Siemens SINAMICS S120 Function Manual page 176

Application examples
8.1 Input/output interconnections of a safety switching device with TM54F
TM54F: Interconnecting F-DI with a plus-minus switching output on a safety switching 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
Test pulses from F-DOs
There are safety modules, whose F-DOs send test pulses for self-testing and for checking
the circuit (transmission route). These test pulses can trigger incorrect alarms, which then
require safe acknowledgement. In order to avoid these incorrect alarms, the discrepancy
time p10002 should be set long enough so that a fault of the safety function itself is
excluded. According to the experience that we have gained, a setting of approx. 150 ms has
proven itself in practice; however, it is necessary to take into account the function description
of the test pulses from the F-DOs of the safety control.
In accordance with IEC 61131 Part 2, Chapter 5.2 (2008), when interconnecting the digital
inputs of the TM54F with digital semiconductor outputs, only outputs that have a maximum
residual current of 0.5 mA when in the "OFF" state can be used.
Debounce
Test signals from the controls can be filtered out using parameter p10017 (SI digital inputs,
debounce time) so that faults are not misinterpreted.
F-DI = safety-oriented dual-channel digital input
F-DO = safety-oriented dual-channel digital output
If digital outputs from another device (e.g. F-DOs on a safety PLC) with a residual current
greater than 0.5 mA in the "OFF" state are connected to the F-DIs of the TM54F, then F-DI
load resistors should be connected up in the channel involved.
The maximum permissible voltage for a TM54F F-DI when "OFF" is 5 V (in accordance with
IEC 61131-2, 2008).
The following two diagrams show exactly how the protective circuits for F-DIs with additional
load resistors are wired.
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WARNING
WARNING
Function Manual, (FHS), 11/2009, 6SL3097-4AR00-0BP0
Safety Integrated