Incremental optical encoders are the most popular choice of sensors in applications where mechanical motion must be processed into digital information. Compared with alternate technologies (such as resolvers, tachometers, etc.), optical encoders represent the best combination of accuracy, resolution, reliability, ruggedness, ease of use, value and variety of solutions in the industry. For these reasons, optical encoders are the overwhelming choice where speed, rate, velocity, distance, position, or direction must be accurately and economically measured. Resolutions up to 30,000 counts per revolution (CPR) and operating temperatures up to 120° C are just some of features.
Incremental optical encoders contain a LED which provides a beam of light, passed through a rotating transparent disk with opaque lines. The beam is picked up by a photosensor which processes the light to provide an electrical squarewave or pulse train.
Quadrature encoders have two channels (A and B) separated by 90° electrical. Rotation direction can be determined by evaluating the leading and lagging channel in their phase relationship. A once-per-revolution pulse (“marker” or “index”) is usually provided on a separate channel (Z) and can be used to position motion control applications to a known reference.