1-encoder concept – FS external encoder (with MOVISAFE® CSA31A only)

The motion variables required by the system are derived from a single distance encoder certified to a recognized FS standard for this purpose.

The encoder concept can be used for non-slip, slip, and non-linear applications.

Safe double SSI encoder

There is a functionally safe double SSI encoder with 2 separate SSI interfaces on the travel path. Both interfaces are connected to the encoder interface of the safety option via the UEA31A SSI combi-box or a suitable cable.

The encoder has a safe internal functional design and provides an absolute position. This position is transmitted separately for evaluation via both SSI interfaces.

The encoder can be rotary or linear. The connection between encoder and application must be fail-safe and slip-free.

The encoders require additional diagnostics, which are described in the chapter for the respective encoder. All diagnostics for SSI single encoders remain active.

On the drive train, the absolute encoder is configured as encoder 2 and encoder 3. Encoder 2 is evaluated in parallel by the inverter and the safety option, encoder 3 is evaluated exclusively by the safety option.

Certification of the safe double SSI encoder is only ensured if both channels are involved in the process value calculation. Encoder 2 and encoder 3 can be set to process value calculation, or only encoder 2 can be set to process value calculation and encoder 3 set to comparison value. This applies both to the "Position" process value and the "Speed" process value.

There is no general restriction for safe double SSI encoders with regard to the safety sub-functions. In a planned application, it must be checked whether the resolution and accuracy are sufficient to obtain suitable values for position, speed, and acceleration for Safety over EtherCAT® and CIP Safety™.

Restrictions with Safety over EtherCAT® and CIP Safety™

The following encoder combinations are not possible with the Safety over EtherCAT® and CIP Safety™ safe communication protocols:

  • EI7C FS with additional encoders
  • Use a sin/cos encoder as encoder 1 or determine the process value speed from encoder 2 and encoder 3. Encoder 1 is therefore not used by the CSA31A safety option.
  • Encoder 1 with CDx75 or FBPS617i
  • Determine the process value speed from encoder 2 and encoder 3. Encoder 1 is therefore not used by the CSA31A safety option.