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Fail-Safe Modules
7.7 4 F-DO DC24V/2A PROFIsafe digital electronic module
Note
The EM 4 F-DO DC24V/2A PROFIsafe carries out a bit pattern test every 15 minutes or so.
The module then sends an impulse for max. 4 ms. This test is run with a time offset between
the P and M-switches in order to prevent the actuator from being activated. This impulse
may cause the corresponding relay to tighten, which may reduce its service life.
We therefore recommend adhering to the wiring scheme detailed below.
Application 3: Wiring two loads in parallel to each digital output
Avoiding/Managing Cross Circuits:
To protect against cross-circuits between P and M-switches in fail-safe digital outputs, we
recommend the following wiring scheme. This configuration achieves safety class
SIL3/Category 4/PLe.
Figure 7-53
Note
With a parallel connection of two relays on one digital output (as shown above) the "wire
break" fault is only detected if the wire break disconnects both relays from P or M. This
diagnosis is not safety-related.
170
Wiring diagram for in each case 2 relays parallel on 1 F-DO of the EM 4 F-
DO DC24V/2A PROFIsafe
ET 200S Distributed I/O System - Fail-Safe Modules
Installation and Operating Manual, 08/2008, A5E00103686-07
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