Capacitive Crosstalk Of Digital Input/Output Signals; Operation On Grounded Infeed - Siemens SIMATIC S7-1500/ET 200MP System Manual

Wiring

7.3 Operation on grounded infeed

7.2.3

Capacitive crosstalk of digital input/output signals

Readback errors may occur on the F-DQ modules if the fail-safe digital output signals and fail-
safe digital input signals are routed through a single cable.
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 due to 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.
Solution:
• Separate cables for fail-safe DI modules and fail-safe DQ modules / non-fail-safe DQ
modules
• Coupling relay or diodes in the outputs
• Disable the short-circuit test of the sensor supply 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.
Solution:
• Spatially disconnect the inductive loads or shield against the magnetic field.
• Configure the "Max. readback time dark test" to 50 ms or higher.
7.3 Operation on grounded infeed
Introduction
Information is provided below on the overall configuration of an S7-1500 automation
system/ET 200MP distributed I/O system on a grounded infeed (TN-S system). The specific
subjects discussed are:
• Shut-off devices, short circuit and overload protection in accordance with
– IEC 60364, corresponds to DIN VDE 0100
– IEC 60204, corresponds to DIN VDE 0113
• Load current supplies and load circuits
Grounded infeed
In the case of grounding 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.
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Automation system
System Manual, 01/2023, A5E03461182-AK