.
In order to detect the direction of the relative motion,
another set of photocells is positioned with a half a window
offset from the former set of photocells. The detection of
the light by one set before the other set allows the user
to identify the direction of the movement.
This technique applies to both encoder types: transmissive
and reflective. Where transmissive codestrips have transparent
windows, reflective codestrips have reflective windows.
Both encoder systems exist with analog and digital outputs.
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