Siemens SIMATIC ET 200S Installation And Operating Manual page 67

Capacitive Crosstalk of Digital Input/Output Signals
When fail-safe digital output signals and fail-safe digital input signals are routed through one
cable, readback errors can occur on the PM E-F pm DC24V PROFIsafe power module or the
F-DO modules. The module then signals a short-circuit.
Cause
During the sensor supply tests of the 4/8 F-DI DC24V PROFIsafe module, the steep
switching edge of the output driver can cause crosstalk with other inactive output channels
due to the coupling capacitance of the wire, for example on the PM E F pm DC24V
PROFIsafe power module. In these channels, this can lead to a response in the readback
circuit. A short is detected leading to a safety-related shutdown.
Remedy
• Use separate cables for F-DI modules and F-DO modules or standard DO modules
• Coupling relay or diodes in the outputs
• Turn off the sensor supply test if this is permitted by the required safety class (safety
See also
Assigning Modules of an ET 200S (Page 2-4)
Properties of the 4 F-DO DC24V/2A PROFIsafe digital electronic module (Page 7-80)
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04
driven by a PM-E F pm DC24V PROFIsafe
integrity level).
7.2 PM-E F pm DC24V PROFIsafe Power Module
Fail-Safe Modules
7-7