Referencing; Synchronizing Encoders - Siemens Simatic Manual

Fail-safe function blocks for storage and retrieval machines
Warning
As long as V_VALID outputs a 0 signal, the velocity actual value is not generated
as a safety-related value.
3.2.4.5

Referencing

30. For a positive signal edge at SET a safety-related adjustment is carried out in the book itself,
where, for both position raw values, a separate position offset, relative to the value specified at
input POS_SETPOINT, is determined and saved. The REFERENCED output is set if referenc-
ing was successfully completed.
31. If referencing is to be successfully completed, both encoder actual values must be valid and
referenced (POS1_VALID/REF & POS_SI_VALID/REF = 1 (for POS_CONFIG bit 0 = 0) or
POS1_VALID/REF & POS2_VALID/REF = 1 (for POS_CONFIG bit 0 = 1)
32. REFERENCED is then the set with a rising edge at input SET and the offsets are internally
saved.
33. REFERENCED returns to zero as soon as the position tolerance window
POS_DISC_WINDOW is violated – or as soon as an encoder is no longer referenced.
34. ERROR as well as DIAG bit 5 is set to 1 if the above specified conditions are not satisfied.
After an encoder fault, the block can reproduce SAFE_POS without requiring a reference point
approach.
If POS1_VALID and POS_SI_VALID or POS2_VALID (depending on POS_CONFIG bit 0) have a
rising edge, the position is reproduced in the block according to the following scheme:
35. POS_CONFIG bit 0 == 0:
A check is made as to whether POS1 corresponds to reference value X
count POS_STARTUP_TOL. Reference value X
at POS_VALID and in the safely referenced mode (REFERENCED was set at this instant in
time). The fact that at reactivation POS1 corresponds to the internally saved reference value
X confirms the adjustment. The relative encoder is then automatically calibrated.
REF
36. POS_CONFIG bit 0 == 1:
A check is made as to whether both actual values are referenced (POS1_REF and
POS2_REF == 1), and lie within the tolerance window POS_STARTUP_TOL. If this is the
case, then REFERENCED and POS_VALID are again set to 1.
37. If one of the encoders is not referenced, or if the position tolerance was violated, then
REFERENCED returns to 0.
38. In the case that POS_STARTUP_TOL was exceeded, in order to set REFERENCED back to
1, a reference point approach must be carried out, as described under Point 30.
39. Non-plausible values at POS_SI are flagged using DIAG bit No. 11, and lead to a parameteriz-
ing error. A positive edge at ACK is used for reset.
Note
An encoder fault always leads to the withdrawal of input signal POS1_VALID or
POS_SI_VALID/POS2_VALID. As a consequence, the safety-related actual value
is immediately declared to be invalid, and the position tolerance monitoring is
hidden. As a consequence, an encoder fault does not mean that the safety-
related reference is immediately lost, and the safety-related position can be re-
produced after the encoder returns.
3.2.4.6

Synchronizing encoders

40. Using a positive edge at SYNC, both encoders are synchronized, i.e. the descrepancy that
has accumulated between the two encoders is set to 0. Both encoder actual values must be
valid to do this.
S7-Distributed Safety/SIMATIC Safety - fail-safe function blocks for storage and retrieval machines
REF
was previously saved with a falling edge
REF
, taking into ac-
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