Siemens PM-E F pm DC24V PROFIsafe Installation And Operating Manual page 66

Fail-Safe Modules
7.2 PM-E F pm DC24V PROFIsafe Power Module
Capacitive Crosstalk of Digital Input/Output Signals
Readback errors may occur on the PM-E F pm DC24V PROFIsafe power module or on the
F-DO modules if the fail-safe digital output and fail-safe digital input signals are routed
through one cable. The module signals a short circuit in this situation.
Cause
The steep switching edge of the output driver during the sensor supply test of the 4/8 F-
DI DC24V PROFIsafe module may lead to crosstalk on other inactive output channels due to
the coupling capacitance of the wire, for example, on the PM-E F pm DC24V PROFIsafe
power module. This situation may lead to a response in the readback circuit in these
channels. The module detects a cross circuit and performs safety-related shutdown.
Remedy
● Use separate cables for the F-DI modules and F-DO modules or standard DO modules
● Coupling relay or diodes in the outputs
● Disable the sensor supply test if safety class requirements allow this.
See also
Assigning Modules of an ET 200S (Page 22)
Properties of the 4 F-DO DC24V/2A PROFIsafe digital electronic module (Page 163)
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that are controlled by a PM-E F pm DC24V PROFIsafe.
ET 200S Distributed I/O System - Fail-Safe Modules
Installation and Operating Manual, 08/2008, A5E00103686-07