What is quadrature?

Hey guys, I was asked this question yesterday, and still don't have a clear explanation in terms of something concrete for an answer. Can anyone elaborate on their understanding of the concept, mainly along the lines of encoder output. Thanks.

Russ

The two signals are set 90 deg. apart. 90 degrees is one quarter of 360. Or a quadrant. Hence the word quadrature.

So at 0 phase one comes on, then at 90 phase 2 comes on, then at 180 phase one comes off, then at 270 phase 2 comes off, then at 360, (back to 0), phase one comes on...etc.. This allows you to track direction as well as position.

With 1 output, you can determine speed. With 2, you can also determine direction.
By shifting them a little out of phase, you check direction by testing to see if output 1 or output 2 is leading.
90 degrees is the midpoint. A redundant, offset output sounds too dull. Let's get really fancy and call it a quadrature output.

A short but good explaination with a diagram is here:
http://www.dancon.com/techsup/faq_answer_encoder.htm

Thanks guys. I understood how an encoder works, but the way the question was asked led me to believe it was more of a high level math question. I really didn't think that quadrature stood for quadrant. I guess it makes sense though, and that perhaps I was just making the question harder than it really was. Thanks again.

Russ