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  3. Absolute encoders

Absolute encoders

Absolute encoders provide an absolute numerical value for the shaft position, either for only one revolution (singleturn) or including the number of shaft revolutions (multiturn).

  • The output is given in binary form. The larger the number of bits, the greater the resolution
  • Optical technology
  • Single turn RN*, Multiturn RM*
  • Resolutions: 13, 24 and 25 bits
  • Versions with connector, cable or terminal chamber
  • Versions as solid shaft with clamp/synchro flange or as hollow shaft
  • Interfaces: SSI, PROFIBUS, PROFINET, CANopen, DeviceNet
Versions
Type HousingØ Solid shaftØ Hollow shaftØ Resolution Features

Absolute
singleturn		 58 mm 6 mm
10 mm		 - 13 bits • resolution and signal can be set
• Profibus and Can interface

Absolute
multiturn		 36.5 mm
42 mm
58 mm		 6 mm
10 mm
12mm		 24 bits
25 bits		 • resolution and signal can be set
• Profibus, ProfiNet DeviceNet, SSI and CANopen interface

Absolute multiturn encoders

  • Determine the exact position by looking at the code on the disc over multiple rotations
  • Encoders provide a unique coded value consisting of the position on the disc (resolution) and the position of the gear train (revolutions).

Absolute encoders are available with parallel, serial or fieldbus outputs to transmit shaft position data.

  • Absolute encoders with parallel outputs require an output for each bit of information. For example, an absolute encoder with a 12-bit parallel output would require twelve separate outputs to transmit the data. This encoder would have a resolution of 4096.
  • Data on the position of the encoder can also be transferred via the synchronous serial interface (SSI).

The common fieldbus outputs of absolute encoders comprise DeviceNet, Profinet, Profibus, CANopen, Ethernet IP and EtherCAT.

Absolute singleturn encoders

  • Determine the exact position by looking at the code on the disc
  • Absolute singleturn encoders provide a unique coded value for each increment on the shaft, they are used in applications in which the shaft does not rotate more than 360 °.
  • In case of a power failure, the unique position of the shaft is maintained in absolute encoders. There is no need to return to a “home position” to determine the shaft position.

All incremental encoders from ifm operate like absolute singleturn encoders when used on IO-Link. They detect and save their position value even if power fails.