Starting Characteristics - Siemens Simatic Manual

Fail-safe function blocks for storage and retrieval machines
9. You can switch over between the mode for one and two direct encoders using the WORD pa-
rameter specified at POS_CONFIG. When the 0 bit is set, then the block is in the mode for
two direct encoders, otherwise in the mode for one direct encoder.
10. The significance of inputs POS2_VALID and POS2_IS_REF or POS_SI_REF and POS_SI
_VALID is equivalent to the corresponding inputs for POS1.
11. As described above, the modulo range configured in the drive is parameterized at
POS_SI_MODULO.
When parameterizing (assigning parameters) it should be ensured that the following
relationships can be represented
POS_SI_MODULO / 1000
(POS_SI_MODULO/1000) * POS_SI_RESOLUTION / 360
SLU_DEFINITION * 1000 / POS_SI_RESOLUTION
POS_SI_RESOLUTION * 60 / (POS_SI_T_SAMPLE * SLU_DEFINITION)
V_SYNC_INTERVALL / T_SAMPLE
Further, the following relationship between the input variables
V_MAX >= V_STANDSTILL
MAX_POS >= MIN_POS
Sampling rates/isochronous mode
To calculate the velocity, the block clock cycle of the F_SAFE_POS block on the CPU
(T_SAMPLE, generally, the interval in which the safety program is called) is not used
as time basis, but instead, the SI clock cycle in the drive. (POS_SI_T_SAMPLE)
To achieve this, the communication between the CPU and drive must be isochronous;
the bus cycle must be less or equal to the SI clock cycle in the drive. The safety pro-
gram does not have to be called at an isochronous execution level. Further, it must be
guaranteed that T_SAMPLE <= 2x POS_SI_T_SAMPLE. Otherwise, inadmissibly high
subsampling will occur (as a result of calculations executed in the block).
The permissible value ranges of the individual inputs should be taken from the table describing
the inputs.
The block identifies if not all of the mentioned preconditions are satisfied, and this is signaled
as parameterizing error with the appropriately set DIAG bits.
Note
The block only checks the parameterization at the 1st call. This results in a sub-
sequent increased block performance.
As a consequence, reparameterization is not permitted when safety operation is
deactivated. The safety program must be regenerated and loaded each time that
any of the block operating parameters are changed.

3.2.4.2 Starting characteristics

12. After a CPU restart, outputs V_VALID, POS_VALID and REFERENCED initially have a 0 sig-
nal.
13. V_VALID is set to 1 after acknowledgment using a positive signal edge at ACK.
14. To be able to travel to the reference point, POS_VALID must be set to 1 by synchronizing both
encoders using a positive signal edge at SYNC. Now, the position value is valid as such, and
can be used for information regarding the relative position; however, it is not permissible to
evaluate the position as safety-related absolute position as long as REFERENCED has a 0
signal.
S7-Distributed Safety/SIMATIC Safety - fail-safe function blocks for storage and retrieval machines
as integer numbers:
must apply:
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