Achievable Safety Classes with F-I/O
5.3 Safety Functions for Achieving Safety Classes for F-I/O with Outputs
Safety Engineering in SIMATIC S7
5-12
System Manual, 04/2006, A5E00109529-05
5.3
5.3
Safety Functions for Achieving Safety Classes for F-I/O with Outputs
Test Signal Injections for F-I/O with Outputs
For F-I/O with outputs, the necessary safety class is achieved by injecting test signals.
Table 5-3
Achievable Safety Classes for F-I/O with Outputs
Safety Class ...
In accordance with
IEC 61508
In accordance with EN
954-1
... Test Signal Injection Required
SIL2
Category 3
•
Dark period
SIL3
Category 4
•
Light period
•
Dark period
Dark Period
Dark periods occur during switch-off tests and during complete bit pattern tests. This
involves test-related "0" signals being fed to the output by the F-I/O with outputs while the
output is active. The output is then switched off briefly (dark period). A sufficiently slow
actuator does not respond to this and remains switched on.
Light Period
Light periods occur during complete bit pattern tests. This involves test-related "1" signals
being fed to the output by the F-I/O with outputs while the output is deactivated (output signal
"0"). The output is then switched on briefly (light period). A sufficiently slow actuator does not
respond to this and remains deactivated.
Light periods occur with two-channel, single-pin activation of the outputs. Light periods do
not occur with two-channel, two-pin activation of current sourcing and current sinking outputs
(ET 200S, ET 200pro F-modules and SM 326; DO 8 ☓ 24 VDC/2 A PM).
Daily (or More Frequent) Signal Change
If the signal changes daily or more often, SIL3/Category 4 can be achieved for S7-300 F-
SMs even without a light period.
Required User Steps
For S7-300 F-SMs parameterized using
STEP 7:
•
Operate the F-I/O in SIL2/Category 3 or SIL3/Category 4 (implicitly defines the type of
test signal injection)
•
Daily (or more frequent) signal change
For ET 200S, ET 200pro and ET 200eco F-DO modules, no settings are required, since
they are usually designed for safety class SIL3/Category 4.
