Siemens SIMATIC S7 F Manual page 338

Check Lists
Sensors and Actuators
The sensors and actuators used in F-systems are not described in this
documentation. All the usual sensors and actuators are supported by S7 F/FH
Systems and the usual operating modes (single-channel, two-channel, non-
equivalent, etc.) can be selected during configuration.
Since sensors and actuators are decisive factors to be included in safety
considerations, the following check list ought to be of assistance when you
configure the F-system with sensors and actuators.
Demands on Sensors and Actuators
Are your sensors and actuators of adequate quality and suitable for
environments with polluted air and corrosive fumes?
Do you make use of the possibilities of double redundancy for sensors,
where appropriate?
Do you make use, where appropriate, of the possibilities for actuators of
reading back auxiliary contacts or process-linked sensors?
Have you set sufficiently short proof test intervals, if necessary
individually?
A-6
Check
Fail-Safe Systems
A5E00085588-03