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6.9
Requirements placed on sensors for fail-safe modules
Definition
There are certain requirements for the safety-related use of sensors, which are briefly described
below.
General sensor requirements
For safety-related use of sensors, you must observe the following important warning:
Sensor requirements
Note that a significant responsibility for safety of instrumentation lies with the sensors. Also
keep in mind that sensors generally do not have proof-test intervals of 20 years according to
IEC 61508:2010 without a significant loss of safety.
The probability of dangerous faults or the rate of dangerous faults of a safety function must
adhere to an SIL-dependent upper limit.
You will find the values achieved by the F-modules in their technical specifications.
To achieve the respective safety class, correspondingly qualified sensors are required.
(FAIW-010)
Additional sensor requirements
Safe reaction of the safety program in case of sensor error
With the fail-safe analog input modules, the affected input is passivated and the substitute
value is forwarded to the F-CPU after errors have been detected. You therefore need to take care
that the safe reaction of the safety program is achieved with the substitute value.
(FAIW-011)
F-AI 8xI 2-/4-wire HART HA
Equipment Manual, 09/2021, A5E50557845-AA
WARNING
WARNING
6.9 Requirements placed on sensors for fail-safe modules
Applications of the F-I/O module
57
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