Interrelationship Between The Assignment Of The Block Inputs And The Drive Configuration; Figure 9: Scaling Factor P9574 - Siemens Simatic Manual

Fail-safe function blocks for storage and retrieval machines
3.2.3 Interrelationship between the assignment of the block inputs and the drive
configuration
In Distributed Safety, only the INTEGER value range is available for analog values; it is not possible to
use the DINT or REAL data types – known from the standard program – in the safety program. As
result, not only a coarse resolution (only an integer number of millimeters) is obtained when parame-
terizing the safety functions in SLU, but also restrictions apply with reference to the internal plausibility
monitoring of the two encoder signals as well as the velocity monitoring. As a consequence, it is not
feasible to calculate the velocity, based on an absolute position actual value of telegram 901.
However, in order to allow the velocity to be calculated based on the motor encoder, the axis must
always be configured in Safety Integrated as rotary axis with modulo correction. In this case, the spin-
dle pitch is also taken into account in the gearbox ratio, so that the absolute values of positions and
velocities have the units of mm and mm/min.
For users, there is then only a deviation in the displayed unit (degrees and rpm) in the SI dialogs in
STARTER.
Depending on the scaling factor p9574 of safety-related telegram 901, the modulo range p9505 is set
to a multiple of 360. This means that the position actual value cannot overflow beyond the 16-bit inte-
ger range.
Scaling factor p9574 defines the resolution of the safety-related position actual value in telegram 901,
and therefore input parameter POS_SI_RESOLUTION.
This means that the SI position actual value (capable of overflow and with a high resolution) can be
transferred to the F-CPU, where the velocity actual value is calculated.
Correspondingly, the 16-bit position actual value should always be interconnected as modulo value at
input POS_SI.
The modulo range p9505 configured in the drive, multiplied by 1000/p9574, is parameterized at input
POS_SI_MODULO.
S7-Distributed Safety/SIMATIC Safety - fail-safe function blocks for storage and retrieval machines
p9574

Figure 9: Scaling factor p9574

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