Siemens PM-D F DC24V PROFIsafe - Page 65

Fail-Safe Modules
7.2 PM-E F pm DC24V PROFIsafe Power Module
ET 200S Distributed I/O System - Fail-Safe Modules
Installation and Operating Manual, 08/2008, A5E00103686-07
65
Switching Grounded Loads
If the PM-E F pm DC24V PROFIsafe switches loads that have a chassis-ground connection
(for example to improve EMC characteristics) and if chassis and ground are connected at the
power supply being used, a "short-circuit" is detected.
From the perspective of the F-module, the M-switch is bridged by the chassis-ground
connection (refer to the diagram below as an example of an PM-E F pm DC24V PROFIsafe).
For the PM-E F pm DC24V PROFIsafe, as of Order No. 6ES7138-4CF02-0AB0, release
version 02, the resistance to capacitive loads between the M switch and chassis was
increased from approx. 1 μF to around 20 μF.
Remedy:
● Using the PM-E F pp DC24V PROFIsafe
● The value of the resistance between chassis and ground at the load end must be greater
than 100 kΩ
● The capacity value at the load end between chassis and ground must be less than 20 µF.
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Figure 7-2 Switching Grounded Loads (resistance exists between chassis and ground)
WARNING
During startup, the PM-E F pm DC24V PROFIsafe carries out a power on self-test that
takes around 3 ms. The load capacitance between chassis and ground is charged by way
of the load resistance. This low charging current may briefly trigger sensitive load circuits.