Siemens SIMATIC ET 200S Hardware Installation And Operating Manual page 210

Digital Electronics Module 1 F-RO DC24V/5A AC24..230V/5A
2.4 Wiring of the EM 1 F-RO DC24V/5A AC24..230V/5A
Load voltage and load connection
The relay output connections are potential-free contacting elements. This means that the
supply voltage must be provided externally. Connect the load supply (supply 1) and the load
(load 1) in series on the connections OUT 1 (terminals 9;13)/(terminals10;14). This
guarantees that the relay contacting elements interrupt the current flow of the load supply
with the load. The power supply can still be disconnected with the two relay contacts
connected in series in case on of the two relays is defective.
The second electric circuit is not electrically dependent on the first one. They are connected
logically through their shared control. This means that the electric circuit from OUT 2
(terminal 11;15)/(terminals 12;16), supply 2 and load 2 can control a different potential.
Warning
If an extra low voltage (SELV/PELV) is connected to the channel of F-RO-module, than an
extra low voltage (SELV/PELV) may only be connected on the other channel.
Relay contact readback
The readback value from F-RO-module must be compared with the control status in the
safety program. For this purpose you can use the F-Systems S7 Distributed Safety
F-application block FB 216 "F_FDBACK": feedback loop monitoring in your safety program
(refer to the manual
In case the control voltage DC 24V falls below the required value for relay pick-up or the wire
for input connections breaks, the relays will be released and "0" will be readback instead of
"1." This error is only detected if the control voltage is switched on.
In case one of the two relays gets stuck (contacting element remains closed) then "1" is read
back from the module. This readback value is compared with the expected value of "0" in the
safety program and the error is detected. This error is only detected if the control voltage is
switched on.
Note
In order to attain SIL3/Kat.4 a signal change is required at least once a day.
2-8
S7 Distributed Safety, Configuration and Programming)
Product Information for the Distributed I/O System ET 200S, Fail-Safe Systems Manual
.
Product information, 07/2006, A5E00825271-01