Safe Absolute Encoder Function; Functional Specification; Encoder Evaluation - Kübler Sendix 58 FS2 Serie Manual De Instrucciones

3.4.2.2 Safe Absolute Encoder Function

Loss of safety
The digital absolute information is not part of the certification.
The digital absolute position cannot be used alone to realize
safety functions.
To obtain safe information on the absolute position with the
encoder, the encoder evaluation unit must also count the in-
cremental information (relative position) and compare it with
the absolute position also provided by the encoder.
The comparison of the digital position data with the sine and
cosine signals allows continuously checking the reported pos-
ition and detecting a deviation of the two signals. Since this
function requires both the incremental information and the ro-
tation direction information for the check, the achievable
safety level is limited to this.
Before switching the facility off, the absolute position value
must be saved by the encoder evaluation unit. When switch-
ing it back on, the encoder evaluation unit must compare the
saved value with the absolute value newly measured after
switching on. If both values are identical, the position is still
safe. If the position values are not identical, the position is not
safe and must be newly verified.
BA Sendix® 58xxFS2 / 58xxFS3 - R60049.0009 - 05
NOTICE

3.4.2.3 Functional Specification

Incremental value
The incremental sin-cos signals are safety-assessed. The
monitoring of the unit circle allows achieving a diagnostic cov-
erage of 99 %. The function can be examined at any time.
This means that, for an encoder resolution of 2048 sine-co-
sine periods, the validity can be checked by the encoder eval-
uation unit 2048 times per revolution. With a tolerance of the
sin²(x) + cos²(x) function of ± 0.5, the max. possible error path
will be 10 % of a signal period (36° electrically).
Typical limits and tolerances see chapter
Technical Data [} 43].
The sine-cosine signal alone does not allow realizing abso-
lute safety sub-functions and a safe rotation direction can
achieve at the maximum SIL2. Additional signal paths are re-
quired to be able to use both to a full extent up to SIL3.

3.4.2.4 Encoder Evaluation

Only operate the encoder together with a safe encoder evalu-
ation unit / controller. Only this equipment can monitor the
proper function and achieve a safe system.
Monitoring in the encoder evaluation unit must be carried out
directly on the encoder signal. Previous processing, e.g. in-
terpolation, is not allowed.
The encoder cannot prevent the automated restarting of the
facility after a malfunction. If this is necessary, it must be en-
sured by the encoder evaluation unit.
EN - 39