Crosstalk Of Digital Input/Output Signals; Operating The Et 200Sp On Grounded Incoming Supply - Siemens SIMATIC ET 200SP System Manual

5.2.3

Crosstalk of digital input/output signals

When fail-safe digital output and input signals are in a single cable, F-DQ modules and F-
PM-E modules may experience readback errors.
Cause: Capacitive crosstalk
During the bit pattern test of the outputs or the sensor supply of the inputs, the steep
switching edge of the output drivers caused by the coupling capacitance of the line may
result in crosstalk to other non-activated output or input channels. This may then lead to a
response of the readback circuit in these channels. The module detects a cross circuit/short
circuit and performs a safety-related shutdown.
Remedy:
● Separate cables for F-DI modules, F-DQ modules, and F-PM-E modules or non-fail-safe
DQ modules
● Separate cables for F-DQ channel and F-DI channels for the F-PM-E module
● Coupling relay or diodes in the outputs
● Disable the sensor supply test if safety class requirements allow it.
Cause: magnetic crosstalk
Note that an inductive load connected to the F-DQ channels can induce coupling of a strong
magnetic field.
Remedy:
● Separate the inductive loads spatially or shield against the magnetic field.
● Configure the readback time to 50 ms or higher.
5.3

Operating the ET 200SP on grounded incoming supply

Introduction
Below you will find information on the overall configuration of an ET 200SP distributed I/O
system on a grounded incoming supply (e.g. TN-S network). The specific subjects discussed
are:
● Disconnecting devices and short-circuit and overload protection according to IEC 60364
(corresponds to DIN VDE 0100) and IEC 60204 (corresponds to DIN VDE 0113)
● Load power supplies and load circuits.
Grounded incoming supply
In the case of grounded incoming supplies (TN-S system) the neutral conductor (N) and the
protective conductor (PE) are each grounded. Both conductors form a part of the overvoltage
concept. When a plant is in operation, the current flows across the neutral conductor. When
a fault occurs, for example, a single ground fault between a live conductor and ground, the
current flows through the protective conductor.
Distributed I/O system
System Manual, 12/2015, A5E03576849-AF
5.3 Operating the ET 200SP on grounded incoming supply
Wiring
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