JUMO 14597 safetyM STB/STW Ex - Safety Temperature Limiter and Safety Temperature Monitor Operating Manual - Manual (Page 49)

6 Safety Manual
43 2013-04-01
The sensor, logic unit, and actuator together form a safety-related system that performs a safety function. The "average proba-
bility of dangerous failures of the entire safety-related system" (PFD
avg
) is usually divided up into the sensor, logic unit, and ac-
tuator subsystems according to the following diagram.
Figure 1:
Typical subdivision of the "average probability of dangerous failures of a safety function on demand" (PFD
avg
) into subsystems
The specifications related to functional safety in this Safety Manual include sensor systems (resistance temperature probes,
thermocouples), logic unit (701155), and (as signal contact) the relay output in the JUMO safetyM STB/STW Ex system.
The actuator (for example a power contactor) is plant-related and must be taken into consideration separately according to the
standard for the safety loop.
Table 7: Low demand table PFD
Safety Integrity Level
(SIL)
Operating mode with low demand rate
PFD
avg
(low demand mode)
4 ≥ 10
-5
to < 10
-4
3 ≥ 10
-4
to < 10
-3
2 ≥ 10
-3
to < 10
-2
1 ≥ 10
-2
to < 10
-1