Requirements for SSI encoders

  • The SSI encoders that comply with the technical data of the encoder interface for SSI encoders (encoder 2 and encoder 3) are permissible. Observe the notes in chapter "Safety requirements" regarding cable length and SSI clock frequency and, if necessary, reduce the clock frequency to 250 kHz or 125 kHz for long cable lengths.
  • The MOVISAFE® CSA31A safety option supports the evaluation of error bits and warning bits. SEW-EURODRIVE recommends activating the error bits and warning bits in the encoders as a means of additional fault detection.
  • For single-turn encoders and encoders with few multi-turn bits (< 3 bits), make sure that the range of values does not overflow within one SSI evaluation cycle. This applies in particular to encoders that are directly connected with the motor shaft.
  • For single-turn encoders, the following maximum speeds apply under the respective conditions (see following tables):
  • 2000 min-1

Frame rate

Update time

Fault tolerance

1ms

Encoder 2 (8713.52)

Encoder 3 fixed to 1 ms

≥ 5 ms

Encoder 2 (8382.29)

Encoder 3 (8599.29)

1

Encoder 2 (8713.51)

Encoder 3 (8714.51)

  • 1750 min-1

Frame rate

Update time

Fault tolerance

2ms

Encoder 2 (8713.52)

≥ 5 ms

Encoder 2 (8382.29)

1

Encoder 2 (8713.51)

  • 1750 min-1

Frame rate

Update time

Fault tolerance

1ms

Encoder 2 (8713.52)

Encoder 3 fixed to 1 ms

≥ 5 ms

Encoder 2 (8382.29)

Encoder 3 (8599.29)

2

Encoder 2 (8713.51)

Encoder 3 (8714.51)

  • 1400 min-1

Frame rate

Update time

Fault tolerance

2ms

Encoder 2 (8713.52)

≥ 5 ms

Encoder 2 (8382.29)

2

Encoder 2 (8713.51)

  • For single-turn SSI encoders that are mounted directly on the motor, the SSI fault tolerance parameter is allowed to be set to a maximum of 2.
  • Single-turn SSI encoders with an update time of > 5 ms must not be mounted directly on the motor.
  • The frame rate, i.e. the polling cycle of the safety option to the SSI encoder, can be set to 1 ms or 2 ms (default: 2 ms). The shorter the polling cycle, the more accurately the position, speed, and acceleration are calculated.
  • A frame rate of 1 ms can be selected under the following conditions:
    • PWM frequency of the inverter: 4 kHz, set to "no noise".
    • Pause time: maximum 0.08 ms
    • Clock frequency: ≥ 250 kHz
    • Frame length: maximum 27 bits
  • PROFIsafe safe communication profile
  • The MOVISAFE® CSA31A safety option does not evaluate 3 encoders.