Siemens Sinamics S110 Function Manual page 457

Interconnecting an F-DI with a plus-minus switching output on a safety device
In contrast to mechanical switching contacts (e.g. Emergency Stop switches), leakage
currents can still flow in semiconductor switches such as those usually used at digital
outputs even when they have been switched off. This can lead to false switching states if
digital inputs are not connected correctly.
The conditions for digital inputs/outputs specified in the relevant manufacturer
documentation must be observed.
Note
F-DO test pulses
Some safety blocks have F-DOs which emit test pulses for self-test purposes and in order to
check the transmission path. These test pulses may trigger false alarms requiring a safe
acknowledgment. To avoid these false alarms, discrepancy time p10002 should be set at a
sufficiently high level to prevent any interference with the safety function itself. Our
experience has shown a setting of approx. 150 ms to be adequate, but it is essential to take
into account the description of functions for the F-DO test pulses of the safety control.
In accordance with IEC 61131 Part 2, Chapter 5.2 (2008), only outputs that have a
maximum residual current of 0.5 mA when "OFF" can be used to connect CU305 digital
inputs with digital semiconductor outputs.
Debouncing
Parameter p10017 (SI digital inputs debounce time) can be used to filter out test signals from
controls. This avoids faults generated by misinterpretations.
If digital outputs from another device (e.g. F-DO of a safety PLC) with a residual current
greater than 0.5 mA in the "OFF" state are connected to the F-DIs of the CU305, then F-DI
load resistors should be connected in the appropriate channel.
The maximum permissible voltage for a CU305 F-DI when "OFF" is 5 V (in accordance with
IEC 61131-2, 2008).
Function Manual
Function Manual, 01/2011, 6SL3097-4AB10-0BP3
WARNING
WARNING
Safety Integrated Functions
8.8 Application examples
455