Most rotary encoders are single-turn devices, but absolute multiturn units are available, which obtain feedback over several revolutions by adding extra code disks. The additional disk stages are geared to the main disk and have their own photodetectors. The choice of an incremental or absolute encoder is very application dependent, but price is a factor. Incremental encoders are less costly than absolutes, but generally offer fewer functions and lower resolution. They re also more susceptible to electrical noise.
Some techniques can improve resolution and noise immunity.
If this is done for both Channels A and B, 4X basic resolution is obtained. However, system bandwidth limits must be kept in mind. Rotary encoders offer a rich variety of sizes, features, and capabilities. Models with speeds up to 30,000 rpm and operating temperatures well above 100 C are available.