Absolute Encoders

Absolute value encoders (absolute shaft encoders) are designed on the same scanning principle as incremental encoders, but have a greater number of tracks. For example, if there are 13 tracks, then 213 = 8192 steps are included in the case of single turn encoders. The code used is a one-step code (Gray code), which prevents any scanning errors from occurring. After switching on the machine, the position value is transmitted immediately to the controller. There is no need to travel to a reference point. The data are transmitted between encoder and controller either via the synchronous serial interface (SSI), via EnDat or via PROFIBUS-DP 1). SSI and EnDat have advantages in time-critical applications.

In plants with a large number of encoders, PROFIBUS DP is more of an advantage due to the reduced wiring expense. The encoders with PROFIBUS DP are programmable.Single turn encoders resolve one rotation (360 degrees mechanical) into a specific number of steps, i.e 8192. A unique code word is assigned to each position. After 360 degrees the position values are repeated.Multiturn encoders also record the number of revolutions, in addition to the absolute position within one revolution. To do this, further code discs which are coupled via gear stages with the encoder shaft are scanned. When evaluating 12 additional tracks, this means that 212 = 4096 revolutions can be included.