In some applications the movement of the output shaft must be monitored even when electronics are powered down. In others, it is impractical to include the limit switch required to use an incremental encoder for positioning. In these situations, an absolute encoder is required.

  
         

Magnetic Specification
Supply Voltage: 5Vdc
Output: Differential SSI or 5V Analogue
Max. Rev. Count: 1rev. single-turn, 32000rev. multi-turn
Position retention: no limit single-turn, upto 100 hours multi-turn
Angle Resolution: 0.35º (10 bit)
Accuracy: ±1.5º
Maximum SSI frequency: 1Mhz
Connector: 10 way molex

  

Rotalink's magnetic absolute encoder uses hall effect based
electronics to produce the same analogue output from a smaller package. It also gives the option to report position via SSI (synchronous serial interface), which is immune to the noise that can disrupt an analogue output.

  
         

Mechanical Specification
Supply Voltage: 5-30Vdc
Output: 5-30V Analogue
Max. Rev. Count: 1rev. single-turn, 10rev. multi-turn
Position retention: no limit single-turn, no limit multi-turn
Angle Resolution: only limited by EMI
Accuracy: ±1.5º
Connector: Soldered leads

  

A mechanical absolute encoder - commonly known as a potentiometer - is the simplest way track shaft movement over one or ten turns. Its resistance rises as the gearbox turns, providing an analogue signal. The single-turn version drops back to its minimum resistance (~30Ω) when a full rotation in completed. The multi-turn version increases to maximum resistance over 10 turns, then hits an end stop.