Siemens SIMATIC S7 Functional Safety Manual

Fail-Safe signal module (SM) applications
3.1 Digital input applications
S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA
67
3.1
Digital input applications
You should consider the application modes presented here along with the features of the SM
1226 F-DI 16 x 24VDC as described in the overview. Refer to "SM 1226 F-DI 16 x 24 VDC"
(Page 20).
These are the main features to keep in mind:
● You configure each channel as a 1oo1 or part of a 1oo2 evaluation pair.
● The corresponding channels from input bytes "a" and "b" (a.0, b.0), (a.1, b.1)...(a.7, b.7)
form a 1oo2 channel group.
● Within this restriction, you can assign 1oo1 and 1oo2 in any order.
● Short-circuit testing requires use of the internal sensor supply. VS1 must be used with
inputs a.0...a.7, and VS2 must be used with inputs b.0...b.7.
● If you enable the short-circuit test, both Vs1 and Vs2 are configured with the same
parameters. All channels you configured for internal sensor supply will be subject to the
same short-circuit test. You configure a test duration (length of dark time) and test interval
(time between dark tests).
● The sensor supply is monitored to detect short-circuit or overload. It is cycled once on
each power up to assure control and readback are working, and the readback is
monitored during input short circuit tests.
● You configure a discrepancy time to identify unacceptable differences between 1oo2
inputs.
● You configure a filter time for each channel or each 1oo2 pair.
You can achieve Category 3 in 1oo1 configurations if you diagnose external wiring faults or
exclude them according to standards by proper routing, protection, and proof testing of
conductors:
● Each F-DI input includes sufficient diagnostics and redundant components such that no
single internal fault can cause a dangerous failure.
● An appropriately-rated, single sensor can reach Category 3 by internal fault tolerance.
● The external wiring of a single sensor to a single input is vulnerable to single fault
dangerous failure unless additional measures are applied.
You can achieve Category 4 in 1oo2 configurations if you diagnose external wiring faults or
exclude them according to standards by proper routing, protection, and proof testing of
conductors:
● With 1oo2 evaluation, a pair of F-DI inputs is not subject to dangerous internal failure
within a reasonable number of accumulated internal faults.
● Appropriately-rated, external-paired sensors or equivalent redundancy can achieve
Category 4.
● The duplicated external wiring of 2 sensors to 2 input points is vulnerable to accumulated
fault dangerous failure unless additional measures are applied.
The F-DI is recommended for SIL 3/PL e only when 1oo2 evaluation is selected. A single
high-integrity sensor can be rated up to SIL 3/PL e, but it should be wired and configured for
1oo2 evaluation for the channel to achieve SIL 3/PL e.

Siemens SIMATIC S7 Specifications

General

Brand	Siemens
Model	SIMATIC S7
Category	Controller
Language	English