Capacitive Crosstalk Of Digital Input/Output Signals; Electrical Configuration - Siemens SIMATIC S7-1500 System Manual

Connecting

6.3 Electrical configuration

6.2.3

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 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 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.
6.3 Electrical configuration
A system with the SIMATIC Drive Controller consists of several individual components. For a
system configured with these components to meet the EMC and safety standards, certain
design guidelines must be followed.
Grounding concept and radio interference suppression measures
The individual system components are attached to a metal cabinet panel.
In addition to the protective grounding of system components, special precautions must be
taken to guarantee safe, error-free operation of the system. These measure include:
● Shielded signal lines
● Special equipotential bonding connections
● Isolation and shielding measures
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SIMATIC Drive Controller
System Manual, 11/2019, A5E46600094-AA